Aim: My aim of this investigation is to find out the concentration of Sulphuric Acid (H2SO4) in a solution between 0.05 and 0.15 mol dm-3.
During this investigation, I will be making a standard solution of Sodium Carbonate, of strength of 0.1 molar (M). In order to create this solution, I will be using a 250ml volumetric flask
Firstly, I will need to know how much sodium carbonate I will need to use in my standard solution, which means that I will need to know the amount of moles and grams needed.
For 1dm3: M = 0.1x106 = 10.6g
For 250ml: 10.6 x 0.25 = 2.65g of Sodium carbonate
By looking at above, you can see that by working out the amount of mass needed, I will need to use 2.65g of sodium carbonate to make my standard solution.
For my solutions, I will be using an indicator solution, which is called methyl orange. This indicator is often chosen to be used in titrations because of its clear colour change. For the reason that it changes colour at the pH of a mid-strength acid, it is usually used in titrations for acids. Unlike a universal indicator, methyl orange does not have a full spectrum of colour change, but has a sharper end point. The reason why I will be using this indicator is because I am going to be using a strong acid and a weak alkali. As a result, for a titration that involves a strong acid and a weak alkali I would have to use this type of indicator.
- To start off, I am going to make my standard solution. I will do this by weighing 2.65 grams of sodium carbonate in a glass bottle on a mass balance. But first, I will weigh the bottle, measure the mass of the bottle and then change the scale to read 0 grams. I will then add 2.65 grams of sodium carbonate into the bottle.
- I will then wash a 250ml volumetric flask using distilled water. The reason being is so that it removes any other molecules from previous experiments.
- Then I will pour in the sodium carbonate into the volumetric flask.
- After pouring the sodium carbonate, I will then rinse out my weighing bottle three times using distilled water to dissolve any excess sodium carbonate left in the bottle. Each time, I will pour the water into the volumetric flask using a funnel.
- Then I will fill the volumetric flask with water until the bottom of the meniscus is touching the line. In order for me to this correctly, I will fill the water just below the line and then fill the final drop by drop in order to get the meniscus to sit just on the line. However, to ensure that the meniscus is touching the line, I will look at the volumetric flask at eye level. If I by any chance overfill it, I will have the start all over again as overfilling it would alter its concentration.
- Having mixed the distilled water and sodium carbonate together, I will then mix the solution in the volumetric flask by inverting it 10 times with the lid on.
- I will then sterilise a conical flask with distilled water to get rid of any other molecules that may affect the rate of reaction, and therefore affecting my results.
- I will then wash out a glass pipette out with some of my sodium carbonate solution.
- Then I will measure 25ml of my standard solution by holding the pipette at eye level and filling it using pipette filler. I will overfill it to some extent and use my thumb to lower it down slowly until the bottom of the meniscus touches the 25ml line.
- After having made my 25ml of standard solution, I will pour the solution into the conical flask, which I washed out earlier on.
- Then I will wash out a burette using sulphuric acid. I will pour the sulphuric acid using a funnel. I will then burette with sulphuric acid as long as it’s on zero or below that. I will then run the burette tap until the sulphuric acid comes to the bottom of the burette. I will then take the initial reading from the burette.
- After this, I will add three drops of my orange methyl indicator to the 25ml of standard solution in the conical flask. I have to make sure that I do not add more than three drops as it may affect my end points, and my results.
- I will then place the conical flask under the burette. I will also place a white tile under the conical flask so it will make it easier to see the colour change.
- Now, I will start my titration. However, my first titration is going to be a rough titration. I will slowly add the sulphuric acid along with swirling the conical flask to mix the contents. When I have a slight colour change, I will stop adding more sulphuric acid.
- Then after this, I will carry out the experiment accurately, and when the colour is about to change I will add the sulphuric acid drop by drop until the colour permanently changes.
- I will then record my final burette reading and then subtract my initial reading from my final reading to find out how much sulphuric acid is needed.
- I will then conduct this experiment until I am able to achieve two concordant results. I will record the initial burette reading and the final reading each time and then I will subtract my initial reading from my final reading to the get the amount of sulphuric acid needed for titration.