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