AS Chemistry Coursework: Titration Essay
Plan For this experiment, I am to find the concentration of a sulphuric acid solution, which has a concentration of between 0.05 and 0.15mol/dm?. To do so, I will titrate an alkali with a known concentration into the unknown concentration of sulphuric acid solution, along with the indicator phenolphthalein to display to me when the acid has become neutralised. The equipment that I will need for this experiment include: – Unknown solution of Sulphuric acid, 0.05-0.15mol/dm? (50cm) – Sodium carbonate solution, 0.01mol/dm? (100cm?) – Methyl Orange indicator – Distilled water – Burette – Clamp stand – 25cm pipette – Pipette filler – 5cm pipette – White piece of paper – White tile – Glass rod – 100cm conical flask – Volumetric flask – Weighing bottle – Digital balance I have chosen to use Methyl orange as the indicator because I am working with a strong acid, and a weak alkali. Safety Eye protection must be worn at all times when handling chemicals, as exposure to the eyes can be harmful. Experiments should be done standing up, with obstacles put aside so one can move away in the case of an accident. Any spillage should be cleared up immediately, to avoid slippages, with waste being disposed of properly.
Broken glass should be cleared up immediately to avoid any injuries, and disposed of in a container marked broken glass. Long hair should be tied up and tucked out of the way. Protective clothing should be worn at all times. Food or drink must not be consumed in the labs. Strong Acid and alkalis are corrosive, but the diluted concentrations we are working with are much weaker and only irritate the skin. Therefore, protective gloves needn’t be worn, but skin should be washed immediately should one get acid/alkali on themselves. Method The equation for the reaction taking place in this study is: H?SO? + Na?CO? -> Na?SO? + H?O + CO? (aq) (aq) (aq) (l) (g) This equation shows that the Sulphuric acid reacts with Sodium carbonate in a 1:1 ratio, therefore I will need 1mol of Sodium carbonate for every 1mol of Sulphuric Acid. Because the Sulphuric acid has been said to have a concentration of between 0.05 and 0.01mol/dm?, I will use a 0.10mol/dm? concentration of Sodium carbonate.
To make this concentration of Sodium carbonate, I must find out how many grams of the anhydrous substance I will need for 0.10mols. I plan on making 250cm of this 0.10mol/dm? sodium carbonate solution. 2 x Na = 45.99g 1 x C = 12.00g 3 x O = 48.00g 105.99g = 1mol of Na?CO? If I were making a 1mol solution, I would then dissolve 105.99g of anhydrous sodium carbonate into 1dm of distilled water. But because I want 0.1mol, I am to dissolve 10.59g into 1dm of distilled water. I need 250cm, so I must quarter the amount of anhydrous sodium carbonate I will use. 10.59 = 2.65g into 250cm of distilled water 4 Begin by weighing this amount, in a weighing bottle, on digital scales. Then transfer this solid to a volumetric flask, and proceed in dissolving it by stirring with a glass rod. Make sure to wash the rod with distilled water into the flask, to avoid removing any of the solution. Once all of the substance has disappeared, wash the sides of the volumetric flask with distilled water, to ensure no more of our solution remains on the sides. Then fill a pipette with the solution and transfer 25cm into the conical flask. Viewing the measurement mark horizontally, bring the meniscus up to it.
The pipette filler can be removed at the end of the filling, and using your thumb to release solution to obtain the correct amount, will help to give more controllable measurement. Invert the pipette to remove any bubbles held in the tip, and to make sure the solution is evenly mixed. When transferring into the conical flask, place the tip onto the floor of the flask, and avoid touching the sides. When the pipette is empty, some of the solution will remain the tip, do not try to empty this, as this is normal. Next, set up the burette into the clamp with space underneath for the conical flask. Flush acid through beforehand to ensure it does not contain any other substances that might affect my results. Then transfer acid into the burette using a funnel to avoid spillage. The acid should be poured below eye level, to avoid spilling into eyes. Stop just before the calibration mark. Use the 5cm pipette to add the final drops up to the calibration mark, with eyes horizontal to the mark, and a piece of white paper held behind so that one can see the mark and the meniscus clearly and stop filling at the right place. Make note of the start point.
Place 3 drops of methyl orange into the alkali solution and swirl to evenly mix the solution. Place a white tile underneath the conical flask, this will help to make the end point more distinguishable. The titre can now be done. When the indicator comes into contact with the acid, it will turn purple. However, because the alkali is present, the acid will be neutralised and the indicator will return to its original colour. When all of the alkali has been used up, the indicator will remain purple. This is the end point. To begin with, a test titre must be done, to receive a rough point at which the alkali will be used up, so that in the real tests the titre can be slowed down nearing that point and done more accurately. To do the titre, release the valve on the burette and let acid flow into the flask. Continuously swirl the flask to mix the solution and allow the alkali and acid to neutralise. During the real tests, after the rough titre has been taken, slow down nearing this rough point. Use a flow of droplets from the burette, and watch for a permanent colour change, remembering to continue to swirl. Each droplet is 0.5ml.
After the rough titre, it should be repeated, until at least 2 concordant results have been received. For every repeat, wash out the conical flask with distilled water, or use a new one, and fill with more alkali solution and 3 more drops of indicator. Fill up the burette with more acid if there is not enough for the titration, noting the start point. Results Rough titration |Initial Burette |Final Burette | |reading/cm |reading/cm ACID | |0.00 |25.05 | Accurate titrations |0.00 |25.15 | |0.00 |25.10 | |0.00 |25.20 | Analysis The average of my titrations of results that were concordant (my only results in this case) have come to 25.15cm. (25.15 + 25.10 + 25.20 = 25.15) 3 Moles = Concentration x Volume For the Na?CO? solution Moles = 0.1 in 1dm In 1dm there is .
1 moles Therefore in 1 cc (1 x 10-3 dm) there is .0001 moles Therefore in 25cm, there is 0.0025mol This required 25.15 cm3 of acid to neutralise it. So this volume also contained .0025 moles Concentration = moles Volume = .00025 25.15x 1 x 10-3 Evaluation There are a number of errors that could have affected my results.
. Hazcards . www.ocr.org.uk . Chemistry data sheets . http://www.sparknotes.com/chemistry/acidsbases/titrations/section1.html – General information on titrations . http://www.chemguide.co.uk/physical/acidbaseeqia/indicators.html – Acid-Base indicators . http://www.chemistry-react.org/go/Tutorial/Tutorial_4428.html – Equipment and their error percentages . ‘Salter’s Advanced Chemistry: Chemical Ideas’
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