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RACHUONYO DISTRICT CHEMISTRY PRACTICAL QUESTIONS

 

CONFIDENTIAL  

INSTRUCTIONS .

In addition to common fittings, apparatus and chemicals found in the school laboratory.  

Each candidate requires:-

  • 50.0ml burette
  • 250ml pipette
  • Pipette filler
  • Two 25.0ml conical flasks
  • A clean metallic spatula
  • One boiling tube
  • A white tile/plain paper (white)
  • Eight clean dry test-tubes on a rack
  • 1.5g of carbonate A- accurately weighed and placed in a stoppered test-tube
  • 75cm3 of 0.1M sodium hydroxide labeled C
  • 75cm3 of 1M hydrochloric acid labeled solution B
  • 10ml measuring cylinder
  • One filter paper
  • A filter funnel
  • A glass rod
  • 45cm3 of 0.42M glucose, labeled X
  • 130cm3 of 2.0M H2SO4 labelled Z
  • 10ml of 0.04M KMnO4 labelled Y
  • Stop watch/stop clock
  • Thermometer (-10oC – 110oC)
  • 100ml measuring cylinder
  • Solid K (about 2g)
  • Distilled water in a wash bottle
  • A 250ml volumetric flask (one)
  • Means of labeling (one)

 

Access to the following:-

  • Bunsen burner
  • Phenolphthalein indicator solution supplied with a dropper
  • Tripod stand and a wire gauze
  • 2.0M NaOH supplied with a dropper
  • 2.0M HCl
  • 2.0M HNO3 supplied with a dropper
  • 0.5M BaCl2 supplied with a dropper
  • Calcium hydroxide solution in a stoppered container
  • 2.0M ammonia solution supplied with a dropper
  • 0.05M potassium iodide solution supplied with a dropper

 

Preparation of chemicals

  1. Solid A – Calcium Carbonate
  2. Solid K – Mixture of Lead (II) carbonate and sodium sulphate in the ratio 1:1

1.  You are provided with:

  • 1.5g of metal Carbonate A
  • 75cm3 of 1M hydrochloric acid labelled B
  • 75cm3 of 0.1M sodium hydroxide labelled C

You are required to determine the molar mass of the carbonate

 

 

 

Procedure I

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Transfer carefully all solid A into a clean 250ml volumetric flask. Add 50cm3 of the acid labelled

B into the flask containing the carbonate. Wait until the reaction is complete

(No more effervescence takes place)

Question   1.

(a) Find the moles of hydrochloric acid present in 50cm3 of solution B  

Procedure II

When the reaction is complete, add 100cm3 of distilled water to the contents of the flask and shake.

Add more distilled water to top the solution to the mark. Label it as solution D. Pipette 25cm3 of solution D into a 250cm3 of conical flask and titrate with solution C using 1 to 2drops of phenolphthalein indicator. Record your results in table 1 below. Repeat this procedure to obtain

accurate values:

 

I

II

III

Final burette reading (cm3)

   

Initial burette reading (cm3)

   

Volume of solution C used (cm3)

   

 

 

 

 

 

(b) Determine the average volume of solution C used

 

(c) (i) Calculate the volume of sodium hydroxide that would react with 250cm3 of the diluted acid

(ii) Calculate the moles of sodium hydroxide solution C in the volume obtained in c(i)

Above

(d) Write down equation for the reaction between hydrochloric acid and sodium hydroxide  

(e) How many moles of hydrochloric acid are left after the reaction with the metal carbonate A  

(f) Calculate the moles of hydrochloric acid that reacted with 1.5g of the metal Carbonate A  

(g) (i) Write down the ionic equation between carbonate and hydrochloric acid

(ii) Calculate moles of carbonate A

(iii) Calculate the molar mss of the carbonate A

2.  You are provided with:-

  • 2.0M sulphuric (VI) acid solution, solution Z
  • 0.42M glucose, solution X
  • 0.04M potassium manganate (VII) solution Y

You are required to determine the rate of reaction between aqueous glucose solution and

acidified potassium manganate (VII) at different temperatures.  

Procedure

Place 1cm3 of solution Y into a conical flask. Using a 100cm3 measuring cylinder add

25cm3 of solution Z to the conical flask containing solution Y. Warm the mixture to

about 70oC. Stop warming and allow the mixture to cool. When the temperature is exactly

65oC add 7.5cm3 of solution X and start the stop watch immediately. Stir the mixture with a thermometer and measure the time taken for the colour of the mixture to change from purple to colourless. Record the time in table 2 below also record the temperature at which the mixture turns colourless. Clean the conical flask and repeat the procedure at temperature of 60oC, 55oC 50oC

and 45oC instead of 65oC.

 

(a) Calculate 1/time and complete the table

Table 2 (6mks)

Temperature before mixing (oC)

65

60

55

50

45

Temperature when solution becomes colourless (oC)

     

Time in seconds

     

1/time(s-1)

     

 

(b) Plot a graph of 1/time (y-axis)
against the temperature at the point when the solution becomes

Colourless

(c) From your graph, determine the time that the reaction would take if the temperature at

which the solution becomes colourless is 52.5oC

 (d) From your graph, determine the rate of reaction if the temperature at which the solution

becomes colourless is 47oC

  (e) Explain the shape of your graph

3.  You are provided with mixture K. You are required to perform tests on the mixture in order to

determine its composition. Record your observations and inferences in their spaces provided:-

  1. Place a spatula of K on a white tile and observe its appearance:-

  (b) Place the remaining portion of K in a boiling tube and add 10cm3 of distilled water.

Shake vigorously, filter and retain both the residue and filtrate  

  (i) Divide the filtrate into 3 portions. To the first portion sodium hydroxide drop-wise until excess

  (ii) Dip one end of a metallic spatula in 2M HCl and heat it in a Bunsen burner flame for a few

seconds and allow it to cool. Scoop a little of the solution from the second portion with the

heated end of the spatula and place it as the hottest part of the non-luminous flame.  

  (iii) To the third portion add 3-4 drops of dilute HNO3(aq) followed by 3-4 drops of BaCl2(aq)

 (c) Scrap the residue from the filter paper and place a half of it in a clean dry test tube.

Add about 3cm3 of 2M HNO3. Test for any gas produced by use of calcium hydroxide

solution on a glass rod. Preserve the solution for use in procedure (d) below:-

 (d) Add about 3cm3 of distilled water to the solution obtained in (c) above and shake to mix.

Divide the solution into 3 portions  

  (i) To the first portion, add sodium hydroxide drop-wise until in excess

  (ii) To the second portion, add ammonia solution drop-wise until in excess

  (iii) To the third portion, add 2-3drops of potassium iodide solution

 

RACHUONYO DISTRICT CHEMISTRY PRACTICAL ANSWERS

 

1.  a) Moles of Hcl present in 50cm3 = 50×1  = 0.05 moles

 1000

 

 

i) Complete table (1 mark)

– 3 titrations done-

– 2 titrations done

– 1 titration done

NB: Penalise ½ mark to a max of ½ mark for;

– inverted table

– wrong arithmetic

– burette readings beyond 50 cm3 except where explained

– Unrealistic (below 1 cm3)

 

ii)  Use of decimals  (1 mark)

– 1d.p or 2 d.p throughout

– for 2 d.p the 2nd digit is either 0 or 5 otherwise penalize fully

 

iii)   Accuracy  (1 mark)

– Compare to teachers values. If any is within;

0.1 of teachers value

0.2 0f teachers value

Beyond 0.2 of teacher value

 

iv)  Averaging

If 3 averaged within 0.2 of each other

If 2 averaged within 0.2 of each other

If 3 or 2 averaged but outside 0.2 of each other

 

v)   final answer  ( 1 mark)

Compare to teachers average title. If within;

0.1 of teachers value

0.2 of teachers value

Beyond 0.2 of teachers value

 

 c) i) Volume of NaOH = Title x 250

  25

 = correct ans ½

 

 ii) Moles of NaOH = Ans c (i) x 0.1

1000

 = correct ans ½

 

 d) NaOH (aq) + HCL (aq) NaCL (aq) + H2O (s)

 

 e) NaOH: Hcl = 1:1

Moles of HCL = Moles Of NaOH = Ans in C (ii)

 

 f) Moles of HCl that reached with CO32 = 0.05 – Ans ©, ½ mark

Correct aswer ½ mark

 

 OR

Ans (a) – Ans (e) = correct Ans

 

 g)  i) CO32-
(aq) + 2H+ Aq Co2 + H2 Oi

 

ii) Moles of CO32- = Ans (f)

2

= correct Ans

 

iii) Molar mass = 1.5 = correct answer

Ans g (ii)

2.  a) Table 2 (6 marks)

i) Complete table

ii) Accuracy 2.0 c of the teachers 1st value ½

 

iii) Use of decimals

    Accept to 1 d.p or whole number for temp reading for ½

 Award o mk if the 2nd decimal point is not zero or 5. Reject 2 d.p

   iv) Trend- Temperature readings to decrease continuously

Time to increase continuously

 

 b) Graph ( 3 marks)

i) Labelled axes   ½

ii) Scale ½

NB Area occupied by the actual plots should be at least ½ of the total big squares along

the horizontal axis by at least ½ of the total big squares along the vertical axis

 

iii) Plots

iv) Curve

 c) From the graph

 d) From the graph

 

 e) The higher the temperature the higher the rate of reaction

3  a)

Observation

Inferences

White powder ½

Fe 2+, Fe 3+ and Cu 2+

 b)

Observation

Inferences

 

Mixture of soluble and insoluble salt

 i)

Observation

Inferences

No white precipitate ½

Zn2+, Al3+, Pb2+, Mg2+,, Ca2+

 ii)

Observation

Inferences

Yellow flame

Na+ ½ present

 iii)

Observation

Inferences

White precipate

SO42- present

 c)

Observation

Inferences

– Effervescence/ hissing sound ½

 

– Colorless gas forms white precipitate with calcium hydroxide ½

CO32- present ½

– Solid dissolves to give colourless solution

 

 d)  i)

Observation

Inferences

White precipitate ½ soluble in excess

Pb2+, Zn2+ or Al3+

ii)

Observation

Inferences

White precipitate insoluble in excess

Pb2+ or Al3+

iii)

Observation

Inferences

Yellow precipitate

Pb2+ present


 




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