be using Phenolphthaleins. This is colourless in an acid but it goes bright
pink in an alkali. This means that the solution will turn pink when it turns
from an acid to an alkali.
The term concentrated means to have more of the main
substance and less water.
When we mix an acid and alkali, we get a salt and water. It will be
like the following equation:
ethanoic + sodium -> sodium + water
acid hydroxide ethanate
Plan
Independent Variable - I will change the vinegar sample.
Dependent Variable - I will measure the amount of sodium hydroxide
that it takes to turn the solution into an alkali.
Controlled Variables - I will need to keep the following things the same:
* Drops of indicator
* Same amount of vinegar in each beaker.
Apparatus
10ml maesuring cylinder 4 vinegar samples
25ml measuring cylinder indicator
100ml beaker or conical flask sodium hydroxide
safety glasses
dropper
stirring rod
white tile
Method
1) Go and get apparatus.
2) Measure out 10mls of vinegar in a measuring cylinder.
3) Put the vinegar in a 100ml beaker.
4) Add three drops of indicator into the beaker.
5) Measure out 25mls of Sodium Hydroxide into a measuring cylinder.
6) Add the Sodium Hydroxide drop by drop until the solution turns pink.
It has to stay pink, even when you stir it.
7) Check how much Sodium Hydroxide is left at the end and work out
how much you have used.
8) Repeat for the other examples.
9) Repeat the whole experiment to be sure.
10) Tidy everything up.
Safety
* Always wear safety glasses when handing acids.
* Sodium Hydroxide is corrosive so wipe up any spillages immediately.
* Be careful not to work with too much alkali at once as it is dangerous!
Results
Sample Vol. in Ex. 1 Vol. in Ex. 2 Average Price for 10cm
A 12.5ml 13ml 12.75ml 0.024
B 19ml 17.5ml 18.25ml 0.035
C 7.5ml 8ml 7.75ml 0.02
D 5ml 5ml 5ml 0.029
Evaluation
From this graph, I can work out that of the 4 samples, the order of
concentration starting with the most concentrated is: B, A, C, D.
The costs are as follows:
Sample A- £1.20 for 500cm3
Sample B- £1.50 for 400cm3
Sample C- £1.00 for 500cm3
Sample D- £1.30 for 450cm3
The order of cost starting with the most expensive is: B, D, A, C.
Order of concentration Order of Price
MOST CONCENTRATED LEAST EXPENSIvE
B C
A A
C D
D B
I think that A was the best value for money because it is the
second most concentrated and the second least expensive.
B was good value for money because although it is very expensive,
it also is very concentrated.
C was quite good value because it was very inexpensive and didn't
wasn't bad when we tested the concentration.
D was definately the worst because it had hardly any actual
vinegar and was the second most expensive.
I think we worked ok. We should have done the experiment more
times to make sure it was totally accurate but apart from that,
everything went smoothly.