Hydrogen and its Compounds Important Questions And Answers

 Hydrogen and its Compounds Important Questions And Answers

Hydrogen and its Compounds is the most important and interesting chapter of Chemistry. So the practice set of Hydrogen and its Compounds with Important Questions And Answers helps students of class 11 and also for students studying for various competitive exams. Students are advised to practice and understand all the questions accordingly.

1.Which is used as hydrogen generators:

a) NaH

b) Hi

c) S₆H₃

d) None of these

ANS:

NaH + H₂O → NaOH + H₂ ↑

2.Hydrogen burns in air with a:

a) Light bluish flame

b) Yellow flame

c) Green flame

d) None of these

3.Which is distilled first.

a) Liquid CO₂

b) Liquid N₂

c) Liquid O₂

d) Liquid H₂

ANS

Boiling point of liquid hydrogen is lowest of given substances so it is distilled first.

4.On reaction with Mg, very dilute nitric acid produces.

a) NH₃

b) Nitrous oxide

c) Nitric oxide

d) Hydrogen

_ANS:

Mg + 2HNO₃ → Mg(NO₃)₂ + H₂ ↑

5.Which of the following reaction produces hydrogen

a) Mg + H₂O

b) BaO₂ + HCl

c) H₂S₄O₈ + H₂O

d) Na₂O₂+2HCl

ANS

Mg + 2H₂O → Mg(OH)₂ + H₂ ↑

6.The nuclei of tritium (H₃) atom would contain neutrons

a) 1

b) 2

c) 3

d) 4

_ANS:

Number of neutrons =  Mass number – Atomic number

= 3 – 1 = 2

7. Which isotope of hydrogen is used as a trace in organic reactions?

ANS

Hydrogen has three isotopes, H, D and T. Due to differences in masses, the rate constants of three isotopes with the same substance are different. In other words, both D and T show isotopic effect. But since T is not only radioactive but is also least abundant hydrogen isotope. Therefore D is used as a trace to study the mechanism of organic reactions.

8.Ordinary hydrogen at room temperature is a mixture of

a) 75% of o-Hydrogen + 25% of p-Hydrogen

b) 25% of o-Hydrogen + 75% of p-Hydrogen

c) 50% of o-Hydrogen + 50% of p-Hydrogen

d) 1% of o-Hydrogen + 99% of p-Hydrogen

9. The adsorption of hydrogen by metals is called

a) Dehydrogenation

b) Hydrogenation

c) Occlusion

d) Adsorption

ANS

Occlusion is the phenomenon of adsorption of hydrogen by metal.

10.Which of the following produces hydrolith with dihydrogen

a) Mg

b) Al

c) Cu

d) Ca

ANS

CaH₂ is known as hydrolith.

11.Metals like platinum and palladium can absorb large volumes of hydrogen under special conditions. Such adsorbed hydrogen by the metal is known as:

a) Adsorbed hydrogen

b) Occluded hydrogen

c) Reactive hydrogen

d) Atomic hydrogen

ANS

Occluded hydrogen is the hydrogen absorbed by the metal.

12.The difference between heat of adsorption of ortho and para hydrogen is

a) 0.4 kJ mol^-1

b) 0.8kJ mol^-1

c) Zero

d) None of these

13.Cu does not liberate H₂ from dil H₂SO_4. Explain.

ANS

Cu is placed below H in electrochemical series having oxidation potential -0.34 V hence Cu can not transfer electron to H⁺ ions of H₂SO₄ to liberate H₂.

14.When electric current is passed through an ionic hydride in the molten state

a) Hydrogen is liberated at the anode.

b) Hydrogen is liberated at the cathode.

c) No reaction takes place

d) Hydride ion migrates towards cathode.

ANS:

M⁺ H^– → M⁺  + H^–   H^– → \(\frac{1}{2}\) H₂ + e^–  (at anode)

15.Hydrogen acts as a reducing agent and thus resembles

a) Halogen

b) Noble gas

c) Radioactive elements

d) Alkali metals

ANS:

Alkali metals are good reducing agents because of low ionization energy and hydrogen also shows same character.

16.The ratio \(\frac{Cp}{Cv}\) for H₂ is

a) 1.40

b) 1.67

c) 1.33

d) None of these.

ANS:

For diatomic gases (e.g. H₂) r = \(\frac{Cp}{Cv}\)

=1.40 For monoatomic gases r =1.66 For triatomic gases r =1.33

17.Synthetic detergents are more effective in hard water than soaps because

a) They are highly soluble in water

b) Their Ca⁺⁺ and Mg⁺⁺ salts are water soluble

c) Their Ca++ and Mg++ salts are insoluble in water

d) None of these

18.D₂O is used more in

a) Chemical industry

b) Nuclear reactor

c) Pharmaceutical preparations

d)  Insecticide preparation

19. The velocity of neutrons in nuclear reactor is slowed down by

a) Heavy water (D₂O)

b) Ordinary water (H₂O)

c) Zinc rod

d) Fused caustic soda

ANS:

Heavy water i.e., D₂O slows down the speed of neutrons in nuclear reactors.

20. Cu is placed below H in electrochemical series having oxidation potential -0.34 V hence Cu can not transfer electron to H⁺ ions of H₂SO₄ to liberate H₂. Why is hard water softened before its use in boilers?

ANS:

Hard water cannot be used in boilers because on heating it gives precipitates of CaCO₃ and MgCO₃ along with CaSO₄ which forms scales in boilers. To avoid the scales formation, hard water is softened before its use in boiler.

21.The molarity of pure water at 4^∘C is

a) 1 M

b) 2.5 M

c) 5 M

d) 55.5 M

ANS

The density of water is 1 gcm⁻³ at 4°C

so molarity = \(\frac{1000}{18}\) =55.5M.

22. What volume of oxygen at NTP will be obtained by the complete decomposition of 100 ml of H₂O₂ marked 30 volume?

ANS

1 ml H₂O₂ of 30 volume liberates 30 ml O₂ at NTP.

100 ml H₂O₂ of 30 volumes liberate 30

100 ml O₂ at NTP or 3 litre O₂­ at NTP.

23.Permutit is a technical name given to

a) Aluminates of calcium and sodium

b) Silicates of calcium and sodium

c) Hydrated silicates of aluminium and sodium

d) Silicates of calcium and magnesium

ANS

It is Na₂Al₂Si₂O8.xH₂O

24.The alum used for purifying water is

a) Ferric alum

b) Chrome alum

c) Potash alum

d) Ammonium alum

ANS

K₂SO₄.Al₂(SO₄)₃ . 24H₂O Potash alum is generally used for purifying water.

25. Pure water can be obtained from sea water by

a) Centrifugation

b) Plasmolysis

c) Reverse osmosis

d) Sedimentation

ANS

Pure water can be obtained from sea water by reverse osmosis.

26.What happens when Zn reacts with H₂SO₄? Explain.

ANS

Whenever a metal reacts with a acid it gives salt + hydrogen gas so in this case zinc reacts with H₂SO₄ so as a result of it it will give zinc sulphate with the evolution of hydrogen gas

27. Hydrogen peroxide is reduced by

a) Ozone

b) Barium peroxide

c) Acidic solution of KMnO₄

d) Lead sulphide suspension

ANS

PbS + 4H₂O₂ → PbSO₄ + 4H₂O

29.Hydrogen peroxide is used as

a) Oxidising agent

b) Reducing agent

c) Both as oxidising and reducing agent

d) Drying agent

30.Kα of H₂O₂ is of the order of

a) 10⁻¹²

b) 10⁻¹⁴

c) 10⁻¹⁶

d) 10⁻¹⁰

ANS

Kα of H₂O₂  = 1.55  × 10⁻¹² 

31.The volume of oxygen liberated from 0.68gm of H₂O₂ is

a) 112ml

b) 224ml

c) 56ml

d) 336m

ANS

We know that 2H₂O₂  →  2H₂O + O₂

2 × 34g in 22400ml

∵ 2 × 34gm = 68gm of H₂O₂ liberates 22400ml O₂ at STP

∴ .68gm of H₂O₂ liberates

= 68 × 2240/068 = 224ml

32.The structure of H₂O₂ is

a) Open book like

b) Linear

c) Closed book

d) Pyramidal

33.HCl is added to following oxides. Which one would give H₂O₂

a) MnO2

b) PbO2

c) BaO

d) None of these

ANS

MnO₂, PbO₂ and BaO will not give H₂O₂ with HCl.MnO₂ and PbO₂ will give Cl₂ and BaO will react with HCl to give BaCl₂ and water.

34. A commercial sample of hydrogen peroxide is labelled as 10 volume. Its percentage strength is nearly

a) 1%

b) 3%

c) 10%

d) 90%

ANS

10 volume solution of H₂O₂ is 3.035% solution i.e., 3.035 g of H₂O₂ is present in 100ml of the solution.

35.H₂O₂ is a very good solvent for ionic compounds.Explain.

ANS

The dielectric constant of pure H₂O₂ is 93.7 (which also increases on dilution (97 for 90% pure; 120 for 65% pure) which is appreciably high to weaken the electrostatic forces of attraction among ions and to pass them in solution state.

36.A sample of water containing some dissolved table sugar and common salt is passed through organic ion exchange resins.The resulting water will be

a) Tasteless

b) Sweet

c) Salty

d) None of these

ANS

Organic ion exchange resins can remove only ionic impurities.

37.The hardness of water sample containing 0.002 mole of magnesium sulphate dissolved in a litre of water is expressed as:

a) 20 ppm

b) 240 ppm

c) 2000 ppm

d) 120 ppm

38.Difference between Atomic hydrogen and Nascent hydrogen.

ANS

Atomic hydrogen	Nascent hydrogen
It is very reactive and its half-life period is 0.33 s.	Freshly prepared hydrogen is known as nascent hydrogen and is more reactive than ordinary hydrogen

39. How many hydrogen-bonded water molecule(s) are associated in CuSO₄. 5H₂O?

ANS

Only one water molecule, which is outside the brackets (coordination sphere), is hydrogen-bonded. The other four molecules of water are coordinated.

40.Photohydrogen is :

a) Obtain renewable energy from sunlight by using microscopic organism such as bacteria or algae.

b)  Obtain renewable energy from sunlight by using microscopic organism such as bacteria or fungi

c) both of above

d) none of these

41.Describe some important Uses of Dihydrogen

ANS

• In the manufacture of CH₃OH.
• We use liquid hydrogen (LH₂) in fuel
• The largest single use of H₂ is in the synthesis of NH₃ which is used in the manufacture of HNO₃ and fertilizers.
• We use liquid hydrogen (LH₂) in fuel.
• H₂ is used as a reducing agent in extraction of metals.
• H₂ is used in fuel cell for generating electrical energy.
• We is used in the manufacture of synthetic petrol.