Finding out how much acid there is in a solution.

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Heena Patel                Chemistry Coursework 2003


Miss Hyde

Finding out how much acid there is in a solution.


During the extraction of a metal from its ore sulphur dioxide is often produced.  This is converted to sulphuric (VI) acid and sold as a useful by product.

The equation for this titration is:

Na2CO3 (aq)      +    H2SO4 (aq)                       Na2SO4 (aq)         +    H2O (l)      +   CO2 (g)

This experiment will be involving an acid and an alkaline.  I will be mixing both of these together to find out the concentration of the acid in the solution.  I am going to use the method of titration to find this out.

Titration is the process of determining the volume of one reactant solution, which exactly reacts, with a given amount of another reactant.

We are going to be finding out the concentration of sulphuric acid by adding it to a sodium carbonate solution.  Once neutralisation has occurred, this will be the end of the titration.  We are told that the concentration of sulphuric acid will be between 0.05mol dm-3and 0.15 mol dm-3 .  We are going to use the method of titration to find out the exact concentration.

We are also going to be using an indicator. There are many different indicators, which have different properties because the indicator changes colour at different pH numbers therefore the right one should be used which will suit the chemicals being used in the titration.  The titration will involve a strong acid, which will be the sulphuric acid, and a weak alkaline – sodium carbonate.  

Different indicators change their colour according to the hydrogen ion concentration of the solution to which they are added.

Indicators such as universal indicator do not show the pH change but the pH of a solution at a certain point.  Therefore this would not be helpful for our titration.  We will need an indicator that will change its colour quickly and react in different conditions.  In acidic solutions hydrogen ions from the acid react with methyl orange to form a red compound.  In neutral and alkaline solutions the two hydrogen atoms are lost and methyl orange is formed.

This therefore tells us the best indicator to use will be methyl orange, as it is the only indicator that will work for a strong acid and a weak alkali.

If I were using a weak acid and a strong alkali I would use the indicator phenolphthalein, as this would be more suitable.  For a titration between a strong acid and a strong alkali both methyl orange and phenolphthalein can be used, but methyl orange is mostly the chosen one. A titration involving a weak acid and a weak alkali cannot use an indicator as this will not work.  A pH meter will be more suitable.

The solution of which the concentration that will be known will be the sodium carbonate solution, which the sulphuric acid will be added to.  To start this titration, we will have to make up a solution of sodium carbonate.

The table above shows us that one mole of sodium carbonate has a mass of 106g, and one mole of sulphuric acid has a mass of 98g.

As a result we can say that 1cm3  of one mole of sodium carbonate needs a mass of 0.106g.

This is too little an amount, to make up a solution therefore the amount of solution that we have used to make up our sodium carbonate solution is 250cm3 .  To make this solution of 250cm3  we will have to use 2.65g of sodium carbonate.

The apparatus to be used:


  • Burette
  • Burette stand
  • Pipette
  • Pipette filler
  • Funnel
  • White tile
  • Conical flask

  • Volumetric flask
  • Beaker
  • Watch glass on scale
  • Glass rod
  • Spatula
  • Digital scales
  • White tile


  • Indicator – methyl-orange
  • Sulphuric acid
  • Sodium carbonate solution
  • Distilled water

The quantities of the materials to be used:

  • 1 x watch glass
  • 1 x digital scales
  • 1 x spatula
  • 2 x 250 cm3 beaker
  • 1 x glass rod
  • 1 x 250 cm3 volumetric flask

  • 2 x funnel
  • 1 x burette
  • 1 x burette stand
  • 1 x 25 cm3 pipette
  • 1 x pipette filler
  • 1 x pipette
  • 1 x conical flask
  • 1 x white tile

Equipment needed to make up your sodium carbonate solution:

  • Spatula
  • Sodium carbonate, 2.65g
  • Digital scales
  • Distilled water
  • Beaker, 250cm
  • Dropping pipette
  • Glass rod
  • Volumetric flask, 250cm, with label
  • Filter funnel
  • Safety glasses

  • Using a watch glass on a scale weigh out accurately 2.65g of anhydrous sodium carbonate, using a spatula.  Make sure that you wash the watch glass before you use it.  Make sure you weigh 2.65g exactly.
  • Transfer the measured anhydrous sodium carbonate into a 250cm³ beaker.  Again make sure that the beaker has been cleaned with distilled water.  Record the exact mass of the anhydrous sodium carbonate that has been transferred.
  • Dissolve the solid in 50cm³-distilled water. If more water is needed keep adding little amounts of distilled water into the beaker of anhydrous sodium carbonate until the solid has dissolved.  Use a glass rod to stir the solution; this will help speed up the reaction.
  • When all of the solid is dissolved and you are left with a clear colourless solution, transfer the sodium carbonate solution into a volumetric flask.  Make sure that all of the solution has been transferred.  Do this by cleaning out the whole beaker with distilled water making sure that all of the sodium carbonate solution is transferred into the flask.  Make sure that the volumetric flask has been cleaned before use.
  • Keep adding distilled water until you reach the line on the neck of the volumetric flask.  Put on a rubber bung and shake the flask so that the contents mix.
  • Using a pipette to add exactly the right amount of distilled water to your solution so that the bottom of the meniscus touches the line.  Replace the rubber bung and shake the flask again to ensure that the solution is fully mixed.
  • Label your flask, and show your teacher.

Requirements needed to carry out the titration:

  • Safety glasses
  • Tripod stand
  • 2 clamps
  • White tile
  • Conical flask
  • Burette
  • Distilled water
  • Dropping pipette
  • Sulphuric acid - 25cm
  • Filter funnel
  • Sodium carbonate - 2.65g
  • 3 drops of methyl orange indicator

  • Set up a burette, make sure that all the glassware is washed and cleaned properly before using it.  When this is done fill the burette up with the acid solution up to 0 using a funnel. Stand the burette on a stool so that u can see at eye level.  Make sure that the bottom of the meniscus is touched the 0 mark.  Make sure that there are no air bubbles.
  • Use pipette filler and pipette to transfer 25cm³ of the anhydrous sodium carbonate solution into a 250cm³ conical flask.  Make sure that there are no air bubbles in the pipette filler. To make sure that all the solution has come out of the pipette filler, blow out the last drops. Make sure the conical flask has been cleaned out.
  • Add 3 drops of methyl orange solution to the conical flask of 25cm³ solution.  Swirl the flask so that the methyl orange has spread through the 25cm³ solution evenly.  Leave the conical flask to one side.
  • Place the conical flask under the burette and start a rough titration by letting the sulphuric acid run through the burette into the conical flask.   Make sure that you swirl the conical in a circular motion whilst the acid is being added to the conical flask.
  • When your solution in the conical has turned a pale pink colour, stop the tap and record your reading on the burette.  The acid and alkali have neutralized each other.
  • Now start your second titration, but this time make sure that you add the acid solution drop by drop, to get your sodium carbonate solution to become clear.
  • Make sure that you control the flow of acid solution so that too much does not flow into the beaker.
  • Swirl the flask with your hand slowly whilst the acid solution is being added to the 25cm³ solution drop by drop.  This is to make sure that the acid solution is evenly distributed throughout the sodium carbonate solution.  Once the solution in the conical flask becomes clear and colourless stop the tap.  This is the end point of your titration.
  • Keep on repeating the titration until you have achieved a good set of results.  Your values should be within 0.1cm of each other.
  • Remember to record the burette reading.  Make sure that the reading is taken at eye level for accuracy, and is taken at the bottom of the meniscus.
  • Repeat your titration a number of times and at least once during the assessment ask your teacher to observe you perform a titration run.  Repeat your titration until you feel that you have achieved results that will allow you to find a good average and an accurate concentration of the acid solution.
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Risk assessment

  • Always wear a lab-coat to protect your skin and cloths from harmful substances.
  • Wear goggles at all times during an experiments, to protect your eyes from chemicals.
  • Make sure that long hair is tied back and that any dangling clothes and jewellery are tucked away or taken off so that it won’t catch a fire, or become a hazard.
  • Always behave in a well-mannered way in a laboratory.  Running and playing games could be dangerous.
  • If your skin ...

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