Preparing a standard solution and testing it by titration
1. Abstract: The aim of this investigation is to calculate the concentration of an unknown acid.
2. Introduction: The reason why we are doing this investigation is because we want to make a standard solution and calculating the concentration in which we will use that to find the concentration of an unknown acid.
The equipment and chemicals I will need to make a standard solution: * A balance (accurate to 0.01g) * A weighing boat * A spatula * A 100ml measuring cylinder * 250cm3 beaker * Wash bottle of distilled water * Filter funnel * Teat pipette * Stirring rod * Anhydrous sodium carbonate (Refer to CLEAPSS Student Safety Sheet)
The standard procedure for making a standard solution: 1. Weigh out, as accurately as possible, approximately 1.3g of anhydrous sodium carbonate. 2. Transfer all of the sodium carbonate to 100cm3 of distilled water in a beaker. 3. Stir to dissolve all the sodium carbonate. 4. Transfer the solution to the volumetric flask through the filter funnel. Rinse the beaker to make sure that all the solution goes into the flask. 5. Add distilled water from the wash bottle until the level is within 1cm of the line on the neck of the flask. 6. Use the teat pipette to add enough distilled water to bring the bottom of the meniscus to the mark. 7. Insert the stopper and invert the flask 10 times to ensure thorough mixing. 8. Label the flask with your name, the date and the mass of sodium carbonate dissolved to make 250cm3 of solution.
The equipment and chemicals I will need to test the standard solution by titration: * Sodium carbonate solution of known concentration * Hydrochloric acid of unknown concentration (Refer to CLEAPSS Student Safety Sheet) * Phenolphthalein indicator solution * A burette and stand * 25 cm3 pipette * Pipette filler * Filter funnel * 100cm3 beaker * 250 cm3 conical flask * White tile * Wash bottle of distilled water
Standard procedure for carrying out a titration: 1. Set up the apparatus. 2. Rinse the burette with distilled water first, then rinse again with a small amount of the HCl (about 10cm3). 3. Close the tap and fill the burette with HCl – the ‘titre’ – to just above the highest graduation mark. Slowly open the tap and drain until the meniscus ‘sits’ on the mark. 4. There should be no air bubbles in the tip – if there are, repeat the above steps. 5. Using a pipette, transfer 25cm3 of the sodium hydroxide solution to be analysed 6. Add two or three drops of indicator () to the solution. 7. Titrate – your technique should be slow and steady (swirling the conical flask all the time), controlling the tap whilst glimpsing the burette reading. 8. Perform a rough titration and 3 accurate titrations.
| Rough titration | 1st accurate titration | 2nd accurate titration | 3rd accurate titration | Acid at the start | 0 | 0 | 0 | 0 | Acid at the end | 25.8 | 29.4 | 20.1 | 20.4 | Acid used | 25.8 | 29.4 | 20.1 | 20.4 |
Equation: sodium carbonate + hydrochloric acid → sodium chloride + water + carbon dioxide
Na2CO3 (aq) + HCl (aq) → NaCl + H2O + CO2
Calculating the concentration of the sodium carbonate solution: | Working | Answer | 1. Mass of sodium carbonate dissolved to make 250cm3 of solution? | | 26.5g | 2. Mass of sodium carbonate needed to make 1000cm3 (1dm3) of solution? | 26.5g x 8 | 212g | 3. Concentration of sodium carbonate solution in g.dm–3 | 26.5g x 4 | 106g | 4. Chemical formula of sodium carbonate | | Na2CO3 | 5. Relative formula mass of sodium carbonate | | 212g | 6. Moles of sodium carbonate needed to make 1000cm3 of solution…