Chemistry Paper 1 Questions and Answers - Form 3 Term 2 Opener Exams 2023

INSTRUCTIONS TO STUDENTS

• Answer all questions in this question paper.

1.  
   1. State and explain simple method you can use to separate a mixture of sulphur powder and iron fillings.   (2mark)
   2. A mixture of iron and sulphur was heated strongly until it glowed red throughout and then left to cool. Explain why you cannot obtain sulphur and iron from the product using the method you stated in (a) above (2marks)
2. Explain why the following substances are good conductors of electricity:
   1. Molten lead II bromide (1mark)
   2. Aluminium (1mark)
3. Define the term electrolyte (1mark)
4. The following set up was used to investigate the effect of an electric current on silver chloride
   
   1. Label the cathode and anode on the diagram (1mk)
   2. When the switch was closed the bulb did not light. Explain. (1mk)
   3. If the bulb lights, write the equation of the reaction occurring at the cathode.   (1mk)
   4. State and explain the observation made at the anode. (2mks)
5. State three application of electrolysis. (3marks).
6. Calculate the pressure required to compress 4.24 dm³ of a gas at 5.4299 X 10⁴Pascal’s to 1.56 dm³ at constant temperature. (2marks)
7. Draw the structure of;
   1. Hydroxonium ion H₃O⁺ (2mk)
   2. Ammonium ion (Al = 13, 0 = 8) (2mk)
8. The table below shows some properties of substances A-E. Study it and answer the questions that follow.
   

   Substance	Solubility in water	Solubility in chloroform	m.p. (°C)	b.p.(°C)
   A	soluble	soluble	−22	141
   B	insoluble	soluble	115	444
   C	soluble	insoluble	801	1465
   D	insoluble	soluble	−188	−42
   E	insoluble	insoluble	1083	2600

   1. Which of the substances is a gas at room temperature of 25 ᵒC? . (1mark)
   2. What is the physical state of substance A at room temperature of 25 ᵒ C? . (1mark)
   3. How can you separate the mixture of substances B , C and E ? (3marks)
9. What volume of acidified potassium manganate VII of concentration 0.02 moles per dm³ is decolorized by 200 dm³ of hydrogen peroxide of concentration 0.02 moles per dm³ ? (3marks)
   Use the following ionic equation
   2MnO^4- _(aq) + 6H⁺ _(aq) + 5H₂O₂^(aq)  2Mn²⁺ _(aq) + 8H₂O_(l) + 5O_2(g)
10. A mass of 3.6 g magnesium reacts in excess chlorine to form a chloride. If the mass of the chloride formed is 14.25 g, find the formula of the chloride formed. (Mg = 24, Cl =35.5 ).  (2marks)
11. Starting with copper metal describe how a dry sample of copper II carbonate can be prepared in the laboratory. (3 marks).
12. The table below shows the first ionization energies of metals A to D (not their actual chemical symbols) in the same group of the periodic table.
    

    Metal	A	B	C	D
    First ionization energy (kJmol-1)	402	496	520	419

    1. Arrange the metals in order of that they occur in the periodic table starting from the topmost to the lowest. Give a reason to support your answer. (3marks)
    2. Which of the metals has the largest atomic radius? (1mark)
13. When a piece of calcium is dropped into a beaker of water, it sinks to the bottom and bubbles of a gas are observed on the surface of the metal.
    1. Why does calcium sink to bottom of the beaker? (1mark)
    2. Name the gas that is formed in the reaction. (1mark)
    3. Besides effervescence, what else is observed in the beaker as the reaction progresses?Explain this observation. (2marks)
    4. Write an equation for the reaction between calcium and water. 1mk
14. Explain the following statements:
    1. Following a bee’s sting, application of sodium hydrogen carbonates to the affected area of the skin reliefs the irritation. (2marks)
    2. It is not advisable to clean aluminium utensils using wood ash . (2marks)
15. The set-up below was used to investigate some properties of hydrogen gas. Study it and answer the questions that follow:
    
    
    1. Name a suitable liquid that can serve as a drying agent. (1mark)
    2. State the observations you would expect in the combustion tube as the experiment progresses. (2mks)
16. Explain the following terms:
    1. Water of crystallization (1mark)
    2. Hygroscopy (1mark)
    3. Acidic salts (1mark)
    4. Normal salts (1mark)
17. Explain the role of helium in the welding of metals. (2marks)
18. Whereas hydrogen was commonly used in airships and weather balloons earlier on it is no longer used nowadays. Give a reason for this. (1mark)
19. Chebet, Mutua and Waweru are international athletes. Paper chromatography was used to test for the presence of illegal drugs in their blood which enhance the performance. The diagram below shows the chromatogram with the illegal drug labeled N.
    
    1. Who among them tested positive for the illegal drug? Explain. (2marks)
    2. Explain what is meant by ‘solvent front’. (1mark)
20. An aqueous solution of ammonia was added drop wise to a solution of copper (II) Sulphate until in excess .State the observation made when
    1. A few drops of aqueous ammonia were added. (1 mark)
    2. Excess aqueous ammonia was added. (1 mark)
21. The table below gives information about the ions W + and y2-
    

    Ion	W+	Y2−
    Electrons arrangements	2.8	2.8.8
    Number of neutrons	12	16

    1. How many protons are there in the nucleus of
       1. Elements W? (1 mark)
       2. Elements Y? (1 mark)
    2. Write the formula of the compound formed when W and Y reacts.  (1 mark)
    3. State two conditions under which the compound would conduct electricity.   (2marks)
22. The following data gives the PH vales of some solution A, B and C.
    

    Solution	PH
    A	13.0
    B	6.9
    C	2.0

    1. Which solution would produce carbon (IV) oxide gas when reacted with copper (II) carbonate? Explain. (2 mark)
    2. What colour change would occur in solution A on addition of three drops of phenolphthalein indicator. (1 mark)
    3. What volume of 0.2 M hydrochloric acid would react completely with 0.005 moles of pure calcium carbonate? (3 marks)
23. What is an allotrope? (1mark)
    1. Give two allotropes of sulphur. (2marks)
    2. State three uses of sulphur. (3marks)

MARKING SCHEME

1.  
   1. State and explain simple method you can use to separate a mixture of sulphur powder and iron fillings (2mark)
      • Use of magnet, iron is magnetic thus will be attracted by magnet while sulphur is non- magnetic and will not be attracted by magnet
   2. A mixture of iron and sulphur was heated strongly until it glowed red throughout and then left to cool. Explain why you cannot obtain sulphur and iron from the product using the method you stated in (a) above (2marks)
      • A compound FeS is formed. 
2. Explain why the following substances are good conductors of electricity:
   1. Molten lead II bromide (1mark)
      • The ions are free to move
   2. Aluminium (1mark)
      • Has delocalized electrons
3. Define the term electrolyte (1mark)
   • A substance that conducts electricity in molten or in aqueous form and get decomposed
4. The following set up was used to investigate the effect of an electric current on silverchloride
   1. Label the cathode and anode on the diagram (1mk)
   2. When the switch was closed the bulb did not light. Explain. (1mk)
      • Solid silver chloride cannot conduct electric current since ions are fixed
   3. If the bulb lights, write the equation of the reaction occurring at the cathode. (1mk)
      2Ag⁺ + 2e⁻ → 2Ag
   4. State and explain the observation made at the anode. (2mks)
      • Green yellow substance is formed. Cl ions is oxidized at the anode to Cl 2 gas which is green yellow
5. State three application of electrolysis. (3marks).
   • Coating metal with other metals
   • Manufacture of pure substances
   • Extractions of metals i.e sodium
6. Calculate the pressure required to compress 4.24 dm³ of a gas at 5.4299 X 10⁴ Pascal’s to 1.56 dm³ at constant temperature. (2marks)
   P₁V₁ =P₂V₂
   4.24dm³ × 5.4299 × 10⁴Pa = 1.56x
   x = 4.24dm³ × 5.4299 × 10⁴Pa
                      1.56
     = 147581.89Pa
7. Draw the structure of;
   1. Hydroxonium ion H₃O⁺ (H=1, O=8). (2mk)
      
   2. Ammonium ion (N = 7, H = 1) (2mk)
      
8. The table below shows some properties of substances A-E. Study it and answer the questions that follow.
   1. Which of the substances is a gas at room temperature of 25 ᵒC? . (1mark)
      • D
   2. What is the physical state of substance A at room temperature of 25 ᵒ C? . (1mark)
      • Liquid
   3. How can you separate the mixture of substances B , C and E ? (3marks)
      • Add chloroform to the mixture to dissolve B√1 . Filter and evaporate the to obtain. Dry the residue to obtain E. √1
      • Mixture to obtain B√ 1 . Add water to the residue to dissolve C , filter and evaporate the mixture to obtain. Dry the residue to obtain E.
9. What volume of acidified potassium manganate VII of concentration 0.02 moles per dm³ is decolorized by 200 dm³ of hydrogen peroxide of concentration 0.02 moles per dm³ ? Use the following ionic equation. (3marks)
   2MnO^4- _(aq) + 6H⁺ _(aq) + 5H₂O₂^(aq)  2Mn²⁺ _(aq) + 8H₂O_(l) + 5O_2(g)
   1000cm³ of H₂O₄⁻ = 0.02moles
   200cm³                  = x
   x = 200 × 0.02 
            1000
    = 0.004 moles
   Mole ratio = 5 : 2
   Moles of MnO^4- = 0.004 × 2
                                       5
                             = 0.04moles
10. A mass of 3.6 g magnesium reacts in excess chlorine to form a chloride. If the mass of the chloride formed is 14.25 g, find the formula of the chloride formed. (Mg = 24, Cl =35.5 ).   (2marks)
    Mass of Mg = 3.6g
    Mass of Cl = 14.25 − 3.6 = 10.65g ✓½
    Element                Mg                    Cl
    Mass                     3.6                   10.65
    Mole ratio           ^3.6/₂₄ = 0.15       ^10.65/_35.5 = 0.3  ✓½
    Ratio of atoms.  ^0.15/_0.15 =1          ^0.3/_0.15 =2. ✓½
    E. formula            MgCl₂    ✓½
11. Starting with copper metal describe how a dry sample of copper II carbonate can be prepared in the laboratory. (3 marks)
    • Add excess copper turnings to conc. Nitric V acid 1to then filter√ ½to obtain copper II nitrate solution as filtrate. To the filtrate add sodium carbonate √ ½ solutions to precipitate copper II carbonate √ ½. Filter, wash and dry the residue between filter papers. √ ½ 1
12. The table below shows the first ionization energies of metals Ato D (not their actual chemical symbols) in the same group of the periodic table.
    1. Arrange the metals in order of that they occur in the periodic table starting from the topmost to the lowest. Give a reason to support your answer. (3marks)
       • C, B, D, A 2 within a group of metals first ionization energy decreases down the group 1
    2. Which of the metals has the largest atomic radius? (1mark)
       • A ✓½
13. When a piece of calcium is dropped into a beaker of water, it sinks to the bottom and bubbles of a gas are observed on the surface of the metal.
    1. Why does calcium sink to bottom of the beaker? (1mark)
       • Its density is higher than that of water
    2. Name the gas that is formed in the reaction. (1mark)
       • Hydrogen gas
    3. Besides effervescence, what else is observed in the beaker as the reaction progresses?Explain this observation. (2marks)
       • White suspension, calcium hydroxide is slightly soluble in water
    4. Write an equation for the reaction between calcium and water. 1mk
       Ca + 2H₂O⁻ Ca(OH)⁻₂ + H₂
14. Explain the following statements:
    1. Following a bee’s sting, application of sodium hydrogen carbonates to the affected area of the skin reliefs the irritation. (2marks)
       • Bee sting contains methanoic acid (weak acid) which irritates✓1 , the acid is neutralized by sodium hydrogen carbonate.✓1
    2.  It is not advisable to clean aluminium utensils using wood ash . (2marks)
       • Aluminium utensils have a tough aluminium oxide coat on the surface ✓1 that protects the metal beneath, wood ash is alkaline and reacts with amphoteric Al₂O₃ coat removing it thus exposing the metal to corrosion.✓1
15. The set-up below was used to investigate some properties of hydrogen gas. Study it and answer the questions that follow:
    1. Name a suitable liquid that can serve as a drying agent. (1mark)
       • Conc sulphuric acid
    2. State the observations you would expect in the combustion tube as the experiment progresses. (2mks)
       • White anhydrous copper (ii) sulphate turns blue
       • PbO (orange when hot yellow) when cold turns grey
       • Colourless droplets forms at the cooler parts of the apparatus
16. Explain the following terms:
    1. Water of crystallization (1mark)
       • Water of crystallization is a fixed amount of water that is contained in the crystal structure of most salts. ✓1
    2. Hygroscopy (1mark)
       • hygroscopy is the taking up water vapour from the atmosphere by a salt.✓1
    3. Acidic salts
       • Salts with a replaceable hydrogen ion
    4. Normal salts
       • A salt that that does not have a replaceable hydrogen ion
17. Explain the role of helium in the welding of metals. (2marks)
    • Provide an inactive atmosphere which prevent oxidation of ho metal by air
18. Whereas hydrogen was commonly used in airships and weather balloons earlier on it is no longer used nowadays. Give a reason for this. (1mark)
    • Hydrogen gas is explosive
19. Chebet, Mutua and Waweru are international athletes. Paper chromatography was used to test for the presence of illegal drugs in their blood which enhance the performance. The diagram below shows the chromatogram with the illegal drug labeled N.
    1. Who among them tested positive for the illegal drug? Explain. (2marks)
       • L and K
    2. Explain what is meant by ‘solvent front’. (1mark)
       • The furthest distance the solvent can reach
20. An aqueous solution of ammonia was added drop wise to a solution of copper (II) Sulphate until in excess
    1. State the observation made when
       1. A few drops of aqueous ammonia were added. (1 mark)
          • A blue ppt is formed
       2. Excess aqueous ammonia was added. (1 mark)
          • Blue ppt dissolves to a deep blue solution
21. The table below gives information about the ions W⁺ and Y2⁻
    1. How many protons are there in the nucleus of
       1. Elements W? (1 mark)
          • 11
       2. Elements Y? (1 mark)
          • 16
    2. Write the formula of the compound formed when W and Y reacts.    (1 mark)
       
       • W₂Y
    3. State two conditions under which the compound would conduct electricity.   (2marks)
       • Molten state
       • Aqueous state
22. The following data gives the PH vales of some solution A, B and C.
    1. Which solution would produce carbon (IV) oxide gas when reacted with copper (II) carbonate? Explain. (2 mark)
       • C, it has hydrogen ions
    2. What colour change would occur in solution A on addition of three drops of phenolphthalein indicator. (1 mark)
       • pink
    3. What volume of 0.2 M hydrochloric acid would react completely with 0.005 moles of pure calcium carbonate? (3 marks)
       2HCl_(aq) + CaCO_3(aq)  CaCl_2(aq) + CO_2(g) + H₂O_(l)
         0.2M      0.005moles
       Mole ratio  2 : 1
       Moles of HCL = 0.005 × 2
                               = 0.01
       1000cm³ =  0.2Moles
          x           =  0.01moles
          x           = 0.01 × 1000
                                0.2
23. What is an allotrope? (1mark)
    • A substance that occurs in more than one form but same physical state.
      1. Give two allotropes of sulphur. (2marks)
         • Rhombic
         • Monoclinic
      2. State three uses of sulphur. (3marks)
         • Manufacture of sulphuric acid
         • Hardening of rubber
         • Manufacture breaching agent
         • As a fungicide