CHEMISTRY PAPER 1 Marking Scheme - 2019 KCSE Prediction Answers Set 2

1. T₃N₂√1
2. Ionic bond √1
Ethanol forms hydrogen bond√1 while butane has no√1 hydrogen bond
1. X Calcium Carbide / CaC₂√½
  Y Copper (II) sulphate √½
2. b) CaC_2(s) + 2H₂ O_(l) → C₂ H_2(g) + Ca(OH)_2(aq)
Iron (II) sulphate change from green to yellow / brown √1 iron (iii) sulphate
Chlorine oxidizes Iron (ii) ions to Iron (iii) ions √1
Fe²⁺ + Cl
1. Cations Zn²⁺ √½
  Anion NO₃^- √½
2. 2HCl_(aq) + ZnO(s) → ZnCl_2(aq) + H₂O_(l) √1
SiO₂ form giant atomic structure √½
SO₂ simple molecular structure √½
Giant atomic structure requires strong heating to break √1
Heat the mixture and collect NH₄Cl√½ in a cold surface. Add water √½ to the remaining mixture stir then filter. Obtain filtrate√½ Na₂CO₃ and residue√½ as CaCO₃. Heat filtrate √½in a water bath to saturation and allow it to crystallize. √½
1. MnO₄^- = -1
  x + -2 (4) = -1 √1
  x-8 = -1
  x = 7 √1
2. MnO^-₄√1
  Oxidation number of manganese changes from +7 to +2 √1
1. Iron (iii) chloride / FeCl₃ √1
2. 2Fe_(s) + 3Cl_(g)→ 2FeCl_3(s) √1
1. Non metallic √1
  Ironic radius is higher than the atomic radius √1
2. Y<X<Z<W √1
1. Mg²⁺ + 2^e-→ Mg -2.36 √1
  Ag⁺ + e^- → Ag +0.80 √1
  Or
  Mg(s) / Mg²⁺(aq) // Ag⁺(aq) / Ag(s) √1
2. Ered - Eox
  0.80 v - -2.36 √1
  3.16v √1
It reacts with ammonia to form Ammonium Sulphate √1
1. N ≡ N = 944
  3(H-H)           3x436 = 1308
  Total energy required to break bonds
  944 + 1308
  = 2252 (endotherimic)   √1
  
  Bond formation
  2x(3x388) = -2328   √1
  ∆Hr = -2328 + 2252
  = -76kJmcl^- √1
2. Exothermic√½. The heat of reaction is negative √½
1. Propyl ethanoate
2. Alcohol - Prupanol
  Alkanic acid – Ethanoic acid
Q = It
= 2 x 4 x 60
= 480 Columbs √1
Cu²⁺ + 2e⁻ → Cu
Moles of copper deposited
=480 x 1
96500 x 2
=0.002487gm √1

Mass deposited = 0.002487 Mol x 63.5
= 0.1579grams
React excess copper √½ metal with concentrated nitric (v) acid to form Copper (II) nitrate√½ solution.
React the solution obtained above with a soluble carbonate√½
Filter to obtain copper carbonate as the residue. √½
Wash the residue with distilled water and dry it between filter papers. √½
1. MgO √½ and Mg₃N₂√½
2. 1. 2Mg_(s) + O_2(g) → 2MgO_(s) √1
  2. 3Mg_(s) + N_2(g) → Mg₃N_2(s)√1
1. Different crystalline forms of the same element in the same physical state √1
2. In graphite, the fourth electron is delocalized √1 (unbounded) while all the four electrons in diamond are used for bonding√ The delocalized electron is responsible for conductivity
Moles of MgSO₄ X H₂O in 500cm³.
0.011M x 500
1000
= 0.0055mol √1
Mole = ^{Mass in gramm}/_R.F.MRFM = ^1.23/_0.0055= 224 √1
MgSO4. XH2O = (24+32+64+18X) = 224 √½
= 120 +18X = 224
= 18X = 104
X = 6 √½
1. a - Alpha particle
  b - Gamma rays
  c - Beta particles
2. beta particles are lighter√½ than alpha particles hence more deflected√½
1. Hydrolysis of ethane
2. Fuel√½
  - Solvent√½
  - Beverage
1. Curve II √1
2. Increases the kinetic energy√½ of the reacting particles hence increasing the rate of successful collisions. √½
3. Surface area
  Catalyst
1. ∆H₂ Enthalpy of formation of Carbon (II) Oxide (∆H_f CO)
  ∆H₃ Enthalpy of combustion of CO
  (∆H_c CO)
2. ∆H₁ = ∆H₂ + ∆H₃= -110 + -283 √1
  = -393kJmol^-1 √1
Colourless droplets were formed at the cooler part of the test tube√½
A gas that turns a moist red litmus paper blue was produced√½
NH₄SO₄, FeSO₄. 6H₂O is a hydrated√1 salt and ammonium sulphate decomposes to form Ammonia gas √1
Concentration of KOH = ⁴/₅₆= 0.0714M√½
Moles of KOH used=
0.0714 x 25
1000
= 0.001786Mol√½
Mole ratio
2KOH_(aq) + H₂SO_4(aq) → K₂SO_4(aq) + 2H₂O_(l)2:1√½
Moles of H₂SO₄ Used =
0.001786
2
= 0.00089 Moles√½
Concentration of H₂SO₄ =
0.00089 x 1000√½
22
= 0.04√½
1. It does not form scum with hard water √1
2. it causes environmental pollution
  Since it is non-biodegradable
1. It is denser than air√½
  It does not burn neither does it support combustion √½
2. Refrigeration as dry ice
  manufacture of sodium carbonate in Solvay process
  Used in preservation of soft drinks
Ethanoic acid forms more√1 hydrogen bonds between molecules√1 than ethanol
1. Alcohol
  Tobbaco
  Bhang
  Miraa
  Cocaine
  Madrax
2. Hallucinations
  Addiction
  Health problems
  Family break ups