Chemistry Questions and Answers - Form 2 Mid-term Exams Term 1 2022

QUESTIONS

Instructions:
Answer all the questions in the spaces provided

1. An element X exists in two isotopic forms i.e ¹⁰⁷₄₇X and ⁿ₄₇X, If their relative abundance are in ratio of 3:1 respectively, calculate the atomic mass of the other isotope ⁿ₄₇X given the relative atomic mass of X is 107.5. (3mks)
2. Define the following terms. (3mks)
   1. Atomic number
   2. Mass number
   3. Ion
3. Explain these chemical expressions that elements before reaction are electrically neutral. (2mk)
4. The table below shows the atomic numbers of some elements represented by letters which are not their chemical symbols, Study it and answer questions that follow.
   

   Element	J	K	L	M	N	P	Q
   Atomic numbers	11	17	15	14	12	20	19

   1. Write down the electronic configuration of: (2mks)
      1. M
      2. P²⁺
   2.                  
      1. Write the formulae of the compound formed when K and M reacts (1mk)
      2. What type of bond is formed when K and M reacts. (1mk)
   3. How would reactivity of N and P with chlorine compare. Explain. (2mks)
   4. Select the most reactive metal and non-metal from the above list and give reason for your answer. (4mks)
      1. Metal
         Reason
      2. Non-metal
         Reason
   5. Place the elements in their immediate groups and periods.
      

      Element	Group	Period
      J
      L
      Q

5.                
   1. Complete and balance the following chemical equations: (4mks)
      Zn(s) + HCl(aq) →
      Na₂CO₃ + H₂SO₄ →
      Ca(OH)₂ + HNO₃ →
      C₂H₆ + O₂ →
   2. Explain the following observations:
      1. Nitric acid is not used in preparation of Hydrogen gas by reacting metals and nitric acid. (2mks)
      2. Copper as metals does not react with dilute sulphuric acid. (2mks)
6. Using (.) and (x) notations show the bonding in MgCl₂. (3mks)
7. Suggest the type of bonds which is most likely to exist between the following compounds. (2mks)
   1. NaCl
   2. AlCl
   3. NH⁺₄ ion
   4. Cl₂(g)

MARKING SCHEME

Instructions:
Answer all the questions in the spaces provided

1. An element X exists in two isotopic forms i.e ¹⁰⁷₄₇X and ⁿ₄₇X, If their relative abundance are in ratio of 3:1 respectively, calculate the atomic mass of the other isotope ⁿ₄₇X given the relative atomic mass of X is 107.5. (3mks)
   R.A.M = isotopy × abundance
   107.5  = (3/4 × 107) + 1/4 × n
   107.5 = 80.25 + 0.25n
   107.5 - 80.25 = 0.25n
   27.25 = 0.25n
   0.25     0.25
   109 = n
   n = 109 g/mol
2. Define the following terms. (3mks)
   1. Atomic number -  no of protons in an element
   2. Mass number -  sum of protons and neurons in an element
   3. Ion -  charged particle
3. Explain these chemical expressions that elements before reaction are electrically neutral. (2mk)
   The elements have same number/magnitude of protons and electrons which negatively neutralize their effect
4. The table below shows the atomic numbers of some elements represented by letters which are not their chemical symbols, Study it and answer questions that follow.
   

   Element	J	K	L	M	N	P	Q
   Atomic numbers	11	17	15	14	12	20	19

   1. Write down the electronic configuration of: (2mks)
      1. M - 2.84
      2. P²⁺ - 2.88
   2.                  
      1. Write the formulae of the compound formed when K and M reacts (1mk)
         K^- + M⁴⁺ → MK₄
      2. What type of bond is formed when K and M reacts. (1mk)
   3. How would reactivity of N and P with chlorine compare. Explain. (2mks)
   4. Select the most reactive metal and non-metal from the above list and give reason for your answer. (4mks)
      1. Metal O
         Reason
      2. Non-metal K -  halogens are most reactive
         Reason  they have the highest electron affinity
         for halogens affinity decreases down the group
   5. Place the elements in their immediate groups and periods.
      

      Element	Group	Period
      J	I	3
      L	V	3
      Q	I	4

5.                
   1. Complete and balance the following chemical equations: (4mks)
      Zn(s) + HCl(aq) → ZnCl₂ (aq) + H₂(s)
      Na₂CO₃ + H₂SO₄ → NaSo₄(aq) + CO₂ + H₂O(l)
      Ca(OH)₂ + HNO₃ → Ca(No₃)₂ + 2H₂O(l)
      C₂H₆ + O₂ → 4CO₂(s) + 6H₂O
   2. Explain the following observations:
      1. Nitric acid is not used in preparation of Hydrogen gas by reacting metals and nitric acid. (2mks)
         After reaction the hydrogen obtained is oxidised to water since nitric acid is a strong oxidising dilute agent
      2. Copper as metals does not react with dilute sulphuric acid. (2mks)
         Copper is unfer in reacting series than Hydrogen hence cant displace its form 
6. Using (.) and (x) notations show the bonding in MgCl₂. (3mks)
   
7. Suggest the type of bonds which is most likely to exist between the following compounds. (2mks)
   1. NaCl - ionic bond
   2. AlCl₃ - covalent bond
   3. NH⁺₄ ion - co-ordinate bond
   4. Cl₂(g) -  covalent bond