Chemistry [[Module Three]] Alchols: Elimination

- Alcohols with H atom on carbon next to OH group can be dehydrated to alkenes
- 180 degrees

- sulphuric or conc. phosphoric catalyst.


- Mechanism = Elimination

- Reaction occurs in three steps:

1) Protonation (H+ added to OH group)

2) Loss of water (produces an carbocation)
3) Loss of a proton (produces alkene)

Chemistry [[Module Three]] Alcohols: Classifying and Reactions

- alcohols classified as primary, secondary or tertiary

- depends on which the carbon the OH group is attatched to

- Many reactions are the same, regardless of where the OH group is

- but three types of alchol differ when oxidised.

[[Oxidation of Alchol]]

- acidified potassium dichromate

- colour change from Orange to Green as Dichromate ions are reduced - test to distinguish primary and secondary from tertiary alcohols.

[Primary Alcohol]

- oxidised to Aldehydes

- colour change from orange to green

- Aldehyde still has H atom and so can be oxidised further

- Further oxidised to Carboxylic Acid

- To stop this happening, remove the aldehyde as it is produced using a condensor

- To get Carboxylic acid, prevent the product from escaping and heat under reflux

[Secondary Alcohol]

- oxidised to Ketones

- No further oxidation

- colour change from orange to green

[Tertiary Alcohols]

- no oxidation

- no colour change

[[Distinguishing bewteen Aldehydes and Ketones]]

- test for secondary/primary alchols

- use of mild oxidising agent

[[Fehlings Solution]]

- colour change from Blue to red in the presence of Aldehydes

- Not oxidised by Ketones

- Copper (II) Complex reduced to Copper (I)

[[Tollens Reagent]]

- Silver Mirror formed when warmed in the presence of Aldehydes

- Not oxidised by Ketones

- [Ag (NH302]+ reduced to Ag

Chemistry [[Module Three]] Alcohols: Ethanol Production

Alcohols = homologous series with general formula CnH2n+1OH

[[Ethanol Production]]

[Fermentation]
- living yeast
- converts sugars into ethanol and carbon dioxide

C6H12O6 --yeast--> 2C2H5OH + 2CO2

- slow at low temps
- at high temps enzymes are denatured
- compromise temp of 35 degrees

[Direct Hydration]
- produced industrially
- steam
-phosphoric acid catalyst
- pressure = 6.5x103
- temp = 300 degrees

C2H4 +H20 <===> C2H5OH

- currently preferred method of ethanol production in UK
- ethene is raw material

[Comparing]

Hydration:
* Fast reaction rate
* Pure product
* Finite raw material
* Continuous (cheap) process
* Expensive Equipment

Fermentation
* Slow reaction rate
* Impure product
* Infinite raw material
* Batch (expensive, manpower) process
* Cheap Equipment

Chemistry [[Module Three]] Haloalkanes: Elimination

- Hydroxide ion can also act as a base

- which allows elimination to take place

- Hydrogen and Bromide elimated from haloalkane

- Forms an alkene




Mechanism:


[[Importance of Substitution and Elimination]]

1) Structure of Haloalkane
- primary haloalkanes give predominantly substitution reactions
- tertiary alkanes favour eliminatation
- secondary do both

2) Base Strength of the nucleophile
- liklihood increases as base strength on nucleophile increases

3) Reaction Conditions
- higher temps = greater chance of elmination
- Elimination = hot, ethanolic conditions
- Substitution = warm, aqueous conditions.

Chemistry [[Module Three]] Haloalkanes: Nucleophilic Substitution

[[Nucleophilic Substitution]]

Haloalkanes: homologous series of compunds with general formula CnH2n+1X where X represents F, Cl, Br and I.

- Halogens are electronegative

- Carbon Halogen bonds are polar

- The electrons in C-X bond are attracted to the halogen atom which gains a slight negative charge

- Therefore the Carbon has a slightly positve charge

- The slightly positive carbon is suceptable from attack by nucleophil

Nucleophile: And electron pair donor

- Nucleophilic attack occurs and the carbon halogen bond breaks, releasing a halide. The halide is replaced by the nucleophile.

- rate of reaction influenced by strength of C-X bond

- C-F bond is very polar but bond is very strong so Flouroalkanes are unreactive

- Chloroalkanes also react slowley

- Bromoalkanes react at a reasonable rate

[[Nucleophilic Substitution Reactions]]

[1. Hydroxide Ions]

- haloalkanes warned with aqueous sodium or potassium hydroxide

- forms alcohols

[2. Cyanide Ions]

- haloalkanes warmed with aqueous/alcholic solution of KCN

- nitriles formed

- carbon chain extended

[3. Ammonia]

- warmed with excess of ammonia

- sealed container

- Primary Amines

- excess of ammonia minimises chance of further reaction.

Chemistry [[Module Three]] Epoxyethane

- more commonly known as ethylene oxide

- highly reactive

- manufactured on large scale

- used in synthesis of important products

* Ethane 1,2-diol

* non-ionic surfactants

[[Production]]

- produced commercially by direct partial oxidation of ethene

- using oxygen/air

- silver based catalyst

- care needed in making and handling

- product = colourless gas

- product = flammable and explosive

- is toxic and may cause respiratory system irritation and neurological effects

- gas is excellent sterilising agent agaisnt bacteria.

[[Reactions]]

-three membered ring makes epoxyethane very reactive towards nucleophiles

Nucleophiles = An electron Pair Donor

-Exothermic reactions with nucleophiles cause the ring to open

- primary products contain 2-hydroxyethyl groups.

[Reaction With Water]

- half epoxyethane commercial produced is converted to ethane 1,2-diol by reaction with water

- Exothermic reaction

- Slow at room temperature

- acid catalyst used

- In industry = epoxyethane treated with ten-fold molar excess of water,, 60 degrees and sulphuric acid.

- Resulting solution is condensed by evapouration and fractional distilation

- yield is 90%

- other product = HOCH2CH2OCH2CH2OH

Chemistry [[Module Three]] Alkenes: Reactions

[[Hydrogenation]]

NICKEL CAT
150 degrees

- uses = production of margerine

[[Electrophilic Addition]]

Electrophile: positive ions (or electrodeficient atoms) that act as eclectron pair acceptors and seek electron rich sites.

1) Bromine Water

- used as a test for alkenes since alkenes decolourise bromine water and alkanes do not

2) Hydrogen Bromide

3) Sulphuric Acid

[[To unsymmetrical Alkenes]]

If an alkene is unsymetrical, then electrophilic addition can produce two possible compounds.

The one that is more likley to occur is the one which forms the more stable carbocation

Tertiary Carbocations are more stable than Secondary carbocations which are more stable than primary carbocations

[[Direct Hydration of Ethene]]

- steam

- 300 degrees

- 6,5 x 103 KPa

H3PO4 cat

Chemistry [[Module Three]] Alkenes: Structure and Bonding

[[Structure and Bonding]]

Homologous series of hydrocarbons with general formula CnH12
Contain 2 hydrogens fewer than parent alkanes
Said to be unsaturated
Contain double bond which is an area of high electron density and the reason for the high reactivity of alkenes.

Chemistry [[Module Three]] Alkanes: Chlorination

[[Chlorination]]

Alkanes do not react with chlorine at room temp but in the presence of UV light they react explosivly.

Process = Free Radical Substitution

-occurs in several steps

1) Inititaion
Cl2 ---> 2Cl*

The UV light provides activation energy by splitting a cholrine molecule into 2 chlorine free radicals.
This occurs first because Cl-Cl bond is weaker than the C-H bond in alkane.

2) Propagation

Cl* + CH4 --> CH3* + HCl

CH3* + Cl2 ---? CH3Cl + Cl*

A radical is used and a radical is formed, so it leads to a chain reaction.
Each step is exothermic

Overall equation: CH4 + Cl2 ---> CH3Cl + HCl

3) Termination
- two radicals combine to form a stable molecule and sequence of reations stop. Unpaired electrons form covalent bond.

Cl* + CH3* --> CH3Cl

CH3* + CH3* --> CH3CH3


Further Sunstitiution

-can occur to form

CH2Cl* --> CH2Cl2 and CHCl3

further substitution can be reduced if an excess of methane is used.

Chemistry [[Module Three]] Petroleum: Combustion

[[Combustion of Petroleum Fractions]]

Fractions obtained from petroleum are used as fuels
Hydrocarbons burn easily in air with exothermic reactions
Sulphur containing impurities occur with hydrocarbens and when these burn they produce oxides of sulphur which are toxic and dissolve in water producing acid rain.

[[Combustion of alkanes]]

Alkanes burn easily in air/Oxygen with very exothermic reactions

[Complete Combustion]
-Presence of sufficient oxygen
-CO2 and H2O formed
- As carbon chain increases, more oxygen is needed and more energy released

CH4 +2O2 --> C02 +H2O

C4H10 +61/2O2 ---> 4CO2 +5H2O

[[Incomplete Combustion]]
- presence of insufficient oxygen
- water is formed
- carbon monoxide or carbon is formed
- carbon monoxide = hazard = can lead to accidental death by CO poisening

[[Internal Combustion Engines]]
CO also formed by incomplete combustion of petrol vapour in car engine
Other pollutants formed - nitrous oxides mainly
Nitrous oxides formed when petrol/air mix is sparked and explodes -> provides enough energy for nitrogen to react woth oxygen

N2 +O2 --> 2NO

upon cooling it reacts with oxygen

2NO + O2 ---> 2NO2

and then with water and more oxygen

4NO2 + 2H2O + 02 ---> 4HNO3 = acid rain

[[Catalytic Converters]]
-help to remove pollutants from car wxhausts
- cermatic honeycomb coveredwith metals such as platinum, palladium and rhodiun
- These catalyse reactions between pollutants and remove 90% harmful gases

2CO + 2NO --> 2CO2 +N2

Pollutants become - CO2, N2 and H2O which are harmless

Chemistry [[Module Three]] Petroleum: Cracking

[[Cracking]]

Involves breaking C-C and C-H bonds

Higher Mr Alkanes -------> Smaller Mr Alkanes + Alkenes

Molecules can break up several different ways to form a micture of products, which is then seperated by fractional distiliation.

[[Thermal Cracking]]

Results in formation of a high proportion of alkenes
energy required for bond breaking provieded by heat
Temps range from 400 to 900 degrees at pressures of 7000 KPa

At lower end of temperature range, carbon chains break up near to middle of chain
At higher end, carbon chains break up towards the end keading to a greater % low Mr alkenes

The length of exposure has to be short, to avoid decomposition

1) Initiated by homolytic fission of C-C bond to form to alkyl radicals
2) Each alkyl free radical can abstract a hydrogen molecule from an alkane to produce a different alkyl radical and a shorter alkane:

CH3(CH2)6CH3 ---> CH3CH2CH2CH2CH2* + *CH2CH2CH3

CH3(CH2)6CH3 + CH3CH2CH2CH2CH2* ---> CH3(CH2)5C*HCH3

Radical: Species which results from homolytic fission of a covalent bond. They contain an odd n umber of electrons with one unpaired electron. Written as a dot (* on this blog)

[[Catalytic Cracking]]

Involves the use of ZEOLITE catalysts
Slight excess of pressure
Temperature = 450 degrees

Large alkanes converted to branched chain alkanes, cycloalkanes and aromatic hydrocarbons

C14H30 -------> C8H18 + C6H12

Alkene proportion is small
Catalytic cracking = used for producing motor fuels
Branched Chain burn more smoothly than unbranched alkanes

Branched chain alkanes used as fuel to prevent the problem of knocking when the fuel air mixture tries to ignite before spark is produced.

In catalytic cracking, the catalyst acts as a lewis acid and the method involves the formation of carbocations

Chemistry [[Module Three]] Petroleum: Fractional Distilation

[[Petroleum]]

Complex micture of hydrocarbens (mainly alkanes)
Derived from remains of sea creatures and plants which died and sank to the sea floor millions of years ago.
Susequent deposits compressed the material
High pressures, high temperatures and lack of air converted it to oil and gass.

[[Alkanes]]

Homologous series of saturdated hydrocarbens with the general forumula CnH2n+2
Boiling points increase with length of carbons as van der waals forces between the molecules increase
Increase of boiling points allows for seperation of crude oil by fractional distilation

[[Fractional Distilation]]

Seperation of the mixture of alkanes in crude oil into less complicated mixtures (or fractions)

1) Crude Oil Heated
2) Vapour/Mixture passed into a tower
3) Temperature gradient in tower means that it is cooler at the top than it is at the bottom
4) The temperature gradient seperates the mixture into fractions depending on the boiling points of the compounds present

The hydrocarbens with low boiling points reach the top
The other condense in trays at different levels along the tube and are drawn off

The residue still contains useful materials, sich as lubricting oils and waxes
These boil at above 350 degrees at atmospheric pressure
To avoid such high temps (At which other useful products would decompose) the residue is distilled under reduced pressure duing vacuum distillation.
In vacuum distilation, the remaining hydrocarbens can be distilled at lower temperatures without decomposing.

The amount of products produced from fractional distilation does not meet the demand, so to solve this, longer chain alkanes are broken up in a process called Cracking.

Chemistry [[Module Three]] Nomenclature and Isomerism

[[Isomerism]]

Occurs when molecules with the same molecular formula have their atoms aranged in different ways. It is sub divided.

[[Structural Isomerism]]


COMPOUNDS WITH THE SAME MOLECULAR FORMULAE BUT WITH DIFFERENT STRUCTURES


[Chain Isomerism]

occurs when there are two or more ways of arranging the carbon skeleton of a compound. The isomers have similar chemical properties byr slightly different physical properties. Branched isomers have smaller volumes, weaker van der waals and threrefore lower boiling points.


Isomers of C5H12:










[Position Isomerism]



Isomers have the same carbon skeleton and the same functional group but the functional group is joined at different places on the carbon skeleton.



CH3CH2CH2BR = 1-bromopropane
CH3CHBrCH3 = 2-bromopropane



CH2=CHCH2CH3 = but-1-ene
CH3CH=CH2 = but-2-ene



They have similar chemical properties but the different positions cause differences in physical properties.



[Functional Group]



Isomers have different functional groups
they have different physical and chemical properties.



C3H6O:



CH3CH3CHO or CH3COCH3
propanal propanone



C3H6O2



CH3CH2COOH or CH3COOCH3 or HCOOCH2CH3
propanoic acid methyl ethanoate ethyl methanoate



[[Stereoisomerism]]



MOLECULES WHICH HAVE THE SAME STRUCTURAL FORMULA BUT THEIR BONDS ARE ARRANGED DIFFERENTLY IN SPACE



[Geometrical (Cis-Trans0 Isomerism]



Carbon carbon double bonds cannot rotate died to electron clouds above and below plane of the bond.
If there are two different groups at each end of the double bond then cis-trans isomerism results.


Cis: Two identical groups on the same side of the double bond
Trans: Two identical groups on oppersite sides of the double bond



Geometrical Isomerism is not possible when there are two identical groups on the same carbon.

Chemistry [[Module Three]] Nomencalture Naming Organic Compounds

[[Rules]]

1) Identify the length of the carbon chain, and name accordingly
Numbers of carbon in chain:
1 = methane = CH3
2 = ethane = Ch2CH3
3 = propane = CH2CH2CH3
4 = butane = CH2CH2CH2CH3
5 = pentane = CH2CH2CH2CH2CH3
6 = hexane = CH2CH2CH2CH2CH2CH3

2) Number the carbons so that any branches/functional groups fall on the lowest posible carbon

3) Identify branches/functional groups
List functional groups/branches in alphabetical order. This takes precedence over the numbers of the groups.




The Functional Groups:

Chemistry [[Module Three]] Nomenclature and Isomerism

[[Nomenclature]]

Empirical Formula: Simplest ratio of atoms of each element in a compound
Molecular Formula: Actual number of atoms of each element present in a compound.

To find emirical formula: Compoun X is found to contain 40.0% carbon, 6.7% Hudrogen and 53.3% Oxygen by mass.

% Mass 40.0 6.7 53.3
/Ar 40.0/12 = 3.33 6.7/1 = 6.7 53.3/16 = 3.33

/smallest 3.33/3.33 = 1 6.7/3.33 = 2 3.33/3.33 = 1

Simplest 1 2 1
ratio

Empircal Formula = CH2O

Finding the Molecular Formula - you need to know the mass of the compound.

Work out mass of empirical.

Equation = Molecular Formula = mass of molecular/mass of empirical x empircal formula.

Example = mass of empirical = 12 + 2 +16 = 30
mass of molecular = 60

60/30 = 2 x CH20 = C2H4O2



Isomers: Compounds with the same molecular formula, but in which the elements are arranged differently
Structural Isomers: Compounds with the same molecular formular but with different structures and represented by different structural formula

Structural Formula: shows the atoms present and all of the bonds between the atoms

The abbreviated Formulae are used in equations, but Molecular Formulae should not be used. This avoids confusion.

Functional Group: atom or group of atoms which, when present in different molecules, causes them to have simlar chemical properties

Homologous Series: A family of molecules which all contain the same functional group and an increasing number of carbons

CnH2n+2 = alkanes
CnH2n = alkenes and cyclic alkanes
CnH2n+1OH = alcohols

All members of the same homologous series have similar chemical properties.
Their physical properties gradually change as the length of the carbon chain increases. For example, boiling point of alkanes increases as number of carbons increase.

Chemsitry [[The A2 practical]] June 2006 Paper and Mark Scheme

3) Planning - Finding the order of a chemical reaction.

* State appropriate volume of gas - 20-25cm
* Use this volume to calculate the second calculation, in this case the volume of solution needed for dilution.

Apparatus:
* Appropriate container for reaction - any vessel with a gas outlet and a stopper
* Appropriate collection of gas - over water or by syringe
* Apparatus for measuring volume of solution - measuring cylinder, pipette, buerette etc
* Thermostatic control - waterbath

Method:
* measure out specified volume of solution
* Keep mixtures at 20 degrees
* Take volume readings at suitable time interviews (or measure time taken to collect specific volume of gas).
* Experiment with at leats 2 concentrations of gas

Results
* Mesasure volumes at regular untervals
* plot senisble graph of results of volume vs time
* Clear and correct explaination of rate from graph
* clear correct explanation of use of rate data to establish first order

Hazards
* Phenol = toxic/corrosiv = wash spillages with cold water
* Eye protection.
* Pipette filler

Chemistry [[The A2 Practical Exam]] Preparation of Aspirin

[[The preparation of 2-hydroxybenzoic acid]]

1. Set up appartus to heat 30cm3 reaction mixture in a waterbath with the use of a condensor to prevent the loss of product
2. 2g Oil of wintegreen into flask
3. Add 25cm3 of 2 molar sodium hydroxide and antibumping granules
4. Heat over boiling water bath for 30 minutes
5. Pour mixture into beaker surrounded by ice and water
6. Add HCl drop by drop until solution is slightly acidic, stirring at all times
7. Filter product using buchner funnel
8. Wash product with ice water and transfer to weight watch glass
7. Leave to dry over night

[[The preparation of Aspirin]]

1. Use 1g of 2-hydroxybenzoic acid and weigh accuratly
2. Put into pear shaped flask
3. Add 2cm3 ethanoic anhydride and 8 drops of concentrated phosphoric acid. Put condensor on the flask.
4. Warm mixture in hot bath in fume cupboard until all the mixture has disolved and for a further 5 minutes
5. Add 5cm3 of cold water
6. Stand in bath of iced water until ppt is complete - may be necessary to stir vigorously to start ppt process
7. Filter off product using buchner funnel
8. Wash with cold water and transfer to a weighted watch glass
9. Leave to dry over night
10. Weigh product.

[[Recrystallisation]]

1. Dissolve sample in minimum quantity of hot solvent
2. Filter the hot solution using buchner funnel
3. Allow solution to cool slowley
4. Filter cool solution using buchner funnel
5. Wash residue with cold solvent
6. Dry filtrate and Weigh.

Chemistry [[The A2 Practical Exam]] Redox Titrations

The two most widley used oxidising agents and their reduction equation:

Potassium Manganate (VII)
MnO4- + 8H+ + 5 e- ---> Mn2+ + 4H2O

Potassium Dichromate (VI)
Cr2O72- + 14H+ + 6e- ---> 2Cr3+ + 7H20

[[Analysis of Iron Tablets]]

[Introduction]

Iron Tablets from the pharmacist contain anhydrous iron (11) sulphate, cheap and soluble form of iron, plus unreactive binders. Iron tablets are taken to boost Fe2+ concentration in the blood of anaemic people.

Each tablet can be dissolved in dilute sulphuric acid. Assuming that all the iron in the tablet is Fe2+ and that it is all dissolved, it is possible toe estimate the percentage iron (ii) sulphate content of each tablet by titration agaisnt standardised potassium manganate VII.

[Proceedure]

1) Weigh out 8 iron t ablets and record the mass
2) Dissolve the tablets in about 100cm3 of 2M sulphuric acid
3) Outer coat will not dissolve so filter the substance
4) Pour filtrate into 250cm3 volumetric flask, add washings from conical flask and filterpaper. Make up to the mark with distilled water.
5) Pipettes 25cm3 into conical flask and add about 25cm3 of dilute sulphuric acid
6) Titrate agaisnt 0.020M potassium manganate VII. The end point is a colour change from colourless to permanant pink
7) Repeat until concordant results are obtained.

[Notes]

*Potassium Manganate (VII) in burette and acidified iron (II) solution in conical flask.
*Both oxidising agents work strongly in acidic conditions - H+ ions are needed for the reaction.
*Choice of acid is important - HCl cannot be used in manganate titrations because the Mn will oxidise the Cl- to Cl2. But HCL can be used in dichromate titrations since the dichromate ions i=s not strong enough to oxidise the Cl- ions. Weak acids (ethanoic) cannot be uised as they do not provide a high enough [H+]
*No indicator is used for managanate as the solution acts as its own indicator. The purple manganate (VII) is reduced to manganese (II) which is colourless. One drop of manganate (VII) will produce a permantly pale pink colour = endpoint.
* Potassium dichromate needs a indicator = barium N-phenolphenylamine-4-sulphonate. Endpoint = blue green to violet.
* H3PO4 is added to enhance the end point of potassium dichromate titrations.

[results]

Mass of iron tablets = 6.82g
Mean Titre Value = 24.55cm3

1) Find the moles of MnO4- = V/1000 x c = 24.55/1000 x 0.020 = 4.91 x 10-4
2) Molar ratio from equation = 1:5
3) Find moles of Fe2+ in 25cm3 = 4.91 x 10-4 x 5 = 2.45 x 10-4
4) Find moles of Fe2+ in 250cm3 = 2.45 x 10-4 x 10 = 2,45 x 10-3
5) Mr of FeS04 = 152
6) Mass of FeS04 in tablets = m = n x mr = 2.45x10-3 x 152 = 3.373g
7) find % mass =

3.373/6.8 x 100 =

54.7%

Chemistry [[The Practical Exam]] Planning Technique

[[Working Out the Volume to Use]]

* Pick suitable volumes for the equipment that you are using and justify any measurements stated.

E.g,

CuO(s) + H2S04(aq) ---> CuSO4 + H2O

* reaction done in a 100ml beaker
* Saftey issues
* Use 25cm3 of H2SO4

- caluculate mass of CuO to use, using n = m/mr and n = v/1000 x c
= 2grams

In excess?
* think about how to seperate the final products
H2SO4 and CuSO4 cannot be seperated easily
Cu0 and CuSO4 can be seperated by filtering so double the value

= 4g of CuSO4

[[Measuring a Temperature]]
*change the concentraition to create a suitable change in temp

Chemistry [[The Practical Exam]] How to Carry Out a Titration

[[Making A Standar Solution]]

A solution of a known concentration
There are two ways of making a standard solution: Solid and Liquid

[[Liquid]]

1) Use an appropriate sized volumetric flask (250ml)
2) Clean a 25ml pipette with the solution to be diluted using a pipette filler
3) Fill the pipette up to the mark with the solution to be diluted. Read from the bottom of the meniscus
4) Allow solution to drain under gravity into the volumetric flask and touch surface of solution with pipette
5) Make up to the mark with distilled water
6) Shake to ensure contents are mixed.

[[Solid]]

1) Work out the mass of solid needed:

To prepare 250cm3 of 0.1M NaOH solution from NaOH solid:

* Work out the nuumber of moles.

n = v/1000 x c so n = 250/1000 x 0.1 so n = 0.025mols

*Work out the mass

n = m/mr so m = n x mr sp m = 0.025 x 40 so m = 1.00g

2) Mass is weighed out on an accurate mass balance
3) Carefully transfer into volumetric flask
4) Wash weighing boat with distilled water and transfer washings into volumetric flask
5) Make up to the mark with distilled water
6) Shake flask to ensure that contents are mized.

[[The Titration]]
* Acid/Alkali titrations = acid in burette
* Use appropriate size burette and flask

2) Rinse out pipette
3) Fill pipette using pipette filler, up to the mark, and then allow contents to drain under gravity into conical flask.
4) Touch pipette tip to surface of solution to allow for capillary action
5) Add a few drops of appropriate inditcator
6) Rinse out burette
7) Fill burette using funnel ensuring that tap is closed
8) remove air space between tap and tip of burette and remove funnel
9) Read initial volume at eye level of solution in the burette
10) Carry out a rough titration - allow to drain and shake to mix acid with alkali
11) When colour of indicaor permanatly changes, stop adding from burette -> record volume at eye level
12) Volume is always quoted to 2 decimal places, the first one always '0' or '5'
13) Repeat using fresh solution, HOWEVER
i) Towards end point add solution drop by drop
ii) Rinse sides of conical flask with a little distilled water
14) Repeat again until at least two concordant values have been obtained.

[[The results]]

- All results should be recorded
- Average out the concordant values.

[[Health and Safety]]

- Acid and alkali are corrosive
- wear saftey glasses
- rinse spillages from skin immediatly
- mop up spillages on bench
- wear gloves for highly corrosive or toxic materials

[[Errors]]

- There are two types of error in a practical exam
* Measuring
* Procedural

% error in measuring = accuracy of measuring equipment/measurement made x 100

% difference = difference between actual and expected result/expected result x 100

Biology [[Control, Coordination and Homeostasis]] The Structure iof the Kidney

[[Structure of the Kidney]]

Kidneys recieves blood from a renal artery and returns it via a renal vein. Urine is carried from the kidney to the bladder via the ureter. From the bnladder, the uretha carries it to the outside of the body.

The kidney has three main areas.
* The whole kidney is covered by the capsule.
* Underneath the capsule lies the cortex
* The central area is called the medulla
* The area where the ureter joins is called the pelvis

Kidneys are made up of tiny tubes called nephrons
One end of the nephron is cup shaped, and is called a Bowmans capsule (or renal capsule) and these are located in the cortex of the kidney.
The tube then runs towards the center of the kidney, forming a twisted region called the proximal convoluted tuble. Then it runs in a long, hair pin loop called the loop of henle.
The tube runs back up into the cortx where it forms another twisted region called the distal convoluted tube
The tube joins a collecting duct, which leads down through the medulla and into the pelvis of the kidney, where it joins with the ureter.

Each renal capsule is supplied with blood by a branch of the renal artery - 'afferent arteriole' which splits into a glomerulus. These rejoin to form an 'efferent arteriole' and then links back of with other capillaries to go to the renal vein.

Biology [[Control, Coordination and Homeostasis]] Excretion

[[Excretion]]

Metabolic reactions occuring within the body produce unwanted substances.
Some are toxic

Excretion if the removal of these waste products.

The two products made in greater amounts than most in the human body are CO2 and Urea.
* CO2 is produced continuously by every cell in the body by aerobic respiration The waste CO2 is transported via blood to the alveoli where it is excreted into the air that we breath out.

*Urea is produced un only one organ in the body: The Liver
Its is produced from excess amino acides and is transported from the liver to the kidnesy, in solution in blood plasma.
The kidneys remove urea from the blood and excrete it dissolved in water as urine.

[[Deamination]]

More Protien is eaten than is needed, the excess cannot be stored. It is wasteful to get rid of the excess however, as amino acids contain useful energy. The nitrogen atoms are removed from the amino acide molecules in the liver. The amino acide molecule is kept, the nitrogen is excreted as Urea.

This process is deamination.

NH3 is removed from the amino acid, leaving C(R)OCOOH and NH3 (keto acid and ammonia)
The keto acid can be converted into a carbohydrate and used in respiration, or could be converted into fat and stored.

Ammonia is highly soluble and toxic. For this reason, it is immediatly converted to the less soluble and less toxic compound Urea

2NH3 + C02 ---> C(NH2)2O + H2O

An adult produces 25-30g a day

Humans also produce other nitrogenous waste compunds, such as creatinine and uric acid.

Biology [[Control, Coordination and Homeostasis]] Homeostasis

[[Homeostasis]]

Maintaining a stable, internal environment. Internal environment is the conditions inside the body in which cells function. E.g. Tissue Fluid

The fuctioning of a cell can be determined by many things, including:

Temperature
* Low temps slow metaolic reactions, while high temps cause the denaturing of protiens and enzymes

Amount of Water
* lack of water in the tissues causes water to be drawn out of the cell by osmosis causing metabolic reactions to slow and/or stop.
* Too much water entering the cell can ccause it to swell and burst

Amount of Glucose
* lack of glucose causes respiration to slow and/or stop
* too much glucose may draw water in by osmosis

Homeostatic mechanisms wirk by controlling the composition of blood, which controls the composition of tissue fluid.
Most control mechanisms use a negative feedback control loop.

[[Negative Feedback Loops]]

The receptor picks up information about the parameter being regulated. This is known as the input. The input sets of a series of events culminating in some action by the effector. This is called the output. Continuous monitoring of the parameter by the receptor produces continuos adjustments of the output. This keeps the parameter oscilliating around an ideal level.

In negative feedback loops, a rise in parameter result in something happening which makes the parameter fall.

[[Positive Feedback Loops]]

There are a few instances of the opposite thing occuring in living organisms. If a person breathes air with a high percentage of CO2, there is a high percentage of CO2 in the blood. This is sensed by the carbon dioxide receptors, which causes breathing rate to increase. The person breaths faster, taking in even more CO2, which stimulates the receptors even more and makes the person breath faster. This is an example of positive feedback.

Positive feedback plays no role in keeoping things constant.

Biology [[Classification, Selection and Evolution]] Classification

Taxonomy: the study of the classification of organisms

Organisms can be classified accroding to their evolutionary relationships. To do this, taxonomists look for shared homologous features between different organisms.

Homologous Features: features which appear to have similar underlying designs, and so have evolved from the same original design which exsited in a particular organism at one stages.

For example: limb bone of veterbrates
Single bone in upper limb, two bones in the lower limb.
This is the same for all vertabrates

All organisms are grouped into Species. Species which share homologous features are grouped into a Genus.
Every species is given a two word latin name called a binomal, the use of which is global and precises. The binomal is made up of the name of the organisms Genus, followed by that of its species. The first name has a capital letter, the second does not. Both are written in italics, and when italics cannot be used (eg hand writing) the binomal should be underlines.
Genera(Genus) are grouped into Families, which are grouped into Orders, which are grouped into Classes, which are grouped in to Phyla and which are, in turn, grouped into Kingdoms.

For Example: Zebra

Kingdom: Animalia (non-photosynthetic multicellular organisms)
Phylum: Chordata (animals with stiffening rod along back)
Class: Mammalia (chordates with hair and mammary glands)
Order: Perissodactyla (mammals with hooves made up of an odd number of toes)
Family: Equidae (horse-like perissodactyla)
Genus: Equus (horses, zebras and asses)
Species: burchelli (common zebra)

Classification represents evolutionary history of an organism and its relationship with other organisms. The evolutionary history of an organism is known as they phylogeny.

The higher up the classification system we go, we are less certain about relationships between the groups.

[[The Five Kingdoms]]
Traditionally all livings things were divided into plants and animals. Plants = anything that was not an animal, so included fungi and bacteria. As microscopy allows us to see more detail of cell structre, it became clear that the 'plant' group actually contained several groups.

1988 - Margulis and Schwartz proposed that the living world should be divided into 5 Kingdoms
Prokaryotae
Protoctista
Fungi
Plantaw
Animalia

Prokaryotes
Organisms made up of the prokarytic cells.
* no membrane bound organelles
* small ribosomes
* single loop of DNA

Protoctists
Simple Eukaryotic organisms
* many are unicellular
* can be filamentous, colonial or thalloid
* can be auutotrophic or heterotrophic
* most are aquatic or live in moist conditions such as the soil

Fungi
Eukaryotic organisms that feed heterotrophically
* Cells have cell walls
* Unlike plant cells they contain materials such as Chitin
* Cell walls are never made from cellulose
* Considered saprotrophs or parasites
* Can be unicellular

Plants
Multicellular eukaryotic organisms that feed by photosynthesis.
* Cells have cell walls made of cellulose
* Some cells contain chloroplasts
* Cells contain large, sap filled Vacuoles

Animals
Multicelular eukaryotic organisms that feed heterotrophically
* cells do not have cell walls
* cells never contain chloroplasts or vacuoles

This system is widley used but some biologists have reservations about it
Protocists are not related to each other, and are put in that group because they do not fit anywhere else

Biology [[Classification, Selection and Evolution]]Species and Speciation

Speciation: The production of new species

What is a species?
A species is a group of organisms with similar morphological, physiological, biochemical and behavioural features, which can interbreed to produce fertile offspring and are reproductively isolated from other species.

Morphiological: Structural features
Physiological: Way the body works
Biochemical: sequence of bases in DNA.

For Example: Donkeys and Horses.
*Donkeys look and work like other donkeys and can breed with donkeys to produce donkeys. This concludes that all Donkeys are of the same species.
* Donkeys can breed with Horses, which are similar.
* These produce Mules
*Mules cannot breed, so they are infertile (they are a dead end)
* The conclusion is that Donkeys and Horses are not the same species.

This test is not always possible, as the organisms may be dead, museum specimens or fossils, both of the same sex, or perhaps even the biologist does not have the time or the equipment necesary. Some organisms will not breed in captivity, or may be immature and unable to breed. For these reason, it is rare to test this.

Biologists rely on morphiological, physiological, biochemical and behavioural differences to decide whether or not two specimens are of the same species.

To produce a new species, then two groups of the same speices must become reproductivly isolated from each other. This takes time, so experiments are impossible. The evidence is circumstantial.

[[Allopatric Speciation]]

Geographical Isolation

Suggested by the fact that many islands have their unique species. There are species in the Galapagos and Hawaiian Islands found only there.

This type of isolation requires a barrier to prevent the species from mixing.
e.g. Water

For Example: Hawaiian Birds

*Birds arrive on Island, perhaps blown by a storm
*They are seperated from their species by the ocean
*Selection pressures on the island are different from those on the mainland
*The group interbred
*Different Alleles were selected
*Over time, the morphiological, Physiological, biochemical features became so different the species could no longer interbreed
* A new species had evolved.

Other barriers:
Dense forest cut down to leave "islands" of forest will isolate groups of species.

Allopatric = different places

[[Sympatric Speciation]]

A new species arises without the original population being seperated by a geological barrier

The most common way by which this can happen is through Polyploidy

A polyploid organism is one with more than two complete sets of chromosomes in its cell. This can happen if meiosis goes wrong when gametes are being formed and a gamete ends up with two sets of chromosomes. If two such gametes form then the zygote gets for sets of chromosomes instead of one = tetraploid

Tetraploids formed like this are sterile. All four chromosomes try to pair up in meiosis one and get confused, so it is difficult for the cell to divide by meisos and produce new gametes

The organism will still be able to grow and reproduce asexually, as mitosis can still occur. This happens in plants, but rarely in animals

This type of polyploidy is called autopolyploid as all four sets of chromosomes are from the same species. If two sets of chromosomes are from one species, and two sets from another, then it is alloploid. Meiosis happens more easily in an alloploid than an autoploid.

Biology [[Classification, Selection and Evolution]] Darwin-Theory of Evolution by Natural Selection

The original thoery that natural selection might be a mechanism by which evolution could occur was put forward inependantly by Charles Darwin and Alfred Russel Wallace.

They knew nothing of gene mutations nor understood about natural variation and inheritance. There observations are summarised below:

Observation One: Organsism produce more offspring than are needed to replace parents
Obervation Two: Natural populatiosn tend to remain stable in size over long periods

Deduction One: There is a competition for survival

Observation Three: There is variation among the individuals of a given species

Deduction Two: The best adaptad variants will be selected for by the natural conditions operating at the time. Natural selection will occur. 'survival of the fittest'

Biology [[Classification, Selection and Evolution]] Artificial Selection

Selection pressures can be applied by humans, and these are sometimes the most important. Artificial selection is defined as humans purposely applying selection pressures to populations.

For Example: Cattle

Desired features indclude
*Docility
*fast growth rates
*high milk yield

Increses in these characteristics have been achieved by selective breeding.

*Inidviduals showing one or more of these traits to a larger degree than others are selected for breeding. Some of the alleles for theses features are passed on to their offspring.
*The best from the second generations are picked and breed

Over many generations, the allele frequency for the chosen characteristics will increase. In many cases, disadvantageous alleles are lost completely.

Biology [[Classification, Selection and Evolution]] Evolution

[[Evolution]]

Natural selection keeps things the way they are, and this is Stabilising Selection. But if a new environmental factor or new allele is introduced, allele frequencies can change. This is directional selection.

[[A new Environmental Factor]]

If the climate is plunged into a new ice age and snow covers the ground for 11 months out of 12, the white rabbits now have a selevtive advantage, as they are camoflauged agaisnt the white environment. So rabbits with white fur are more likley to survive in this new environment, and reproduce, passing on their alleles.

The allele for the white coat increases in frequency. Over many generations, almost all rabbits will have white coats (but the allele will still be recessive)

[[A New Allele]]

Most mutations are harmful as they produce organisms that are less well adapted to their environments than normal organism is. Some are neutral, which means that they produce neither advantageous or disadvantageous. Occasionally mutations may produce useful features.

Such changes in the allele frequency (rabbit mutation results in change in coat colour which is better camouflaged, so that allele survives and is passed on) are the basis of evolution.

Evolution: occurs when natural selection gives some alleles a better chance if survival than others

Some examples of Evolution.

[[Antibiotic Resistance]]
Antibodies: chemicals produced by living organisms, which inhibit or kill bacteria. They do not usually harm human tissue. Produced by fungi.
First antibiotic discovered = Penecillin
It stops cell wall production and prevents cell reproduction.

If someone takes penecillin to treat a bacterial infection, bacteria sensitive to it are killed. In most cases, this is the entire population. But there may be one or two that have an allele giving resistance to the penecillin. This occurs in Staphylococcus (some individual bacteria produce enzym penicillinase which inactivates penecillin).

Bacteria only have a single loop of DNA so they have one copy of each gene. The mutant allele has an immediate effect on the bacteria's phenotyope.

The bacteria without resistance will be killed, while those with the resistance survive and reproduce rapidly.

[[Industrial Melanism]]
Peppered Moth is a night flying moth which spends most if its time resting on the branches of trees and relies on camouflage to protect it from insect eating birds.

Until 1848, all peppered moths had pale wings with dark markings = speckled appearance
In 1848, a drak individual specimen was caught

Over 19th century, numbers of dark moths increased rapidly in some areas, while remained low in other areas.

The difference in colour is caused by a single gene. The normal speckled colour is recessive and the black is dominant. The frequency of the dominant allele increased near to industrial cities up to 1960s, while it remained the same in non-industrial areas.

The selection pressure which caused this change was predatation from birds. Lichens which cover the trees and make the light moths camouflage are sensitive to pollution levels and do not grow on trees in suc areas. This means that the trees are darker brown, so the lighter moths stand out and are eaten by the birds.

Pollution levels are being reduced, and it is predicted that there will be hardley any specimens left soon.

[[Sickle Cell Anaemia]]

The gene that codes for Beta Polypeptides has to alleles. Hn can produce normal cells while Hs can produce sickling of redblood cells. Homozygous Hs produces a phenotype of sickle cell anaemia (often lethal)

Until recently, almost everyone homozygous for Hs died before they reached reproductive age but their are still very high frequencies of the sickle cell allele is very high. This is due to the high incidence of Malaria in these parts of the world. People who are heterozgous are much less likley to suffer an attack of malaria than people who are homozygous for normal allele

Two selectron pressures:
* Selection agaisnt homozygous Hs people as they are seriously anaemic
* Selection agaisnt people homozygous Hn as they are more likley to suffer from Malaria

Biology [[Classification, Selection and Evolution]] Natural Selection

[[Natural Selection]]

Some rabbits are born with a better chance of survival than others. The variation within the population of rabbits mean that some will have features that will give them an advantage. Coat colour is an example of this, as those rabbits with the phenotype 'white coat colour' stand out agaisnt the environment and are more likley to be killed by predators. The gene for this coat colour is recessive, so the chances of a rabbit passing it onto offspring are small.

Selection Pressure: increase the chances of some alleles being passed on to new generations and decrease the chances of others being passed on.

The effect s f selection pressures on the frequency of alleles in a population is called Natural Selection.

Natural Selection: raises the frequency of alleles resulting in an advantage and reduces the frequency of alleles resulting in a disadvantage.


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Biology 2, OCR