Finding out how much acid there is in a solution

Variables

The Variables involved in this experiment are:

• The amount of sulphuric acid
• The amount of sodium carbonate
• The amount of methyl orange

My independent variable is the amount of sodium carbonate added to the acid and indicator. This is because different amounts of sodium carbonate will be added to make the acid turn pink.

My dependant variable is the amount of sodium carbonate solution before titration and after titration. This is so I can find the amount of acid in a solution.

My control variable is the amount of Methyl orange. If I have too much or too little methyl orange it could affect the PH value. Therefore affecting the results.

Equipment

• Solution of acid with unknown concentration between 0.05 and 0.15 dmˉ ³  
• Sodium carbonate solution 0.01dmˉ ³
• 100 cm³ conical flask
• 10 cm³ pipette
• Pipette filler
• Burette
• Methyl orange

Procedures

1. Before I will start my experiment, I will assume that all the apparatus are unclean and to ensure that I eliminate error, I will clean my apparatus.
2. I will do so by firstly, rinse out my apparatus with distilled water and then rinse it again with a little bit of the reactants that I will use.
3. Use a pipette and pipette filler to transfer 10.0cm³ of the acid solution to a conical flask. Add 5 drops of methyl orange.
4. Fill a burette with 0.01 mol dmˉ ³ sodium carbonate solutions.
5. Record the volume reading in the burette before starting the titration. Then add sodium carbonate solution, in small quantities to the acid solution in the conical flask. Mix the flask contents after each addition.
6. Run in the small volumes of sodium carbonate solution until you first observe the appearance of a permanent red colour in the titration mixture. This is the end point.
7. Record the final burette reading and calculate the volume of sodium carbonate solution you have used.
8. Repeat the titration several times until you record three volumes that agree within 0.1 cm. When you get near the end points of those titrations, you should add the sodium carbonate carefully, adding only one drop of solution at a time until the permanent red colour is produced

I have used this method because of the following reasons:

• I cleaned my apparatus to get rid of any impurities. Therefore to eliminate error
• It is important to try and get 3 titres within 0.1 of each other. This shows that you have successful results. If you do not have 3 titres within 0.1 of each other then you must continue to do further titres until you have 3 successful titres. It is important that each time you do a titration; you must wash out the equipment with distilled water thoroughly, to reduce contamination, providing better results.

Risk assessment

I am using the following chemicals in this experiment: Sodium carbonate, Sulphuric Acid and Methyl Orange.

Sodium carbonate is an irritant. Therefore I will be careful hen handling this chemical and I will wear a lab coat and safety goggles.

Sulphuric Acid is a corrosive acid and addition of water produces a lot of heat. Gloves and safety goggles should be used whenever using this concentrated acid.

Methyl Orange is thought to be highly flammable and it also stains. Therefore safety goggles, a lab coat and gloves should be worn.

Sources

• Hazards for the following chemicals: Sodium carbonate, Sulphuric Acid and Methyl Orange.
• Information sheet on the use of indicators in acid alkali titrations.
• EL2.1 How much iron is in a sample of an iron compound.
• M2.4 Finding out how much acid there is in a solution.
• Letts AS chemistry Page 35 and 40