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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 (-10oC – 110oC)
  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:

ecolebooks.com
  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

 

I

II

III

 

Final burette reading (cm3)

   

 

Initial burette reading (cm3)

   

Volume of solution M used (cm3)

   

(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.

MnO4 (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 70oC 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

 

I

II

III

Final burette reading (cm3)

   

Initial burette reading (cm3)

   

Volume of solution M (cm3)

   

 

(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:  

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

Image From EcoleBooks.comImage From EcoleBooks.comImage From EcoleBooks.comImage From EcoleBooks.com (ii) Add 3 drops of methyl orange to 2cm3 of solution R  

 

 

 

 

 

UGENYA – UGUNJA DISTRICT CHEMISTRY PRACTICAL ANSWERS

 

Q.1. a) Table 1

 

I

II

III

Final burette reading (cm3)

20.0

40.0

20.0

Initial burette reading (cm3)

0.0

20.0

0.0

Volume of solution M used (cm3)

20.0

20.0

20.0

 

 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 MnO4

 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

 

I

II

III

Final burette reading (cm3)

19.4

38.8.

19.4

Initial burette reading (cm3)

0.0

19.4

0.0

Volume of solution M used (cm3)

19.4

19.4

19.4

 

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 SO42-
√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

 

 

Image From EcoleBooks.com  ii)  Observations Inferences

 

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

Image From EcoleBooks.com pink / red.

 




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