Level 3 Applied Science Unit 2- Practical Scientific Procedures and Techniques Learning Aim A: Undertake titration and colorimetry to determine the concentration of solutions.

Level 3 Applied Science Unit 2- Practical Scientific Procedures and Techniques Learning Aim A: Undertake titration and colorimetry to determine the concentration of solutions. Introduction The investigation is to find the unknown concentration of an unknown sample of sodium hydroxide. What I am trying to find out is how titration, colorimetry and pH probe have different ways of finding the concentration of unknown solution and how the calculation have different methods of working out the unknown solution. I calibrate the balance using 0.1g, 1.0g and 10g of weights, adjusting the balance to correct mass. The equipment that I used was 50cm3 burette, 100cm3 conical flask, 100cm3 beaker, 25cm3 pipette, methyl orange, pipette filler, stirring rod, Burette stand and clamp, white tile, sodium hydroxide solution of 0.1M. What I did to make a standard solution was firstly, using a balance, I had to measure accurately 2.5g of anhydrous sodium carbonate on a clock glass. Then, I gradually transfer the sodium carbonate with stirring, to about 50 cm3 of distilled water in a clean 250 cm3 beaker. To certify that all the sodium carbonate is shifted, I will use a wash bottle to rinse the clock glass with distilled water, and add the rinsings to the beaker. Remain stirring the mixture with a stirring rod till the sodium carbonate has completely dissolved. Using a wash bottle, wash off the solution on the stirring rod with distilled water into the beaker. Transfer the solution through a clean funnel into the 250 cm3 volumetric flask. Using a wash bottle, rinse out the beaker several times with distilled water, and add the rinsing’s to the solution in the flask. Rinse the funnel with distilled water, making sure that the water to run into the flask. Titration includes finding the unknown concentration of one solution and this is by reacting it with a solution of known concentration. The solution of unknown concentration, the analyte, is usually positioned in a flask, whereas the solution of known concentration is positioned in a burette. The titrant is added to the analyte till the endpoint has reached until it has been determined by a colour change. Calculation is obtained with the formula: C1V1=C2V2. Titration can be done by finding the unknown concentration of HCl (1M) into a burette, and fill a volumetric flask of the unknown sodium hydroxide and also add a few drops of methyl orange indicator. Making the standard solution of sodium carbonate Aim This practical aim is to first prepare a standard solution of sodium carbonate. This solution will then be titrated with sodium carbonate in the aim of getting the concentration of the sodium carbonate through reading off the graph and finding the volume needed for neutralisation to occur, then using the values to find the unknown concentration of the sodium carbonate. Method- the preparation of a standard solution Firstly, I had to calibrate the electronic balance that I will be using as you don’t want to measure the sodium carbonate without calibrating it as it will not give me an accurate reading of the measurement of sodium carbonate. Firstly, the balance was calibrated to 0.1g 1.0g, 10g and 100g in mass, as I had to make sure that the balance was accurate for a range of masses, to calibrate the balance a mass so when I am weighing the sodium carbonate solution on the electronic balance, I would get an accurate results as I calibrate it first before putting the solution, then I placed the sodium carbonate solution into the balance and recorded the measurement and put the extract mass. Then, after I calibrated the electronic balance, I had to weigh the sodium carbonate to 1.45g as this amount will give me a better result in terms of how much sodium carbonate, I have put in. Then, I had to cautiously move the sodium carbonate to a large beaker and I have to make sure I record the measurement precisely to declare the extract mass that has bee transferred. After that, I add 150cm3 of distilled water to the beaker and I had to stir the beaker to make sure that the sodium carbonate has been completely dissolve so that the water and the anhydrous sodium carbonate is able to mix with each other. Then, I had to get a 250cm3 volumetric flask and pour the 150cm3 of the solution inside the flask. With the remaining 100cm3 , I had to add 100cm3 of more distilled water to fill up the volumetric flask. Pouring the solution should take place at eye level with the meniscus. After that, I did the moles calculation of the sodium carbonate as after you are done with the experiment, you have to calculate the moles by using the formula: Moles=mass/molar mass. Calculation Moles= Mass/Molar mass Mass= 1.4g Molar mass of Na2CO3= 106 Moles= 1.4/106= 0.013 Moles Method- standardisation of sodium carbonate Firstly, I had to calibrate the pipette by picking up the electronic balance and started to calibrate it to zero as I don’t want the reading to be random numbers and by making sure that the pipette is clean and dry to make my result be as perfect and exact. After that, I carefully poured 25cm3 of the sodium carbonate solution into a 250cm3 conical flask and then added a couple of drops of methyl orange indicator as the aim of this practical is to mix the sodium carbonate with the methyl orange indicator. Then, I cleaned and full a burette with a solution of hydrochloric acid, which had a concentration of 0.1M as I will pour down the hydrochloric acid into the sodium carbonate solution little by little until, I see a change. Then, I titrate the sodium carbonate solution with the hydrochloric acid as I poured 1cm3 of hydrochloric acid and stir the beaker and then pour another 1cm3 of hydrochloric acid and stir it until the indicator changes colour at the end point as I record at what measurement did the indicator changes its colour as I accurately record all measurements to declare the exact titre of hydrochloric acid required to make the end point of the titration. To find out the unknown concentration of sodium carbonate when standardised using titration, I read off from where the pH was 7, and then use the concentration formulae to work out its concentration. Moles Calculation Equation: Na2CO3 + 2HCl 2NaCl + CO2 + H2O Ratio: 1:2 Moles of Hydrochloric acid= 0.013 x 2= 0.026 moles Concentration of HCl= moles/volume Concentration of HCl= 0.026/0.025= 1.04 moldm-3 It was close to 1M as maybe the technician didn’t dilute the indicator properly because if they did, then I would have got even closer to 1M. Titration of sodium hydroxide with hydrochloric acid (using an indicator) I will be titrating HCl with NaOH using the methyl orange indicator and the pH probe. Aim: The first titration was carried out using exactly the same technique as was used to standardise the hydrochloric acid. Once again the hydrochloric acid was poured into the burette so this was conditioned with the hydrochloric acid before use. The conical flask needed to contain exactly 25cm3 of sodium hydroxide so after being rinsed with distilled water to remove any contamination it was filled with 25cm3 of sodium hydroxide using the 25cm3 pipette. I have to make a rough titration first to ensure and to see the end point volume and to prevent any mistake that I did in my rough titration. Method: Firstly, I had to calibrate the pipette by making sure that the pipette has a good reading and accuracy as sometimes the pipette is not visible as you can’t see any measurement as pick out a clear pipette that you will be using. In the calibration, I had to make sure that a burette was calibrated and a dry, clean flask was weighed. Then, I poured the distilled water into the burette so that the bottommost of the meniscus lied on the 0.00cm3 line. The distilled water was provided into the flask until the bottom of the meniscus rested on the 50.00cm3 line. The change in mass was considered and the mass of water was figured out to be 49.95g. The laboratory was at a temperature of 18oC so the density of water at that temperature is 0.99862 g/cm3, which is associated to the International Critical Tables of Numerical Data, Physics, Chemistry and Technology, vol III. Consuming the formula: volume = mass x density, the volume of water from the pipette was 49.95 x 0.99862 = 50.0090 cm3. This is near to 50.00cm3 to use for my experiments of the titration of sodium hydroxide using the pH meter. Carefully, transfer 25cm3 of sodium hydroxide solution, which is the unknown concentration that we need to find at the end of this practical, to the 250cm3 conical flask and add a couple of methyl orange indicator as don’t put too much drops of the indicator as it would turn proper orange and you just want the orange to look natural. Then, I had to clean and full a burette with the standardised solution of hydrochloric acid to the end point of the burette so you will have enough hydrochloric acid in the burette and in that way, you will pour 1cm3 of hydrochloric acid and stir it as you will need to this repeatedly. Then, keep on adding 1cm3 of hydrochloric acid until the indicator changes colour at the end point as when the indicator has change colour, you stop and recording at the volume when the indicator changed its colour as you have to record all measurement to declare the exact titre of hydrochloric acid required to meet at the end point of the titration of sodium hydroxide with hydrochloric acid. The reason why I need to do a rough titration is because to reduce human error and prevent from doing the mistakes that I did in my rough titration. Equipment Sodium hydroxide Hydrochloric acid Beakers Methyl orange indicator Distilled water 50cm3 burette Results Table: Rough 1 st 2 nd 3 rd Final volume (cm3 ) 30.00 29.50 22.00 27.10 Volume of HCl used (cm3 ) 30.00 29.50 22.00 26.1