- Fractional distillation of liquid air is usually used to separate various gaseous mixtures in air. Explain how to;
- Remove carbon (IV) oxide. (1mk)
- Remove water. (1mk)
- Obtain nitrogen. (1mk)
- The diagrams below represent two iron nails with some parts covered tightly with zinc and tin respectively. What observations would be made at the exposed points R and Z if the wrapped nails are left in the open for several days? Explain.
- The Diagram below is set-up for the laboratory preparation of oxygen gas.
- Name solid R
- Write an equation for the reaction that takes place in the flask. (2mks)
- Give one commercial use of oxygen. (1mk)
- An element y has an electron arrangement of 2.8.5
- State the period and group which the element belongs. (2mks)
- Write the formula of the most stable ion formed when the element Y ionizes (1mk)
- Explain the difference between the atomic radius of element Y and its ionic radius (2mks)
- Lithium has two isotopes with mass numbers 6 and 7. If the R.A.M (relative atomic mass) of Lithium is 6.94, determine the percentage abundance of such isotope.
- Other than their location in the atom, name two other differences between an electron and a proton.(2mks)
- Write down the electronic configuration of the atoms with the following atomic numbers(2mks)
- 7
- 9
- 14
- 18
- An atom of an element has the electronic configuration 2.8.2
- State its atomic numbers
- To which group of the periodic table does it belong? Explain.
- Is the element a metal or a non-metal? Explain (1mk)
- If the atom has 14 neutrons in its nucleus state its mass number. (1mk)
- Rubidium (Rb) is a member of the alkali metals. Predict how the element reacts with: (3mks)
- Water
- Air
- Chlorine
- Briefly explain the following observations.
- Noble gases are generally unreactive. (1mk)
- Alkaline earth metals are generally less reactive than alkali metals in the same period. (2mks)
Marking Scheme
- Fractional distillation of liquid air is usually used to separate various gaseous mixtures in air. Explain how to;
- Remove carbon (IV) oxide. (1mk)
- Passing air through concentrated sodium hydroxide or potassium hydroxide solution.
- Remove water. (1mk)
- Cool to −25°C to remove water.
- Obtain nitrogen. (1mk)
- Cool to −200°C and carry out fractional distillation to obtain nitrogen gas.
- Remove carbon (IV) oxide. (1mk)
- The diagrams below represent two iron nails with some parts covered tightly with zinc and tin respectively. What observations would be made at the exposed points R and Z if the wrapped nails are left in the open for several days? Explain.
- At R: No rusting occurred √½ . Zinc is more reactive than iron hence it reacts with moist air instead of iron√1.
- At Z: Rusting occurred √ ½. Tin is less reactive than iron hence iron reacts with moist air to form rust.√1
- The Diagram below is set-up for the laboratory preparation of oxygen gas.
- Name solid R
- Manganese (IV) oxide. √1
- Write an equation for the reaction that takes place in the flask. (2mks)
Manganese (IV) Oxide
2H2O2(l) O2(g) + 2H2O(l) + 2H2O(l) - Give one commercial use of oxygen. (1mk)
- Welding
- Steel making
- Breathing aid/ hospitals
Accept any.
- Name solid R
- An element y has an electron arrangement of 2.8.5
- State the period and group which the element belongs. (2mks)
- Group V
- Period 3
- Write the formula of the most stable ion formed when the element Y ionizes (1mk)
Y3− - Explain the difference between the atomic radius of element Y and its ionic radius. (2mks)
- The ionic radius is larger because of the electron-electron repulsion between the existing electrons and the added electron.
- State the period and group which the element belongs. (2mks)
- Lithium has two isotopes with mass numbers 6 and 7. If the R.A.M (relative atomic mass) of Lithium is 6.94, determine the percentage abundance of such isotope.
6x + 7y = 694
(x + y = 100)6
6x + 7y = 694 _
6x + 6y = 600
y = 94%
x = 6% - Other than their location in the atom, name two other differences between an electron and a proton.(2mks)
- Electron – Negative charge
- Proton – Positive charge
- Write down the electronic configuration of the atoms with the following atoms with the following atomic numbers(2mks)
- 7 - 2.5
- 9 - 2.7
- 14 - 2.8.4
- 18 - 2.8.8
- An atom of an element has the electronic configuration 2.8.2
- State its atomic numbers
- 12
- To which group of the periodic table does it belong? Explain.
- Group 2. It has two electrons in its outermost energy level.
- Is the element a metal or a non-metal? Explain (1mk)
- A metal. It has less than 4 electrons in its outermost energy level.
- If the atom has 14 neutrons in its nucleus state its mass number. (1mk)
- 26
- State its atomic numbers
- Rubidium (Rb) is a member of the alkali metals. Predict how the element reacts with: (3mks)
- Water - vigorously
- Air - vigorously
- Chlorine - less vigorously
- Briefly explain the following observations.
- Noble gases are generally unreactive. (1mk)
- Noble gases are chemically stable because their outer energy level are full.
- Alkaline earth metals are generally less reactive than alkali metals in the same period. (2mks)
- Alkali metals react by losing the one electron from their outermost energy level.
- Noble gases are generally unreactive. (1mk)
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