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KAKAMEGA NORTH DISTRICT CHEMISTRY PRACTICAL QUESTIONS
CONFIDENTIAL
INSTUVTIONS.
You are provided with:
- 25cm3 of 0.2M Copper(II) sulphate solution
- 0.5g of metal A
- 0.5g of metal B
- One thermometer of -10 to 110oC range
- Two 100cm3 plastic beakers
You are required to determine the molar enthalpy change for metal A and B and arrange them in order of reactivity
Procedure
1. a) Using the thermometer provided, take the initial temperature of copper (II) sulphate solution
and record your results in table A below
b) Add all the 0.5g of metal A into copper (II) sulphate solution; stir the mixture for about 5 minutes.
Using a thermometer and record the final temperature (highest temperature) in table A below:
TABLE A;
Initial temperature of CUSO4(aq) (C) | |
Final temperature of CUSO4(aq) (C) | |
Temperature change T (oC ) |
Question 2;
2. a) Using a thermometer take initial temperature of another 25cm3 fresh sample of copper(II)
sulphate solution in the plastic beaker and record your results in table B below;
TABLE B;
Initial temperature of CUSO4(aq) (C) | |
Final temperature of CUSO4(aq) (C) | |
Temperature change T (c ) |
a) i) State and explain whether the reactions above between metals A and B
with copper (II) sulphate are endothermic or exothermic
ii) Calculate the moles of copper ions present in 25cm3 of 0.2M copper (II) sulphate
solution
b) i) Calculate the enthalpy change that occurs when 25cm3 of copper (II) solution
reacts with metal A. (Specific heat – capacity of the solution = 4.2Jg-1K-1,
Density of the solution = 1g/cm3
ii) Determine the molar enthalpy change for the reaction of copper (II) sulphate
solution with metal A
c) i) Explain the significance of using powdered metals A and B in this experiment
ii) Record the colour of the powdered metals A and B
d) State and explain major observations made when metal A reacts with copper (II)
sulphate solution
e) i) Determine the molar enthalpy change for the reaction of metal B with 25cm3 of 0.2 M copper
(II) sulphate solution (C = 4.2Jg-1K-1, Density of solution = 1g/cm3, RAM of metal B= 65)
ii) Arrange metals A and B in order of reactivity beginning with the more reactive one. Give a
reason for your answer
Question 2
You are provided with;
- Solution C, 0.1 M hydrochloric acid
- Solution D, MOH(aq) solution of unknown concentration
- Phenolphthalene indicator
You are required to standardize solution D using solution C and to determine the value of M in the formula MOH(aq)
Procedure
1. a) Pipette 25cm3 of solution D into the conical flask. Using a dropper, add 2 drops
of phenolphthalene indicator to solution D
b) Fill the burette with solution C and correct to the “O” mark
c) Titrate solution C against solution D
2. Repeat procedure 1(a), (b) and (c) twice and record your results in a table of results below;
Table of results
a) Volume of pipette used ___________________________ cm3
b) Calculate the average volume of solution C used in this experiment
c) Calculate the number of moles of solution C used in this experiment
d) Given that solution C is hydrochloric acid while solution D is MOH (the base),
i) Write a chemical equation to show the reaction of solution C with D
ii) Write the ionic equation for the reaction of solution C with D in d (i) above
iii) From the reaction equation written in d(i) above, determine the moles of solution D that
reacted with solution C
e) i) Determine the molarity of solution D (i.e. MOH(aq)) used in this experiment
ii) Given that 6016g of solid MOH(s) were dissolved in distilled water and made to 1 litre, calculate
the relative molecular mass of MOH(s)
iii) From your answer in e (ii) above, determine the value of M in the formula MOH
Question 3.
You are provided with solid E. Carry out the following tests on solid E so as to try and find out the ions present in solid E
Complete the table below to show your observation and inference (conclusions)
Experiment | Observation | Inference |
a) Observe solid E and record your findings | ||
b) Dissolve solid E in about ¾ of distilled water in a boiling tube and divide the solution into 5 portions in 5 test tubes | ||
i) To portion 1 add NaOH(aq) drop wise to excess | ||
ii) To portion 2 add NH3(aq) drop wise to excess | ||
iii) To portion 3 add a few drops of Ba(NO3)2 followed by few drops of dilute HNO3(aq) | ||
iv) To portion 4 add lead (II) Nitrate drop wise followed by dil. HNO3(aq) | ||
v) To portion 5 dip a looped nichrome wire to it and put the wire in the Bunsen flame |
KAKAMEGA NORTH DISTRICT CHEMISTRY PRACTICAL ANSWERS
Procedure;
TABLE A;
Initial temp of CuSo4(c ) | 25.5 |
Final temp of CuSO4 | 31.0 |
Temp change T(C ) | 5.5 |
TABLE B;
Initial temp of CuSo4(c ) | 25.5 |
Final temp of CuSO4 | 48.0 |
Temp change T(C ) | 22.5 |
a) i) Exothermic// there is temperature rise heat energy is released to the environment
ii) Moles of CuSO4(aq) = 0.2 x 25/1000 = 0.005
b) i) H = 25gx4.2Jg-1K-1 x5.5K (OR T)
c) i) Powdered metals have increased surface are many metal particles with come in contact
with HCL acid and react
ii) Grey// metallic grey
d) – Metal A dissolves in CuSO4(aq) solution and a green/ pale green solution is formed
– The blue colour of copper (II) sulphate solution fades/ disappears. Brown solid deposited
– Metal A displaces copper; from its solution implying that A(q) is more reactive than Cu(s)
e) i) H = 25gx4.2Jg-1K-1 x T (22.5) K = 2362JJ
If 0.5g _______ 2362.5J
65g _______ (65×2362.5) J = 307125J mol = 307.125KJmol
0.5
ii) B, A
_________ Decreasing reactivity
B gave higher T// more heat energy was released when B reacted with CuSO4(aq)
Procedure;
Table of results
EXPERIMENT | I | II | III |
Final Vol. of solution C (cm3) | |||
Initial Vol.of solution C (cm3) | |||
Vol.of solution C used (cm3) |
1. a) Volume of pipette = 25cm3
b) Average volume of C = 38.5 + 38.5 + 38.5 = 115 = 38.5
3 3
c) Moles of solution C = 0.1 x 38.5/1000 = 0.00385
d) i) HCL(aq) + MOH (aq) _________ MCL(aq) + H2O(L)
Penalize ½ for wrong or missing s
ii) H+(aq) + OH–(aq) _______ H2O(L)
iii) HCL(aq) : MOH(aq)
1 : 1
0.00385 : 0.00385
e) i) MAVA = 1(MR) where A = HCL(aq) B= MOH(aq)
MBVB 1
Therefore MB = 0.1×38.5×1 = 1.54
25×1
ii) R.M.M = mass per litre = 6.16 = 40
molarity 0.154
iii) MOH = 40
M+ 17 = 40
M= 40-17= 23
Observation | Inference |
a) White fine crystal solid | Absence of coloured salts e.g. Cu2+, Fe2+ or Fe3+ absent |
b) E dissolved to form a colourless solution | E is a soluble salt |
i) No observable change No ppt | Absence of insoluble hydroxides |
ii) No observable change No ppt | Absence of ions that form isol. Ppt with NH3(aq) |
iii) White ppt. insoluble in acid | SO42- ions present So32- ions absent |
iv) White ppt. insoluble in acid | Confirms the presence of SO42- ions |
v) Nichrome wire burns with a yellow flame | Confirms the presence of Na+ ions |