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To draw and explain the shape of graphs of pH against volume of titrant for titrations involving monoprotic acids and bases.

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Introduction

Problem: To draw and explain the shape of graphs of pH against volume of titrant for titrations involving monoprotic acids and bases. The combinations we had were: 1) strong acid + strong base (titrant), 2) weak acid + strong base (titrant) and 3) weak base + strong acid (titrant). Data collection: Procedure: We had the different acids and bases in the beaker respectively in the burette and dropped the titrant into the beaker where we had a pH-meter and recorded the result. 1) We had HCl in a 20 ml beaker and NaOH in a 50 ml burette and a few drops of BTB. 2) We had HAc in a 20 ml beaker and NaOH in a 50 ml burette and a few drops of BTB. ...read more.

Middle

5,2 18 5,3 19 5,6 19,5 5,9 20 6,3 20,3 6,8 20,7 10,4 21,1 10,6 21,5 11,0 22 11,1 23 11,4 24 11,55 26 11,75 28 11,9 30 12,0 32 12,1 ml ph 0 1,2 5 1,2 6 1,3 9 1,3 10 1,4 11 1,45 13 1,5 15 1,65 16 1,7 17 1,75 19 1,9 19,5 2,0 20,5 2,2 21 2,2 23 2,35 24 2,7 24,2 4,6 24,5 5,1 24,8 6,0 25 7,1 25,5 7,3 26 7,6 27 7,8 28 8,1 30 8,2 32 8,4 34 8,3 36 8,8 38 8,9 Data processing and presentation: All the results were very much similar - producing very similar graphs. Of course there are uncertainties present. For example it is easy to put in a few drops too much from the burette and the thing is not so accurate any more. ...read more.

Conclusion

There were many interesting steps to go through etc. Looking at the tree different graphs we got from our three attempts, they are all very similar. This leads me to the conclusion that they are correct. As we have no literate value to compare it with I can interpret it as that we got where we wanted. Of course the process can always be better and improved. But I think the method we used here is rather accurate, accept for the uncertainties due to bad measurements. The use of BTB as an indicator makes it very clear to see when the solution is acid respectively basic, which is an advantage. On the other hand, the intervals we dripped the titrant into the other liquid were not even which does not give a good result. It can always be improved. ...read more.

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