# Finding out how much acid there is in a solution.

Finding out how much acid there is in a solution – Chemistry Coursework

PLAN

Aim:

The purpose of this experiment is to find an accurate concentration of sulphuric acid (H SO ) using titration with anhydrous sodium carbonate (Na CO ). I am told that the concentration of sulphuric acid is between 0.05 mol dm  , but the task is to find out the exact concentration.

The followng equation shows a reaction between sulphuric acid and sodium carbonate solution.

Na CO (aq) + H SO (aq)                     Na SO  (aq) + CO (g)

This equation is a neutralization reaction. 1 mole of sodium carbonate reacts with 1 mole of sulphuric acid (see equation). When reacting together, both solutions will have the same number of moles.

From reliable sources, I have been able to determine which of the various indicators to use in the titration. I found that methyl orange was the most suitable due to the fact that the titration to be carried out is between sulphuric acid (strong acid) and sodium carbonate (weak alkali).

Firstly I will have to prepare a solution of sodium carbonate that will be used in the titration with sulphuric acid.

It can be seen from the formula that it takes one mole of sodium carbonate to neutralise 1 mole sulphuric acid.

Molecular mass of Sodium carbonate                = (23X2) + (12) + (16X3)

= 106g

Molecular Mass of Sulphuric Acid                = (2X1) + (32) + (16X4)

= 98g

It would take 106 grams of sodium carbonate to neutralise 98 grams of sulphuric acid if their molar concentrations were equal. As the exact concentration of sulphuric acid is not known an accurate prediction cannot be made. But the concentrations of the solutions are similar, therefore it should take roughly an equal amount of each substance in order that neutralisation occurs. This helps to determine the volume of the sample of sodium carbonate to be used.

As the concentration of the acid solution is between 0.05 and 0.15 mol dm. Then we can calculate the average amount to be used in the experiment.

0.05 + 0.15                 = 0.1 mol dm

2

This would also be the volume for the sodium carbonate solution as the equation shows that sulphuric acid and sodium carbonate have a ratio of 1:1, and therefore approximately equal the same number of volumes.

Firstly I would need to find the number of moles of sodium carbonate in order to find its mass in grams. We do this by using the following equation:

No of moles = concentration × volume

We worked out the average concentration as 0.1 mol dm and the volume used is 250cm. The solid anhydrous sodium carbonate will be dissolved in water. I will be using 250 cm of this solution of sodium carbonate as this is a sufficient amount of sodium carbonate solution in order to complete at least 6 titrations.

However before placing the amounts into the equation I would need to convert the 250cm into dm:

250                = 0.25 dm

1000

Hence, we place the amounts into the equation to achieve the number of moles.

No of moles         = 0.1 mol dm × 0.25dm

= 0.025

To find the mass of sodium carbonate we use the following equation:

Relative Molecular Mass × no of moles         = Mass in grams

106g × 0.025                                        = 2.65g

Therefore, I will be using 2.65g of solid anhydrous sodium carbonate to dissolve in the 250cm water.

Apparatus

These are the requirements, showing the apparatus and the quantities of the materials used:

2. 10 cm pipette
3. Pipette Filler
4. 100 cm beaker
6. 50 cm burette
7. Spatula
8. Methyl Orange indicator
9. Electronic Weighing scale within 0.01g
10. Goggles
11. Wash bottle of distilled water
12. Stirring Rod
13. Filter Funnel
14. Anhydrous Sodium Carbonate (2.65g)
15. Watch Glass

Method:

The burettes and pipettes must be both clean and dry or rinsed before use.

1. Ensuring that the watch glass is perfectly clean Place it on to the electronic weighing scales. Before placing the anhydrous sodium carbonate onto the watch glass, the tier on the electronic weighing scales would need to be to 0. This is to prevent the scales from including the weight of the watch glass in the reading as well as the product being measured. Using a spatula, transfer 2.65g of sodium carbonate on to the watch glass and weigh it on the electronic weighing scales. Ensure that you have exactly 2.65g of sodium carbonate to the nearest 0.01g.

1. Place 50 cm of distilled water into a 100 cm beaker. Transfer the weighed sodium carbonate to the beaker, and mix the solution together until the sodium carbonate is completely dissolved.

1. Transfer the solution to a 250 cm volumetric flask through the filter funnel. Place the stopper on to the top of the flask and shake once again.

1. Rinse the beaker thoroughly and transfer the remaining distilled water bit by bit into the volumetric flask, shaking it each time. Also make sure that the meniscus line does not go over the graduation mark.

1. If necessary, add distilled water until the level is within 1cm of the mark on the neck of the volumetric flask. You can then use a dropping pipette to add enough distilled water to reach the bottom of the meniscus line.

1. Insert the stopper and shake the mixture several times. Not mixing the solution very well can cause common faults.

1. Pipette 10 cm of the sodium carbonate solution to a clean conical flask.

1. Add three drops of the methyl orange indicator using a small dropping pipette into the solution in the conical flask. This ensures that the same amount of indicator is used for each solution, this then gives a constant environment and ensures that all titration end points are based on the same amount of indicator. Methyl Orange produces a yellowish colour in ...