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Simple classification of substances Questions

1.  The diagram below shows the heating curve of a pure substance. Study it and answer the

  questions that follow:

 

 

 

 

 

 

 

 

 

 

 

 (a) What physical changes are taking place at points X and Z?    (b)Explain what happens to the melting point of sodium chloride added to this substance

 

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2.  (a) State two differences between luminous flame and non-luminous flame  

 (b) It is advisable to set a Bunsen burner to luminous flame prior to an experiment.

Explain

3.  The paper chromatography of a plant extract gave the following results:

 

Solvent

Number of spots

X

6

Y

2

Z

3

 

 (a) Which is the most suitable solvent for purifying the extract? Explain

  (b) Ball pen cannot be used to mark solvent front in the above chromatography. Explain  

4.  Name the process which takes place when:

  (a) Solid Carbon (Iv) Oxide (dry ice) changes directly into gas  

 (b) A red litmus paper turns white when dropped into chlorine water

 (c) Propene gas molecules are converted into a giant molecule  

5.  A sample of copper turnings was found to be contaminated with copper (II) oxide. Describe

 how a sample of copper metal can be separated from the mixture

6.  Copper (II) oxide and charcoal are black solids. How would you distinguish between the

 two solids?  

7.  a) What is chromatography?

 b) Give two applications of chromatography

8.  The two elements P and R were separately burned in air, the products gave the results

recorded in the table below:

 

ELEMENTS PHYSICAL STATE AT ROOM TEMPERATURE

P SOLID

R SOLID

Physical states of products

White solid powder only

Colourless gases L and M

Nature of solutions in water

Basic

L strongly acidic M slightly acidic

 

 (a) Suggest the identity of element R. ……………………………………………..……..  

 (b) Describe how the nature of the solutions of the of the oxides were determined

9  The diagram below represents a paper chromatography for the three brands of soft drinks

 containing banned artificial food additives.

    

 

4

1

6

 

2

7

5

3

 
 

A

B

C

BRANDS OF SOFT DRINKS

 A and C found to contain the banned artificial food additives. Which numbers indicate the

banned artificial food additives?

 

10.  Without using any laboratory chemical, describe a simple laboratory experiment to distinguish

 between calcium hydrogen carbonate and sodium hydrogen carbonate

11.   Substance Q has a melting point of 15oC and boiling point of 70oC.

 (a) On the same axes, draw the melting point and boiling point graph for Q and the room

temperature

 

 

 

 

 

 

 

 

 

 

 

(b) State the physical state of substance Q at room temperature  

12.  Cooking oils comprise of a mixture of compounds which have a boiling point range

of 23oC to 27oC.

 (i) What evidence is then to support the statement that cooking oil is a mixture?  

 (ii)Name another experimental technique that could be used to confirm your answer

in part (i) above

 

13.  A form 1 student carried out the separation as shown in the set-up below:-

 

 

 

 

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(i) Identify the method above………………………………………………………………………

(ii) Give one of its disadvantages

(iii) Name a mixture which can be separated by the set-up above  

14.  What is meant by melting point and boiling point of a substance?  

 

15.  The apparatus below were used by a student to study the effect of heat on hydrated

copper II sulphate

 

Image From EcoleBooks.com

 

 

 

 

 

 

 

 

 

 

(a) What is the role of the ice cold water  ……………

 (b) Name liquid P  …………………………………………………………

 (c) What observation is made in the boiling tube

 

 

17.  The diagram below shows chromatograms of blood samples obtained from three athletes.

Image From EcoleBooks.com  One athlete used illegal drug to improve performance in competition.

 

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Image From EcoleBooks.com

 

 

 

Image From EcoleBooks.com

 

 

 

 

 

 

 

(a) Name the line marked M  ………………………………………………….

 (b)Identify the athlete who used illegal drug  ………………  ……………………….  

18.  Classify the following processes as chemical changes or physical changes

 


Process
physical or chemical

Neutralization ………………………………………

Sublimation ………………………………………

Fractional distillation ………………………………………..

Displacement reaction …………………………………………

19.  Give two reasons why a luminous flame is not used for heating purposes

20.  Classify the following processes as chemical changes or physical changes


Process
physical or chemical

Neutralization ………………………………………

Sublimation ………………………………………

Fractional distillation ………………………………………..

Displacement reaction …………………………………………


21.  Give two reasons why a luminous flame is not used for heating purposes

22.  State two criteria for determining the purity of a substance

 

Substance

Water

Concentrated sulphuric(VI)acid

Concentrated sodium hydroxide

Ethene

Slightly soluble

Soluble

Insoluble

Ammonia

Very soluble

Very soluble

Very soluble

Hydrogen

Slightly soluble

Insoluble

Insoluble

23.  Study the information in the table below and answer the questions.

i) A mixture contains ethene, Hydrogen and ammonia gases. Explain how a sample of

hydrogen gas can be obtained from this mixture.

24.  a)i) The diagram below show spots of a pure substance A, B, and C on a chromatography

paper. Spot D is that of a mixture

 

 

 

 

 

 

 

 

 

  After development A, B, and C were found to have moved 8cm, 3cm and 6cm respectively.

 D had separated into two spots which had moved 6cm and 8cm

 On the diagram above;

  I. Label the baseline (origin)

  II. Show the positions of all the spots after development  

  ii) Identify the substances present in mixture D

 b) Describe how solid ammonium chloride can be separated from a solid mixture of

ammonium chloride and anhydrous calcium chloride

 c) The table below shows liquids that are miscible and those that are immiscible

Liquid

L3

L4

L1

Miscible

Miscible

L2

Miscible

Immiscible

 Use the information given in the table to answer that questions that follow;

i) Name the method that can be used to separate L1 and L2 from a mixture of the two  

ii) Describe how a mixture of L2 and L4 can be separated  

25.  A student left some crushed fruit mixture with water for some days. He found the mixture

 had fermented. He concluded that the mixture was contaminated with water and ethanol with

 boiling point of 100oC and 78oC respectively. The set-up of apparatus below are used to separate

 the mixture.

 

 

 

 

 

 

 

 

 

 

 

 

 

(i) Name the piece of apparatus labelled W  

 (ii) What is the purpose of the thermometer in the set-up?

 iii) At which end of the apparatus W should tap water be connected?……………………………

 (iv) Which liquid was collected as the first distillate? Explain

 (v) What is the name given to the above method of separating mixture?  

 (vi) State two applications of the above method of separating mixtures  

 (vi) What properties of the mixture makes it possible for the component to be separated

by the above methods?

Image From EcoleBooks.com26.  The set-up below was used to separate a mixture:-

 

 

 

 

 

 

 

 

 

 

 

 

 (a) Name the apparatus missing in the set-up  

 (b) Give one example of mixture T    

 (c) What is the name of this method of separation  

 

27.  a) The diagram below shows a set – up used by a student to find out what happens

when Copper (II) sulphate crystals are heated.

 

 

Image From EcoleBooks.com

Image From EcoleBooks.com

Image From EcoleBooks.com

Image From EcoleBooks.com

Image From EcoleBooks.com

Image From EcoleBooks.com

 

Image From EcoleBooks.com

 

 

(i) State the observations made when the blue copper (II) sulphate crystals are heated.

(ii) Identify liquid Y and write an equation for its formation.

 b) Pellets of sodium hydrogen and anhydrous Copper (II) sulphate were put in separate Petri-

dishes and left in the open for two hours. Explain the observation in each Petri-dish.

 
 

28.  The chromatography below shows the constituents of a flower extract using an organic solvent:-

 

 

 

 

 

 

 

 

 

 

 

 (a) (i) Name a possible organic solvent you can use for this experiment

  (ii) State one property that makes the red pigment to move the furthest distance from M  

  (iii) Describe how one could get a sample of yellow pigment  

(iv) On the diagram indicate solvent front  

 (b) Describe how Aluminium chloride can be separated from a mixture of aluminium chloride

and sodium chloride  

29. Study the information below and answer the questions that follow:

Solid

Cold water

Hot water

R

Soluble

Soluble

V

Insoluble

Insoluble

S

Insoluble

Insoluble

 

  Describe how the mixture of solid R, S, and V can be separated  

30.  Given a mixture of lead (II) oxide, ammonium chloride and sodium chloride, describe how this

mixture can be separated to obtain a sample of each.  

31. The setup below was used to separate two miscible liquids Q and T


(Boling points; Q =98° C, T=78°C)

Image From EcoleBooks.com

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 (a) Identify the mistakes in the setup above  

 (b)Identify Distillate X

 

32.  Name the process which takes place when:

 a) Solid Carbon (IV) oxide (dry ice) changes directly into gas.  

b) A red litmus paper turns white when dropped into chlorine water.

c) Propene gas molecules are converted into a giant molecule.  

33.  The following diagram shows a paper chromatogram of substances A, B, C, and D which

are coloured

 

 

 

 

 

 

 

 

 

 

(a) Indicate the solvent front on the chromatogram

(b) Which substance is pure?  ………………………………………..

(c) Substance E is a mixture of C and D. Indicate its chromatogram in the diagram

34. Study the information below and answer the following questions. A mixture contains three

solids A, B, and C. The solubility of these solids in different liquids is as shown below:-

 

Solid

Water

Alcohol

Ether

A

Soluble

Insoluble

Insoluble

B

Insoluble

Soluble

Very soluble

C

Soluble

Soluble

Insoluble

 

Explain how you will obtain sample C from the mixture      

35.  State and explain the observations made when iodine crystals is heated in a boiling tube?  

 

2. Simple classification of substances Answers

1.  a) X – melting point √ ½

Z – Boiling point √ ½  b) Its melting point is lowered and becomes less sharp due to the introduction of an impurity √1

 

2.   Luminous flame produces soot while non- luminous flame does not√1  

Luminous flame is yellow in colour while non- luminous flame is blue in colour

OR accept any correct answer

 

b) The luminous flame is moderately hot and is clearly visible hence no danger is posed

3.  a) X

Gives the greatest number of spots hence the greatest number of pure substances √ 1

b) The ink is made of more than one pure substance hence will also undergo chromatography

4.  (a) sublimation

(b) Bleaching action

(c) Polymerization

5.  Adds excess dilute hydrochloric acid/ sulphuric (vi) acid

 Filter to obtain copper metal

 Wash with distilled water

6.  To separate samples of CUO and charcoal in test tubes, dilute mineral acid is added with

shaking CUO black dissolves to form blue solution ½

 Charcoal does not dissolve in dilute mineral acids

7.  a) Is the process for the separation of a mixture of solutes by their different rates of movement

over a porous medium caused by moving solvent

 b)  – Separation of dyes

– To analyse and identify mixtures of substances which are difficult to separate by

other means

– Used to analyze dyes in food colouring  (Any two each one mark)  

8  a) Element R – Sulphur

b) Mix solid P oxide with water

put blue and litmus paper, Blue litmus paper remains blue, red litmus paper changes to blue.

Put blue and red litmus papers in water

Blue changes to red, red remain red.

9.   5 and 4 BOTH MUST BE CORRECT

10. EITHER

  • In separate test tubes, boil about 5cm3 of each solution.
  • Sodium hydrogencarbonate solution remains colourless forms no precipitate
  • Calcium hydrogencarbonate solution changes from colourless to white precipitate  

 OR

2NaHCO3aq   Na2CO3 + CO2(g)n + H2O(e)

  Ca (HCO3)2
(aq) CaCO3(s) + CO2
(g) + H2O(e)

  HEAT must be mentioned or implied.

 

Image From EcoleBooks.com

Image From EcoleBooks.comImage From EcoleBooks.com11. a)

 

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Image From EcoleBooks.comImage From EcoleBooks.com

Image From EcoleBooks.com

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Image From EcoleBooks.com

 

b) Liquid

Image From EcoleBooks.comImage From EcoleBooks.com12.  (i) Range of boiling points / no sharp boiling points

 (ii) Carry out fractional distillation

Image From EcoleBooks.com13.  (i) Evaporation

Image From EcoleBooks.com  (ii) Uses a lot of fuel

 (iii) Any soluble salt and water

14. Melting points is the specific √ ½ constant temperature√ ½ for a particular substance when a solid √ ½

change to a liquid√ ½

16.  (a) To cool/condense vapour. √1  (1 mk)

 (b) Water. √1  (1 mk) 3

 (c) Blue solid √1 changes to white solid. √1 (1 mk)

17.  (a) Solvent front √  

 (b) C √  

18.  a) Chemical √ ½

 b) Physical √ ½

 c) Physical √ ½

 d) Chemical √ ½  

 

19.  – Smoky/ sooty

 – Not hot enough

 

20.  a) Chemical √ ½

 b) Physical √ ½

 c) Physical √ ½

 d) Chemical √ ½  

 

21.  – Smoky/ sooty

 – Not hot enough

 

22.  – Boiling point

 – Melting point

 – Density

 – Refractive index

 

23.  i) Pass the mixture of gases through concentrated sulphuric (vi) acid √ ½ . Ammonia and

ethane will dissolve √ ½

 – Hydrogen √ ½ being insoluble √ ½ is then obtained

 

24.  a)  i)

 

 ii) A and C

 

 b) Since NH4CL sublimes but CaCL2 does not, sublimation process would do. Heat the

mixture, NH4CL sublimates into vapour and condences on the upper cooler parts of the test

tube. CaCL2 remains at the bottom of the heating tube

 

 c)  i) Fractional distilation

ii) Separating funnel method 8

Since the two liquids are immiscible pour the mixture into the separating funnel and

allow to settle. The denser liquid will settle down and the less dense one will form

the second layer on top. Open the tap and run out the liquid in the bottom layer leaving

the second layer in the funnel

25.   (i) Condenser

 (ii) To indicate when a liquid is boiling, a thermometer reads a constant temperature

  (iii) A

Image From EcoleBooks.comImage From EcoleBooks.com  (iv) Ethanol

  Reason:- It has a lower boiling of 78oC compared to water with a boiling point of 100oC

Image From EcoleBooks.comor – The liquid with the lower boiling point boils first and its vapours are condensed

and the condenser to Image From EcoleBooks.com be collected as the first distillate

  (v) Fractional distillation

  (vi) – To separate components of crude oil

  • To isolate O2 and N2 from air
  • To manufacture spiritsImage From EcoleBooks.com

 (vii)- They are immiscible liquids

  • Image From EcoleBooks.comThey have different but close boiling points

26.  (a) Wire gauze  

 (b) Sodium chloride solution (or any named slat solution)

 (c) Evaporation  

 

27.  a) i) – Colourless liquid is seen on the cooler parts of the test tube. 1 mk.  

  – Blue crystals change to a white powder. 1 mk  

 

  ii) Water 1 which was originally water crystallization.

  CuSO4 , 5H2O(s) CuSO4(s) + 5H2O(l) 1

 

 b) NaOH(s) absorbs water from the air and forms a solution. It is a deliquescent substance. 1  Anhydrous CuSO4 absorbs water from air to form hydrated Copper (II) sulphate which is blue

but no solution is formed 1  it is hygroscopic

28.  a)i)Ethanol, acetone (any organic solvent)

  ii) Its most soluble in the solvent and less sticky

  iii) – Cut out the yellow pigment

  • put in organic solvent to dissolve the pigment
  • filter and evaporate the filtrate to get the pigment

 iv)Above the red pigment and below the edge.

 

b)-Heat the mixture aluminum chloride sublime and collect be cooler part of the tube

and sodium chloride left at bottom of the tube

  – Scratch the condense alcl3 place in a beaker

(c)Add cold water to the mixture, and stir to dissolve R. Filter to get solid S and V on residue . Evaporate the future to get R. put S and in no water and stir to dissolve and filter to get S as residue evaporate future to get V

 

29.  Add cold water to the mixture, and stir to dissolve R. Filter to get solid S and V on residue . Evaporate the future to get R. put S and in no water and stir to dissolve and filter to get S as residue evaporate future to get V

 

30.   Heat the mixture Ammonium chloride sublimes and is collected on the cooler parts. Add water

to the remaining mixture, stir and filter. Lead (ii) Oxide remains as residue. Evaporate the

filtrate to dryness to obtain sodium chloride  

 

31.  a)  – Fractionating column must have beads

– Wrong cold water circulation in the condenser

 b)  T

32.  a) Sublimation. 1  (3 mks

 b) Bleaching 1

 c) Polymerisation 1

33.

 

 

 

 

 

 

 

(a) See Diagram above

  – Solvent front should be slightly above the furthest pigment

Image From EcoleBooks.com(b) C

  – It contains only one pigment

 

34  . – Add either to the mixture. Stir and filter  

 – Add alcohol to the residue, stir and filter

Image From EcoleBooks.com   – Evaporate to filtrate to obtain C

 

35.   – Black crystals changes directly into purple vapour√1

– The iodine crystals (sublimes) changed directly into a purple vapour without passing

liquid state and changed back to black iodine crystals on the upper cooler parts of boiling

tube√ (Correct colour must be stated 2 mks


 




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