UGENYA –UGUNJA DISTRICTS CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS

UGENYA –UGUNJA DISTRICTS CHEMISTRY PRACTICAL QUESTIONS

CONFIDENTIAL

IDENTITIES OF SOLIDS

M- Potassium manganate (VII) crystals, KMnO₄

N – Ammonium Ferous sulphate hexahydrate, (NHa)₂ .Fe(SO₄)₂. 6H₂O

S – Oxalic acid H₂C₂O₄.2H₂O

Q- Hydrated Barium Chloride, BaCl₂. 2H₂O

R- Oxalic acid

Note: S and R are the same substances

INSTRUCTIONS

In addition to the apparatus and chemicals found in the chemistry laboratory, each

candidate will require the following:

1. 150cm³ of solution M
   
2. 100cm³ of solution N
   
3. 100cm³ of solution S
   
4. One 50cm³ burette
   
5. One 25cm³ pipette and pipette filter
   
6. One thermometer (-10^oC – 110^oC)
   
7. One filter funnel
   
8. Two conical flasks
   
9. Tripod stand and wire gauze
   
10. Source of heat
    
11. 8 clean dry test tubes in a rack
    
12. 2 boiling tubes
    
13. 1 metallic spatula
    
14. 250ml of distilled water in a wash bottle
    
15. About 1g of solid R
    
16. About 1g of solid Q
    
17. 1 red and 1 blue litmus paper
    

Access to:

1. 2M NaOH supplied with a dropper
   
2. 0.5M Na₂SO₄ supplied with a dropper
   
3. 0.1M Pb(NO₃)₂ supplied with a dropper
   
4. Methyl orange indicator
   
5. 0.5M Ba(NO3)2 supplied with a dropper
   

Notes:

1. Solution M is prepared by dissolving 3.16g of solid M in 400cm³ of 2M H₂SO₄ and making it up to 1 litre of solution with distilled water.
   
2. Solution N is prepared by dissolving 23.5g of solid N in 200cm³ of 2M H₂SO₄ and making it up to 1 litre of solution with distilled water.
   
3. Solution S is prepared by dissolving 5g S in 600cm³ of distilled water and making it up to 1 litre of solution with distilled water
   

1. QUESTION 1
   

You are provided with:

• Acidified aqueous Potassium manganate (VII) KMnO₄, solution M(to be used also in question 3).
• Solution N, containing 23.5g of ammonium iron (II) sulphate, (NH₄)₂ Fe(SO₄)₂
  . 6H₂O, per litre.
• Solution S, containing 5.0g of a dibasic acid, H2X.2H2O per litre

You are required to:-

• Standardize the potassium manganate (VII), solution M, using the ammonium

• iron (II) sulphate, solution N.
  

• Use the standardized potassium manganate (VII), solution M to determine the

concentration of the dibasic acid H₂ X•2H₂O, solutions S and then the formula mass of X.

Procedure I

Fill the burette with solution M.

Pipette 25.0cm3 of solution N into a conical flask. Titrate solution N with solution

M until a permanent pink colour just appears. Record your results in table I below.

Repeat this procedure to complete table I

(a) Table I

(b) Determine the average volume of solution M used,

(c) Calculate the concentration of the ammonium iron (II) sulphate, solution N, in moles

per litre. (RFM of (NH₄)₂ Fe(SO₄)₂ .6H₂O = 392 )

(d) Calculate the number of moles of iron (II) ions in the 25.0cm³ of solution N

(e) Using the ionic equation for the reaction between manganate (VII) and iron (II) ions, given

below, calculate the concentration of manganate (VII) in solution M in moles per litre.

MnO^–_{4 (aq)} + 5Fe²⁺ _(aq) + 8H⁺_(aq) Mn²⁺ _(aq) + 5Fe³⁺_(aq) + 4H₂O_(l)

Procedure II

Pipette 25.0cm³ of solution S into a conical flask. Heat this solution to about 70^oC and titrate

the hot solution S with solution M until a permanent pink colour just appears. Shake thoroughly

during the titration. Record your results in table II. Repeat this procedure to complete the table II

(f) Table II

(g) Record the average volume of solution M used (show how you arrive at the answer)

V₂=…………………………………………………………………………………

(h) Calculate the number of moles of the manganate (VII) ions in volume V₂

(i) Given that 2 moles of the manganate (VII) ions react with 5 moles of the dibasic acid,

H₂X•2H₂O, calculate the number of moles of the dibasic acid, H₂X . 2H₂O in 25cm³

of solution S

(j) Calculate the concentration of the dibasic acid H₂X . 2H₂O, in moles per litre

(k) Calculate the formula mass of X in the dibasic acid, H₂X . 2H₂O. (H= 1.0, O = 16.0

2. You are provided with solid Q. Carry out the following tests and write your observations and

inferences in the spaces provided

(a) Place about one-half of solid Q in a dry test tube. Heat strongly and test any gas produced

using litmus papers

b) Place the remaining solid Q in a boiling tube. Add about 10cm³ of distilled water and shake well.

i) To about 2cm³ of the solution in a test tube add sodium hydroxide solution till in excess

ii) To about 2cm³ of solution Q in a test tube add about 2cm³ of 0.5M sodium sulphate solution

iii) To about 2cm³ of solution Q in a test tube, add about 4cm3 of barium nitrate solution

(iv) To about 2cm³ of solution Q in a test tube, add 3 drops of lead (II) nitrate solution and

heat the mixture to boiling

3. You are provided with solid R. Carry out the following tests and write your observations and inferences in the spaces provided

 (a) Place a little of solid R in a clean metallic spatula and ignite with a bunsen flame

(b) Place all the remaining solid R in a boiling tube. Add about 6cm³ of distilled water

and shake well. Use 2cm³ portions to carry out the test below:

(i) Add 2cm³ of solution obtained by diluting 1cm³ of solution M with 5cm³ of distilled water to 2cm³ of solution R.

(ii) Add 3 drops of methyl orange to 2cm³ of solution R

UGENYA – UGUNJA DISTRICT CHEMISTRY PRACTICAL ANSWERS

Q.1. a) Table 1

 Complete table – 1 mk

 Decimal – 1 mk

 Accuracy – 1 mk

 Principle of averaging – 1 mk

 Final Answer – 1 mk

 b) Average volume of solution M used V₁ = (20.0 + 20.0) cm³

2

= 20.0 cm³

 c) Mass per litre = 23.5
√½ = 0.0599 √½

Molar mass 392

 d) 25 x Answer (c) = 25 x 0.0599 √½

1000 1000

 = 0.0014987 √½

 e) 20 cm³ of solution M contains Answer in (d) x 1 moles of MnO^–₄

 5

= 0.0014987 x 1√½

5

= 0.0002997 moles. √½

∴ 1000 cm³ of solution M contains 1000 x Answer in (d)

1. 5
   

 = 1000 x 0.0002997 √½

20

 = 0.014985 moles √½

 f) Table II

Complete table – 1 mk

Decimal – 1 mk

Accuracy – 1 mk

Principle of averaging – 1 mk

Final Answer – 1 mk

 g) Average volume of solution M used, V₂ = (19.4 + 19.4 + 19.4) cm³

3

= 19.4 cm³

 h) Average volume x Answer in (e)

1000

19.4 x 0.014985√½ = 0.0002907 √½

1000

 i) 1 Mole of MnO₄ reacts with 2.5 moles of S.

∴ Moles of MnO₄ in (h) reacts with 2.5 x moles in (h) of S.

∴ 25 cm³ of S will contain 2.5 x 0.0002907 √1 = 0.0007267 √1

 j) 1000 x Answer in (i)

25

1000 x 0.0007267 √½ = 0.029068 M √½

25

 k) Answer in (j) ⇒ 5.0g

1 Mole of S = 1 x 5.0

Answer in (j)

= 1 x 5.0

0.029068 √½

= 172.0g √½

H₂X∙2H₂O = 172.0

2(l) + X + 2(18) = 172.0 √1

X + 38 = 172.0

X = 172.0 – 38 √½

= 134.0 √½

Q. 2. a) Observations Inferences

– Colourless vapour condenses on the Hydrated salt / water crystallization√1

cooler parts of the test tube /OH^–

– Moist blue litmus paper remains blue

and red litmus paper remains red.

– White powder.

Any 2 = 1 mk

 b) Observations Inferences

Dissolve
√½ to form a Soluble salt / substance / compound. √½

colorless√½ solution.

 i) Observations Inferences

White precipitate √½ Ca²⁺, Mg²⁺, Ba²⁺

Insoluble√1 in excess 3 = 1 mk

2 = ½ 1 = 0 mk

 ii) Observations Inferences

White precipitate √1 Ca²⁺, Ba²⁺ 2 = 1 mk

1 = ½ mk

 iii) Observations Inferences

No white precipitate. √1 SO₄^2-
√1 absent

 iv) Observations Inferences

White precipitate dissolves
√½

on boiling and re-appears √½ Cl^-1
√1

on cooling

Q.3 a) Observations Inferences

Burns with yellow √1 smoky/ C = C or -C≡C-, Long chain

sooty flame hydrocarbon, unsaturated

organic compound, hydrocarbon with high

C : H ratio. Any 1 = 1 mk

 b) Observations Inferences

Dissolves√1 to form a Polar organic √1 compound / polar substance

colourless solution.

 i) Observations Inferences

KMnO₄√1 decolorized / changes C = C -C ≡C-

from purple to colourless.

2 = 1 mk 1 = ½ mk

 ii) Observations Inferences

Methyl Orange turns √1 √1 H⁺ / H₃O⁺ / – C

pink / red.