Questions
- Element K has atomic number 20 while element M has atomic number 8.
- Write the electron configuration of K and M
K ______________________ (1mk)
M ______________________ (1mk) - Write the symbol of the most stable ion of K and M
K ____________________________ (1/2 mk)
M ___________________________ (1/2mk)
- Write the electron configuration of K and M
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- Molten lead (ii) iodide is electrolyzed using inert electrodes. Write the half equation of the reactions that occur at the anode and cathode.
- Anode _______________________________________ (1mk)
- Cathode ______________________________________ (1mk)
- Explain why the conductivity of metals decrease with increase in temperature
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- Molten lead (ii) iodide is electrolyzed using inert electrodes. Write the half equation of the reactions that occur at the anode and cathode.
- Some sodium chloride was found to be contaminated with copper (ii) oxide. Describe how a sample of dry sodium chloride can be obtained from the mixline
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________________________________________________________________________ - Hot platinum wire was lowered into a flask containing concentrated ammonia solution as shown below
State and explain the observations made (3mks)
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- What is a dative boud? (1mk)
________________________________________________________________________ - Draw a dot (.) and cross (x) diagram to show bouding in carbon (ii) oxide (2mks)
- What is a dative boud? (1mk)
- Air was passed through several reagents as shown in the flow chart diagram
- What is the purpose of concentrated potassium hydroxide solution? (1mk)
________________________________________________________________________ - Write an equation for the reaction which takes place in the chamber with magnesium powder (1mk)
________________________________________________________________________ - Name one gas which escapes from the chamber containing magnesium powder (1mk)
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- What is the purpose of concentrated potassium hydroxide solution? (1mk)
- Name the following substances
- CH2CH CH2CH3 ______________________________________ (1mk)
- CH3CHCHCH2CH3 _______________________________________ (1mk)
- State the observation made when compound in (a) above was passed through acidified potassium (vii) manganite (1mk)
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- The diagram below shows a wooden splint that was placed horizontally across the middle part of a non-luminous flame.
- Explain the observation made (2mks)
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________________________________________________________________________ - Explain why non-luminous flame is preferred for heating than luminous flame (1mk)
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- Explain the observation made (2mks)
- Explain giving reasons why?
- Sulphuric(vi) acide is not used with marble in the preparation of carbon(iv) oxide (2mks)
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________________________________________________________________________ - Water cannot be used to extinguish oil fire
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- Sulphuric(vi) acide is not used with marble in the preparation of carbon(iv) oxide (2mks)
- 15cm3 of a solution containg 2.88g/dm3 of an alkali XOH completely reacts with 20.0cm3 of 0.045m sulphuric(vi) acid. Calculate the molarity and relative atomic mass of x present in the alkali
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________________________________________________________________________ - An hydrocarbon Q was found to decolourise potassium manganate(vii)solution. When two moles of Q were burnt completely six moles of carbon(iv)oxide and six moles of water were formed.
- Write the structural formula of Q (2mks)
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________________________________________________________________________ - Name the homologous series to which Q belongs
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- Write the structural formula of Q (2mks)
- The diagram below represents an electrochemical cell
- On the diagram label the salt bridge (1mk)
- State two observations made in cell B (1mk)
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________________________________________________________________________ - Write the overall ionic equation of the cell (1mk)
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- During the extraction of copper and zinc from their ores, some of the processes include
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- Crushing
- Mixing of the crushed ore with oil and water and bubbling air through it.
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- Name the process (ii) above (1mk)
________________________________________________________________________ - What is the purpose of (ii) above
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- Name the process (ii) above (1mk)
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- Dry chlorine gas was passed through two pieces of coloured cotton cloth as shown
- State what is observed in each experiment (1mk)
Experiment I
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Experiment II
______________________________________________________________________ - Explain your observation using an equation (1mk)
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- State what is observed in each experiment (1mk)
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- what is meant by solubility? (1mk)
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________________________________________________________________________ - In an experiment to determine the solubility of solid Y in water at 30oC the following results were obtained.
Mass of evaporating dish = 26.2g
Mass of evaporating dish + saturated solution = 42.4g
Mass of evaporating dish + dry solid y = 30.4g
Using the information, determine the solubility of solid Y at 30oc in grams per 100g of water (2mks)
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________________________________________________________________________
- what is meant by solubility? (1mk)
- the molar heat of formation of carbon(ii) oxide is -105kjmol-1, molar heat of combustion of carbon is -393 kjmol-1 by using an energy cycle diagram, determine the molar heat of combustion of carbon(ii)oxide (3mks)
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________________________________________________________________________ - The diagram below was used to study the effect of heat on copper(ii)sulphate crystals
- Name liquid M (1mk)
_____________________________________________________________________ - State and explain the precaution that should be made before stopping heating (2mks)
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- Name liquid M (1mk)
- Deuterium 21D and tritium 31T are two isotopers of hydrogen. They react to form element Y and neutron particles according to the equation below.
21D + 31T → abY + 10n- Find the value of a and b (2mks)
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________________________________________________________________________ - What name is given to the type of reaction undergone by the isotope of hydrogen (1mk)
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- Find the value of a and b (2mks)
- A gas occupies 4dm3 at -230c and 152mmHg. At what pressure will its volume be halved, if the temperature then is 2270c? (2mks)
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________________________________________________________________________ - Ammonium nitrate was gently heated and the products collected as shown in the diagram
- Identify
- Colourless liquid H (1mk)
____________________________________________________ - Gas G (1mk)
- Colourless liquid H (1mk)
- Describe one chemical test that can be used to identify gas G
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- Identify
- The diagram below shows the acidic and basic oxides fit into the general family of oxide
- State the type of oxide that would be placed in the shaded area (1mk)
_____________________________________________________________________ - Name an oxide that would be placed in the shaded area (1mk)
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- State the type of oxide that would be placed in the shaded area (1mk)
- A dynamic equilibrium between dichromate and chromate ions is established as shown in the equation below.
Cr2O72-(aq) + ZOH-(aq) ⇌ 2Cro2-4 + H2O (l)
Orange Yellow- What is meant by dynamic equilibrium? (1mk)
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_____________________________________________________________________ - State and explain the observation made if a dilute hydrochloric acid is added to the equilibrium mixture (2mks)
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- What is meant by dynamic equilibrium? (1mk)
- An experiment showed that the composition of a compound to be 5838% Barium, 13.72% Sulphur and 27.47% oxygen. Calculate the empirical formula of the compound (Ba = 137; S=32, O=16) (3mks)
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________________________________________________________________________ - In an experiment to study diffusion of gases, the following set up was used
- State and explain observations made in the experiment (2mks)
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________________________________________________________________________ - Write an equation for the reaction that occurs in the experiment (1mks)
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- State and explain observations made in the experiment (2mks)
- The figure below is an energy level diagram for the reaction 2Z (g) + 2B(g) = 2AB(g)
Explain the effect of yield AB by- Increase in pressure (1 ½ mk)
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_____________________________________________________________________ - Decrease in temperaline (1 ½ mk)
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- Increase in pressure (1 ½ mk)
- Study the following changes that took place when the following substances are exposed to air.
- I
NaOH(s) → NaOH(aq) - II
Na2CO3.IOH2O(s) → Na2CO3(s) + IOH2O(l) - III
CuSO4(s) + 5H2O(l) → CuSO4.5H2O(s)
Name the process (3mks)
I _______________________________
II ______________________________
III _____________________________
- I
- A white solid K was heated. It produced a brown gas A and another gas B which relights a glowing splint. The residue left was yellow when hot and white when cold.
- Identify gases A and B (2mks)
A ______________________________
B ______________________________ - Write an equation for the decomposition of solid K (1mk)
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_____________________________________________________________________ - Bronze is an alloy of copper and another metal. Identify the other metal.
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- Identify gases A and B (2mks)
Marking Scheme
-
- K 2. 8.8.2 √1mk
M 2.6 √1mk - K 2+
M 2-
- K 2. 8.8.2 √1mk
-
- Anode: I- (l) I2 (g) + 2e- √1mk
Cathode: Pb2+ + 2e- Pb (s) √1mk - Increase in temperature increases the kinetic energy (1/2 mrk) of positive centres and electrons making them to vibrate more. These increase collisions of positive centres and electrons hence increased resistance (1/2mrk)
- Anode: I- (l) I2 (g) + 2e- √1mk
- Add water to the mixture and stir sodium chloride dissolve leaving copper (ii) oxide which is insoluble. (√1mk )
Filter (1/2) to remove copper (ii) oxide and sodium chloride as the filtrate
Evaporate the filtrate to saturation and cool to obtain sodium crystals (√1mk )
Dry them between filter papers/leave them in the open to dry (√1mk ) - Hot platinum wire glows red. (√1mk )
Brown fumes are observed (√1mk )
Reaction between oxygen gas and ammonia gas over platinum wire is exothermic. (1/2mrk)
Ammonia is oxidized to nitrogen (ii) oxide which reacts with excess oxygen to form nitrogen (iv) oxide,(1/2 mrk) -
- A bond formed by two atoms/elements by share of electrons from one of the atoms/element(√1mk)
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- Remove / absorb carbon (iV) oxide (√1mk )
- 3Mg (s) + N2 (g) → Mg3N2 (s) (√1mk )
- Neon/ Argon (√1mk )
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- But – 1 – ene (√1mk )
- Pent – 2 –ene (√1mk )
- Potassium manganate (VII) is decolourised/ Potassium manganate (VII) changes colour from purple to colourless (√1mk )
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- The outer zone has complete combustion and hence hotter tha the middle zone forming the charred black part (1mrk) Middle zone has incomplete combustion and hence less hot forming unburnt part (√1mk )
- - Non – luminous flame is hotter than luminous flame (1mrk)
Non – luminous flame does not produce soot (1mrk) Any one (√1mk )
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- Sulphuric (VI) acid react with marble (Calcium carbonate) forming insoluble calcium sulphate(1mrk) which form a coat over marble stopping any further reaction (√1mk )
- Oil is less dense (1/2) than water making oil float(1/2) on top hence continues to burn.
- 2XOH(aq) + H2SO4(aq) → X2SO4 (aq) + 2 H2O(l)
XOH = 2 = 15 X M
H2SO4 1 20 X 0.045 (√1mk)
M = 2 X 20 X 0.045
1 X 15
= 0,12 moles/l (1/2)
1mole = 2.88 = 24 (1/2)
0.12
RFM of XOH = X + 16 + 1 (1/2)
X = 7 1/2) -
- 2CxHy X CO2 + y/2 H2O
X = 6/2 = 3 (1/2)
Y = 12/ 3 = 6 (1/2)
MF = C3H6 (1/2)
Structural fprmula = CH3 CH = CH2 (1/2) - Alkenes
- 2CxHy X CO2 + y/2 H2O
- on the diagram
- √1mk
- arrow from zinc half-cell towards copper half cell √1mk
- Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) √1mk
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- Froath floatation √1mk
- Concetrating the mineral ore by making impurities to sink atb the bottom. √1mk
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- Exp. 1 – The colour of dry cloth did not turn to white/ cloth not bleached, because of the absence of hypochloric (I) acid which is responsible for bleaching
- Exp 2 – Wet cloth turned white due to bleaching as chlorine dissolves in water to form hypochloric(I) acid√1mk
- Cl2(g) + H2O(g) + Dye {Dye + [O]} + 2HCl(g) √1mk
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- Solubility is the maximum mass in grams of solute that will dissolve in 100g ofvwater at a given temperature/ is the mass in grams of solute required to make a saturated solution with 100g of water at given temperature. √1mk/
- Mass of solid Y = 30.4 – 26.2
= 4.2g (1/2mrk)
Mass of water in the solution = 42.4 – 30.4 = 12g (1/2 mrk)
12 g of water dissolve 4.2g solid Y
100g of ware will dissolve
100 x 4.2 (1/2mrk)
12
= 35g / 100g of water (1/2mrk)
- Solubility is the maximum mass in grams of solute that will dissolve in 100g ofvwater at a given temperature/ is the mass in grams of solute required to make a saturated solution with 100g of water at given temperature. √1mk/
- AH0f(CO) + AH0c(CO) = AH0c(C)
-105 + AH0c(CO) = -393 √1mk
AH0c(CO) = -393 + 105 √1mk
= -188kJMol-1 √1mk -
- Water √1mk
- The delivery tube should first be removed √1mk to avoid sucking back of liquid M √1mk
-
- Atomic mass of Y 2 + 3 = a + 1
a = 4 √1mk
Atomic number 1 + 1 = b + 0
b = 2 √1mk - Nuclear fusion √1mk)
- Atomic mass of Y 2 + 3 = a + 1
- V1 = 4dm3 ; P1 = 152mmHg ; V2 = 2dm3 ; T1 = 250K ; T2 = 500K P2 = ?
152 x 4 = P2 x 2
250 500 √1mk
P2 = 152 x4 x 500
250 x 2 √1mk
= 608mmHg √1mk -
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- Liquid H is Water √1mk
- Gas G is Nitrogen (i) oxide √1mk
- turn white anhydrous copper (II) sulphate to blue / Turns blue cobalt(II) chloride to pink √1mk
-
-
- Amphoteric oxide √1mk
- Lead (II) oxide / Zinc oxide / Aluminium (III) oxide (Any one) √1mk
-
- Rate of forward reaction equals to the rate of backward reaction. √1mk
- Orange colour of the solution intensifies √1mk
Equilibrium shift to the left/ backward reaction is favoured to replace OH- that react with H+ √1mk
- Element Ba S O
% composition 58.81 13.72 24.47
RAM 137 32 16
No. of moles 58.81 13.72 24.47 (1/2mrk)
137 32 16
0.4293 0.4281 1.768
Mole ratio 1 1 4 (1/2mrk)
E . F. BaSO4 (√1mk) -
- A white ring/ solid (1/2mrk) was formed inside the combustion tube closer to the cotton wool soaked in concentrated hydrochloric acid (1/2mrk). Ammonia is lighter/less dense than hydrochloric acid hence diffuse faster ( √1mk)
- NH3 (g) + HCl(g) → NH4Cl(s) (√1mk)
-
- The yield of AB is increased. (√1mk)
The forward reaction is accompanied by a decrease in volume(1/2mrk). Equilibrium shifts to the right following increase of the forward reaction (1/2mrk) - The yield of AB is increased’ (√1mk)
The forward reaction is exothermic.(1/2mrk) Decrease in temperature favours the forward reaction, equilibrium shifts to the right.(1/2mrk)
- The yield of AB is increased. (√1mk)
-
- Deliquescence (√1mk)
- Efflorescence (√1mk)
- Hygroscopy (√1mk)
-
- A – Nitrogen (IV) oxide/ NO2 (√1mk)
B – Oxgygen/ O2 (√1mk) - 2ZnNO3 (g) 2ZnO(s) + 4 NO2 (g) + O2(g) (√1mk)
- A – Nitrogen (IV) oxide/ NO2 (√1mk)
- Tin (√1mk)
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