Chemistry Paper 1 Questions And Answers - Form 3 Term 2 Opener Exams 2021

CHEMISTRY
PAPER 1
TERM 2 OPENER EXAM

INSTRUCTIONS

• Answer all the questions 

1. Dyes W,X, Y and Z were analysed using P as the purest sample of the dye required by a chemist .the result obtained were as shown on the chromatogram below.
   
   1. What names are given to the lines marked?
      1. A 1mk
      2. B 1mk
   2. State with a reason the most unsuitable dye for the chemist to use . 2mks
2.       
   1. Distinguish between allotropes and isotopes. 2mks
   2. Name the two allotropes of sulphur . 2mk
3. The table below shows the atomic numbers of elements F G and H.
   

   Element	F	G	H
   Atomic  Number	4	12	20

   Which of the elements is the least reactive? Explain 2mks
4. Classify the changes below as physical or chemical changes.
   

   	Type of charge
   Magnetization of iron
   Heating iron until it softens
   Souring of milk

5. A student prepared ammonia gas and wanted to make it solution in water. Complete the diagram to show how he made the solution.
   
6. Element J belong to period 3 and group V.
   1. Write the electron arrangement of J. 1mk
   2. The equation of the reaction when J reacts with oxygen gas. 2mks
7. A fixed mass of a gas has a volume of 200cm3 at a temperature of 47oC and 750mmHg .calculate the volume the gas would occupy at 7oC and 750mmHg pressure. 3mks
8. The diagram below represents a luminous flame.
   
   Mark and label on the diagram the hottest and coolest parts 2mks
9. Burning magnesium was lowered in a gas jar full of dry sulphur IV oxide.
   1. State the observation that was made. 2mks
   2. Write the equation for the reaction occurring. 1mk
   3. State the reducing agent in the above reaction. 1mk
10. Draw a dot (.) and cross (X) diagram to show the bonding in the molecules of :
    (Atomic number of carbon is 6, Oxygen is 8 and hydrogen is 1)
    1. Carbon II oxide
    2. Water.
11. Explain the following observation
    1. Magnesium is a better electrical conductor than sodium. 1mk
    2. A solution of aluminum chloride has PH of 3.0. 1mk
12. A compound W consist of 26.7%carbon, 2.2%hydroen and the rest oxygen. It has a relative formula Mass of 90(C=12, H=1, O=16,)
    1. Determine it empirical formula. 2mks
    2. Workout its molecular formula 2mks
13. Hydrogen was passed over copper II oxide in a combustion tube.
    1. Write an equation for the reaction that took place. 1mk
    2. What observation was made in the combustion tube? 2mks
    3. Name two other gases which could be used to reduce copper II oxide. 2mks
14.      
    1. State grahams law of diffusion. 1mk
    2. 20cm³ of oxygen diffused through a porous partition in 70s .how long would it take 20cm3. Of sulphur VI oxide to diffuse through the same portion under the same condition. 3mks
15. He set up below was used to collect gas Z produced by the reaction between water and calcium metal.
    
    1. Give a chemical test for gas Z. 2mks
    2. Write the equation of the reaction between the calcium metal and water. 2mks
16. The diagram below shoes the bonding between aluminium chloride and ammonia
    
    1. Name the type of bond labeled
       1. X. 1mk
       2. Y 1mk
    2. How many electrons are used for bonding in the molecule? 1mk
17. Graphite is a non metal, yet it conduct an electric current .explain this observation. 1mk
18. A sample of air contaminated with carbon monoxide and sulphur dioxide was passed through the apparatus shown in the diagram below.
    
    Which contaminant was removed by passing the contaminated air through the apparatus?
    Explain. (2mks)
19. Explain how you would show chemically that a given gas is ammonia. 2mks
20. Chlorine water was exposed to sunlight for a few hours .Colourless gas F was collected in the boiling tube as shown.
    
    1. Name gas F. 1mk
    2. Write an equation for the formation of gas F.2mks
21. The equation below shows the action of heat on three metal nitrates.
    2S(NO₃)₂ → 2SO + 4NO₂ +O₂
    2TNO₃  → 2TNO₂ + O₂
    2UNO₃ → 2U +2NO₂ + O₂
    1. Arrange the metals S,T and U in the order of reactivity from least to the most reactive. 3mks
    2. Give one element that could be used. 1mk
22.        
    
    1. Define the term transition temperature concerning the allotropes of sulphur. 1mk
    2. Draw the structure of a sulphur molecule. 1mk
23. Dilute hydrochloric acid was added to a compound Z of sodium. The solid reacted with the acid to form a colorless solution H and a colourless gas K which formed a white precipitate when bubbled through lime water.
    1. Write the formula of:
       1. Compound Z 1m
       2. Colorless gas K 1mk
       3. Write an equation for the reaction that took place. 2mks
24. The diagram below represents the extraction of sulphur by Frasch process
    
    1. Name the substance that passes through tube;
       I ½ mk
       II ½ mk
    2. What is the purpose of hot compressed air in this process? (1mk)
25. A student used the setup below to prepare oxygen gas in the laboratory. Study it and answer the questions that follow.
    
    1. Identify solid K. 1m
    2. Name the apparatus labeled L. 1mk
    3. Write an equation for the reaction in the conical flask. 2mk
26. Nitrogen gas is used as an inert atmosphere in electric lamps.
    1. Explain in terms of structure and bonding why nitrogen gas is so stable .2mks
    2. Give a reason why despite this stability nitrogen reacts with burning magnesium metal. 1mk

MARKING SCHEME

1. Dyes W,X, Y and Z were analysed using P as the purest sample of the dye required by a chemist .the result obtained were as shown on the chromatogram below.
   
   1. What names are given to the lines marked?
      1. A - Solvent front
      2. B - Baseline
   2. State with a reason the most unsuitable dye for the chemist to use . 2mks
      • Z is the most impure with 3 substances not in the pure dye
2.       
   1. Distinguish between allotropes and isotopes. 2mks
      • Allotropes are two or more forms of an element in the same physical state
      • Isotopes are atoms of the same element having the same atomic number but different mass numbers
        
        
   2. Name the two allotropes of sulphur . 2mk
      • Rhombi sulphur
      • monoclinic sulphur
        
        
3. The table below shows the atomic numbers of elements F G and H.
   

   Element	F	G	H
   Atomic  Number	4	12	20

   Which of the elements is the least reactive? Explain 2mks
   • F- Has the smallest atomic radius/size and has the least tendency to lose electrons
     
     
4. Classify the changes below as physical or chemical changes.
   

   	Type of change
   Magnetization of iron	Physical
   Heating iron until it softens	Physical
   Souring of milk	Chemical

5. A student prepared ammonia gas and wanted to make it solution in water. Complete the diagram to show how he made the solution.
   
   
   
6. Element J belong to period 3 and group V.
   1. Write the electron arrangement of J. 1mk
      • 2.8.5
   2. The equation of the reaction when J reacts with oxygen gas. 2mks
      • 4J_(s) + 3O_2(g) → 2J₂O_5(g)
        
        
7. A fixed mass of a gas has a volume of 200cm3 at a temperature of 47oC and 750mmHg .calculate the volume the gas would occupy at 7oC and 750mmHg pressure. 3mks
   • v1=200cm³
     T1=47º=47+273=320k
     P1=750mmhg
     T2=7º=7+273=280k
     P2=750mHg
     ^V1/_T1=^V2/_T2
     V2=^V1T2/_T1=2^{00 x 280}/₃₂₀=175cm³
     
     
8. The diagram below represents a luminous flame.
   
   Mark and label on the diagram the hottest and coolest parts 2mks
9. Burning magnesium was lowered in a gas jar full of dry sulphur IV oxide.
   1. State the observation that was made. 2mks
      • White ash and yellow specks formed
   2. Write the equation for the reaction occurring. 1mk
      • 2Mg_(s) + SO_2(g) → 2Mg_(s) + S_(s)
        
        
   3. State the reducing agent in the above reaction. 1mk
      • Magnesium
        
        
10. Draw a dot (.) and cross (X) diagram to show the bonding in the molecules of :
    (Atomic number of carbon is 6, Oxygen is 8 and hydrogen is 1)
    1. Carbon II oxide
       
    2. Water.
       
11. Explain the following observation
    1. Magnesium is a better electrical conductor than sodium. 1mk
       • Magnesium has 2 delocalised electrons compared to sodium which has 1
         
         
    2. A solution of aluminum chloride has PH of 3.0. 1mk
       • Aluminium chloride hydrolyses in solution to form an acidic solution
         
         
12. A compound W consist of 26.7%carbon, 2.2%hydroen and the rest oxygen. It has a relative formula Mass of 90(C=12, H=1, O=16,)
    1. Determine it empirical formula. 2mks
       • %age of oxygen= 100-(26.7+2.2)=71.1%
         

         	C	H	O
         % composition	26.7	2.2	71.1
         RAM	12	1	16
         No. of molecules	26.7/12	2.2/1	71.1/16
         	2.2	2.2	4.4
         	2.2/2.1	2.2/2.2	4.4/2.2
         	1	1	2

    2. Workout its molecular formula 2mks
       (CHO₂)n=90
       12n+n+32n=90
       n=2
       MF is C₂H₂O₄
13. Hydrogen was passed over copper II oxide in a combustion tube.
    1. Write an equation for the reaction that took place. 1mk
       H_2(g) + CuO_(s) → H₂O_(l) + Cu_(s)
    2. What observation was made in the combustion tube? 2mks
       • Black copper(ii) oxide turned brown
    3. Name two other gases which could be used to reduce copper II oxide. 2mks
       • Ammonia gas and carbon(ii)oxide gas
14.      
    1. State grahams law of diffusion. 1mk
       • Graham's law of diffusion states that under the same conditions of temperature and pressure, the rate of diffusion of a gas is inversely porporional to the sqaure root of its density
         
         
    2. 20cm³ of oxygen diffused through a porous partition in 70s .how long would it take 20cm3. Of sulphur VI oxide to diffuse through the same portion under the same condition. 3mks
       • MO₂=2 x 16=32
         MsO₃=(32+16x3)=80
         TO₂=70secs 
         TsO₃=?
         TsO₃=√MsO₃
         TO₂     √MO₂
         TsO₃= ^70√80/_√32 - -70 x 8.944/5.657=110secs
         
         
15. He set up below was used to collect gas Z produced by the reaction between water and calcium metal.
    
    1. Give a chemical test for gas Z. 2mks
       • It burns with a pop sound
    2. Write the equation of the reaction between the calcium metal and water. 2mks
       • Ca_(s) + 2H₂O_(l) → Ca(OH)_2(aq)+H_2(g)
         
         
16. The diagram below shoes the bonding between aluminium chloride and ammonia
    
    1. Name the type of bond labeled
       1. X.- co-ordinate/dative bond
       2. Y - covalent bond
    2. How many electrons are used for bonding in the molecule? 1mk
       • 14 electron
         
         
17. Graphite is a non metal, yet it conduct an electric current .explain this observation. 1mk
    • Graphite has delocalised electrons in its structure.
      
      
18. A sample of air contaminated with carbon monoxide and sulphur dioxide was passed through the apparatus shown in the diagram below.
    
    Which contaminant was removed by passing the contaminated air through the apparatus?
    Explain. (2mks)
    • Sulphur(iv)oxide
      Carbon(ii)oxide gas does not react with lime/ lime water nor conc H₂SO₄ but SO₂ being acidic is absorbed by the lime water.
      
      
19. Explain how you would show chemically that a given gas is ammonia. 2mks
    • Dip a glass rod in concentrated hydrochloric acid and introduce if near the unknown gas if denser white fumes are formed, then the gas is ammonia 
      OR
    • if turns damp red litmus paper blue, it is ammonia.
20. Chlorine water was exposed to sunlight for a few hours .Colourless gas F was collected in the boiling tube as shown.
    
    1. Name gas F. 1mk
       • Gas F- Oxygen gas
    2. Write an equation for the formation of gas F.2mks
       • 2HOCl_(aq) →2HCl_(aq) + O_2(g)
21. The equation below shows the action of heat on three metal nitrates.
    2S(NO₃)₂ → 2SO + 4NO₂ +O₂
    2TNO₃  → 2TNO₂ + O₂
    2UNO₃ → 2U +2NO₂ + O₂
    1. Arrange the metals S,T and U in the order of reactivity from least to the most reactive. 3mks
       U → S → T
       least →most
    2. Give one element that could be used. 1mk
       • silver or mercury
22.        
    
    1. Define the term transition temperature concerning the allotropes of sulphur. 1mk
       • Transition temperature is the temperature at which one allotrope of sulphur changes to another
    2. Draw the structure of a sulphur molecule. 1mk
       
23. Dilute hydrochloric acid was added to a compound Z of sodium. The solid reacted with the acid to form a colorless solution H and a colourless gas K which formed a white precipitate when bubbled through lime water.
    1. Write the formula of:
       1. Compound Z 1m
          • Na₂CO₃
       2. Colorless gas K 1mk
          • CO₂
       3. Write an equation for the reaction that took place. 2mks
          • Na2CO_3(s) + 2HCl_(aq) → CaCl_2(aq) + H₂O_(l)+CO_2(q)
24. The diagram below represents the extraction of sulphur by Frasch process
    
    1. Name the substance that passes through tube;
       I - Molten sulphur
       II - superheated water
    2. What is the purpose of hot compressed air in this process? (1mk)
       • To force out molten sulphur from underground.
25. A student used the setup below to prepare oxygen gas in the laboratory. Study it and answer the questions that follow.
    
    1. Identify solid K. 1m
       • Sodium peroxide
    2. Name the apparatus labeled L. 1mk
       • Beehive stand
    3. Write an equation for the reaction in the conical flask. 2mk
       • 2Na₂O_2(s) + 2H_2(l) → 4NaOH_(aq) + O_2(g)
         
         
26. Nitrogen gas is used as an inert atmosphere in electric lamps.
    1. Explain in terms of structure and bonding why nitrogen gas is so stable .2mks
       • Atoms of nitrogen are bonded by three strong covalent bonds which need a lot of energy to break
    2. Give a reason why despite this stability nitrogen reacts with burning magnesium metal. 1mk
       • Burning magnesium releases a lot of heat energy which gets absorbed by the nitrogen molecule breaking the triple covalent bond.