250+ TOP MCQs on Mineral Acids – Nitric Acid and Hydrochloric Acid and Answers

Corrosion Engineering Question Paper on “Mineral Acids – Nitric Acid and Hydrochloric Acid”.

1. Which of the following is/are the class1 corrosion resistance materials in nitric acid?
a) High-silicon cast irons
b) Stainless steels (type 430)
c) Titanium
d) High-silicon cast iron, stainless steels, and titanium
Answer: d
Clarification: Class1 materials are the materials that are used for a particular environment and it is generally recommended for a variety of conditions of temperature and concentration. Class1 materials for nitric acid includes high-silicon cast irons, stainless steels, and titanium.

2. Which of the following steels will have less corrosion rate in boiling 65% nitric acid?
a) 4.5% chromium steel
b) 8% chromium and 8% nickel steel
c) 18% chromium and 8% nickel stainless steel
d) 18% chromium stainless steel
Answer: c
Clarification: The corrosion resistance of steel in nitric acid increases as the alloying elements such as chromium and nickel increases. The minimum percentage of chromium required for adequate corrosion resistance is 15%.

3. Duriron exhibits excellent corrosion resistance in concentrations over 45% at temperatures including boiling.
a) True
b) False
Answer: a
Clarification: Duriron is high-silicon cast iron with 14.5% silicon exhibits excellent corrosion resistance in concentrations over 45% at temperatures including boiling. It is a class1 material in the usage of nitric acid.

4. The corrosion resistance of Durichlor to nitric acid is better than that of Duriron.
a) True
b) False
Answer: b
Clarification: Durichlor is high-silicon cast iron with 14.5% silicon and 3% molybdenum. It is not better corrosion resistant to nitric acid than that of Duriron. Because molybdenum doesn’t increase the corrosion resistance to nitric acid.

5. What are the principal applications of Duriron?
a) Cast forms of pumps, valves, heat exchangers for chemical plant
b) In manufacturing and handling of nitric acid
c) In the ammonia oxidation process
d) Cast forms of pumps, valves, heat exchangers for chemical plant, in manufacturing and handling of nitric acid and ammonia oxidation process
Answer: d
Clarification: Principal applications of Duriron are:
i. Cast forms of pumps, valves, heat exchangers for chemical plants
ii. In manufacturing and handling of nitric acid
iii. In the ammonia oxidation process.

6. Which of the following statements is/are true about titanium?
a) It has excellent corrosion resistance to fuming nitric acid
b) It is used as an oxidizer in fuel systems for rockets
c) It has excellent corrosion resistance to fuming nitric acid and it is used as an oxidizer in fuel systems for rockets
d) It doesn’t exhibit pyrophoric tendencies in red fuming nitric acid
Answer: c
Clarification: Titanium has excellent corrosion resistance to fuming nitric acid and it is used as an oxidizer in fuel systems for rockets. Whereas it exhibits pyrophoric tendencies in red fuming nitric acid if the water content of the acid is below 1.5% and the nitrogen dioxide content is above 2.5%.

7. Which of the following is/are the class2 corrosion-resistant materials in nitric acid?
a) Aluminum and Stainless steels
b) Aluminum, Hastelloy, and Inconel
c) Hastelloy and Inconel
d) Hastelloy and Titanium
Answer: b
Clarification: Class2 corrosive resistance materials of nitric acid are the materials that are used in only certain specific conditions of temperature and concentration because of limited corrosion resistance and cost. This includes Aluminum, Hastelloy, and Inconel.

8. Which of the following polymer has excellent corrosion resistance to nitric acid?
a) Teflon
b) Polyvinyl chloride
c) Polystyrene
d) Polyethylene
Answer: a
Clarification: Teflon shows excellent corrosion resistance to nitric acid. Glass filled Teflon is widely used for rotating rings in mechanical seals for nitric acid pumps.

9. Which of the following is/are the class3 corrosion-resistant materials in nitric acid?
a) Copper and its alloys
b) Nickel and its alloys
c) Low-alloy steels
d) Low-alloy steels, copper, nickels and their alloys
Answer: d
Clarification: Class3 materials are recommended for use in a particular environment because of its less corrosion resistance. This includes copper and its alloys, nickel and its alloys and low-alloy steels.

10. Which of the following metal is used for hydrochloric acid to avoid contamination?
a) Titanium
b) Tantalum
c) Molybdenum
d) Cupronickels
Answer: b
Clarification: Hydrochloric acid is the most difficult of the common acids to handle regarding corrosion. Tantalum is an expensive metal but it is often used to avoid contamination.

11. Which of the following is/are the class1 corrosion resistance materials in hydrochloric acid?
a) Chlorimet 2 and Chlorimet 3
b) Hastelloy B and C
c) Zirconium and molybdenum
d) Chlorimet 2 and 3, Hastelloy B and C, Zirconium, Molybdenum and Tantalum
Answer: d
Clarification: Class1 materials are the materials that are used for a particular environment and it is generally recommended for a variety of conditions of temperature and concentration. Class1 materials for hydrochloric acid include Chlorimet 2 and 3, Hastelloy B and C, Zirconium, Molybdenum, and Tantalum.

12. Duriron has better corrosion resistance than Durichlor in hydrochloric acid.
a) False
b) True
Answer: a
Clarification: Durichlor is high-silicon cast iron with 14.5% silicon and 3% molybdenum is more corrosion resistant than Duriron in hydrochloric acid.

13. Which of the following is/are the class2 corrosion resistance materials in hydrochloric acid?
a) Bronzes and Cupronickels
b) Hastelloy D and Duriron
c) Bronzes, Stainless steels, Bronzes, Cupronickels, Hastelloy D and Duriron
d) Stainless steels and Duriron
Answer: c
Clarification: Class2 corrosive resistance materials of nitric acid are the materials that are used in only certain specific conditions of temperature and concentration because of limited corrosion resistance and cost. This includes bronzes, stainless steels, bronzes, cupronickels, Hastelloy D, and Duriron.

14. Which of the following metals will have a high influence on aeration and oxidizing agents in hydrochloric acid?
a) Copper and its alloys
b) Nickel and its alloys
c) Nickel-molybdenum alloys, copper, nickel and their alloys
d) Nickel-molybdenum alloys
Answer: c
Clarification: Nickel-molybdenum alloys, copper, nickel, and their alloys will have a high influence on aeration and oxidizing agents in hydrochloric acid. These materials show excellent corrosion resistance in reducing conditions but are rapidly attacked in oxidizing conditions.

15. Which of the following impurity in hydrochloric acid results in pitting corrosion?
a) Ferrous chloride
b) Ferric chloride
c) Potassium chloride
d) Sodium chloride
Answer: b
Clarification: Ferric chloride in small amounts is more destructive than oxygen in hydrochloric acid. It initiates pits and results in pitting corrosion on various metals in the hydrochloric environment.