Chemistry Questions and Answers - Form 2 End Term 1 Exams 2021

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Answer all the questions in the spaces provided.

The set up below can be used to prepare oxygen gas. Study it and answer the questions that follow.
1. Identify substance X. (1mk)
2. What property of oxygen makes it possible for it to be collected as shown in the above set up? (1mk)
3. State two uses of oxygen. (2mks)
Describe an experimental procedure that can be used to extract oil from nut seeds.(3mks)
In terms of structure and bonding, explain the following observations:
1. The melting point of water H₂O is higher than that of H₂S. (2mks)
2. Melting point of chlorine is lower than that of sulphur. (2mks)
1. Define the term salt. (1mk)
2. Apart from direct synthesis name two other methods of salt preparation. (2mks)
3. The diagram below illustrates a method of preparing salts by direct synthesis.
4. This method can be used to prepare either aluminum chloride or iron (III) chloride. Explain. (1mk)
5. What is the purpose of anhydrous calcium chloride? (1mk)
Define the following terms. (3mks)
1. Normal salt
2. Efflorescent salts
3. Deliquescent salts
1. What is meant by an allotrope? (1mk)
2. Give two allotropes of carbon. (2mks)
The grid below is part of the periodic table. Use it answer the questions that follow. (The letters are not the actual symbols of the elements).
1. Which is the most reactive non-metallic element shown in the table? Explain.
  (2 mks)
2. 1. Write the formula of the compound formed when element A reacts with element B. (1 mk)
  2. Name the bond type in the compound formed in b (i) above. (1 mk)
3. What is the name given to the group of elements where C, G and H belong?
  (1 mk)
4. The melting points of elements F and G are 1410 0C and -101 0C respectively. In terms of structure and bonding, explain why there is a large difference in the melting points of F and G. (2 marks)
5. D forms two oxides. Write the formula of each of two oxides. (1 mark)
6. J is an element that belongs to the 3rd period of the periodic table and is a member of the alkaline earth elements. Show the position of J in the grid.
  (1 mark)
1. Define the term isotope. (1mk)
2. The table below gives the number of electrons, protons and neutrons in substances X, Y and Z. Study it and answers the questions that follow.
  
  Substance Electrons Protons Neutrons
  
  X 10 10 10
  
  Y 10 8 10
  
  Z 8 8 8
  1. Which letter represents an ion? (1 mark)
  2. Which of the substances are isotopes? Give a reason. (2 marks
  3. Show the electron arrangement of Y (1mk)
1. What is an impurity? (1mk)
2. The curve below represents the variation of temperature with time when pure and Impure samples of a solid were heated separately.
  
  Which curve sows the variation in temperature for the pure solid? Explain.(2mks)
The diagram below shows the physical state of matter. Study it and answer the questions that follow.
1. Identify the processes R, V, W and U. (4mks)
2. Name the process S and T. (1mk)
3. Name two substances which can undergo the process represented by S and T. (2mks)
Define the term ionization energy. (1mk)
The table below gives the energy required to remove the outermost electron for some group I elements.

Element I II III IV

Ionization Energy kJmol^-1 494 418 519 376

Arrange the elements in order of their reactivity starting with the most reactive. (2mks)

The table below shows some properties of substances D, F and E. Study it and answer the questions that follow.

Substance	M.P (°C)	Solubility in water	Electrical solid state	Conductivity molten stated
E	−39	Insoluble	Good	Good
D	1610	Insoluble	Poor	Poor
F	801	Soluble	Poor	Good

Select substance:

With a giant molecular structure. (1mk)
That has ionic bonding. (1mk)
That is a metal. (1mk)

An element Y has the electronic configuration 2.8.5
1. Which period and group of the periodic table does the element belong? (2mks)
  1. Group
  2. Period
2. Write electron arrangement of the ion of Y. (1mk)
3. Explain the difference between the atomic radius of element Y and its ionic radius. (2mks)
The table below shows the PH values of solutions I, II, III and IV.

Solution I II III IV

pH 2 7 11 14

Which solution is likely to be that of: (3mks)
1. Calcium hydroxide
2. Sodium chloride
3. Potassium hydroxide
1. What is the chemical name for rust? (1mk)
2. State three conditions necessary for rusting. (3mks)
3. State three methods of preventing rusting. (3mks)
Write an equation to show the effect of heat on: (3mks)
1. NaNO₃
2. Zn (NO₃)₂
3. AgNO₃

Marking Scheme

The set up below can be used to prepare oxygen gas. Study it and answer the questions that follow.
1. Identify substance X. (1mk)
  - Water
2. What property of oxygen makes it possible for it to be collected as shown in the above set up? (1mk)
  - Oxygen is slightly soluble in water
3. State two uses of oxygen. (2mks)
  - Used by mountain climbers and deep sea divers
  - Used in welding and cutting of metals
  - Used to burn rocket fuel
  - Used in hospitals by patients with breathing problems
Describe an experimental procedure that can be used to extract oil from nut seeds.(3mks)
- Crush grind using a pestle and mortar, add suitable solvent of propanone ethanol alcohol and stir to dissolve oil. Filter the mixture to obtain a solution of the oil. Leave the solution in the sun for propanone to evaporate leaving the oil.
In terms of structure and bonding, explain the following observations:
1. The melting point of water H₂O is higher than that of H₂S. (2mks)
  - H₂O has Hydrogen bond which is stronger than weak van der waal forces in H₂S
2. Melting point of chlorine is lower than that of sulphur. (2mks)
  - The molecular forces in Sulphur are stronger than that in Cl₂, Therefore Sulphur requires more energy to break its bonds than Cl₂
1. Define the term salt. (1mk)
  - An ionic substance formed when a cation derived from a base combines with anion derived from an acid.
2. Apart from direct synthesis name two other methods of salt preparation. (2mks)
  - Action of acid on insoluble bases.
  - Action of acid on soluble bases.
  - Precipitation
  - Action of acid on carbonates
3. The diagram below illustrates a method of preparing salts by direct synthesis.
4. This method can be used to prepare either aluminum chloride or iron (III) chloride. Explain. (1mk)
  - They do sublime
5. What is the purpose of anhydrous calcium chloride? (1mk)
  - To prevent entry of moisture
  - Iron (III) Chloride is hygroscopic
Define the following terms. (3mks)
1. Normal salt
  - A salt that does not contain any replaceable hydrogen ions.
2. Efflorescent salts
  - Salts that looses water of crystalization to the atmosphere without necessarily heating.
3. Deliquescent salts
  - Salts that absorb moisture from the atmosphere but do not dissolve to form a solution.
1. What is meant by an allotrope? (1mk)
  - Different forms of substances in the same physical state.
2. Give two allotropes of carbon. (2mks)
  - Graphite
  - Diamond
The grid below is part of the periodic table. Use it answer the questions that follow. (The letters are not the actual symbols of the elements).
1. Which is the most reactive non-metallic element shown in the table? Explain.
  (2 mks)
  - C- has the highest afinity for an electron.
2. 1. Write the formula of the compound formed when element A reacts with element B. (1 mk)
    - AB₂ or AB
  2. Name the bond type in the compound formed in b (i) above. (1 mk)
    - Covalent Bond.
3. What is the name given to the group of elements where C, G and H belong?
  (1 mk)
  - Halogens
4. The melting points of elements F and G are 1410 0C and -101 0C respectively. In terms of structure and bonding, explain why there is a large difference in the melting points of F and G. (2 marks)
  - Element F has a giant atomic structure which requires a lot of energy to break its bond.
  - Element C has very weak van der waals forces which requires very little energy to break its bond.
5. D forms two oxides. Write the formula of each of two oxides. (1 mark)
  - D₂O and D₂O₂
6. J is an element that belongs to the 3rd period of the periodic table and is a member of the alkaline earth elements. Show the position of J in the grid.
  (1 mark)
1. Define the term isotope. (1mk)
  - Element with the same atomic number but different mass number.
2. The table below gives the number of electrons, protons and neutrons in substances X, Y and Z. Study it and answers the questions that follow.
  
  Substance Electrons Protons Neutrons
  
  X 10 2:8:2 10 10
  
  Y 10 2:8:2 8 10
  
  Z 8 2:6 8 8
  1. Which letter represents an ion? (1 mark)
    - Y
  2. Which of the substances are isotopes? Give a reason. (2 marks)
    - Y and Z - Has the same number of protons but different number of Neutrons
  3. Show the electron arrangement of Y (1mk)
    - 2:8:2
1. What is an impurity? (1mk)
  - A substance that rises the boiling point of a substance and lowers the melting point of a substance.
2. The curve below represents the variation of temperature with time when pure and Impure samples of a solid were heated separately.
  
  Which curve sows the variation in temperature for the pure solid? Explain.(2mks)
  - II.
    Because pure substances have sharp MP and BP as shown by the flat regions of curve II. (accept systematic)
The diagram below shows the physical state of matter. Study it and answer the questions that follow.
1. Identify the processes R, V, W and U. (4mks)
  - R - Melting
  - V - Evaporation
  - W - Condensation
  - U - Freezing
2. Name the process S and T. (1mk)
  - S - Sublimation
  - T - Deposition
3. Name two substances which can undergo the process represented by S and T. (2mks)
  1. Iron(III)Chloride
  2. Benzoic acid
  3. Iodine
  4. Aluminium Chloride
Define the term ionization energy. (1mk)
- Energy required to remove an electron from the outermost energy level in gaseous state.
The table below gives the energy required to remove the outermost electron for some group I elements.
Arrange the elements in order of their reactivity starting with the most reactive. (2mks)
IV, II, I, III
→
The table below shows some properties of substances D, E and F. Study it and answer the questions that follow.
Select substance
1. With a giant molecular structure. (1mk)
  - D
2. That has ionic bonding. (1mk)
  - F
3. That is a metal. (1mk)
  - E
An element Y has the electronic configuration 2.8.5
1. Which period and group of the periodic table does the element belong? (2mks)
  1. Group
    - V
  2. Period
    - III
2. Write electron arrangement of the ion of Y. (1mk)
  - 2:8:8
3. Explain the difference between the atomic radius of element Y and its ionic radius. (2mks)
  - Ionic radius is bigger than atomic radius. When an element gains electrons the nuclear force reduces.
The table below shows the PH values of solutions I, II, III and IV.
Which solution is likely to be that of: (3mks)
1. Calcium hydroxide
  - III
2. Sodium chloride
  - II
3. Potassium hydroxide
  - IV
1. What is the chemical name for rust? (1mk)
  - Hydrated Iron (III) Oxide
2. State three conditions necessary for rusting. (3mks)
  - Water/moisture
  - Oxygen
  - Iron
3. State three methods of preventing rusting. (3mks)
  - Oiling
  - Galvanizing
  - Electroplating
Write an equation to show the effect of heat on: (3mks)
1. 2NaNO_3(s)→ 2NaNO_(s) + O_2(g)
2. 2Zn (NO₃)_2(s) → 2ZnO(s) + 4NO_2(s)+O_2(g)
3. 2AgNO_3(s) → 2Ag_(s) + 2NO_2(g) + O_2(g)