This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “P-Block Elements – Simple Oxides”.
1. What type of oxides is formed by metals?
a) Oxides with pH = 7
b) Oxides with pH > -log10[1 x 10-7]
c) Oxides with pH <= -log10[1 x 10-7]
d) Amphoteric oxides
Explanation: Metals usually form basic oxides. E.g. sodium, potassium, calcium. Meaning, the pH of the salts is greater than 7 on the pH scale. pH is calculated as the negative logarithm of concentration of hydronium ions. Metals form oxides because upon dissolution, they release oxide ions which in turn give hydroxide (basic) ions. However, a few metals form oxides which are both acidic and basic, called amphoteric oxides. E.g. zinc, lead.
2. What type of oxides is formed by non-metals?
a) Oxides with pH <=7
b) Amphoteric oxides
c) Oxides with pH > 7
d) Oxides which are acidic
Explanation: Non-metals form acidic oxides because upon dissolution in water they liberate free H+ ions. Oxides with pH <=7 also include neutral oxides and not acidic only. Oxides with pH > 7 are basic in nature. Amphoteric oxides behave both like acid and base.
3. Which of the following can classified as an amphoteric oxide?
a) Iron (III) oxide
b) Zinc oxide
c) Mercury (II) oxide
Explanation: Zinc oxide is the only amphoteric oxide out of these four. On dissolution in acid like HCl, it acts as a base and forms ZnCl2 salt. On dissolving in base like NaOH, it acts an acid to form sodium zincate, Na2ZnO2.
4. What is the starting substance fed into the electrolytic cell in Hall-Heroult process?
b) Sodium hydroxide
c) Aluminum hydroxide
Explanation: Hall-Heroult process is used to extract aluminum by using an electrolytic cell. Alumina means aluminum oxide. It is dissolved in cryolite, Na3AlF6, to increase electrical conductivity, reduce melting point and achieve greater yield of aluminum metal.
5. What is the primary constituent of sand?
a) Silicon tetroxide
Explanation: Sand is primarily composed of silicon dioxide, also called silica. Silicon tetroxide is not a compound but an oxo-anion of silicon. Silicon metal does not form native in nature and feldspar is a mineral ore consisting of several tectosilicate compounds.
6. Before subjecting Mg ribbons to flame, it is rubbed with sandpaper. Why?
a) To increase surface area for combustion
b) To increase roughness of surface
c) To remove oxide layer
d) To remove moisture
Explanation: In order to ensure effective burning of the magnesium ribbon, it is cleaned with sandpaper to remove dust particles along with the layer of magnesium oxide, which may prevent it from burning completely.
7. What product is formed when iron metal is dipped into concentrated nitric acid?
a) Iron (III) nitrate + NO2
b) Iron (II) nitrate + NO
c) Iron (III) oxide
d) Iron (III) nitrite
Explanation: Iron becomes passive when treated with concentrated nitric acid. The formation of a tough oxide layer prevents it from further reacting with the acid, hence inhibiting the reaction.
8. Which of the following processes involves heating a carbonate ore to form metal oxide?
c) Ore Reduction
Explanation: In general metallurgy, calcination is the process of heating a metal ore to convert it to its corresponding metal oxide. For e.g. zinc carbonate (calamine ore) is heated to form zinc oxide which is then reduced by electrolysis in the presence of sulfuric acid to obtain zinc metal.
9. Which of the following metals does not react with hot water to form an oxide?
Explanation: Iron is relatively unreactive with respect to other metals mentioned. Iron forms iron (III) oxide on heating vigorously. However, lithium, magnesium and calcium all form hydroxides and oxides on reaction with hot water.
10. What is formed when amphoteric oxides react with an alkali solution?
a) Salt only
b) No reaction
d) Salt and water
Explanation: Amphoteric oxides react with both acids and alkalis. On treatment with alkali solution, they behave as acids and undergo reactions analogous to neutralization, thus forming salt and water. For e.g. Al2O3 + NaOH → NaAlO2 + H2O.
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