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Acid-Base titration by double indicator method

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Introduction

Date: 01/12/2010 Objective To determine the proportions of sodium carbonate and sodium hydroxide in a mixture solution using double indicator method. Procedures 1. 25 cm3 of the mixture solution was pipetted into a conical flask. 2. Two drops of phenolphthalein indicator were added into the conical flask. 3. The mixture solution was titrated with the given standard hydrochloric acid(0.098M). 4. The mixture was titrated to the end-point. 5. At the end point, the pink colour of phenolphthalein indicator was just discharged. 6. The burette reading (x) was recorded. 7. Two drops of methyl orange and a further quantity of acid were added 8. The mixture was titrated to the end-point. ...read more.

Middle

/ cm3 12.30 12.30 12.20 12.40 Mean value of x= (12.30+12.20+12.40)/3 =12.30 cm3 y Trial 1 2 3 Final burette reading / cm3 19.50 38.80 36.60 19.80 Initial burette reading / cm3 12.40 31.80 29.40 12.70 Volume of acid used(x) / cm3 7.10 7.00 7.20 7.10 Mean value of y= (7.00+7.20+7.10)/3 =7.10 cm3 Questions: 1. Volume of hydrochloric acid required for the complete neutralization of sodium carbonate in 25 cm3 of solution =2y =2 x 7.10 =14.20 cm3 No. of mole of hydrochloric acid required= (14.20/1000)(0.098) =0.0013916mol. By Na2CO3 + 2HCl --> 2NaCl +H2O +CO2 ?No. of mole of hydrochloric acid required =2( No. of mole of sodium carbonate in 25 cm3 of solution) ...read more.

Conclusion

?The concentration of sodium carbonate in the solution in gdm-3 =[0.0005096x(22.99+ 16.00+ 1.008)]/(25/1000) =0.815319232 ~0.82 gdm-3 ?The proportions of mass of sodium carbonate to sodium hydroxide in the mixture solution =(2.94991368 x 25/1000)/(0.815319232 x 25/1000) =1 : 0.276387488 ~ 1 : 0.276 ?The proportions of number of mole of sodium carbonate to sodium hydroxide in the mixture solution =0.0006958/0.0005096 =1 : 0.732394366 ~1 : 0.732 Conclusion The proportions of mass of sodium carbonate to sodium hydroxide in the mixture solution was 1 : 0.276 while that of number of mole of sodium carbonate to sodium hydroxide was 1 : 0.732 Reference Yahoo!Mini http://www.titrations.info/ http://en.wikipedia.org/wiki/Titration http://hk.knowledge.yahoo.com/question/question?qid=7010032200973 http://www.creative-chemistry.org.uk/alevel/module1/documents/N-ch1-49.pdf HKCEE Chemistry Notes Section IV by Ms Sin W L F.6 Chemistry Notes Section I by Ms Sin W L The End ?? ?? ?? ?? F.6 Chemistry/TAS 8/P.1(3) ...read more.

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Response to the question

Initially, the candidate should expand on the objectives to include their predictions. It is also recommended to put some of the known theory before the method to help agree with your predictions. The method and results sections are excellent. A ...

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Response to the question

Initially, the candidate should expand on the objectives to include their predictions. It is also recommended to put some of the known theory before the method to help agree with your predictions. The method and results sections are excellent. A diagram could have aided the method but wasn't essential.

Level of analysis

The analysis in the questions is generally good but explaining what is being calculated would have been helpful. If the student had made a hypothesis initially, it would have been possible to compare this with the final result and make a better conclusion, looking at the reliability and accuracy of the results. The references are good but should be shown where they have used through the text.

Quality of writing

Spelling, punctuation and grammar is very good. Technical terms are used appropriately. Overall a good piece of work.


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