INSTRUCTIONS TO CANDIDATES
- Write your name, class and admission number in the spaces provided above.
- Answer all questions in the spaces provided.
- This paper consists of Question 1 to 7
- Students should check the question paper to ascertain that all the pages are printed as indicated and no questions are missing.
FOR EXAMINER’S USE ONLY
Question |
Maximum Score |
Candidate’s score |
1 |
12 |
|
2 |
12 |
|
3 |
13 |
|
4 |
11 |
|
5 |
11 |
|
6 |
11 |
|
7 |
10 |
|
TOTAL |
80 |
|
QUESTIONS
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- Draw the structures of the following compounds. (2mks)
- 2-methylbut-2-ene
- Heptanoic acid
- Study the flow chart below and answer the questions that follow.
- Identify the organic compound K. (1mk)
- Write the formula of M. (1mk)
- Give one reagent that can be used in:
Step I (1mk)
……………………………
Step II (1mk)
…………………………… - Write the equation of the reaction in Step III. (1mk)
- Name the process that occurs in: (2mks)
Step II
………………………………………………
Step IV
……………………………………………... - The structure below represents a type of cleansing agent
Describe how the cleansing agent removes grease from a piece of cloth. (3mks)
- Draw the structures of the following compounds. (2mks)
- Below is part of the periodic table. The letters are not the actual symbols of the elements. Study it and answer the questions that follow.
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- State and explain the differences in the melting point of D and F. (2mks)
- Explain the difference in the atomic radii of G and N. (2mks)
- Select the element that is the strongest reducing agent. Explain. (2mks)
- Compare the nature of the aqueous solution of the oxide of C and that of L.
Explain. (2mks)
- Study the table below and answer the questions that follows:
Substance
MP(k)
BP (k)
Electrical conductivity
Solid
Molten
J
365
463
NIL
NIL
K
1323
2773
Good
Good
L
1046
1680
NIL
Good
M
2156
2776
NIL
NIL
- Which of the substance J, K, L and M represents the following:
- Silicon (IV) Oxide (1mk)
- Barium Sulphate (1mk)
- In terms of structure and bonding, explain why Silicon (IV) Chloride (SiCl4) is a liquid at room temperature while Magnesium chloride (MgCl2) is a solid. (2mks)
-
-
-
- What is meant by the term ‘Enthalpy of formation’. (1mk)
- The enthalpies of combustion of Carbon, Methane and Hydrogen are indicated below:
C(s) + O2(g) → CO2(g) ; ∆H = -393kJmol-1
H2(g) + ½ O2(g) → H2O(l) ; ∆H = -286kJmol-1
Enthalpy of combustion of CH4 = -890kJ/mol.- Draw an energy cycle diagram that links the enthalpy of formation of methane to enthalpies of combustion of carbon, hydrogen and methane. (2mks)
- Determine the enthalpy of formation of methane. (2mks)
- An experiment was carried out where different volumes of dilute hydrochloric acid and aqueous sodium hydroxide both at 25ºC were mixed and stirred with a thermometer. The highest temperature reached by each mixture was recorded in the table below.
Volume of Hydrochloric acid (cm3)
5
10
15
20
25
30
35
40
45
Volume of sodium hydroxide (cm3)
45
40
35
30
25
20
15
10
5
Highest temperature of mixture (oC)
27.2
29.4
31.6
33.8
33.6
31.8
30.0
28.4
26.6
- On the grid provided, plot a graph of highest temperature (vertical axis) against volume of hydrochloric acid (horizontal axis). (3mks)
- Using your graph, determine the
- Highest temperature reached. (½mk)
- Volume of acid and base reacting when highest temperature is reached. (1mk)
- Calculate the amount of heat liberated during the neutralization process. (Specific heat capacity 4.2Jg-1k- and the density of solution is 1.0g/cm3. (1½mks)
- On the grid provided, plot a graph of highest temperature (vertical axis) against volume of hydrochloric acid (horizontal axis). (3mks)
- The molar enthalpy of neutralization between hydrochloric acid and ammonia solution was found to be -52.2kJ/mol-, while that of hydrochloric acid and sodium hydroxide was -57kJmol-1. Explain the difference in these values. (2mks)
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-
- What is meant by rate of reaction. (1mk)
- In the space provided sketch the diagram of a set-up that can be used to determine the rate of reaction between manganese (IV) oxide and hydrogen peroxide. (3mks)
- A state of equilibrium between dichromate ions is established as shown below:
Cr2O72-(aq) + 2OH- ↔ 2CrO42-(aq) + 4H2O(l)
Orange Yellow- What is meant by dynamic equilibrium. (1mk)
- State and explain observation made, when a few drops of hydrochloric acid are added to the equilibrium mixture. (2mks)
- Some plants have seeds that contain vegetable oil.
- Describe how the oil can be obtained from the seeds. (3mks)
- Explain how it could be confirmed that the liquid obtained from the seeds in oil. (1mk)
- Use the standard electrode potential given below to answer the questions that follows:
Half reaction Eθ volts
Zn2+(aq) + 2e- → Zn(s) -0.76
Pb2+(aq) + 2e- → Pb(s) -0.13
Ag+(aq) + e- → Ag(s) +0.80
Cu2+(aq) + 2e- → Cu(s) +0.34-
- Choose a pair that will form a cell with the higher Eθ value. (1mk)
- Draw a diagram to represent the cell formed by the pair in (i) above (3mks)
- Give a cell representation for the cell in (I) above (1mk)
- State two functions of the salt – bridge. (2mk)
-
- Using a well labelled diagram, explain how an iron spoon can be electroplated with silver. (2mks)
- 2.34g of metal Q were deposited when a current of 4.0 amperes was passed through a salt of Q for 30 minutes. (RAM of Q = 65, 1 Faraday = 96,500C) calculate the amount of electricity in coulomb:
- Used to deposit 2.34g of metal Q. (1mk)
- Needed to deposit one mole of Q. (1mk)
-
-
- Two reagents that can be used to prepare chlorine gas are Manganese (IV) oxide and concentrated hydrochloric acid.
- Write an equation for reaction. (1mk)
- Give the formula of another reagent that can be reacted with concentrated hydrochloric acid to produce chlorine gas. (1mk)
- Describe how the chlorine gas would be dried in the laboratory. (2mks)
- In an experiment, dry chlorine gas was reacted with aluminium as shown in figure below
- Name substance A. (1mk)
- Write an equation for the reaction that took place in the combustion tube. (1mk)
- 0.84g of aluminium reacted completely with chlorine gas. Calculate the volume of chlorine gas used (Molar gas volume is 24dm3 Al=27) (3mks)
- Give two reasons why Calcium oxide is used in the set up. (2mks)
- Two reagents that can be used to prepare chlorine gas are Manganese (IV) oxide and concentrated hydrochloric acid.
- Extraction of iron involves two main processes, smelting and refining. Below is the blast furnace which is used to smelt iron from its ore.
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- The chief ore is Hamematite. Name one other ore used in extraction iron. (1mk)
- Name the reducing agent in the process. (1mk)
- What is the role of the hot air blast in the process. (1mk)
- Write equations for the reaction that took place of the region marked A, B and C. (3mks)
A ………………………………………………………………………………….
B ………………………………………………………………………………….
C …………………………………………………………………………………. - What is the purpose of limestone in the extraction process. (1mk)
- Write equations to show how impurities are removed from the ore. (2mks)
- State one environmental effect of the process. (1mk)
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MARKING SCHEME
-
-
-
-
Accept open structural formula.
CH3 may or may not be open.
OH may or may not be open.
-
-
- Ethane/ C2 H6
- C3 H6 Cl2
-
- Water/ steam/ conc. H2 SO4 1mrk
- Acidified KMnO4 /KMnO4/Acidified K2 Cr2 O7 Any 1mrk
- 2CH3 CH2 CH2 OH + 2Na → 2CH3 CH2 CH2 ONa + H2 1 mrk
Ignore missing or wrong state symbols.
Penalize fully if not balanced.
- Ethane/ C2 H6
-
- Oxidation 1mrk
- Decarboxylation 1mrk
- Cleansing agent has polar end ½ and non – polar end ½ Non – polar end attracts ½ Grease while polar end attracts water molecules ½ This lower the surface tension of water/ emulsification of grease ½
-
-
-
- D has a lower melting point than F ½ because F has more valence electrons ½ and smaller atomic radius hence stronger metallic bonds which require a lot of energy to break.
- G has a larger atomic radius than N. N has more protons than G/ N has a greater nuclear attraction than G./ N has a more effective nuclear charge than G.
- D 1mrk; Has the largest atomic radius / thus loses it’s outermost electrons most readily.
- Oxide of L is acidic ½ while that of C is basic/alkaline1/2 Oxide of L dissolves in water to form H+ ions ½ while that of C dissolves in water to form OH- ions ½
-
- M 1mrk
- L 1mrk
- In SiCl4 molecules are joined together by weak van der waals forces ½ . Forming a simple molecular structure while in Mg Cl2 ions are linked by strong ionic bonds / electrostatic forces of attraction ½ forming giant ionic structure ½
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-
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- Heat change that occurs when one mole of a substances is formed from its constituent elements ( in their normal State) 1mrk
Or
Heat absorbed or evolved when one mole of a substance is formed from its constituent elements in their normal states. -
Equation for CH4 formation ½
Equation for CO2 and H2O combustion 1mrk
Equation for CH4 combustion 1/2mrk Total= 2mrks- Δhf = ΔH2 – ΔH1
= -393+ 2(-286) + 890
=-75kJMol-1
Penalize ½ for wrong or missing units.
- Heat change that occurs when one mole of a substances is formed from its constituent elements ( in their normal State) 1mrk
-
- Plotting
9 correct plots 1
8 correct plots ½
< 8 correct plots 0
Scale
Horizontal scale – ½
Vertical scale ½
Line Extrapolation ½
Inverted ½ -
- Value read from graph = ½
- Acid volume from graph ½
Base volume = 50cm3 acid volume from graph ½
- ΔT value (Final Temp from graph -25ºC) ½
- Plotting
- NH3 is a weak base hence some of the heat evolved is used to completely ionize NH3(aq)
-
-
- measure of how much of the reactants are consumed or how much products are formed per unit time.
-
-
- Reaction in which rate of forward reaction is equal to the rate of reverse/ backward reaction. 1mrk
-
- Crush(1mrk) the seeds using a mortal and pestle, add suitable solvent such as propanone / acetone/ ethanol/ propanol ½ and continue crushing. The liquid is filtered / decanted/sieved ½ in an evaporating dish. The dish is placed out into the sun to allow the solvent to evaporate leaving the oil behind. ½
- The liquid left after evaporation is placed on apiece of paper. If it leaves a translucent mark then it approves it is oil.
-
-
- Ag/Ag+(aq) and Zn(s)/Zn2+(aq) Or 1mrk
Zn/Zn2+(aq) // Ag+(aq)/Ag(s) 1mrk
Or
Zn and Ag half cells. -
- Zn(s)/Zn2+(aq)//Ag+(aq)/Ag(s) 1mrk
- Completes the circuit 1mrk
Maintains charge balance 1mrk
Replenishes the used ions in the two half cells
- Ag/Ag+(aq) and Zn(s)/Zn2+(aq) Or 1mrk
-
Workability ½- Q = It
= 4 x 30 x 60 ½
= 7200C ½ Penalize if missing units. - 2.34g → 7200C
65g → ?
= 65g x 7200C ½
2.34g
=200 000C ½
- Q = It
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-
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- MnO2(s)+ 4HCl(aq) → MnCl2(aq) + Cl2(g) + 2H2 O(l) 1mrk
- KMnO4(s)/ Pb O2(s) / CaOCl2(s)
- By passing Cl2(g) through a U – tube containing anhydrous CaCl2
Drying agent 1mrk
Suitable Apparatus 1mrk
By passing Cl2(q) through concentrated H2 SO4 in a flask or bulling tube.
Or
-
- Aluminum chloride/Al Cl3
- 2Al(s) + 3Cl(s) → 2AlCl3(g)/ Al2 Cl6(g)
- Mol Al used = 0.84 = 0.0311 1 mrk
27
Mol of Cl2 = 0.0311x 3 = 0.047 1 mrk
2
Volume of Cl2 = 0.047 x 24 = 1.12 dm3
Or
0.84 x 3 x 24 = 1.12dm3 3mks
27
This part is consequential to part iii)
If more raha not used give a maximum of 2mrks - Prevent moisture from entering its apparatus by absorbing it/ prevent hydrolysis of AlCl2
To react with excess Cl2 / preventing environmental pollution by Cl2.
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-
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- Magnetite/ Siderite 1 mrk
- Carbon (ii) oxide 1mrk
- React with coke/charcoal / carbon to form carbon (iv) Oxide
Rise the temperature at the bottom of the finance to about 200K (165ºC)
- A; C(s)+O2 (g) → CO2(g) 1mrk
B; Fe2 O3(s) + 3CO(g) → 2Fe(s) + CO2(s) 1mrk
C; CaCo3(s) → CaO(s) + CO2(g) 1mrk - Decompose to quick lime (calcium oxide) which react to remove impurities and produce more carbon (iv) oxide gas.
- CaO + Si O2(s) → Ca Si O3(s) 1mrk
CaO + Al2 O3(s) → Ca Al2 O4(s) 1mrk - Carbon (iv) Oxide gas causes global warming if allowed to escape. 1mrk
Carbon (iv) Oxide is highly poisonous/ toxic that can kill.
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