NON-MEATALS, B. Hydrogen and its Compounds

Total Questions: 28

11. Heavy water is that water — [41" B.P.S.C. (Pre) 1996]

(a) The temperature of which is kept constant at 4°C
(b) In which insoluble salts of Calcium and Potassium are present
(c) In which isotopes take the place of Hydrogen
(d) In which isotopes takes place of Oxygen

Correct Answer: (c) In which isotopes take the place of Hydrogen

Solution:

Heavy water ( $D₂ O$ ) is chemically similar to ordinary water ( $H₂ O$ ), but the hydrogen atoms are replaced by deuterium, which is an isotope of hydrogen with one proton and one neutron.

12. Heavy water — [U.P.P.C.S. (Mains) 2007]

(a) Contains more dissolved air
(b) Contains deuterium in place of Hydrogen
(c) Contains more dissolved minerals and salts
(d) Contains organic impurities

Correct Answer: (b) Contains deuterium in place of Hydrogen

Solution:Heavy water (

D₂ O

) is chemically similar to ordinary water (

H₂ O

), but the hydrogen atoms are replaced by deuterium, which is an isotope of hydrogen with one proton and one neutron.

13. Who among the following discovered heavy water? [I.A.S. (Pre) 2008]

(a) Heinrich Hertz
(b) H.C. Urey
(c) G. Mendel
(d) Joseph Priestly

Correct Answer: (b) H.C. Urey

Solution:Harold Clayton Urey, an American chemist, discovered deuterium and heavy water in 1931. He was awarded the Nobel Prize in Chemistry in 1934 for his discovery.

14. Heavy water has molecular weight: [U.P. Lower Sub. (Mains) 2015]

(a) 18
(b) 20
(c) 36
(d) 54

Correct Answer: (b) 20

Solution:Heavy water (D₂O), also called deuterium oxide, is composed of deuterium, a hydrogen isotope with double the mass of ordinary hydrogen. Therefore, heavy water has a molecular weight of about 20, compared to ordinary water's molecular weight of 18.

Molecular weight of ordinary water ( $H₂ O$ ): (2 $\times$ Atomic weight of H) + (1 $\times$ Atomic weight of O) = (2 $\times$ 1) + 16 = 18.

Molecular weight of heavy water ( $D O$ ): (2 $\times$ Atomic weight of D) + (1 $\times$ Atomic weight of O) = (2 $\times$ 2) + 16 = 4 + 16 = 20.

15. Consider the following statements: [I.A.S. (Pre) 2000]

Hard water is not suitable for:

Drinking
Washing clothes with soap
Use in boilers
Irrigating crops

Which of these statements are correct?

(a) 1 and 2
(b) 2 and 3
(c) 1, 2, and 4
(d) 1, 2, 3, and 4

Correct Answer: (d) 1, 2, 3, and 4

Solution:Hard water is described as hard due to the presence of highly dissolved minerals specifically sulphates and chlorides of calcium and magnesium. Hard water is salty and therefore not used for drinking. It is very difficult to wash clothes with hard water as it requires more soap and leaves a messy so that cannot be washed out easily. When hard water is boiled at home or in industries, it leaves deposits of calcium and magnesium salts. These deposits reduce the efficiency of boilers, kettles and pipes and can cause blockages and even burst of the boilers. If salt level increases in irrigation water it becomes harder for lawns and landscape plant to take up water even though the soil is moist. Hard water blocks Xylem tissues of the plants and thus not suitable for irrigation

16. Permanent hardness of water is due to — [Uttarakhand P.C.S. (Pre) 2006, 40th B.P.S.C. (Pre) 1995]

(a) Chlorides and sulphates of Calcium and Magnesium
(b) Calcium bicarbonate sulphates
(c) Magnesium bicarbonate
(d) Chlorides of Silver and Potassium

Correct Answer: (a) Chlorides and sulphates of Calcium and Magnesium

Solution:

Permanent hardness is caused by the presence of dissolved chlorides and sulfates of calcium ( $CaCl₂$ , $CaSO₄$ ) and magnesium ( $MgCl₂$ , $MgSO₄$ ). This type of hardness cannot be removed by boiling.

Temporary hardness, on the other hand, is caused by bicarbonates of calcium and magnesium, which can be removed by boiling.

17. The pH-value for water is — [Uttarakhand P.C.S. (Pre) 2005]

(a) Nearly zero
(b) Nearly 7
(c) 5 or less than 5
(d) 8.7 or more

Correct Answer: (b) Nearly 7

Solution:Ans. (b) Nearly 7

The pH value of pure water is 7. Pure water is neutral by nature. The solution with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline.

18. The pH value of water is — [66th B.P.S.C. (Pre) (Re. Exam) 2020, 65th B.P.S.C. (Pre) 2019]

(a) 4
(b) 7
(c) 12
(d) 18
(e) None of the above/More than one of the above

Correct Answer: (b) 7

Solution:The pH value of pure water is 7. Pure water is neutral by nature. The solution with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline.

19. Which is the purest form of water? [M.P.P.C.S. (Pre) 2000]

(a) Tap water
(b) Sea water
(c) Rainwater
(d) Distilled water

Correct Answer: (c) Rainwater

Solution:Among the given options rainwater is the purest form of water. The water on the earth is mixed with alkaline and acidic materials that make the water impure.

20. Water is a good solvent of ionic salts because — [I.A.S. (Pre) 1994]

(a) It has a high boiling point
(b) It has a high dipole moment
(c) It has a high specific heat
(d) It has no colour

Correct Answer: (b) It has a high dipole moment

Solution:Water is a good solvent due to its polarity (it is dipolar in nature) and high dipole moment which can easily dissolve polar compounds. Water dissolves ionic salts by hydrating their component ions. For example, water dissolves NaCl by hydrating and stabilizing the Na⁺ and Cl⁻ ions.

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