Who's cheating on the vinegar?

Titration is a form of neutralisation. This is a process of determining the concentration of a substance in solution. A measured amount of a known solution concentration (molarity) is added to an unknown volume of a second solution in carefully measured amounts until a reaction of definite and known proportion is completed. Neutralisation is when a Hydrogen ion and a Hydroxide ion react together to form water which is neutral.

Variables:  

• Amount of acid (vinegar)
• Sample of Vinegar

I will be changing the vinegar samples as I will be testing shop A, B, C and Safe Way. The amount of alkali will change because the vinegars may have different molarities.

Apparatus: 

• An Acid                          

 

• An Alkali                      

 

• A Burette  

• A conical flask

• A stand and a clamp

• A beaker

       

• A Pipette

• An Indicator (methyl orange)

.  

Theory: 

Whichever vinegar needs the most alkali to neutralise the acid has been watered down, once this has been done the results have to be calculated into the same units, I will be using moles (M). the difference between the molarity of the acids can tell me which has been watered down the most.

Prediction:

The acid with the lowest molarity has been watered down, but unless I test pure ethonoic acid, or find out its molarity then I don’t know if the highest molarity of acid has been watered down.

Diagram:

Method:

Step 1: Wash out all equipment.

Step 2: Set up the stand and fit the burette in place with the clamp above the conical flask.

Step 3: Take out the burette and fill with sodium carbonate.

Step 4: Measure the first acid (shop A) in the pipette then put into beaker underneath, then take the conical flask from under the burette and pure in acid.

Step 5: Dilute the acid with pure H2O so there is a higher volume to work with

Step 6:  Start the titration by turning the tap of the burette very slightly and adding a small amount of sodium carbonate at a time.

Step 7: Record results in a table.

Step 8: Repeat the experiment so you have two sets of results

Step 9: Repeat all steps with the other acids

Test results:

Working out the molarity:

Na2CO3 = sodium carbonate

CH3COOH = ethonoic acid

Equation for the reaction of neutralisation with ethonoic acid and sodium carbonate:

2 CH3COOH + Na2CO3 → 2CH3COONa + CO2 + H2O

This equation shows that;

2 moles CH3COOH = 1 mole Na2CO3

So to work out the molarity of each acid I need to use the equation below: (V = volume M = molarity)  

V CH3COOH * M CH3COOH = 2 * ( V Na2CO3 * M Na2CO3)

   

Molarity of CH3COOH = ?

Volume of CH3COOH = 10cm^3

In order of highest molarity:

1.  Shop A          =  0.031 M
2. Shop B          =  0.021 M
3. Safe Way     =  0.014 M
4. Shop C          =  0.0088 M

Conclusion:

The acid with the lowest molarity has been watered down. I know this because it took less alkali to neutralise it. Shop B, Safe Way and Shop C have obviously been watered down because they have a lower molarity than shop A. So the chip shop owner should only buy shop A vinegar as it is the strongest and he is getting more vinegar for his money.

Evaluation:

To ensure my experiment was a fair test I had to make sure all the variables were the same. I made sure the factors, which needed to be constant, were constant, for example the volume of vinegar was measured accurately. I also made sure any human errors such as not switching the tap off in time were to the best of my ability. This made the experiment a fair test. These are important factors because it can be detrimental to how accurate my results are.

 

The test was a success because we found out which was the strongest vinegar for the chip shop owner to buy.