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Titration-chemistry OCR

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Chemistry AS-level Titration coursework Aim: The aim of this GCE chemistry investigation was to find out the accurate concentration of sulphuric acid in a solution using, titrations. This acid solution is thought to have a concentration between 0.05 and 0.15 mol dm-3, but as part of this investigation I was asked to find out the accurate concentration of sulphuric acid. Fair testing: Definition: 'Fairness' implies that the outcome of the activity truly depends on what is being investigated, and is not being distorted by other external factors. Therefore a fair test is one where all the variables are kept constant or the same, except the variable that is being investigated. A variable is anything that can change and which may influence the outcome of the investigation. List of variables: The different variables are: > Amount of sulphuric acid > Concentration of sulphuric acid > Mass of alkali- anhydrous sodium carbonate (2.65g) > Indicator Variables that needs to be controlled: The variable that needs to be controlled are as follows: > The mass of the alkali (this has to be determined first before the titration) > The amount of sulphuric acid. These variable needs to be controlled because even the slightest miss calculation of the mass of the alkali of the amount of sulphuric will bring about a huge change in the values that represent the titration. Statement of fairness: For the investigation to be fair, the mass of the alkali used must be exact, the temperature of the surroundings must be constant and all equipment must work properly. Anhydrous sodium carbonate (working out the mass of anhydrous sodium carbonate). The molecular formula for this substance is: Na2CO3 Relative masses can be used to compare the masses of any chemical species. Much of the matter is made up of compounds. The Relative Molecular Mass of a compound is the sum of the masses of all the atoms present in the molecule. ...read more.


The equipment which you need are Weighing Scale, Burette, Pipette, Pipette filler, Plastic bottle, Conical flask, Stirring road, Funnel, Spatula, Cock, Beaker (with different measurement scales) such as the 250cm3 beaker and 100 cm3 beaker, Distilled water, Iron or wooden stand with clamp attached and an Indicator. 2. Next step is to make sure that you wash all the equipments with distilled water and then again with hydrochloric acid (HCl) to make sure that you remove all the unwanted substances form the all the equipment which includes the burette, pipette, conical flasks and the beakers. Distilled water is water that has been recondensed from steam. Water is heated to boiling and the water vapor (steam) is collected and condensed back into a pure liquid. Any impurities like minerals stay as a residue in the original liquid, separate from the distilled water. Distilled is probably considered the most pure. And this is the reason why we should use distilled water to wash out all the equipments. Normal water contains many impurities. Also when washing out all the equipments make sure you wash out the equipments thoroughly as even a minor impurities could cause error in the readings, and when washing the burette make sure you wash it the stopcock both open and closed, as this will review if there is any blockages of damages to the tap, before you start the experiment. 3. After doing all the work illustrated above, the next step is to take ensure that you are wearing all the safety equipments like the goggles, lab coat and make sure if you have long hair you tie it backward short, so that by any chance it wouldn't come in contact with the acid, and also avoid wearing contact lenses. And also never sniff any chemicals; if you can smell any chemicals it means that you are exposing yourself to dangerous chemicals. 4. Now the actual experiment starts, the first part of this experiment is to accurately weight 2.65gm of anhydrous sodium carbonate. ...read more.


One of the other things that I made sure is that I have washed out the inside of the conical flask as I was shaking the conical flask regularly and as we know that a single drop of acid could change the colour of the solution immediately depending on the indicator which I have used, and the use of white tile underneath the conical flask helped me to find if the colour change due to the indicator was correct or not. And also to test the indicator I dropped a little bit or a single drop of the indicator to the white tile and a single drop of the acid to see what colour change am I going to see as the acid is let out of the burette in to the weak base solution. The next thing I have done is working out the percentage uncertainty of the result; these are mainly dues to the errors that could happen due to errors in the graduation mark of the instrument which I have been using. The percentage for all the instruments which I have used is shown below, including the formula which I need to use in order to find the percentage error of certain objects. The formula for finding the percentage error is shown below: Percentage error = error/value x 100 Percentage error for burette = 0.05 = 0.05/50 x 100 = 0.01 Percentage error for pipette = 0.06 = 0.06/25 x 100 = 0.24 Percentage error for the weighing scale = 0.005= 0.005/2.65 x 100 = 0.18 Total percentage error = 0.01 + 0.24+ 0.18 = 0.42 This shows that the maximum error that I could possibly have is a total of 0.42%, this shows that there weren't any anomalies in my results and this proves that the concentration of the sulphuric acid will still remain the same, as there is no huge difference between the data or the result which I produced. ...read more.

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