Chapter 9 Hydrogen

Question 1. Hydrogen resembles halogens in many respects for which several factors are responsible. Of the following factors which one is most important in this respect?

(i) Its tendency to lose an electron to form a cation.

(ii) Its tendency to gain a single electron in its valence shell to attain stable electronic configuration.

(iii) Its low negative electron gain enthalpy value.

(iv) Its small size.

Question 2. Why does H+ ion always get associated with other atoms or molecules?

(i) Ionisation enthalpy of hydrogen resembles that of alkali metals.

(ii) Its reactivity is similar to halogens.

(iii) It resembles both alkali metals and halogens.

(iv) Loss of an electron from hydrogen atom results in a nucleus of very small size as compared to other atoms or ions. Due to smal size it cannot exist free.

Question 3. Metal hydrides are ionic, covalent or molecular in nature. Among LiH, NaH, KH, RbH, CsH, the correct order of increasing ionic character is

(i) LiH > NaH > CsH > KH>RbH

(ii) LiH < NaH < KH < RbH < CsH

(iii) RbH > CsH > NaH > KH > LiH

(iv) NaH > CsH > RbH > LiH > KH

Question 4. Which of the following hydrides is electron-precise hydride?

(i) $B_2H_6$

(ii) $NH_3$

(iii) $H_2O$

(iv) $CH_4$

Question 5. Radioactive elements emit $\alpha$, $\beta$ and $\gamma$ rays and are characterised by their half-lives. The radioactive isotope of hydrogen is

(i) Protium

(ii) Deuterium

(iii) Tritium

(iv) Hydronium

Question 6. Consider the reactions

(A) $H_2O_2 + 2HI \rightarrow I_2 + 2H_2O$

(B) $HOCl + H_2O_2 \rightarrow H_3O^+ + Cl^– + O_2$

Which of the following statements is correct about $H_2O_2$ with reference to these reactions? Hydrogen perioxide is ________.

(i) an oxidising agent in both (A) and (B)

(ii) an oxidising agent in (A) and reducing agent in (B)

(iii) a reducing agent in (A) and oxidising agent in (B)

(iv) a reducing agent in both (A) and (B)

Question 7. The oxide that gives $H_2O_2$ on treatment with dilute $H_2SO_4$ is —

(i) $PbO_2$

(ii) $BaO_2 \cdot 8H_2O$

(iii) $MnO_2$

(iv) $TiO_2$

Question 8. Which of the following equations depict the oxidising nature of $H_2O_2$?

(i) $2MnO_4^– + 6H^+ + 5H_2O_2 \rightarrow 2Mn^{2+} + 8H_2O + 5O_2$

(ii) $2Fe^{2+} + 2H^+ + H_2O_2 \rightarrow 2Fe^{3+} + 2H_2O$

(iii) $2I^– + 2H^+ + H_2O_2 \rightarrow I_2 + 2H_2O$

(iv) $KIO_4 + H_2O_2 \rightarrow KIO_3 + H_2O + O_2$

Question 9. Which of the following equation depicts reducing nature of $H_2O_2$?

(i) $2[Fe(CN)_6]^{4–} + 2H^+ + H_2O_2 \rightarrow 2[Fe (CN)_6]^{3–} + 2H_2O$

(ii) $I_2 + H_2O_2 + 2OH^– \rightarrow 2I^– + 2H_2O + O_2$

(iii) $Mn^{2+} + H_2O_2 \rightarrow Mn^{4+} + 2OH^–$

(iv) $PbS + 4H_2O_2 \rightarrow PbSO_4 + 4H_2O$

Question 10. Hydrogen peroxide is _________.

(i) an oxidising agent

(ii) a reducing agent

(iii) both an oxidising and a reducing agent

(iv) neither oxidising nor reducing agent

Question 11. Which of the following reactions increases production of dihydrogen from synthesis gas?

(i) $CH_4(g) + H_2O(g) \xrightarrow{1270K, Ni} CO(g) + 3H_2(g)$

(ii) $C(s) + H_2O(g) \xrightarrow{1270K} CO(g) + H_2(g)$

(iii) $CO(g) + H_2O(g) \xrightarrow{673K, Catalyst} CO_2(g) + H_2(g)$

(iv) $C_2H_6 + 2H_2O \xrightarrow{1270K, Ni} 2CO + 5H_2$

Question 12. When sodium peroxide is treated with dilute sulphuric acid, we get ______.

(i) sodium sulphate and water

(ii) sodium sulphate and oxygen

(iii) sodium sulphate, hydrogen and oxygen

(iv) sodium sulphate and hydrogen peroxide

Question 13. Hydrogen peroxide is obtained by the electrolysis of ______.

(i) water

(ii) sulphuric acid

(iii) hydrochloric acid

(iv) fused sodium peroxide

Question 14. Which of the following reactions is an example of use of water gas in the synthesis of other compounds?

(i) $CH_4(g) + H_2O(g) \xrightarrow{1270K, Ni} CO(g) + H_2(g)$

(ii) $CO(g) + H_2O(g) \xrightarrow{673K, Catalyst} CO_2(g) + H_2(g)$

(iii) $C_nH_{2n+2} + nH_2O(g) \xrightarrow{1270K, Ni} nCO + (2n+1)H_2$

(iv) $CO(g) + 2H_2(g) \xrightarrow{\text{Cobalt Catalyst}} CH_3OH(l)$

Question 15. Which of the following ions will cause hardness in water sample?

(i) $Ca^{2+}$

(ii) $Na^+$

(iii) $Cl^–$

(iv) $K^+$

Question 16. Which of the following compounds is used for water softening?

(i) $Ca_3(PO_4)_2$

(ii) $Na_3PO_4$

(iii) $Na_6P_6O_{18}$

(iv) $Na_2HPO_4$

Question 17. Elements of which of the following group(s) of periodic table do not form hydrides.

(i) Groups 7, 8, 9

(ii) Group 13

(iii) Groups 15, 16, 17

(iv) Group 14

Question 18. Only one element of ________ forms hydride.

(i) group 6

(ii) group 7

(iii) group 8

(iv) group 9

Question 19. Which of the following statements are not true for hydrogen?

(i) It exists as diatomic molecule.

(ii) It has one electron in the outermost shell.

(iii) It can lose an electron to form a cation which can freely exist

(iv) It forms a large number of ionic compounds by losing an electron.

Question 20. Dihydrogen can be prepared on commercial scale by different methods. In its preparation by the action of steam on hydrocarbons, a mixture of CO and H2 gas is formed. It is known as ____________.

(i) Water gas

(ii) Syngas

(iii) Producer gas

(iv) Industrial gas

Question 21. Which of the following statement(s) is/are correct in the case of heavy water?

(i) Heavy water is used as a moderator in nuclear reactor.

(ii) Heavy water is more effective as solvent than ordinary water.

(iii) Heavy water is more associated than ordinary water.

(iv) Heavy water has lower boiling point than ordinary water.

Question 22. Which of the following statements about hydrogen are correct?

(i) Hydrogen has three isotopes of which protium is the most common.

(ii) Hydrogen never acts as cation in ionic salts.

(iii) Hydrogen ion, H+, exists freely in solution.

(iv) Dihydrogen does not act as a reducing agent.

Question 23. Some of the properties of water are described below. Which of them is/are not correct?

(i) Water is known to be a universal solvent.

(ii) Hydrogen bonding is present to a large extent in liquid water.

(iii) There is no hydrogen bonding in the frozen state of water.

(iv) Frozen water is heavier than liquid water.

Question 24. Hardness of water may be temporary or permanent. Permanent hardness is due to the presence of

(i) Chlorides of Ca and Mg in water

(ii) Sulphates of Ca and Mg in water

(iii) Hydrogen carbonates of Ca and Mg in water

(iv) Carbonates of alkali metals in water

Question 25. Which of the following statements is correct?

(i) Elements of group 15 form electron deficient hydrides.

(ii) All elements of group 14 form electron precise hydrides.

(iii) Electron precise hydrides have tetrahedral geometries.

(iv) Electron rich hydrides can act as Lewis acids.

Question 26. Which of the following statements is correct?

(i) Hydrides of group 13 act as Lewis acids.

(ii) Hydrides of group 14 are electron deficient hydrides.

(iii) Hydrides of group 14 act as Lewis acids.

(iv) Hydrides of group 15 act as Lewis bases.

Question 27. Which of the following statements is correct?

(i) Metallic hydrides are deficient of hydrogen.

(ii) Metallic hydrides conduct heat and electricity.

(iii) Ionic hydrides do not conduct electricity in solid state.

(iv) Ionic hydrides are very good conductors of electricity in solid state.

Question 28. How can production of hydrogen from water gas be increased by using water gas shift reaction?

Question 29. What are metallic/interstitial hydrides? How do they differ from molecular hydrides?

Question 30. Name the classes of hydrides to which $H_2O$, $B_2H_6$ and NaH belong.

Question 31. If same mass of liquid water and a piece of ice is taken, then why is the density of ice less than that of liquid water?

Question 32. Complete the following equations:

(i) $PbS(s) + H_2O_2(aq) \rightarrow$

(ii) $CO(g) + 2H_2(g) \xrightarrow{\text{Cobalt Catalyst}}$

Question 33. Give reasons:

(i) Lakes freeze from top towards bottom.

(ii) Ice floats on water.

Question 34. What do you understand by the term ‘auto protolysis of water’ ? What is its significance?

Question 35. Discuss briefly de-mineralisation of water by ion exchange resin.

Question 36. Molecular hydrides are classified as electron deficient, electron precise and electron rich compounds. Explain each type with two examples.

Question 37. How is heavy water prepared? Compare its physical properties with those of ordinary water.

Question 38. Write one chemical reaction for the preparation of $D_2O_2$.

Question 39. Calculate the strength of 5 volume $H_2O_2$ solution.

Question 40.

(i) Draw the gas phase and solid phase structure of $H_2O_2$.

(ii) $H_2O_2$ is a better oxidising agent than water. Explain.

Question 41. Melting point, enthalpy of vapourisation and viscosity data of $H_2O$ and $D_2O$ is given below :

On the basis of this data explain in which of these liquids intermolecular forces are stronger?

Question 42. Dihydrogen reacts with dioxygen ($O_2$) to form water. Write the name and formula of the product when the isotope of hydrogen which has one proton and one neutron in its nucleus is treated with oxygen. Will the reactivity of both the isotopes be the same towards oxygen? Justify your answer.

Question 43. Explain why HCl is a gas and HF is a liquid.

Question 44. When the first element of the periodic table is treated with dioxygen, it gives a compound whose solid state floats on its liquid state. This compound has an ability to act as an acid as well as a base. What products will be formed when this compound undergoes autoionisation?

Question 45. Rohan heard that instructions were given to the laboratory attendent to store a particular chemical i.e., keep it in the dark room, add some urea in it, and keep it away from dust. This chemical acts as an oxidising as well as a reducing agent in both acidic and alkaline media. This chemical is important for use in the pollution control treatment of domestic and industrial effluents.

(i) Write the name of this compound.

(ii) Explain why such precautions are taken for storing this chemical.

Question 46. Give reasons why hydrogen resembles alkali metals?

Question 47. Hydrogen generally forms covalent compounds. Give reason.

Question 48. Why is the Ionisation enthalpy of hydrogen higher than that of sodium?

Question 49. Basic principle of hydrogen economy is transportation and storage of energy in the form of liquid or gaseous hydrogen. Which property of hydrogen may be useful for this purpose? Support your answer with the chemical equation if required.

Question 50. What is the importance of heavy water?

Question 51. Write the Lewis structure of hydrogen peroxide.

Question 52. An acidic solution of hydrogen peroxide behaves as an oxidising as well as reducing agent. Illustrate it with the help of a chemical equation.

Question 53. With the help of suitable examples, explain the property of $H_2O_2$ that is responsible for its bleaching action?

Question 54. Why is water molecule polar?

Question 55. Why does water show high boiling point as compared to hydrogen sulphide? Give reasons for your answer.

Question 56. Why can dilute solutions of hydrogen peroxide not be concentrated by heating. How can a concentrated solution of hydrogen peroxide be obtained?

Question 57. Why is hydrogen peroxide stored in wax lined bottles?

Question 58. Why does hard water not form lather with soap?

Question 59. Phosphoric acid is preferred over sulphuric acid in preparing hydrogen peroxide from peroxides. Why?

Question 60. How will you account for $104.5^\circ$ bond angle in water?

Question 61. Write redox reaction between fluorine and water.

Question 62. Write two reactions to explain amphoteric nature of water.

Question 63. Correlate the items listed in Column I with those listed in Column II. Find out as many correlations as you can.

Column I

(i) Synthesis gas

(ii) Dihydrogen

(iii) Heavy water

(iv) Calgon

(v) Hydrogen peroxide

(vi) Salt like hydrides

Column II

(a) $Na_2[Na_4(PO_3)_6]$

(b) Oxidising agent

(c) Softening of water

(d) Reducing agent

(e) Stoichiometric compounds of s-block elements

(f) Prolonged electrolysis of water

(g) Zn + NaOH

(h) Zn + dil. $H_2SO_4$

(i) Synthesis of methanol

(j) Mixture of CO and $H_2$

Question 64. Match Column I with Column II for the given properties/applications mentioned therein.

Column I

(i) H

(ii) $H_2$

(iii) $H_2O$

(iv) $H_2O_2$

Column II

(a) Used in the name of perhydrol.

(b) Can be reduced to dihydrogen by NaH.

(c) Can be used in hydroformylation of olefin.

(d) Can be used in cutting and welding.

Question 65. Match the terms in Column I with the relevant item in Column II.

Column I

(i) Electrolysis of water produces

(ii) Lithium aluminium hydride is used as

(iii) Hydrogen chloride is a

(iv) Heavy water is used in

(v) Atomic hydrogen

Column II

(a) atomic reactor

(b) polar molecule

(c) recombines on metal surface to generate high temperature

(d) reducing agent

(e) hydrogen and oxygen

Question 66. Match the items in Column I with the relevant item in Column II.

Column I

(i) Hydrogen peroxide is used as a

(ii) Used in Calgon method

(iii) Permanent hardness of hard water is removed by

Column II

(a) zeolite

(b) perhydrol

(c) sodium hexametaphosphate

(d) propellant

Question 67. Assertion (A) : Permanent hardness of water is removed by treatment with washing soda.

Reason (R) : Washing soda reacts with soluble magnesium and calcium sulphate to form insoluble carbonates.

(i) Statements A and R both are correct and R is the correct explanation of A.

(ii) A is correct but R is not correct.

(iii) A and R both are correct but R is not the correct explanation of A.

(iv) A and R both are false.

Question 68. Assertion (A) : Some metals like platinum and palladium, can be used as storage media for hydrogen.

Reason (R) : Platinum and palladium can absorb large volumes of hydrogen.

(i) Statements A and R both are correct and R is the correct explanation of A.

(ii) A is correct but R is not correct.

(iii) A and R both are correct but R is not the correct explanation of A.

(iv) A and R both are false.

Question 69. Atomic hydrogen combines with almost all elements but molecular hydrogen does not. Explain.

Question 70. How can $D_2O$ be prepared from water? Mention the physical properties in which $D_2O$ differs from $H_2O$. Give at least three reactions of $D_2O$ showing the exchange of hydrogen with deuterium.

Question 71. How will you concentrate $H_2O_2$? Show differences between structures of $H_2O_2$ and $H_2O$ by drawing their spatial structures. Also mention three important uses of $H_2O_2$.

Question 72.

(i) Give a method for the manufacture of hydrogen peroxide and explain the reactions involved therein.

(ii) Illustrate oxidising, reducing and acidic properties of hydrogen peroxide with equations.

Question 73. What mass of hydrogen peroxide will be present in 2 litres of a 5 molar solution? Calculate the mass of oxygen which will be liberated by the decomposition of 200 mL of this solution.

Question 74. A colourless liquid ‘A’ contains H and O elements only. It decomposes slowly on exposure to light. It is stabilised by mixing urea to store in the presence of light.

(i) Suggest possible structure of A.

(ii) Write chemical equations for its decomposition reaction in light.

Question 75. An ionic hydride of an alkali metal has significant covalent character and is almost unreactive towards oxygen and chlorine. This is used in the synthesis of other useful hydrides. Write the formula of this hydride. Write its reaction with $Al_2Cl_6$.

Question 76. Sodium forms a crystalline ionic solid with dihydrogen. The solid is nonvolatile and non- conducting in nature. It reacts violently with water to produce dihydrogen gas. Write the formula of this compound and its reaction with water. What will happen on electrolysis of the melt of this solid.