CHEMISTRY Paper 1 Questions and Answers - KCSE 2022 Past Papers

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QUESTIONS

1. State one property that can be used to distinguish between a proton and a neutron.(1 mark)
2. An ion of element Y has the formula:
  1. Write the electron arrangement of the ion. (I mark)
  2. Identify the group and period in the Periodic Table to which the element belongs.
    Group .....................(¹/₂mark)
    Period. .....................(/₂ mark)
1. Complete Table 1 by writing the formula and naming the structure of the chlorides of the elements (2 marks)
  
  Element Sodium Magnesium Silicon Phosphorus
  
  Formula of chloride
  
  Name of the Structure of chloride
2. Select from Table 1 an acidic chloride and write the equation for its reaction with water.(1 mark)
1. Write a thermochemical equation for the formation of carbon(II) oxide. (1 mark)
2. Use the energy level diagram in Figure 1 to answer the questions that follow.
  
  Determine the enthalpy change of
  1. formation of carbon(II) oxide (1 mark)
  2. combustion of carbon(II) oxide (1 mark)
1. Give a reason why painting or galvanising iron sheets protects them from rusting (1 mark)
2. Explain the advantage of galvanising over painting of iron sheets (2 marks)
1. The structure of compound A is
  
  Give its:
  1. name (1 mark)
  2. empirical formula (1 mark)
2. Draw the structure of an alkanoic acid whose molecular formula is C,HO (1 mark)
The following equilibrium exists in a closed system.

State and explain two conditions under which the intensity of the brown colour of the equilibrium mixture can be increased.
Condition I (1¹/₂ marks)
Condition II (1¹/₂marks)
1. Determine the oxidation numbers of
  1. hydrogen in CaH₂(1 mark)
  2. oxygen in OF₂(1 mark)
2. Write an ionic equation for the reaction between aqueous sodium hydrogen carbonate and ethanoic acid. (1 mark)
The mass of one molecule of a hydrocarbon is 9.33 x 10^-23g. (Avogadro's number-6.0 x 10 mol, C-12.0, H-1.0)
1. Determine its:
  1. molecular mass (1mark)
  2. molecular formula (1 mark)
2. Draw a structure of the hydrocarbon in 8(a). (1 mark)
1. Water reacts with hydrogen ions:
  1. write the formula of the product formed (¹/₂mark)
  2. Name the type of bond formed (¹/₂mark)
2. The melting point of iodine is higher than that of chlorine. Explain. (2 marks)
A sample of ammonia gas can be prepared by heating a mixture of ammonium bromide and barium hydroxide.
1. Write an equation for the reaction. (1 mark)
2. State why the gas cannot be dried using anhydrous calcium chloride (1 mark)
3. Name a suitable drying agent. (1 mark)
In an experiment to test for hardness of water from different boreholes, soap solution was added to 1000 cm of water and the volume of soap solution required for lather to start forming recorded. The results are given in Table 2
1. Select water samples that show:
  1. temporary hardness (¹/₂ mark)
  2. no hardness(¹/₂ mark)
  3. both temporary and permanent hardness (¹/₂ mark)
2. Describe how water hardness can be removed using an ion exchange resin. (1¹/₂ marks)
Products of electrolysis at the electrodes for aqueous solutions depend on three factors. Two of these factors are concentration of electrolyte and nature of electrode
1. State another factor that affects the products of electrolysis (1 mark)
2. Complete Table 3 to show products of electrolysis for dilute calcium chloride and concentrated calcium chloride at the anode and cathode
  
  Electrolyte Anode Cathode
  
  Dilute calcium chloride
  
  Concentrated calcium chloride
  
  (2 marks)
1. Carbon exhibits different boiling points. Explain. (1 mark)
2. It takes 4-4 seconds for nitrogen(IV) oxide gas to effuse through an opening. Calculate how long it will take for an equal volume of chlorine gas to effuse through the same opening (N-14.0: 0-16.0: C1-35.5). (2 marks)
1. Give an example of a natural polymer made of
  1. cellulose material (1⁄2 mark)
  2. a hydrocarbon (¹/₂marks)
2. Part of the structure of perspex is:
  1. Draw the structure of the monomer of perspex. (1 mark)
  2. Give two properties of perspex that make it suitable for use in making lenses. (1marks)
Two allotropes of carbon are graphite and diamond
1. Explain why the density of diamond is higher than that of graphite. (1mark)
2. Give one use of each of the allotropes and relate the use to properties of the allotrope
  1. Graphite
    use (¹/₂mark)
    property (¹/₂mark)
  2. Diamond
    use (¹/₂mark)
    property (¹/₂ mark)
The graph in Figure 2 shows radioactive decay curve of a radioactive isotope.

Use the graph to determine the:
1. half life of the radioactive isotope (1 mark)
2. rate of decay at time 150 hours (1 mark)
3. The half life of two radioactive isotopes A and B are 8 days and 5.2 years respectively Given that both of them emit beta radiation, explain why A would be more suitable in the treatment of a disease (1 mark)
The formula of a hydrated salt of manganese is MnSO, XHO Given that the salt contains 24,7% manganese, determine the value of X (Mn-550, S-120.0-160, H1.0) (3 marks)
Describe the correct procedure of heating a liquid in a test tube using a Bunsen burner. (3 marks)
The melting and boiling points of naphthalene are 80°C and 218°C, respectively A sample of naphthalene was cooled from 250°C to 25 °C. On the axes provided, sketch and label the cooling curve that would be obtained. (3 marks)
Draw a labelled diagram of a setup that can be used to prepare a dry sample of chlorine gas using potassium manganate(VII) and concentrated hydrochloric acid ( marks)
Table 4 gives the boiling points of three liquids

Liquid Boiling point (C)

Hexane 68.7

Butanol 99.5

Water 100.0

Describe how the following mixtures can be separated
1. hexane and butanol (1¹/₂ marks)
2. hexane and water (1¹/₂marks)
Complete Table 5 by writing the observations made when aqueous ammonia and aqueous sodium sulphate are added to solutions containing calcium, aluminium and iron(II) ions.(3 marks)

lons present Aqueous ammonia Aqueous sodium sulphate

Ca²⁺

Al³⁺

Fe²⁺
1. Iron is extracted from haematite ore. If the ore contains oxides of silicon and aluminium, explain how these impurities are removed (2 marks)
2. The extraction process of iron produces waste gases. State how these waste gases can be used to lower the operational cost of the extraction process (1 mark)
When chlorine is bubbled into a sample of water, the solution smells strongly of chlorine. If aqueous sodium hydroxide is added to the solution, the smell of chlorine disappears
The following equation shows the reaction that occurs.

With reference to the equation for the reaction, explain why the
1. solution smells strongly of chlorine (1 mark)
2. addition of sodium hydroxide removes the smell (2 marks)
Figure 3 shows how nitrict V) acid can be obtained
1. Identify the chamber in which a catalyst is used. (1 mark)
2. Name substance Z. (1 mark)
3. Write an equation for the reaction that takes place in Chamber III.(1 mark)
The fomula of complex ion formed when aqueous zinc sulphate reacts with aqueous sodium hydroxide is given as ;(Zn(OH)₄)
Explain how the value of x is determined; (2marks)
Copper can be obtained from copper(ii)oxide using carbon (ii)oxide or coke .
1. Name another reagent that can be used to obtain copper from copper(ii)oxide (1marks)
2. The equation from the reaction with carbon(ii)oxide is ;
  CuO(_S) + CO(_g) → Cu(_s) +CO(_g)
  Calculate the maximum mass of copper that would be obtained using 200dm³of carbon(ii)oxide (Cu =63.5; Molar of gas =24.0dm³⁾ (2marks)

MARKING SCHEME .

1. State the property that can be used to distinguish between a proton and aneutron . (1mark)
  - mass
  - charge
2. An ion element Y has the fomula
  1. write the electron arrangement of the ion .
    - 2. 8.8 or 2.8 .8
  2. Identify the group and peariod in the periodic table to which the element belongs
    Group ii
    period 4

Complete the table by writting the fomula and naming the structure of the chloride of the elements

Element	Sodium	Magnesium	silicon	Phosphorus
Formula of chloride	NaCL	MgCl₂	SiCl₄	PCl₃/PCl₅
Name of the structure of chloride	grant ionic	Grant ionics	Simple Molecular	Simple molecular

Select from the table 1 an acidic chloride and write the equation for its reaction with water . (1mark)
- PCl_3(l) + 3H₂O_(l) → H₃PO₃ _(aq) +3HCl_(aq)PCl₅(L) +4H₂O(L) → H₃PO4_(aq) + 5HCl_(aq)

1. Write a thermochemical equeation for the formation of carborn(ii)oxide (1mark)
  C(s) + 1/2O2 → CO(3) ;(ΔH°f)
2. Use the energy level in figure 1 to answer the equation that follow.
  
  Determine the enthalpy change of ;
  1. formation of carbon|(ii0oxide
    ΔH°f = -110ki/mol
  2. combination of carbon(ii)oxide
    ΔH -400 -(-110) =-290kj
1. Give a reason why painting ir galvanising iron sheets protects them from rusting .
  - both methods provides coating /that keeps iron from oxygen and water
2. Explain the advantage of galvanising over painting if iron sheets (2marks)
  - In galvanising , zinc acts as sacrificial metal source
  - it is more reactive than iron thus prevent rusting ,
1. The structure of compound A is ;
  
  Give its ;
  1. name
    Decane (1mark)
  2. emperical fomula
    C₅H₄ (1mark)
2. Draw the structure of an alkanoic acid whose moleccular formula is C₄H₁₀O₂ (1mark)
The following equilibrium exists in a closed system

state and explain two conditions under which the intensity of the brown colour of the equilibrium mixture can be increased .
conditon 1
increase temperature ,¹/₂ the forward reaction is endothermic / form of NO_2(g) is formed by increase in temperature
conditon II
Deduction in pressure ,¹/₂ forward reaction proceeds with increase in number of pressure .production od NO2 is there for fevoured by low pressure
1. Determine the oxidation number of ;
  1. hydrogen in CaH₂ (1mark)
    O.N of CaH₂ = +2+2H =0(¹/₂)
    2H = -2
    O°N_O of H =-1 (¹/₂)
  2. oxygen in Of₂
    O'No of OF2 = O +2(-1)
    O= +2
2. Write an ionic equation for the reation between aqueous sodium hydrogen carbonate and ethanoic acid . (1mark)
  - CH3COOH(aq) = HCO₃‾(aq) → CH3COO‾(aq) =CO₂ +HO₂
The mass of one molecule of a hydrocarbon is 9.33 ×10^-23g. (Avogadro's number = 6.0×10²³ mol^-1 , C = 12.0;H =1.0)
1. Determine its:
  1. molecular
    9.33 × 10^-23× 6.0 × 10
  2. molecular formula (1mark)
    C₄ H₈
2. Draw a structure of the hydrocarbon in 8 (a) (1mark)
1. Water reacts with hydrogen ions :
  1. Write the chemical fomular of the product formed (¹/₂ mark)
    H₃O⁺
  2. Name the type of bond formed (¹/₂marks)
    Co-ordinate
2. The melting point of iodine is higher than that if chlorine . Explain (2marks)
  - Iodine has larger molecular mass the stronger vender walls forces of attractions then chlorine which has smaller mass .
A sample of ammonia gass can be prepared by heating a mixture of ammonia bromide and barium hydroxide .
1. Write an equation for the reaction
  2NH₄Br_(s) + Br(OH)_2(s) → BaBr_2(s) + 2NH_3(g) +2H₂O_4(g)
2. State why the gas cannot be dried using anhydrous calcium chloride (1mark)
  - Ammonia reacts with calcium chloride to form CaCl₂•2NH₃ which is a complex salt .
3. Name a suitable drying agent .
  - CaO_(s)/Calcium oxide
In an experiment to test for hardness of water from different boreholes , soap solution was added to 1000cm³ of water and the volume od soap solution required for lather to start forming recorded. The results are given in table 2
1. Select water sample that shows :
  1. temporary hardness (¹/₂marks)
    - Sample 1
  2. no hardness (¹/₂marks)
    - Sample 4
  3. both temporary and parmanent hardness (¹/₂marks)
    - Sample 2
2. Describe how water hardness can be removed usingind an ion exchange resin (1¹/₂marks)
  1. Hard water is run into a column containing the ion exchange resin
  2. Ca²⁺ and Mg²⁺ ion arte exchanged for Na⁺ ion
  3. therefore water coming out is soft .
Product of electrolysis at the electrode for aqueous solution depend on the factors . Two of these factors are concentration of electrolyte and of electrode.
1. State another factor that affects the product of electrolysis (1mark)
  - Position of the ion/element in the ractevity searies
2. Complete the table 3 to show products of electrolysis for dilute calcium chloride and concentrated calcium chloride at the anode and cathode. (2marks)
  
  Electrolyte anode Cathode
  
  Dilute calcium chloride Oxygen
  Hydrogen
  
  Concentrated calcium chloride Chloride Hydrogen
1. Carbon exhibits different boiling points . Explain. (1mark)
  - Carbon exist in defferent crystoline forms same physical state hence different boiling point because of their different structure.
2. It takes 4-4 seconds for nitrogen(IV) oxide gas to effuse through an opening. Calculate how long it will take for an equal volume of chlorine gas to effuse through the same opening (N-14.0: 0-16.0: C1-35.5). (2 marks)
1. Give a example of a natural polymer made of :
  1. cellulose material (¹/₂marks)
    - Cotton wool ,wood ,paper
  2. a hydrocarbon (¹/₂marks)
    - Rubber
2. Part of the structure of perspex is
  1. Draw the structure of the monomer of perspex. (1 mark)
  2. Give two properties of perspex that make it suitable for use in making lenses . (1mark)
    - Transparent - free from change of refraction index
    - strong -consistant in refraction index
Two allotropes of carbon are graphites and diamond .
1. Explain why the desity of diamond is higher than that of graphite . (1mark)
  Diamon has tetrahedral structure with all atoms forming four cobalent bond while in the graphite each atom form three covalent bonds in a layer structure which are far from each other .
2. Give one use of each of the alltropes and relate the use to propertiesof the allotrope.
  1. Graphite
    use (¹/₂mark)
    - Lubricant / Electrode
      property (¹/₂mrks)
    - conduct of electricity
  2. Diamond
    use (¹/₂mark)
    - tips od driling tips
      property (¹/₂marks)
    - Hardand abrasive
    - cutting instrument
1. The graph in fugure 2 shows a radioactive decay curve of a radioactive isotope .
  Use the graph to determine the ;
  1. half life of the radioactive isotope (1mark)
    - Half ; life = 85 hours
  2. rate of decay at time 150hours (1mark)
    ^{3.0 - 0.5}/_{80 -240}
    -0.016g/hrs
2. The half life of two radioactive isotopes A and B are 8 days and 5.2 years respectively Given that both of them emit beta radiation, explain why A would be more suitable in the treatment of a disease (1 mark)
  - A has a shoter half-life the B will clear from the body faster thus not expose the patient to radiation for a long time
The formula of a hydrated salt of manganese is MnSO, XHO Given that the salt contains 24,7% manganese, determine the value of X (Mn-550, S-120.0-160, H1.0) (3 marks)
Describe the correct procedure of heating a liquid in a test tube using a Bunsen burner. (3 marks)
- Hold the test tube with a test tube holder , keep it slanting with the open end facing away ,heat from top downwards and not from bottom to the top while rotating
The melting and boiling points of naphthalene are 80°C and 218°C, respectively A sample of naphthalene was cooled from 250°C to 25 °C. On the axes provided, sketch and label the cooling curve that would be obtained. (3 marks)
Draw a labelled diagram of a setup that can be used to prepare a dry sample of chlorine gas using potassium manganate(VII) and concentrated hydrochloric acid ( marks)
Table 4 gives the boiling points of three liquids

Liquid Boiling point (C)

Hexane 68.7

Butanol 99.5

Water 100.0

Describe how the following mixtures can be separated
1. hexane and butanol (1¹/₂ marks)
  - Fraction distilation
    put the two liquidin fractionating column ;heat the mixture gently ;hexone will distill ;
2. hexane and water (1¹/₂marks)
  - separating funnel ;burette
    this are immiscible liquids ;hexane will float on water from the bottom of flask , hexane remove in the funnel

Complete Table 5 by writing the observations made when aqueous ammonia and aqueous sodium sulphate are added to solutions containing calcium, aluminium and iron(II) ions.(3 marks)

lons present	Aqueous ammonia	Aqueous sodium sulphate
Ca²⁺	white precipitate	white precipitate
Al³⁺	white precipitate	No white precipitate
Fe²⁺	Green precipitate	No Green precipitate

1. Iron is extracted from haematite ore. If the ore contains oxides of silicon and aluminium, explain how these impurities are removed (2 marks)
  - they react with calcium oxide ;to form CaSiO₃ whic are removed as slag
2. The extraction process of iron produces waste gases. State how these waste gases can be used to lower the operational cost of the extraction process (1 mark)
  - The waste gase are at high temp , the head can be recycle to pre-heat incoming air
When chlorine is bubbled into a sample of water, the solution smells strongly of chlorine. If aqueous sodium hydroxide is added to the solution, the smell of chlorine disappears
The following equation shows the reaction that occurs.

With reference to the equation for the reaction, explain why the
1. solution smells strongly of chlorine (1 mark)
  - chlorine reacts partialy with water , there is strong smell due to presence of chlorine molecules .
2. addition of sodium hydroxide remove the smell (2marks)
  - Addition of NaOH neutralize HCl _(aq) and HOCl_(aq) ,equilibrium shifts to the right chlorine molecule are consum hence the smell disappears.
Figure 3 shows how nitrict V) acid can be obtained
1. Identify the chamber in which a catalyst is used. (1 mark)
  - chamber 1
2. Name substance Z (1mark)
  - Nitrogen (ii)oxide (No)
3. Write an equation for the reaction that takes place in chamber III (1mark)
  - 3NO_2(g) + H₂O_(l) → 2HNO_3(aq)
The fomula of complex ion formed when aqueous zinc sulphate reacts with aqueous sodium hydroxide is given as ;(Zn(OH)₄)
Explain how the value of x is determined; (2marks)
- Oxidation state of zinc is =2
- OH‾ has a charge of -1
- +2 + (-1× 4) = X
- x=-2
Copper can be obtained from copper(ii)oxide using carbon (ii)oxide or coke .
1. Name another reagent that can be used to obtain copper from copper(ii)oxide (1marks)
  - hydrogen gas
2. The equation from reaction with carbon(ii)oxide is
  - CuO_(s) + CO_(g) → Cu_(s) + CO_2(g)Calculate the maximum mass of copper that would be obtained using 200dm³of carbon(ii)oxide (Cu =63.5; Molar of gas =24.0dm³⁾ (2marks)
    CuO_(s) + CO_(g) → Cu_2(g) ,
    Mole CO= mole cu =^200dm3/_24dm3
    mass =²⁰⁰/₂₄ × 63.5 =529.2