KAKAMEGA NORTH DISTRICT CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS

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 110^oC 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;

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;

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 = 4.2^Jg^-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)

KAKAMEGA NORTH DISTRICT CHEMISTRY PRACTICAL ANSWERS

Procedure;

TABLE A;

TABLE B;

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

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) M_AV_A = 1(MR) where A = HCL_(aq) B= MOH_(aq)

M_BV_B 1

Therefore M_B = 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