Chemistry Paper 3 Question Paper
2015 KCSE Cross Country Mock
Chemistry Paper 3
You are provided with:- ï‚·
- Solution A, Hydrochloric acid. ï‚·
- Solution B, 0.024 M Sodium hydroxide. ï‚·
- Solution C, containing 15.74g of Na2CO3, x H20 in 250ml of the solution.
You are required to:-
(a) Prepare a dilute solution of the hydrated sodium carbonate, C.
(b) Determine:-
(i) The concentration of solution A.
(ii) The value of x in the carbonate.
Procedure a
- Using a pipette and pipette filler, place 25.0 cm3 of solution C into a 250ml volumetric flask.
- Add about 200cm3 of distilled water. Shake well.
- Add more distilled water to make upto the mark.
- Label this solution D.
- Retain solution D for use in procedure b and c.
Procedure b
- Fill a burette with solution A.
- Using a clean pipette and pipette filler, place 25.0 cm3 of solution B into a 250ml conical flask.
- Add two drops of phenolphthalein indicator and titrate with solution A.
- Record your results in table 1.
- Repeat the titration two more times and complete the table.
Table 1
| Experiment | I | II | III |
| Final burette reading | ............ | ............ | ............ |
| Initial burette reading | ............ | ............ | ............ |
| Volume of solution A (cm3) added | ............ | ............ | ............ |
(4 marks)
(a) Determine the:-
(I) Average volume of solution A used. (1mark) ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(II) Number of moles of sodium hydroxide in 25cm3 of solution B used. (1 mark) ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(III) Number of moles of acid in volume of solution A used. (1mark) ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(IV) Concentration of solution A in moles per litre. (1mark) ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
Procedure C
- Fill the burette with solution A.
- Using a pipette and pipette filler, pipette 25.0cm3 of solution D into a conical flask.
- Add 2 drops of methyl orange indicator and titrate with solution A.
- Record your results in the table. ï€ Repeat the titration two more times and complete the table.
Table 2
| Experiment | I | II | III |
| Final burette reading | ............ | ............ | ............ |
| Initial burette reading | ............ | ............ | ............ |
| Volume of solution A (cm3) added | ............ | ............ | ............ |
(4 marks)
(b) (i) Determine the:-
(I) Average volume of solution A used. (1 mark) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(II) Moles of the acid in the average volume of solution A used. (1mark) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(III) Concentration in grammes per litre of the carbonate in solution C. (1mark) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(ii) Write an equation for the reaction that occurred between the acid and the carbonate. (1mark) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(iii) Determine:-
(I) number of moles of the carbonate in 25cm3 of solution D used. (1 mark) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(II) Number of moles of carbonate in 250cm3 of solution D. (1 mark) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(III) Concentration of solution C in moles per litre. (1mark) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
(IV) Value of x in Na2CO3.xH2O. (h = 1.0, C = 12.0, O = 16.0 Na = 23.0) (2 marks) ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….
20 marks
You are provided with 2.5g of solid S in a boiling tube. Carry out the following tests and record your
observations and inferences in the spaces provided.
(a)
- Add 10.0cm3 of distilled water to solid S in the boiling tube.
- Shake well.
- Filter the mixture into a clean boiling tube.
- Label the filtrate as solution S and residue as R.
- Retain both the filtrate and the residue.
(i) Place about 2cm3 of solution S in a test tube, add 3 drops of 2M sodium chloride.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(ii) Place about 2cm3 of solution S in a test tube, add 2M ammonia solution dropwise till in excess.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(iii) Place about 2cm3 of solution S in a test tube, add 3 drops of 0.5M Nitric Acid.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(iv) Place about 2cm3 of Solution S in a test tube, add 3 drops of Lead (II) Nitrate solution and warm.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(v) Place about 2cm3 of the solution in a test tube, add Barium Nitrate then excess 0.5M Nitric acid.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(b) Dry the solid residue R in between 2 filter papers. Divide the residue into two.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(i) Place one portion of the residue R in a test tube. Heat gently then strongly. Test any gas with a PH
indicator paper.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(ii) To the other half residue R add few drops of 2M Nitric (v) acid. Test any gas produced with lime
water – using the glass rod.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(c) You are provided with solid P. Carry out the following tests and record your observations and inferences in the spaces provided.
Divide solid P into two portions.
(i) Place one portion of solid P in a metallic spatula.
Heat using a non-luminous flame.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(ii) Place one portion in a boiling tube. Add 5 cm of distilled water. Shake well. Label this (boiling
tube) as solution P.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
|
(iii) Place about 2cm3 of solution P in a test tube. Test with litmus papers.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
(iv) Place about 2cm3 of solution P in a test tube. Add one drop of acidified Potassium Chromate (VI)
and warm.
Observations .......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... | Inferences ​.......................................................................... ​.......................................................................... ​.......................................................................... ​.......................................................................... |
20 marks