concentration of acid rain

Determination of the concentration of acid rain

The burning of fossil fuels has released tonnes of sulphur dioxide into the atmosphere, the consequence of which has been the formation of acid rain. Rain water is naturally acidic due to the presence of hydrocarbonate ions, but for this exercise it is to be assumed that all the acidity is caused by the presence of sulphuric acid.

Aim: to calculate the concentration of sulphuric acid in acid rain.

After consideration I have decided to use sodium hydroxide to calculate the concentration of the acid rain by means of an acid base reaction in a simple titration. Sodium carbonate was another alkali that I could have used but there are complications when using it in an acid base reaction. When the Na2CO3 reacts with the H2SO4 the CO32- ions react with the H+ to form CO2 and H2O.

The carbon dioxide gas will bubble out of the titrated solution, this my distort the solution so it will be harder to see where the end point is.

I know that the rough concentration of the acid rain is about 0.01 moles, so by means of a balanced equation I can determine the concentration of sodium hydroxide that would be suitable to titrate.

H2SO4 + 2NaOH → Na2SO4 + 2H2O

As you can see we need twice as much sodium hydroxide compared to the sulphuric acid, so a concentration of 0.02 moles will be suitable.

To make a ...

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The carbon dioxide gas will bubble out of the titrated solution, this my distort the solution so it will be harder to see where the end point is.

I know that the rough concentration of the acid rain is about 0.01 moles, so by means of a balanced equation I can determine the concentration of sodium hydroxide that would be suitable to titrate.

H2SO4 + 2NaOH → Na2SO4 + 2H2O

As you can see we need twice as much sodium hydroxide compared to the sulphuric acid, so a concentration of 0.02 moles will be suitable.

To make a solution of 0.02 moles I will need:

A mass balance that goes to two decimal places.
A 25ml pipette
Sodium hydroxide crystals
Deionised water
A 250ml volumetric flask
A 500ml beaker
A weighing bath

First weigh and record the weighing bath. Then weigh out 2g of the sodium hydroxide crystals. Pour the crystals into the 500ml beaker and dissolve in 100ml of deionised water. Reweigh the weighing bath to see if any of the crystals have been left behind.
Pour the aqueous sodium hydroxide into the volumetric flask, washing all the equipment thoroughly into the volumetric flask. Then fill the flask to the 250ml mark, making sure the meniscus is on the line.
Then pipette out 25ml and transfer to another 250ml volumetric flask, fill with deionised water to the 250ml line making sure all the meniscuses are on the lines. Then you will have a sodium hydroxide solution of 0.02 molar concentration.

Sodium hydroxide is a deliquescent molecule, this means that it will absorb water from the atmosphere, which will in turn decrease the concentration. If the concentration is lower this means that my concentration calculations will be wrong.

So it is important that a fresh batch of sodium hydroxide is made so that the concentration will be exact.

For my titration I have decided to use bromothyml blue because its transition pH range is approximately 6.0-7.6. This range is very close to a neutral solution, which is the pH we are trying to achieve.

METHOD: