Chemistry Paper 1 Questions and Answers - Lanjet Joint Mock Exams 2020

INSTRUCTIONS TO CANDIDATES

• Write your name and index number in the spaces provided.
• Answer all questions in the spaces provided
• KNEC mathematical tables and silent electronic calculators may be used for calculations.
• All workings must be clearly shown where necessary.
• Candidates should check the question paper to ascertain all the pages are printed as indicated and no questions are missing.

1. State the observations made when a piece of sodium metal is dropped into a beaker containing water. (2mks)
2. During a class experiment, students passed gas X over heated copper metal, the metal changed its colour to black.
   1. Identify gas X. (1mk)
   2. Name the black substance formed. (1mk)
3. Aluminium is extracted from its ore by electrolysis.
   1. Name the main ore of Aluminium . (1mk)
   2. The Aluminium ore in (a) above has a very high melting point.(20150C),though it is electrolyzed at a lower temperature of about 9000 C. Explain how the low temperature is achieved. (1mk)
   3. In the above process, graphite electrodes are used. What is the disadvantage of using this kind of electrodes (1mk)
4. A student added 50cm3 of 1.0M aqueous Sulphuric (VI) acid to 50cm3 of 2.0M Potassium Hydroxide and the temperature of the resulting solution rose by 40 C.
   1. Define the term Molar heat of neutralization. (1mk)
   2. Calculate the molar heat of neutralization
      (C=4.2KJKg-1 K-1 ,Density of solution=1g/cm3) (2mks)
5. Use the table below to answer the question that follow:
   

   Element	Atomic number
   A	11
   B	13
   C	14
   D	17
   E	19

   1. Write an equation for the reaction between element A and water. (1mk)
   2. Explain the trend of atomic radii between elements A and D. (2mks)
6. In terms of structure and bonding, explain why graphite is used as a lubricant. (2mks)
7.    
   1. State the Boyles Law. (1mk)
   2. A given mass of the gas occupies 20cm3 at 250 C and 670mmHg pressure. Find the volume it will occupy at 100 C and 335mmHg. (2mks)
8. Study the flow chart below and answer the questions that follow.
   
   
   1. Name
      
      1. Cations present in mixture M. (1mk)
      2. Anion present in thecolourless solution. (1mk)
   2. Write an equation to show how the white precipitate in step 3 dissolves. (1mk)
   3. Name the process outlined in step 4 above. (1mk)
9. The solubility of potassium nitrate is 85g/100g of water at 50 0 C and 32g/100g of water at 25 0 C.
   
   1. Define the term solubility. (1mk)
   2. Calculate the mass of the crystals formed if a saturated solution of potassium nitrate in 50g of water at 50 0 C is cooled to 25 0 C. (2mks)
10. Magnesium Chloride dissolves in water to form a neutral solution while iron (III) chloride forms an acidic solution. Explain. (2mks)
11. The diagram below is a set up to prepare a certain gas X. Study it and use it to answer the questions that follow.
    
    
    1. Identify gas X. (1mk)
    2. Why is the gas collected over water? (1mk)
    3. Why are Copper (II) Sulphate crystals added to the flask where the reaction takes place?
12.  
    1. Give the systematic names of the following organic compounds. (2mks)
       
       1. CH₃CH₂CH₂CH₂OH
       2. CH₃CH₂COOCH₂CH₃
    2. Explain why an organic compound with the formula C4H8burns with a more sooty flame than C4H10. (2mks)
13. When solid Zinc Carbonate was added to a solution of Hydrogen Chloride in methylbenzene there was no observable change. On addition of some water to the mixture there was effervescence. Explain the observation. (2mks)
14. In titration experiment,25.0 cm3 of sodium hydroxide containing 8.0 g per litre was required for complete neutralization of 0.245 g of a dibasic acid. Calculate the relative molecular mass of the acid. (3mks)
15.    
    1. 100g of a radioactive isotope was reduced to 12.5g after 81 days. Calculate the half lifeof the radioisotope. (2mks)
    2. ²¹²₈₀Y decays by beta emission. What is the mass number and the atomic number of the product after decay? (1 mk)
16. Distinguish between ionization energy and electron affinity. ` (2mks)
17. The diagram below represents a paper chromatography for three brands of juice suspected to contain unwanted food additives.
    
    From the results, it was found that unwanted additives are present in Y and Z only.
    On the chromatogram;
    
    1. Circle the spots which show unwanted food additives. (1mk)
    2. Name the solvent commonly used in paper chromatography. (1mk)
    3. State two applications of chromatography. (2mks)
18.    
    1. Show bonding in Aluminium Oxide. (1mk)
    2. Identify the type of bonds represented by p and q in the substances below.
       
       p- (½ mk)
       q- (½ mk)
19. The following diagram represents a charcoal burner. Study it and answer the questions that follow:
    
    Write the equations for the reactions at A,B and C regions. (3mks)
    A -
    B –
    C -
20. Use the scheme below to answer the question that follow.
    
    1. Identify process N. (1mk)
    2. Identify the solids
       H- (½ mk)
       J- (½ mk)
21. Ammonia gas is prepared by Harber process according to the equation below:
    N2(g)+3H2(g) 2NH3(g) +Heat
    State and explain the effect on equilibrium when the following conditions are applied.
    1. Pressure increased. (1mk)
    2. Temperature increased. (1mk)
    3. State Le Chatelier’s principle. (1mk)
22. You are given the following half equations.
    I₂(s) +2e  2I (aq) E^Ѳ=+0.54V
    Br₂(l) +2e  2Br - (aq) E^Ѳ=+1.09V
    1. Write an overall equation for the cell reaction. (1mk)
    2. Calculate the EѲ value of the cell. (1mk)
    3. Name the oxidizing agent. (1mk)
23. When a current of 0.8Ampheres was passed for 44 minutes and 20 seconds through fused iodide of metal Z, 0.7167g of Z was deposited. Determine the charge of the ion of metal Z.
    (1 Faraday=96500C,RAM of Z=65) (2mks)
24. The set up below shows how small pieces of copper are heated in nitrogen (I) Oxide.
    
    
    1. Write an equation for the reaction which occurs in the glass jar. (1mk)
    2. Give one use of the Nitrogen (I) Oxide. (1mk)
25. State what would be observed if concentrated Sulphuric (VI) Acid is added to:
    1. Sugar crystals. (1mk)
    2. Hydrated Copper (II) Sulphate crystals. (1mk)
    3. What type of reaction has taken place above. (1mk)
26. Explain why commercial indicators are preferred to flower extracts as acid base indicators. (2mks)
27.    
    1. Magnesium reacts with hydrochloric acid according to the following equation.
       Mg(s) +2HCl(aq) MgCl2(aq) +H2(g)
       Identify the reducing agent. Give a reason for your answer. (2mks)
    2. Iron sheets are dipped in molten Zinc to prevent rusting .Name this process. (1mk)
28. Explain why a balloon filled with helium gas deflates faster than a balloon of the same size filled with argon gas. (2mks)
29. Complete the table below. (2mks)
    

    Solution	PH	Nature of Solution
    H	1.0
    I		Neutral
    J		Weak acid
    K	13.0

30. A farmer intended to plant cabbages in his farm. he first tested the PH of the soil and found it to be 3.0.If cabbages do well in alkaline soils, explain the advice that would be given to the farmer in order to realize a high yield. (2mks)
31. Name an appropriate apparatus:
    1. That is used to prepare standard solutions in the laboratory. (1mk)
    2. That is used in heating solid substances strongly. (1mk)
    3. That can be used to separate two immiscible liquids. (1mk)
32. Some plants have seeds that contain vegetable oil.
    1. State the reagent and apparatus used to extract the oil from the seeds. (1mk)
       Reagent-
       Apparatus-
    2. Explain how it could be confirmed that the liquid obtained from the seeds is oil? (1mk)
    3. State an application of the method of extracting oil above. (1mk)

MARKING SCHEME

1. State the observations made when a piece of sodium metal is dropped into a beaker containing water. (2mks)
   Sodium melts into a silvery ball
   Hissing sound produced
   The piece of sodium darts on surface of water
   All three correct-2mks
   Two correct-1mk
   Only one-no mark
2. During a class experiment, students passed gas X over heated copper metal, the metal changed its colour to black.
   1. Identify gas X. (1mk)
      Oxygen
   2. Name the black substance formed. (1mk)
      Copper (II) Oxide
3. Aluminium is extracted from its ore by electrolysis.
   1. Name the main ore of Aluminium . (1mk)
      Bauxite
   2. The Aluminium ore in (a) above has a very high melting point.(20150C),though it is electrolyzed at a lower temperature of about 9000 C. Explain how the low temperature is achieved. (1mk)
      By addition of cryolite as an impurity which lower the melting point.
   3. In the above process, graphite electrodes are used. What is the disadvantage of using these kind of electrodes (1mk)
      At high temperatures oxygen gas produced at the anode reacts with graphite electrode to form Carbon (IV) Oxide and hence the electrode is depleted with time.
4. A student added 50cm3 of 1.0M aqueous Sulphuric (VI) acid to 50cm3 of 2.0M Potassium Hydroxide and the temperature of the resulting solution rose by 40 C.
   1. Define the term Molar heat of neutralization. (1mk)
      Is the heat change that occurs when one mole of H+ ions (from an acid) reacts with one mole of OH- (from an alkali) to form one mole of water.
   2. Calculate the molar heat of neutralization
      (C=4.2KJKg-1 K-1 ,Density of solution=1g/cm3)
5. Use the table below to answer the question that follow:
   

   Element	Atomic number
   A	11
   B	13
   C	14
   D	17
   E	19

   1. Write an equation for the reaction between element A and water. (1mk)
      2A_(s) +2H2_(l) 2AOH_(aq)+H2_(g)
   2. Explain the trend of atomic radii between elements A and D. (2mks)
      Atomic radii decrease from A to D.
      This is because protons are added into the nucleus resulting in higher nuclear charge between the positive nucleus and outermost electrons hence atomic radii decrease across a period.
6. In terms of structure and bonding, explain why graphite is used as a lubricant. (2mks)
   Graphite structure has layers that are held together by weak Van der Waals forces; the layers slide over each other.
7.  
   1. State the Boyles Law. (1mk)
      The volume of a given mass of gas is inversely proportional to its pressure at a constant temperature.
   2. A given mass of the gas occupies 20cm3 at 250 C and 670mmHg pressure. Find the volume it will occupy at 100 C and 335mmHg. (2mks)
      P1V1 =P2V2
        T1       T2
      But P₁=670mmHg
      V1=20cm³
      T₁=(25+273)=298K
      P₂=335mmHg
      V₂=?
      T₂=(10+273)=283K
      V₂=(670×20×283)
              (335×298)
      = 38cm³
8. Study the flow chart below and answer the questions that follow.
    
   1. Name
      1. Cations present in mixture M. (1mk)
         Cu²⁺½ mk and Zn²⁺√½mk
      2. Anion present in the solution. (1mk)
         SO₄^2-
   2. Write an equation to show how the white precipitate in step 3 dissolves. (1mk)
      Zn(OH)₂ (s) +4NH₃(aq)→ [Zn(NH₃)₄]²⁺(aq) +2OH^-(aq)
   3. Name the process outlined in step 4 above. (1mk)
      Neutralization
9. The solubility of potassium nitrate is 85g/100g of water at 50 0 C and 32g/100g of water at 25 0 C.
   1. Define the term solubility. (1mk)
      The amount of a substance that can dissolve in 100g of water at a certain temperature.
   2. Calculate the mass of the crystals formed if a saturation of potassium nitrate in 50g of water at 50 0 C is cooled to 25 0 C. (2mks)
      (85×50)=22.9g in 50g of water.
        185
      (32×50)=12.1g in 50g of water
         132
      22.9-12.1=10.8g KNO₃
10. Magnesium Chloride dissolves in water to form a neutral solution while iron (III) chloride forms an acidic solution. Explain. (2mks)
    Magnesium chloride does not hydrolyze in water √ ;Iron (III) Chloride hydrolyse in water producing hydrogen ions.
11. The diagram below is a set up to prepare a certain gas X. Study it and use it to answer the questions that follow.
    1. Identify gas X. (1mk)
       Hydrogen
    2. Why is the gas collected over water? (1mk)
       It is slightly soluble in water.
    3. Why are Copper (II) Sulphate crystals added to the flask where the reaction takes place?
       Copper (II) Sulphate act as a catalyst to speed up the reaction.
12.    
    1. Give the systematic names of the following organic compounds. (2mks)
       1. CH₃CH₂CH₂CH₂OH
          Butanol /Butan-1-ol
       2. CH₃CH₂COOCH₂CH₃
          Ethyl propanoate.
    2. Explain why an organic compound with the formula C4H6 burns with a more sooty flame than C₄H₁₀. (2mks)
       C₄H₈ is unsaturated hydrocarbon whose double bond requires excess oxygen for complete combination whereas C₄H₁₀ is a saturated hydrocarbon which burns completely.
13. When solid Zinc Carbonate was added to a solution of Hydrogen Chloride in methylbenzene there was no observable change. On addition of some water to the mixture there was effervescence. Explain the observation. (2mks)
    HCL in methylbenzene exists in a molecular form and has no H+ ions hence no effect on ZnCO³.On addition of water, HCL ionizes to give H+ ions which react with ZnCO³ ,producing Carbon (IV) oxide.
14. In titration experiment,25.0cm³ of sodium hydroxide containing 8.0 g per litre was required for complete neutralization of0.245 g of a diabasic acid. Calculate the relative molecular mass of the acid. (3mks)
    Molarity of NaoH = g/litre
                                 RFM
    =8.0=0.2M
       40
    Moles of NaOH that reacted=  vol  ×M
                                              1000
    =0.005mole
    2NaOH(aq)+H₂A(aq) Na₂A(aq) +2H₂O(l)
    From the equation
    Moles of H₂A that reacted= ½(0.005)
    =0.0025mole
    RFM of H₂ A= mass = 0.245 
                         moles  0.0025
    =98
15.    
    1. 100g of a radioactive isotope was reduced to 12.5g after 81 days. Calculate the half life of the radioisotope. (2mks)
       
       3 half lifes take 81 days
       1 half life ?
       t ½ = ⁸¹/₃ =27 days
    2. ²¹²₈₀Y decays by beta emission. What is the mass number and the atomic number of the product after decay?
       ²¹²₈₀Y → ²¹²₈₀Y
       Mass number is 212 √½
       Atomic number is 81√ ½
16. Distinguish between ionization energy and electron affinity. ` (2mks)
    Ionization energy is the energy required by an atom to lose one electron in gaseous state ,while electron affinity is the amount of energy released when an electron is added to a neutral atom in gaseous sate to form a negative ion.
17. The diagram below represents a paper chromatography for three brands of juice suspected to contain unwanted food additives.
    From the results, it was found that unwanted additives are present in Y and Z only.
    On the chromatogram;
    1. Circle the spots which show unwanted food additives.
    2. Name the solvent commonly used in paper chromatography. (1mk)
       Propanone.
    3. State two applications of chromatography. (2mks)
       Testing purity of drugs in pharmaceutical industry.
       Identifying banned substances in sports
       In food industry to identify contaminants in food and drinks.
       In the cosmetics industry to identify harmful substances.
18.  
    1. Show bonding in Aluminium Oxide. (1mk)
    2. Identify the type of bonds represented by p and q in the substances below.
       
       p-Covalent bond √ ½ mk ( ½ mk)
       q-Hydrogen bond√ ½ mk ( ½ mk)
19. The following diagram represents a charcoal burner. Study it and answer the questions that follow:
    Write the equations for the reactions at A,B and C regions. (3mks)
    
    1. 2CO (g) +O₂(g) 2CO₂(g)
    2. CO₂ (g)+C(s) 2CO(g)
    3. C(s) +O₂(g) CO2(g)
20. Use the scheme below to answer the question that follow.
    
    1. Identify process N. (1mk)
       Decomposition/Thermal decomposition
    2. Identify the solids
       H. Lead (II) nitrate( ½ mk)
       J. Lead (II) Oxide ( ½ mk)
21. Ammonia gas is prepared by Harber process according to the equation below:
    N₂(g)+3H₂(g) 2NH₃(g) +Heat
    State and explain the effect on equilibrium when the following conditions are applied.
    1. Pressure increased. (1mk)
       Equilibrium shift to the right. This is because there are few number of moles of gas molecules on the right than on the left hand side.
    2. Temperature increased. (1mk)
       Equilibrium shift to the left; heat is absorbed or reaction is endothermic in the backward reaction.
    3. State Le Chatelier’s principle. (1mk)
       It states that when a change in conditions is applied to a system in equilibrium, the system moves as to oppose that change.
22. You are given the following half equations.
    I2(s) +2e2I (aq) EѲ=+0.54V
    Br2(l) +2e 2Br - (aq) EѲ=+1.09V
    1. Write an overall equation for the cell reaction. (1mk)
       Br₂(l) +2I- 2Br - (aq)+I₂(s)
    2. Calculate the EѲ value of the cell.(1mk)
       E.M.F=EѲ(reduction)-EѲ(oxidation)
       1.09-0.54
       =0.45V
    3. Name the oxidizing agent. (1mk)
       Br₂ (l)
23. when a current of 0.8Ampheres was passed for 44 minutes and 20 seconds through fused iodide of metal Z, 0.7167g of Z was deposited. Determine the charge of the ion of metal Z.
    (1 Faraday=96500C,RAM of Z=65) (2mks)
    Q=It
    =(44×60 +20=26605(convert time into seconds)
    2660×0.8
    2128Coulombs √ ½ mk
    0.7167g of Z = 2128C
    65g(RAM) of Z ?
    65×2128
      0.7167
    =192995.6C√ ½ mk
    96500C = 1F
    192995.6C ?
    = 192995.6×1
           96500
    1.99995F
    ~2.0F√ ½
    2F discharges 2 electrons hence ,change of metal Z ion is Z²⁺ √ ½
24. The set up below shows how small pieces of copper are heated in nitrogen (I) Oxide.
    1. Write an equation for the reaction which occurs in the glass jar. (1mk)
       Cu(s)+ N₂O(g) CuO(s)+N₂(g)
    2. Give one use of the Nitrogen (I) Oxide. (1mk)
       Used as an anaesthesia for minor surgery and dental surgery.
25. State what would be observed if concentrated Sulphuric (VI) Acid is added to:
    1. Sugar crystals. (1mk)
       A black mass will be seen.
    2. Hydrated Copper (II) Sulphate crystals. (1mk)
       Turn from blue to white.
    3. What type of reaction has taken place above. (1mk)
       Dehydration.
26. Explain why commercial indicators are preferred to flower extracts as acid base indicators. (2mks)
    The composition of commercial indicators remains constant hence gives consistent results.
    The composition of flower extracts changes with time giving inconsistent results.
27.    
    1. Magnesium reacts with hydrochloric acid according to the following equation.
       Mg(s) +2HCl(aq) MgCl2(aq) +H2(g)
       Identify the reducing agent. Give a reason for your answer. (2mks)
       Mg/Magnesium; Oxidation number of magnesium increased.
    2. Iron sheets are dipped in molten Zinc to prevent rusting .Name this process. (1mk)
       Galvanisation
28. Explain why a balloon filled with helium gas deflates faster than a balloon of the same size filled with argon gas. (2mks)
    Helium is less dense that argon; hence it diffuses out faster than argon
    (Rej deflates for diffuses)
29. Complete the table below. (2mks)
    

    Solution	PH	Nature of Solution
    H	1.0	Strong acid
    I	7.0	Neutral
    J	4.0 - 6.9	Weak acid
    K	13.0	Strong base

30. A farmer intended to plant cabbages in his farm. he first tested the PH of the soil and found it to be 3.0.If cabbages do well in alkaline soils, explain the advice that would be given to the farmer in order to realize a high yield. (2mks)
    Add calcium oxide /lime to raise the soil PH. Calcium Oxide is a basic oxide hence dissolve in water in the soil to form alkaline solution that reacts with acidic soil to raise soil PH.
31. Name an appropriate apparatus:
    1. That is used to prepare standard solutions in the laboratory. (1mk)
       Volumetric flask
    2. That is used in heating solid substances strongly. (1mk)
       Crucible
    3. That can be used to separate two immiscible liquids. (1mk)
       Separating funnel
32. Some plants have seeds that contain vegetable oil.
    1. State the reagent and apparatus used to extract the oil from the seeds. (1mk)
       Reagent-acetone/ethanol ½ √
       Apparatus-motar and pestle ½ √
       (*mortar and pestle must both be mentioned for the mark)
    2. Explain how it could be confirmed that the liquid obtained from the seeds is oil? (1mk)
       The liquid left after evaporation is placed on a piece of paper. It leaves a translucent mark, which proves it is oil.
    3. State an application of the method of extracting oil above. (1mk)
       Used in extraction of oil from corn seeds e.g Elianto oil
       Extraction of natural dyes from plants.
       In dry cleaning to remove dirt.