KCSE 2019 General Science Paper 2 Questions with Marking Scheme

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General Science Paper 2 (237/2)

Answer all the questions in this section in the spaces provided.

    1. State three ways in which the cactus plant is physically adapted to arid habitats.(3 marks)
    2. Explain three effects of discharging raw sewage into Lake Victoria. (3 marks)
  2. Explain what is meant by each of the following terms:
    1. sexual reproduction(1 mark)
    2. gestation(1 mark)
  3. The graph below illustrates the hormonal changes that occur during the menstrual cycle.
    1. Name the hormone represented by the curve labelled F.(1 mark)
    2. Explain the effect of the hormone labelled E on the lining of the uterus.(1 mark)
    3. Name the hormone whose concentration increases on the 14" day of the menstrual cycle.(1 mark)
    4. A female human being expects ovulation to occur on the 14th day of her menstrual cycle. Give a reason why she is likely to conceive if she had sex few days before and after the 14th day.(1 mark)
  4. The diagram below illustrates a germinating seed.
    1. Name the type of germination illustrated.(1 mark)
    2. Explain how the type of germination illustrated occurs.(1 mark)
    3. State one function of the part labelled G.(1 mark)
    4. Explain how the seedling finally straightens.(2 marks)
  5. Explain how a man determines the sex of a child.(3 marks)
  6. A mother of blood group B has two children. One child is blood group A while the other is blood group 0.
    1. State the blood group of the father.(1 mark)
    2. What is the probability that the next child will be of blood group AB? Show your working.(2 marks)
  7. The diagram below illustrates a setup used by students to investigate responses in plants.
    1. Name the response illustrated by the roots of the seedlings.(1 mark)
    2. State the survival value of the response illustrated by the roots of the seedlings.(1 mark)
    3. Explain how the response illustrated by the roots of the seedlings occurs.(1 mark)
  8. The diagram below illustrates an eye defect.
    1. Name the eye defect illustrated.(1 mark)
    2. Draw a well labelled diagram to show how the defect is corrected.(2 marks)
  9. The diagram below illustrates support structures in passion and garden pea plants. Carefully study the position of tendrils in each plant.
    1. In evolution, what name is given to the structures represented by tendrils in both passion and garden pea plants?(1 mark)
    2. Give a reason for your answer in (a) above.(1 mark)
  10. The diagram below illustrates a bone from the hind limb of a mammal.
    1. Name the bones labelled (1 mark)
    2. Name the type of joint found at the posterior end of H.(1 mark)

Answer all the questions in this section in the spaces provided.

  1. A mixture of butene and hydrogen gases was passed over finely divided nickel catalyst at 250°C.
    1. Draw the structure of the compound that was formed.(1 mark)
    2. State one industrial use of the process described above.(1 mark)
  2. Study figure 1 and answer the questions that follow.
    1. Write an equation for the reaction between ammonia and the hot copper(II) oxide.(1 mark)
    2. State the property of ammonia demonstrated in figure 1,(1 mark)
    1. Explain the meaning of the term mole as used in Chemistry.(1 mark)
    2. A sample of a gas occupies a volume of 300 cm' of 760 mm Hg pressure. Calculate the pressure at which the gas will occupy a volume of 800cm(2 marks)
    1. Draw a labelled diagram to show extraction of sulphur by Frasch process.(3 marks)
      1. Explain why the volume of concentrated sulphuric(VI) acid increases when it is left in an open beaker for three days.(1 mark)
      2. State one use of concentrated sulphuric(VI) acid that depends on the property described in 14(b)i).(1 mark)
  5. Consider the following reaction at equilibrium.
    2RO2(g) + O2(g) = 2RO3(g); ΔH = - ve
    State the effect of the following:
    1. Removal of RO, from the system on the position of the equilibrium.(1 mark)
    2. Increase in the temperature of the system on the yield of RO,(1 mark)
    1. Study figure 2 and answer the questions that follow.
      1. Identify the heat of reaction denoted by ΔH.(1 mark)
      2. Give the sign of ΔH.(1 mark)
    2. Explain why the molar heat of neutralisation of strong acids by strong bases is approximately constant at -57.2 kJmol-1(1 mark)
    3. Give two characteristics of a fuel.(2 marks)
    1. What is meant by the term polymer?(1 mark)
    2. Polyvinyl chloride (PVC) is a synthetic polyıner. State one use of this polymer.(1 mark)
    1. Two new metals Caburam (Cb) and Laboran (Lb) have just been discovered. The ore of Caburam, Caburam Chloride has the formula CbCl and that of Laboran, Laboran oxide has the formula LbO. Their relative positions in the reactivity series are:
      Na > Mg > Al > Cb > C> Zn > Lb > Fe
      Name a suitable method of extracting:
      1. Caburam(1 mark)
      2. Laboran(1 mark)
    2. Draw a diagram to represent a set-up that can be used to extract caburam from its ore.(3 marks)
    1. What is meant by the term concentration as used in preparation of solutions?(1 mark)
    2. 28 g of sodium hydroxide was dissolved in enough water to make 2 litres of solution.
      1. Calculate the number of moles of sodium hydroxide.(2 marks)
      2. Calculate the molarity of the solution.(1 mark)
      3. Convert the molarity in (b)(ii) to concentration in grams per litre. [Na = 23.0;O= 16.0; H = 1.0 ](1 mark)
  10. Figure 3 shows a curve obtained from reacting a certain mass of zinc powder with 2 M hydrochloric
    1. State the effect on rate of evolution of hydrogen gas if 4M hydrochloric acid is used in place of 2 M hydrochloric acid.(1 mark)
    2. Sketch on the same axes, a curve that would be obtained when the concentration of hydrochloric acid is halved.(1 mark)

Answer all the questions in this section in the spaces provided.

    1. State two characteristics of images formed by a concave mirror.(2 marks)
    2. Figure 4 shows an image formed by a concave mirror.
      Complete the figure by drawing a ray diagram to show the position of the object.(3 marks)
  2. Figure 5 shows a ray of light moving from water to kerosene.
    Given that kerosene is optically denser than water, complete the figure to show the path of the ray in kerosene.(1 mark)
  3. Figure 6 shows a fixed positively charged rod placed between two freely suspended charged rods X and Y.
    1. Identify the type of charge on rods X and Y.(1 mark)
    2. Explain why sparks are observed when a person combs dry hair using a plastic comb in a dark room.(2 marks)
  4. Draw a diagram to show the following:
  5. Figure 7 shows the displacement - time graph of a certain wave motion.
    On the diagram, indicate the wavelength () and amplitude (a) of the wave using the symbols and a respectively.(2 marks)
    1. Define the term "echo".(2 marks)
    2. Describe how wind affects the speed of sound in air.(2 marks)
    1. State the reason why a freely suspended magnet always settles in a particular direction.(1 mark)
    2. State one application of magnets in hospitals.(1 mark)
  8. Draw a circuit diagram using circuit symbols to show how a variable resistor, a bulb, 2 dry cells in series, an ammeter and a voltmeter may be connected in order to determine whether the bulb obey's Ohm's law.(4 marks)
  9. Figure 8 shows a heater used to heat some water initially at 20°C.
    State two factors that determine the time taken for the water to boil.(2 marks)
  10. A radioactive material of mass 20g is observed to reduce to 5g in 48 hours. Determine its half life.(2 marks)
    1. Define the term "doping”.(1 mark)
    2. Draw the circuit symbol of a junction diode.(1 mark)
    1. State two properties of cathode rays.(2 marks) 
    2. State one use of X-rays.(1 mark)
  13. State the reason why in a house the bulbs that are not being used should be switched oif.(1 mark)


      • Leaves modified into thorns/are needle like to reduce evapotranspiration;
      • Succulent stems to store water;
      • Deep rooted to absorb water from deep horizons;
      • Few stomata to reduce transpiration; -
      • Sunken stomata to reduce rate of transpiration;
      • Have waxy cuticle to reduce rate of respiration;
      • Suffocation of aquatic animals due to reduced dissolved oxygen levels;
      • Rapid growth of aquatic weeds;
      • Disease agents in sewage contaminated water;
      • Toxic chemicals in sewage kill aquatic organisins;
      • Accumulation of heavy metals causing blood poisoning, nervous problems and death;
        Rj poilutes the water alone.
    1. The production of an offspring as a result of the fusion of a male and a female gamete;
    2. is the duration between fertilization and birth;
    1. Progesterone; RJ wrong spelling.
    2. Repair and healing of the endometrium/ uterine wall;
    3. Luteinising hornone (L.H); Rj abbreviations
    4. Sperms/ova remain viable in the female reproductive system for 2-3 days;
    1. Epigeal germination; RJ wrong spelling.
    2. Due to faster elongation of the hypocotyl than the epicotyl the cotyledons and plumule are pushed above the ground;
    3. Protects the plumule/Photosynthesis;
    4. Exposure of the hypocotyl to light makes auxins to migrate to the lower side; Higher concentration of auxins on the lower side makes the lower sides to grow faster enabling the seedling to straighten;
  5. Man/male has X and Y sex chromosomes while woman/female has X chromosomes only; Fusion of X and Y chromosomes produces a male child; while X and X produces a female child;
    1. Blood group A. Rj AO;AA
    2. Blood groups    
      Probability of AB = 1/4
      1 1 1 1
      F, Genotypes      AB   A0   B0  00 
       F, Blood groups  AB    A    B   0;
                                1    1     1    1
      Probability of AB
      = 1/4 /25%; Rj 0.25
    1. Hydrotropism; Rj wrong spelling. Acc. Positive hydrotrphism.
    2. Enables plant roots to seek for water;
    3. On sensing moisture, the auxins migrate to the side with moisture where they inhibit the rate of growth; side away from moisture grows at a higher rate making the root to curve towards the direction of water;
    1. Long sightedness (hypermetropia). Acc long sighted.
    1. Analogous structures
    2. Tendrils in passion are modified axillary buds while in pea plant they are modified leaflets but they all carry out the function for providing mechanical support;
    1. H-Fibula;
    2. Hinge joint;
    2. manufacture of margarine from oil
      manufacture of fats from oils/
      Conversion of oils into fats
    1. 3CuO(s) +2NH3(g) +3Cu(s) +3H2O(l)+N2(g)
    2. reducing agent
    1. A mole refers to the amount of a substance that contains as many particles as carbon-12
      The amount of a substance that contains Avogadro's number of particles. The particles could be atoms, molecules, ions, electrons etc
    2. P₂V₂=P₁V₁
      →p₂ = P₁v₁ 
      760 x 300
      = 285mmHg
      1. Concentrated sulphuric (VI) acid is hygroscopic hence absorbs water from the atmosphere thereby increasing the volume
      2. Used as a drying agent
    1. The equilibrium will shift to the right as more of the reactants are consumed to produce more RO3
    2. The yield of RO3 will decrease because increase in temperature will favour a reaction that absorbs the excess heat.
      • ΔH - Heat of solution
      • Negative (-ve)
    2. This is because strong acids and strong bases are all fully dissociated/ionized
      • Ease of combustion
      • Availability
      • Environmental effects
      • High heat value
    1. Polymer is a big molecule of high molecular mass formed from the reaction of the small molecules. 
      • making PVC pipes
      • Raincoats, handbags, hosepipes, floor tiles
      • Electrolysis
      • Reduction 
    1. Concentration refers to the amount of substance dissolved in a definite volume of solution
      1. No. of moles = Mass/RFM RFM of NaOH
        = 23 + 16 +1
        = 40
        = 0.7

      2. 0.7moles → 2 litres
                 ?    →1 litre
        ½ x 0.7(½mark) = 0.35M(½ mark)

      3. 1mole → 40g
        0.35moles →?
        28g → 21
           ? → 12
        0.35 x 40 (1/2)
        = 1/2 x28
    1. The rate of hydrogen production doubles/ increases
      • Virtual
      • Upright
      • Inverted
      • Same size as object
        (Any two correct)
      Any two correct rays 2
      Correct position of object(beyond )
      • Y is positively charged.
      • X is negatively charged.
      • Both hair and comb get charged by rubbing.
      • Hair attracts air ions of opposite charge and a spark is formed as hair is discharged. (2 marks)
    1. An echo is a second sound heard after the actual (first) sound is reflected from a barrier./ Reflected sound 
    2. Wind may increase the speed of sound if in the same direction as the sound or reduce the speed of sound if in the opposite direction
    1. It aligns itself with the earth's magnetic field.
    2. Removal of small pieces of iron from a patient's eye. /electric bells for emergencies
    • amount of current/voltage/resistance/
    • The amount of water. ✓
    • The power rating of the heater.
    • amount of heat
    • Pressure of the surrounding.
  30. 20 → 10 → 5
    2 half lifes in 48 hours ✓ OR
    ∴ half-life = 48/2
    = 24 hours
    1. The process of adding impurities to a semiconductor in order to increase its conductivity. 
      • Carry negative charge.
      • Deflected by both magnetic and electric fields.
      • Move in straight lines.
      • Affect photographic plates.
      • Cause fluorescence.
      • X-ray photography 
      • Sterilize equipment -
      • Detect flaws in metals
    • to minimize cost of electricity/ wastage of power
    • for bulbs to last longer


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