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Titration experiment - write up

Extracts from this document...

Introduction

To analyse a solution of dilute sulphuric acid and calculate the concentration of acid it contains Aim: To determine the precise concentration of sulphuric acid solution, using a solution of accurately known strength, called a 'standard solution'. Introduction: A titration is a laboratory technique used in chemical analysis. A solution containing an unknown quantity of a known substance is placed in a conical flask, and a solution of known strength is then added from a burette. 1 The addition of this solution continues until an end point of the titration is reached. This is signified by a colour change in an indicator (or some other visible effect) and at this point the titration is stopped. The equivalence point of the titration occurs when the two solutions have reacted exactly. An indicator is a substance that changes colour when the reaction is complete. In an acid - base titration, the indicator is one colour at one pH and a different colour at another pH. The indicator I will be using is methyl orange. I will be using sodium carbonate, as it is suitable for use as a primary standard for titrations of strong acids. The strong acid I will be using is sulphuric acid, which is a strong mineral acid. It is soluble in water at all concentrations. It has many applications, and is one of the top products of the chemical industry.2 A problem is that it produces acid rain. Acid rain is rain or any other form of precipitation that is unusually acidic. It has harmful effects on plants, aquatic animals and buildings. Acid rain is mostly caused by human emissions of sulfur and nitrogen compounds which react in the atmosphere to produce acids.3 An acid is a substance which contains hydrogen and when dissolved in water furnishes hydrogen ions. e.g.: H2SO4 = 2H+ + SO4 2- A base is a substance which will react with hydrogen ions to give a salt and water only. ...read more.

Middle

Do this at eye level so that it is accurate. 9) Place the stopper on the flask and invert it by continuously shaking about 10 to 15 times. Preparing the burette: 1) Before beginning, make sure that all the glassware has been properly cleaned and are all dry, so that the solution doesn't get contaminated. (burette, pipette, conical flask and volumetric flask) 2) Set up the boss and clamp stand. 3) Rinse out the burette with sulphuric acid twice; this will help avoid inaccuracy of results due to contamination. 4) Close the burette tap and use a 250 cm3 beaker and funnel to fill the burette with sulphuric acid solution. 5) Open the tap, and allow the solution to run out space under the tap is full of solution. 6) Using a white tile let the solution run out of the burette until it reads 0.00, and the bottom of the meniscus is exactly on the line. Make sure to be eye level with the meniscus so that an accurate reading can be made. 7) Check for air bubbles if there are some present, empty then fill the burette again. If there are no air bubbles then precede the experiment. 8) Remove the funnel from the top of the burette. 9) Record the volume of the acid before starting the experiment to the nearest 0.05 cm3 10) Rinse out the pipette with sodium carbonate solution twice. Twirl the pipette round with your fingers and hold it at an angle to the body, so that the solution rinses it out completely and there are no inaccuracies. 11) Pipette out sodium carbonate solution using the pipette filler, do this to the graduation mark on the pipette. 12) Carefully transfer the solution in the pipette in to the conical flask. Try to avoid any spillages as this would give major errors in results, they would be inaccurate and incorrect. ...read more.

Conclusion

The outcome was that at neutralisation the number of moles of Na2CO3 will equal the number of moles of H2SO4, and an indicator change signaled the acid-base reaction was complete. Percentage errors Experimental error is always with us; it is in the nature of scientific measurement that uncertainty is associated with every quantitative result. This may be due to inherent limitations in the measuring equipment, or of the measuring techniques, or perhaps the experience and skill of the experimenter. Certain apparatus have different percentage errors, as they are all unlike in volume etc. The formula for working out percentage error is: 25cm3 pipette The error for 25 cm3 pipette is 0.06 The equation is: % error = 0.06/25 x 100 = 0.24% 50cm3 burette The error for 50 cm3 burette is 0.05 The equation is: % error = 0.05/28.5 x 100 = 0.175 = 0.18% 250cm3 volumetric flask The error for 250 cm3 volumetric flask is 0.6 The equation is: % error = 0.6/250 x 100 = 0.24 % Balance error The error for the weighing balance is 0.005 The equation is: % error = 0.005/2.65g x 100 = 0.18% To find the overall % error in my experiment I will add the four errors of these four pieces of apparatus. 25cm3 pipette = 0.24% 50cm3 burette = 0.18% 250cm3 volumetric flask = 0.24% Weighing balance = 0.18% Overall % error = 0.24 + 0.18 + 0.24 + 0.18 = 0.84 Therefore the overall % error in this experiment is = 0.84% % errors can affect the results especially if they are large. The highest % error = 0.24% for the pipette and the volumetric flask. Statistics The concentration of the sulphuric acid solution is = 0.09 mol dm -3 I am confident about my values, the minimum and maximum error boundaries show that I have accounted for all the inaccuracies that could have altered my results. They are not too high nor to low which shows that all the errors during my experiment were not highly significant. ...read more.

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