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NYAMIRA DISTRICT CHEMISTRY PRACTICAL QUESTIONS

 

CONFIDENTIAL  

INSTRUCTIONS  

Each candidate should be provided with:  

  • About 1g of malleic acid – solid P
  • A clean metallic spatula
  • Bunsen burner
  • 500ml distilled water in a wash bottle
  • Six test-tubes in a rack
  • One test tube holder
  • 2 boiling tubes
  • About 1g of AlCl3 – solid M
  • One blue and one red litmus paper
  • One volumetric flask (250ml)
  • One pipette 25cm3
  • One pipette filter
  • One label
  • Solid G – oxalic acid (exactly 3g) in a stoppered container
  • 50ml or 100ml measuring cylinder
  • 100cm3 beaker
  • One thermometer
  • One stopwatch/clock
  • About 0.2g NaHCO3 solid
  • 100ml of solution H
  • One burette (50ml)
  • 2 conical flasks

Access to:-

  • 0.2M Pb(NO3) Solution supplied with a dropper
  • 0.2M Ba(NO3)2 Solution supplied with a dropper
  • 0.1M KI Solution supplied with a dropper
  • 2M NaOH Solution supplied with a dropper
  • 2M NH3(aq) Solution supplied with a dropper
  • Acidified K2CV2O7 Solution supplied with a dropper

Preparation instruction

– Dissolve 6.4g of KMnO4 in 400cm3 2M H2SO4 and top to 1litre using distilled water  

 

1.  You are provided with:

  • 0.0238 Moles (equivalent to 3g) of solid G
  • Solution H, 0.04M acidified potassium manganate (VII)  

You are required to:

I. Determine the enthalpy of solution of solid G

II. The number of moles of water of crystallization in solid G  

 

Procedure I:-

Using a measuring cylinder place 50cm3 of distilled water into a 100cm3 of beaker.

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Stir the water gently with a thermometer and take its temperature after every half-minute.

Record the reading in table I below. At exactly two minutes, add all solid G to the water

at once. Stir well and take the temperature of the mixture after every half minute up to

the fourth minute. Record your results in table I. Keep the solutions for procedure II below:

Table I

(a)

Time (min)

0

½

1

1 ½

2

2 ½

3

3 ½

4

Temperature (oC )

    

X

    

 

 

  (b) On the grid provided, plot a graph of time (x-axis) against temperature

 (c) (i) On the graph, show the change in temperature T

(ii) Calculate :

The molar enthalpy of solution (H solution)

(Assume density of solution = 1g/cm3 and show the sign of H solution specific heat

capacity of solution = 4.2jg-1k-1)

Procedure II

Transfer the contents of the beaker into a 250ml volumetric flask. Rinse both the beaker

and the thermometer with distilled water and add to the volumetric flask. Add more distilled

water to eh mark.

Label this solution G

Fill the burette with solution H

Using a pipette and pipette filter, place 25.0cm3 of solution G into a conical flask. Warm the

mixture to about 60oC. Titrate the hot solution G with solution H until a permanent pink colour

persists (while shaking). Record your readings in table 2. Repeat the titration two more times

and complete table 2

Table 2.

Titre

I

II

III

Final burette reading

   

Initial burette reading

   

Volume of solution H used (cm3)

   

 

(e) Calculate the:

  1. Average volume of H used

  II. Number of moles of potassium manganate VII used

  III. Number of moles of G in 25cm3 solution G given that 2moles of potassium manganate

(VII) reacted completely with 5moles of G

  IV. Relative formula mass of G

 (f) Formula of G has the form G. XH2 Determine the value of X in the formula given

the relative formula mass for G is 90.0 and atomic mass of Oxygen is16 and that

of Hydrogen is 1.0

 

  2.  You are provided with solid M and carry out the tests below write your observations and

inferences in the spaces

 (i) To a dry boiling tube, place all solid M and add 12cm3 of distilled water and use the

solution for the tests below:-

 (ii) To 2cm3 of solution, add both litmus papers

 (iii) To 2cm3 of solution, add aqueous sodium hydroxide drop wise until excess

 (iv) To 2cm3 of solution, add aqueous ammonia drop wise until in excess

 (v) To 2cm3 of the solution, add 2 drops of aqueous potassium iodide

 (vi) To 2cm3 of solution, add 3 drops of aqueous lead (ii)nitrate

 (vii) To 2cm3 of solution, add 3 drops of aqueous Barium nitrate solution

 

2.  B. You are provided with solid P. Carry out the test below. Write your observations and

inferences in the spaces provided:-  

(a) Place one third of solid P on a metallic spatula and burn it using a Bunsen burner

  (b) Place the remaining of solid P in a test-tube . Add about 6cm3 of distilled water and shake

the mixture (retain the mixture for use in test (c)

 (c) (i) To 2cm3 of the mixture in (b) above add a spatula end full of NaHCO3 solid

  (ii) To 2cm3 of the mixture, add 2cm3 of acidified potassium dichromate (VI) and warm

(iii) To 2cm3 of the mixture add two drops of acidified potassium manganese (VII) and shake well

 

NYAMIRA DISTRICT CHEMISTRY PRACTICAL ANSWERS

1.  (a)

Time (min)

0

½

1

1 ½

2

2 ½

3

3 ½

4

Temperature (oC )

19.0

19.0

19.0

19.0

X

16.0

15.0

15.0

15.0

Image From EcoleBooks.com

Complete  – 1mk

  • 8 readings – 1mk- penalize – ½ of space not filled
  • ½ for unrealistic values T 100 or 40
  • ½ all constant t = 0 to t = 4
  • ½ if T( T(2 ½ )

Decimal place – 1mk

– Accept whole number or to 1d.p of 0.5 or 0.0

Accuracy  – 1mk S.V  2units

Trend – 1mk

Award ½ – where t = 0 – t – 1 ½ min = all constant

t = ½ – t ½ min – constant

Award ½ – t – 2 ½ to 4min –show a drop

(b)  Graph

Ans – ½ – both axis correctly labelled

Scale = ½ – use more than ¾ big squares in both axis

Plotting -1

Labeling -1

3 mks

Penalize ½ inverted and scale to accommodate all plots

Plotting  – all 8 points award 1mk

– 6pts & 7 award

 5 award 0mk

Labelling  – Award ½ for two straight lines.

– ½ for extrapolation

 

 

(b)  (i) T = correct reading

(ii) Heat of solution = MCT

= 50g x 4.2Jg-1K-1 x 4.5K

= -50 x 4.2 x 45J

= –50 x 4.2 x 4.5 KJ

1000

Hsoln = ?

0.0238moles = -50 x 4.2 x4JKJ

1000

1mole= ?

= -50 x 4.2 x 4.5 KJ/mol

1000 x 0.0238

= -Ans

Penalized if H – sign is + and not –ve (total 3mks)

 

TABLE 2

Titre

I

II

III

Final burette reading

24.4

24.5

24.3

Initial burette reading

0.0

0.0

0.0

Volume of solution H used (cm3)

24.4

24.5

24.3

Image From EcoleBooks.comConditions:-  A complete table …

3 consistent titrations  1ms

2 titrations done and are consistent…1mk

3 inconsistent titrations done and averaged 0mk

only 1 titration done…………….0mk

Penalty:

(i) Penalize ½mk for inverted table.

(ii) Penalize ½mk to unrealistic titre values e.g. volume cm3 unless explained.

(iii) Penalize ½mk for wrong arithmetic.

 

B- Use of decimals ….1mk

(Tied to 1st and 2nd rows)

Conditions

  1. Accept 1 decimal place / point if used consistently.
  2. Accept 2 decimal points , however the 2nd decimal point must be either 0.0 or 5.

 

Penalty

  1. Penalize fully if decimals are not used consistently

 

(C) Accuracy ….1mk

(i) Conditions (i) If any of the volume used is within 0.1cm3 of the school value (S.V)…

(ii) If there is one value within 0.2cm3 of the school value (S.V)… ( ½mk)

 

(D) Principles of averaging…..1mk

Conditions

  1. If 3 titrations done are consistent and averaged….
  2. If 3 titrations done and 2 are consistent and averaged ….1mk
  3. If 2 titrations done and are consistent and averaged….1mk
  4. If titration done …1mk
  5. If 3 titrations done and are inconsistent and averaged ….0mk
  6. If 2 consistent titrations averaged…0mk
  7. If 3titrations are done and are consistent but are averaged …..0mk

 

(E) Final answer …..1mk

Conditions

  1. If the answer of the titre value is within 0.1cm3 of the school value (S.V) award….1mk
  2. If the answer of the titre value is within 0.2cm3 of the school value …. ½mk
  3. If the answer is not within 0.2cm3of the school value (S.V) award….0mk

 

Image From EcoleBooks.comImage From EcoleBooks.com(e) Average volume of solution H used

24.5 + 24.4 + 24.3 = 24.4

3

 

Image From EcoleBooks.comImage From EcoleBooks.comII. 24.4 x 0.04 = 0.000976

Image From EcoleBooks.comImage From EcoleBooks.com 1000

 

III. 5/2 x 0.000976 = 0.00244  (penalize ½ for wrong units)

 

Image From EcoleBooks.comIV. 3

   250 x 0.00244

25

= 3 = 122.95

0.0244

= 123(no units) penalize for units

Image From EcoleBooks.com

(f)  123-90 = 33

16 + (2×1) = 18x = 33

x = 33/18 = 1.833

Image From EcoleBooks.comx = 2

 

2.  (a) (i)

Observation

Inference

– Solid dissolves, yellowish solution.

– Colourless fumes/vapour are produced.

– boiling tube becomes warm.(1 mk)

– Soluble compound.

– Mix with water is exothermal heat is produced. (1 mk)

(ii)

Observation

Inference

– Blue litmus turns red.

– No effect on litmus paper.

– Presence of H+/H3O in the solution.

– Solution is acid (1 mk)

 

 

 

 

Observation

Inference

– White ppt. soluble in excess. (1 mk)

– Pb2+, Zn2+, Pb3+ present. (1 mk)

 

(iii)

 

 

 

(iv)

Observation

Inference

– White ppt. persisted insoluble in excess

– Al3+ or Pb2+ probably present

 

 

 

 

(v)

Observation

Inference

– Mixture remains colourless/ No yellow ppt. seen. (1 mk)

– Pb2+ absent (1glim).

– Al3+ present

 

 

 

 

(vi)

Observation

Inference

– White ppt. seen. (1 mk)

– SO42-, CO32-, SO32- absent

– Cl- is present (probably present)

 

 

 

 

(B(b)

Observation

Inference

– Solid melts forming a colourless and ignites /burns with

Smoky / sooty flame. (1 mk)

– Low compound organic compound/presence

of

or –C C

(accept absence of saturated organic compound). (1 mk)

 

Observation

Inference

– Dissolves in water forming colourless solution

– Solution compound /polar compound

 

(c) (i)

 

 

 

Observation

Inference

– Effervescence/ fizzling/bubbles of a colourless gas.

– No effect on litmus paper.

Presence of – COOH/ H+/H3O+ ions.

Solution is acid . (1 mk)

 

 

 

(ii)

Observation

Inference

– The solution remained orange.

– Absence of R-OH. (1 mk)

 

 

 

(iii)

Observation

Inference

Solution turns from purple to colourless solution is decolourised (1 mk)

– Presence of of –C C-

 

 

 

 





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