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

Share via Whatsapp
  1.  
    1. Alkali metals
    2. Q and J – Q is more reactive than J; this is due to stronger metallic bond.
      M and P - P is more reactive them M, this is because P requires to gain a single electron  for it to react which M requires two. This indicates that it is more electronegative as compared to M.
    3. The atomic radius of K is smaller them that of L. This is because of increase in nuclear charge across the period.
    4. Group (IV) period 2.
    5. As we move down the group, the melting point and the boiling points reduce. This is due to the subsequent increase in the atomic radius down the group which reduces the electrostatic force.
    6. KP3
    7. Ionic bond
    8. Street lightening
      In Bulbs
    9.  H – 2 .8.8     M – 2 . 8
  2.  
    1.  
      1. CaCO3(g) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
      2. Drying agent / To dry carbon (iv) oxide
      3. Anhydrous calcium chloride
      4. C(s) + CO2(g) → 2CO(g)
      5. Reducing property
      6. Its poisonous
    2.  
      1. Graphite
      2. K – Covalent
        L – weak vanderwalls forces / intermolecular forces
      3. Forms white ppt which dissolves later to form a colourless solution
        Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
        CaCO3(s) + H2O(l) + CO2(g) →  Ca(HCO3)2(aq)
  3.  
    1. Cotton / silk / sisal / banana fibre    ( Award 1mk for any correct fibre)                                  
    2. Last longer
      Less easily attacked by acids and alkali  (Award any one correct property )                              
      Stronger
      Durable
    3.  
      1. Hydrolysis of ethene gas with conc sulphuric acid  (deny hydrolysis of alkenes)               
      2. Reagent - Hydrogen gas   √½
        Catalyst - Nickel     √½                                                                                         
      3. Sodium ethoxide √     (accept the formulae )                                                                 
      4. CH3COONa + NaOH → Na2CO3 + CH4
      5. It causes pollution since it is non biodegradable  √
      6. Ethylethanoate   √    (deny ester)   
        chemp2ans3cvi                            
      7. Ester / Alkyalkanoate √                                                             
      8. Step I Dehydration   √1/2                                                                                                        
        (IV) Oxidation   √1/2                                                                                         
      9. Used in manufacturing of margarine   √                   
  4.  
    1. Electrolytic cells uses electrical energy to decompose substances while electrochemical cells produces electrical energy by chemical reaction
    2.  
      1. Anode graphite
        Cathode Zinc can
      2. Ions more freely in paste    (deny electron)
      3.  Zn(s)  → Zn2+(aq) + 2e-
      4. It oxidizes hydrogen gas to water. Hydrogen bubbles lowers the efficiency of the cell.
    3.  
      1. Cathode
        2H+(aq) + 2e- → H2(g) √                      

        Anode
        4OH-(aq) →  4e- + H2O(l) + O2(g) √            
      2. In dilute NaCl. OH- and H+ ion are preferentially discharged. The ratio of Hydrogen to oxygen atoms in water molecules is 2:1 therefore the volume of hydrogen is larger than that of oxygen.
      3. Chlorine       √                                                  
        Chloride ions are more concentrated than OH- ions in brine   √                
      4. Concentration of electrolyte                            
        Nature of the electrodes used      (award any two correct factors)
        Position in electrochemical series
  5.  
    1.  
       Time  t-1
       8  0.125
       6  0.167
       5  0.200
       4  0.250
       3  0.330
       2.5  0.400
      Award 4 correct entries 1mark
      All correct award 2mks)                                                                                                                                                                                                     
    2. scale √
      Correct plotting√
      Straight line√
      P2ANS5B.jpg
    3. The rate of reaction is directly proportional to the amount of the catalyst used √
    4. The rate of production would be lower√ Granular MnO2 has a small surface area compared with powdered MnO2
    5. KClO3
      39 + 35.5 + 3(16)
      = 122.5g     √ ½                      (molar mass of KClO3 √½)                                                               
      1Mole              122.5g
      ?                      5g
      0.0408mole                       (moles of KClo3 √½ )                                           
      2KClO3  → 2KCl + 3O2     √½       
                                                  
      Mole ratio        2:3                  (mole ratio √½ )                                        
      0.0408

      Moles of      0.0408 x 3/2            (working √½ )                                                                                          
      Oxygen gas                             (moles of oxygen √½)                                          
      0.0618
      24 x 0.0618 = 1. 4694dm3        (answer √½)
       Total = 3mks                                      
  6.  
    1. 4CH(s) + 5O2(g) → 4CO2(g) + 2H2O(l)
    2. Hydrocarbon
    3. To condense the steam
    4.  Forms white ppt which dissolves later to form a colourless solution
      Ca(OH)(aq) + CO2(g)  → CaCO3(s) + H2O(l)
      CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq)
    5. Put liquid in a boiling tube, heat at boiling. The boiling should be at 1000c at sea level.
  7.  
    1. Copper pyrite
      Cuprite                   (any one)
      Chalcocite
    2. Substance X Copper (I) Oxide
      Gas G   Sulphur (IV) oxide   (accept correct formula)
    3. X is denser and immiscible with FeSiO3, so it is tapped off from the bottom of the vessel.
    4. 2Cu2O(l) + Cu2S(s) → 6Cu(s) + SO2(g)   (correct balanced equation √½) (state symbol √½)                                                                              
    5. O2 gas produced lead to acid rain
    6. Impure copper is used as the the anode in a solution of copper (II) sulphate where it  dissolves    (√½)                                        
      Cu(s) → Cu2+ + 2e- ( √½)                                        
      At the cathode pure copper in used where copper is deposited on the pure metal.(√½ )                                        
      Cu2+ + 2e→ Cu(s)   (√½)                                        
    7. Used as electrical cables
      Coins
      Alloy of copper & Zinc is used in medal     (any two correct uses)
Join our whatsapp group for latest updates

Download CHEMISTRY PAPER 2 Marking Scheme - 2019 KCSE Prediction Answers Set 2.


Tap Here to Download for 50/-




Why download?

  • ✔ To read offline at any time.
  • ✔ To Print at your convenience
  • ✔ Share Easily with Friends / Students


Get on WhatsApp Download as PDF
.
Subscribe now

access all the content at an affordable rate
or
Buy any individual paper or notes as a pdf via MPESA
and get it sent to you via WhatsApp

 

What does our community say about us?

Join our community on:

  • easyelimu app
  • Telegram
  • facebook page
  • twitter page
  • Pinterest