his set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “P-Block Elements – Oxoacids of Sulphur”.
1. What class of compounds do the oxygen based compounds of sulfur represent?
c) Neutral oxides
Explanation: The oxygen compounds of sulfur represent the class of ‘oxoacids’ of sulfur. Generally, a non-metallic oxide is usually acidic in nature (given that exceptions like CO, N2O, NO). Examples include sulfurous acid (H2SO3), sulfuric acid (H2SO4) and many more.
2. Which of the following is the most popular oxoacid of sulfur?
a) Sulfurous acid
b) Sulfuric acid
c) Peroxodisulfuric acid
d) Pyrosulfuric acid
Explanation: Sulfuric acid is commonly used in industrial chemical manufacturing as a reactant or a laboratory reagent. The formula is H2SO4. It is one of the most powerful oxidizing and dehydrating agents in the chemical field and finds a number of application, such as production of fertilizers and dyes and many more.
3. Which of the following is produced third in the contact process?
a) Sulfur dioxide
b) Sulfur trioxide
c) Pyrosulfuric acid
d) Sulfuric acid
Explanation: In the first step, sulfur is converted to sulfur dioxide. Second step involves reacting it with more oxygen to form sulfur trioxide. Instead of reacting sulfur trioxide with water to form sulfuric acid directly, an alternative, safer method is utilized to dissolve sulfur trioxide gas in sulfuric acid to form oleum, also known as pyrosulfuric acid.
4. Why is sulfur trioxide not dissolved in water and but treated with existing sulfuric acid?
a) It is not economically feasible
b) Manufacturing plants cannot withstand the great pressure of dissolving sulfur trioxide in water
c) Sulfur trioxide just hydrates on dissolving with no chemical bonds form
d) The heat of dissolution is very high and potentially dangerous
Explanation: The reaction between sulfur trioxide and water is highly exothermic and releases great amount of energy that no plant, currently, has the ability to withstand. Due to potential risks of explosion and fire hazard, sulfur trioxide is not dissolved in water but treated with sulfuric acid to produce oleum. This can be diluted to desired concentrations.
5. What is the primary product when carbon is treated with concentrated sulfuric acid?
a) Carbon dioxide
b) Carbon monoxide
c) Carbon sulfate
d) Carbon sulfide
Explanation: Since sulfuric acid is a very strong oxidant, it oxidizes carbon to carbon dioxide. With excess of oxygen available from sulfuric acid and water, carbon monoxide is rarely formed. Carbon sulfate does not exist and carbon sulfide formed as a reaction between carbon and sulfur.
6. What is the acidity of peroxodisulfuric acid?
d) Does not exist
Explanation: Acids do not bear acidity. The number of hydrogen ions released by an acid is referred to as its basicity. The formula of peroxodisulfuric acid is H2S2O8 and can release 2 H+ ions, hence the acidity is 2.
7. What is the basicity of oleum?
Explanation: Basicity of acids refer to the number of H+ ions that can be released upon dissolution. In the case of oleum, which is also known as pyro sulfuric acid, the chemical formula being H2S2O7, the basicity is 2.
8. In the contact process, SO2 is passed twice through the catalytic converted. Why?
a) To produce less while converting to SO3
b) Since the energy and power consumed is less
c) To increase the yield
d) To avoid choking hazards
Explanation: Sulfur dioxide is passed twice to increase the yield and conversion to form more sulfur trioxide. In the first pass, only 63-65% of sulfur dioxide is converted to sulfur trioxide. When passed for the second time, the conversion increases to 80% hence increasing the yield of sulfur trioxide. This can be repeated to achieve a maximum 99% conversion.
9. Which of the following conditions is the most suitable for manufacture of sulfuric acid in contact process?
a) High temperature and high pressure
b) Low temperature and high pressure
c) High pressure and low temperature
d) Low pressure and low temperature
Explanation: Since the forward reaction is exothermic, lower temperatures will favor higher yield. This is in accordance with the Le Chatelier’s principle that an equilibrium tends to attain its original form when external conditions are changed. Since the reactant is in gas phase, increasing pressure increases yield.
10. In the 17th century, Johann Glauber first prepared sulfuric acid by burning sulfur with potassium nitrate with steam. A famous salt was then called to be Glauber’s salt. Which of the following is it?
a) Potassium nitrate
b) Potassium sulfate
c) Sodium sulfate
d) Potassium hydroxide
Explanation: Glauber salt is the famous name for the deca-hydrate sulfate salt of sodium. Its chemical formula is Na2SO4.10H2O. It is also known as mirabilite. It is widely used as laxatives in several medications and helps removing excess doses of drugs from human body, such as paracetamol.
11. Which oxoacid of sulfur is commonly used for disinfecting swimming pools as well as delignification of wood?
a) Sulfuric acid
b) Peroxydisulfuric acid
c) Sulfoxylic acid
d) Peroxymonosulfuric acid
Explanation: The chemical formula of peroxymonosulfuric acid is H2SO5. Popularly known as Caro’s acid, it is widely known for its disinfecting properties. Due to its strong oxidizing property, it is used as the last option to remove any traces of organic compounds present as impurities.
12. Which of the following is also referred to as ‘Marshall’s acid’?
Explanation: Marshall’s acid is the common name for peroxydisulfuric acid. It is prepared by the reaction between chlorosulfuric acid and hydrogen peroxide. Another method includes the electrolysis of concentrated sulfuric acid (60% – 70%) with platinum electrodes at high current density and voltage.
13. What is the pH of 1mM concentrated sulfuric acid?
Explanation: pH refers to the power of hydrogen ions in the acid solution. It is calculated as the negative logarithm of the concentration of hydrogen ions. In case of 1mM of conc. sulfuric acid it is found that the concentration of hydronium ions is 10-2.75mol dm-3.
14. Which of the following oxoacid sulfur is known not to bear any acid salt?
a) Sulfuric acid
b) Thiosulfuric acid
c) Sulfonic acid
d) Dithionic acid
Explanation: Dithionic acid is formulated as H2S2O6 and is known to possess no acid salts i.e. salt formed due to the loss of one hydrogen ion. The diprotic salts of dithionic acid is known as dithionates which are mild oxidizing and reducing agents as well.
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