Study of the First Element - Hydrogen - Questions & Answers

1. Potassium
K + H₂O → 2KOH + H₂ [g]
Balanced: 2K + 2H₂O → 2KOH + H₂

2. Sodium
Na + H₂O → 2NaOH + H₂ [g]
Balanced: 2Na + 2H₂O → 2NaOH + H₂

3. Calcium
Ca + H₂O → Ca(OH)₂ + H₂ [g]
Balanced: Ca + 2H₂O → Ca(OH)₂ + H₂

4. Magnesium
Mg + H₂O → MgO + H₂ [g]
Balanced: Mg + H₂O → MgO + H₂

5. Aluminium
Al + H₂O → Al₂O₃ + 3H₂ [g]
Balanced: 2Al + 3H₂O → Al₂O₃ + 3H₂

6. Zinc
Zn + H₂O → ZnO + H₂ [g]
Balanced: Zn + H₂O → ZnO + H₂

7. Iron
Fe + H₂O ⇌ Fe₃O₄ + 4H₂ [g]
Balanced: 3Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂

8. Magnesium
Mg + HCl → MgCl₂ + H₂ [g]
Balanced: Mg + 2HCl → MgCl₂ + H₂

9. Aluminium
Al + H₂SO₄ → Al₂(SO₄)₃ + 3H₂ [g]
Balanced: 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂

10. Zinc
Zn + HCl → ZnCl₂ + H₂ [g]
Balanced: Zn + 2HCl → ZnCl₂ + H₂

11. Iron
Fe + HCl → FeCl₂ + H₂ [g]
Balanced: Fe + 2HCl → FeCl₂ + H₂

12. Zinc
Zn + NaOH → Na₂ZnO₂ + H₂ [g]
Balanced: Zn + 2NaOH → Na₂ZnO₂ + H₂
Zn + KOH → K₂ZnO₂ + H₂ [g]
Balanced: Zn + 2KOH → K₂ZnO₂ + H₂

13. Lead
Pb + NaOH → Na₂PbO₂ + H₂ [g]
Balanced: Pb + 2NaOH → Na₂PbO₂ + H₂

14. Aluminium
Al + NaOH + H₂O → 2NaAlO₂ + 3H₂ [g]
Balanced: 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂
Al + KOH + H₂O → 2KAlO₂ + 3H₂ [g]
Balanced: 2Al + 2KOH + 2H₂O → 2KAlO₂ + 3H₂

15. Zinc
Zn + HCl → ZnCl₂ + H₂ [g]
Balanced: Zn + 2HCl → ZnCl₂ + H₂

16. Step I - Production of water gas
C + H₂O → (1000°C) [CO + H₂] - Δ

17. Step II - Reduction of steam to hydrogen by carbon monoxide
CO + H₂ + H₂O → (450°C / Fe₂O₃) CO₂ + 2H₂ [g]

18. Step III - Removal of unreacted carbon dioxide and carbon monoxide from the above mixture
KOH + CO₂ → K₂CO₃ + H₂O
Balanced: 2KOH + CO₂ → K₂CO₃ + H₂O
CuCl + CO + H₂O → CuCl.CO.2H₂O
Balanced: CuCl + CO + 2H₂O → CuCl.CO.2H₂O

19. Water
H₂ + O₂ → 2H₂O
Balanced: 2H₂ + O₂ → 2H₂O

20. Hydrogen chloride
H₂ + Cl₂ → 2HCl

21. Ammonia
N₂ + H₂ ⇌ 2NH₃
Balanced: N₂ + 3H₂ ⇌ 2NH₃

22. Hydrogen sulphide
H₂ + S → H₂S

23. Zinc oxide
ZnO + H₂ → Zn + H₂O

24. Iron [III] oxide
Fe₂O₃ + H₂ → 2Fe + 3H₂O
Balanced: Fe₂O₃ + 3H₂ → 2Fe + 3H₂O

1. Name an element - which reacts violently with water at room temperature.
Sodium (or Potassium).

2. State - what do the following symbols [or formula] denote: 2H ; H₂ ; H⁺. [two atoms, molecule, ion]
2H denotes two atoms of hydrogen.
H₂ denotes one molecule of hydrogen.
H⁺ denotes one hydrogen ion (a proton).

3. Name a gas - which burns in air or oxygen forming water.
Hydrogen gas.

1. Write correctly balanced equation - for the following "word equation" : calcium + water → calcium hydroxide + hydrogen.
Ca + 2H₂O → Ca(OH)₂ + H₂

2. When steam is passed - over red-hot iron, magnetic oxide of iron and hydrogen are obtained. "The reaction between steam and red-hot iron is a Reversible Reaction." What is meant by this statement.
It means the reaction can proceed in both forward and backward directions depending on the conditions. Iron and steam react to form magnetic oxide of iron and hydrogen, while magnetic oxide of iron can also react with hydrogen to yield back iron and steam.

3. State how can you obtain - hydrogen from sodium hydroxide [not by electrolysis].
By heating concentrated sodium hydroxide solution with an amphoteric metal like zinc, aluminium, or lead. Example: Zn + 2NaOH → Na₂ZnO₂ + H₂

4. Write balanced equation for the following reaction : magnesium + dil. hydrochloric acid →
Mg + 2HCl → MgCl₂ + H₂

5. Write correctly balanced equation for the following: When steam is passed over red hot iron.
3Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂

6. Explain the following: Two jars of H₂ are collected - "one burns quietly and the other does not".
The jar containing pure hydrogen burns quietly in air with a pale blue flame. The other jar likely contains a mixture of hydrogen and air (oxygen), which undergoes a rapid explosive reaction and burns with a characteristic 'pop' sound.

7. Write correctly the balanced equation for the following: 'When zinc filings are added to a concentrated solution of sodium hydroxide'.
Zn + 2NaOH → Na₂ZnO₂ + H₂

8. Describe one chemical test - applied to the following gases, which would enable you to distinguish between them : 'carbon monoxide and hydrogen'.
Burn both gases. Hydrogen burns forming water vapor which condenses on a cold surface. Carbon monoxide burns forming carbon dioxide, which turns lime water milky.

9. Write down the "word equation" for the following reaction: sodium hydroxide solution + zinc →
Sodium hydroxide + Zinc → Sodium zincate + Hydrogen

10. Explain briefly - how hydrogen is manufactured on a large scale, from steam.
In the Bosch Process, steam is first passed over white-hot coke at about 1000°C to produce water gas (CO + H₂). This water gas is then mixed with excess steam and passed over a heated catalyst (Iron [III] oxide with a chromic oxide promoter) at 450°C. This converts the carbon monoxide into carbon dioxide, yielding a further volume of hydrogen gas. The unreacted CO and CO₂ are then separated out.

11. State the products of the reaction - "when steam is passed over red-hot iron".
Magnetic oxide of iron (Fe₃O₄) and Hydrogen gas (H₂).

12. How can you obtain - hydrogen from a mixture of hydrogen & carbon monoxide.
By passing the mixture with excess steam over a catalyst (Iron [III] oxide and chromic oxide) at 450°C, CO is oxidized to CO₂, producing more hydrogen. The CO₂ is then removed by dissolving in water under high pressure or using caustic potash solution. Any unreacted CO is removed using an ammoniacal cuprous chloride solution.

13. State what do you observe - when a piece of sodium is dropped into cold water.
The reaction is violent and highly exothermic. The sodium melts into a silvery globule and darts rapidly around the surface of the water, liberating hydrogen gas. The heat liberated is usually enough to ignite the hydrogen, making it catch fire.

14. Give reasons for the following : 'Though hydrogen is lighter than air, it is not collected by the downward displacement of air'.
Hydrogen forms a highly explosive mixture with air, making collection by displacement of air very dangerous.

15. Complete the following word equations:
i] Sodium hydroxide + zinc → hydrogen + sodium zincate
ii] Calcium + water → calcium hydroxide + hydrogen

16. How would you obtain - 'hydrogen from sodium hydroxide' solution other than by electrolysis.
By heating it with an active amphoteric metal like Zinc, Aluminium, or Lead.

17. Complete and balance the following equations:
Al + NaOH + H₂O → NaAlO₂ + H₂
Balanced: 2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

18. Write balanced equation of the reaction in the preparation of : hydrogen from a solution of potassium hydroxide [other than by electrolysis].
Zn + 2KOH → K₂ZnO₂ + H₂

19. Describe briefly, with equations - the Bosch Process for the large scale production of hydrogen.
Step 1: Steam is passed over white hot coke at 1000°C to produce water gas.
C + H₂O → CO + H₂
Step 2: Water gas and excess steam are passed over a catalyst (Fe₂O₃) at 450°C to reduce steam to hydrogen.
CO + H₂ + H₂O → CO₂ + 2H₂
Step 3: CO₂ is removed using water under pressure or KOH. Unreacted CO is removed using ammoniacal cuprous chloride.

20. Account for the following facts :
i] Though lead is above hydrogen in the activity series, it does not react with dilute hydrochloric acid or dilute sulphuric acid.
Lead reacts initially but forms an insoluble coating of lead chloride (PbCl₂) or lead sulphate (PbSO₄) on its surface, which prevents further reaction with the acid.
ii] Potassium and sodium are not used to react with dilute hydrochloric acid or dilute sulphuric acid in the laboratory preparation of hydrogen.
The reaction of highly active metals like potassium and sodium with dilute acids is violently explosive and exothermic, making it unsafe for laboratory preparation.

21. Place the metals - calcium, iron, magnesium and sodium in order of their activity with water, placing the most active first. Write the equation for each of the above metals which react with water.
Order of activity: Sodium > Calcium > Magnesium > Iron.
Equations:
2Na + 2H₂O → 2NaOH + H₂
Ca + 2H₂O → Ca(OH)₂ + H₂
Mg + H₂O → MgO + H₂
3Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂

22. State - why is copper not used to prepare hydrogen by the action of dilute hydrochloric acid or dilute sulphuric acid on the metal.
Copper is placed below hydrogen in the metal activity series, meaning it is less reactive than hydrogen and cannot displace hydrogen from dilute acids.

1. State - the electronic configuration of hydrogen [at. no. 1].
1 (It has one valence electron in its first shell).

1. State a reason - why hydrogen can be placed in group 1 [IA] and group 17 [VIIA] of the periodic table.
Hydrogen has a dual nature. It can be placed in Group 1 because, like alkali metals, it has one valence electron and acts as a strong reducing agent by forming a positive ion (H⁺). It can be placed in Group 17 because, like halogens, it is a non-metal, exists as a diatomic molecule, and requires just one electron to achieve the nearest stable noble gas configuration (forming H^-).

2. State - the general group characteristics applied to hydrogen with respect to similarity in properties of hydrogen with - (a) alkali metals of group 1 [IA] (b) halogens of group 17 [VIIA]. with special reference to valency electrons & ion formation.
(a) Alkali metals: Both hydrogen and alkali metals possess one valence electron in their outermost shell and exhibit electropositive character by losing one electron to form a univalent positive ion (e.g., H → H⁺ + 1e^-).
(b) Halogens: Both hydrogen and halogens have one electron less than the nearest noble gas configuration and exhibit electronegative character by gaining one electron to form a univalent negative ion (e.g., H + 1e^- → H^-).

3. State - how hydrogen occurs in the combined state.
In the combined state, hydrogen occurs abundantly in water (about one-ninth by mass), in plant and animal tissues (in proteins, carbohydrates, fats), and as a major constituent in natural gas, petroleum, acids, and alkalis.

4. Give balanced equations - for obtaining hydrogen from cold water using -
(a) A monovalent active metal
2Na + 2H₂O → 2NaOH + H₂
(b) A divalent active metal
Ca + 2H₂O → Ca(OH)₂ + H₂

5. Give balanced equations - for obtaining hydrogen from -
(a) Boiling water using a divalent metal
Mg + H₂O → MgO + H₂
(b) Steam using a trivalent metal
2Al + 3H₂O → Al₂O₃ + 3H₂
(c) Steam using a metal - and the reaction is reversible.
3Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂

6. State - why hydrogen is not prepared in the laboratory by the action of -
(a) Sodium with cold water
The reaction is extremely violent, highly exothermic, and the liberated hydrogen catches fire instantly, making collection impossible.
(b) Calcium with dilute sulphuric acid
The reaction is explosive and practically not feasible for safe laboratory preparation.
(c) Lead with dilute hydrochloric acid.
Lead reacts to form an insoluble coating of lead chloride over the metal surface, which immediately stops further reaction.

7. Give balanced equations - for the following conversions.
(a) Sodium zincate from zinc
Zn + 2NaOH → Na₂ZnO₂ + H₂
(b) Sodium plumbite from lead
Pb + 2NaOH → Na₂PbO₂ + H₂
(c) Sodium aluminate from aluminium.
2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂

8. Give reasons for the following : In the laboratory preparation of hydrogen from zinc & dilute acid.
(a) The complete apparatus is air-tight.
To prevent hydrogen gas from leaking and mixing with the outside air, as hydrogen forms a highly explosive mixture with air.
(b) Dilute nitric acid is not preferred as the reactant acid.
Nitric acid is a powerful oxidizing agent. It oxidizes the newly formed hydrogen gas into water, defeating the purpose of preparation.
(c) The lower end of the thistle funnel should dip below the level of the acid in the flask.
This minimizes the chance of the lighter hydrogen gas escaping upwards through the thistle funnel.
(d) Hydrogen is not collected over air.
Because it forms an explosive mixture with air and is lighter than air.

9. In the Bosch process - State the conditions & give balanced equations for the conversion of -
(a) coke to water gas,
Condition: Steam is passed over white-hot coke at around 1000°C.
Equation: C + H₂O → CO + H₂
(b) water gas to hydrogen
Condition: Water gas mixed with excess steam is passed over a catalyst of Iron [III] oxide with a chromic oxide promoter at around 450°C.
Equation: CO + H₂ + H₂O → CO₂ + 2H₂

10. State - how are the unreacted gases separated out in 'Bosch process' in the manufacture of hydrogen.
Carbon dioxide is separated by dissolving the mixture in water under 30 atmospheres of pressure, or by passing through caustic potash solution. Unreacted carbon monoxide is removed by dissolving the mixture in an ammoniacal cuprous chloride solution.

11. Compare - the combustibility of - (a) pure hydrogen (b) hydrogen-air mixture.
(a) Pure hydrogen burns quietly in air with a pale blue flame to form water.
(b) A hydrogen-air mixture burns with a characteristic explosive 'pop' sound due to rapid reaction with oxygen.

12. State - the reactant added to hydrogen to obtain the respective product in each case.
(a) Ammonia
Nitrogen gas.
(b) Hydrogen chloride
Chlorine gas.
(c) Water
Oxygen gas.
(d) Hydrogen sulphide
Sulphur vapours.

13. State - the use of hydrogen -
(a) As a fuel
Used as liquid hydrogen for non-polluting fuel and as a constituent in coal gas and water gas.
(b) In hydrogenation of oil & coal
Used to convert liquid vegetable oils into semi-solid fats (hydrogenation of oil) and to convert coal into petroleum-like products.
(c) In extraction of metals
Acts as a strong reducing agent to extract less active metals (like zinc, iron, copper) from their heated oxides.

14. Explain the terms - oxidation & reduction in terms of addition & removal of oxygen/hydrogen - with suitable examples.
Oxidation is the addition of oxygen to a substance (e.g., 2Cu + O₂ → 2CuO) or the removal of hydrogen from a substance (e.g., H₂S + Cl₂ → 2HCl + S).
Reduction is the removal of oxygen from a compound (e.g., CuO + H₂ → Cu + H₂O) or the addition of hydrogen to a compound (e.g., Cl₂ + H₂S → 2HCl + S).

15. Explain the term - redox reaction with an example involving - the reaction of hydrogen sulphide with chlorine.
A redox reaction is a chemical reaction involving the simultaneous oxidation of one substance and the reduction of another. In the reaction H₂S + Cl₂ → 2HCl + S, Hydrogen sulphide is oxidized to sulphur (by removal of hydrogen) while chlorine is reduced to hydrogen chloride (by addition of hydrogen).

16. State - what are oxidising & reducing agents. Give examples of oxidising & reducing agents in the gaseous, liquid & solid form. Give two tests each generally answered by oxidising & reducing agents respectively.
Oxidizing agents are substances that accept electrons, provide oxygen, or remove hydrogen. (Examples: Gas - O₂; Liquid - H₂O₂; Solid - MnO₂).
Reducing agents are substances that donate electrons, provide hydrogen, or remove oxygen. (Examples: Gas - H₂; Liquid - HCl; Solid - Carbon).
Tests for Oxidizing agents: Decompose to give a colorless gas which rekindles a glowing splint. React with conc. HCl on heating to liberate chlorine.
Tests for Reducing agents: Turn yellowish-brown Iron [III] salts to light green. React with acidified KMnO₄ solution (purple) giving a colorless solution.

1. The element with which, hydrogen does not show similarity.
(a) Li (b) K (c) F (d) C
Answer: (d) C

2. A metal which reacts with hot conc. alkali to give hydrogen, but not with dil. acid to liberate the same.
(a) Zn (b) Pb (c) Fe (d) Al
Answer: (b) Pb

3. A metal which reacts with steam and with an alkali, to liberate hydrogen.
(a) Al (b) Fe (c) Pb (d) Mg
Answer: (a) Al

4. State which of the statements pertaining to the laboratory preparation of hydrogen, is incorrect.
(a) Granulated zinc is placed in a flat bottom flask & dilute HCl added through the thistle funnel.
(b) The apparatus is airtight, since hydrogen forms an explosive mixture with air.
(c) Hydrogen like ammonia gas, is lighter than air & hence like ammonia is collected by the downward displacement of air.
(d) Dil. sulphuric acid or dil. hydrochloric acid, are preferred to dilute nitric acid in the laboratory preparation.
Answer: (c) Hydrogen like ammonia gas, is lighter than air & hence like ammonia is collected by the downward displacement of air.

5. In Bosch process [industrial preparation], pick the incorrect statement in each step of the production
(a) Step 1 - involves production of, water gas by passage of steam over white hot coke, at temperatures around 1000°C.
(b) Step 2 - involves production of hydrogen by reaction of water gas with excess steam, in presence of a catalyst - iron [III] oxide.
(c) The conversion of water gas to hydrogen in the above reaction, is an oxidation process.
(d) In the above process - both potassium hydroxide solution & ammoniacal cuprous chloride solution- can be used, for removal of unreacted CO & CO₂ in the above mixture.
Answer: (c) The conversion of water gas to hydrogen in the above reaction, is an oxidation process.

6. Assertion (A) : Hydrogen is now replaced by helium, in meteorological balloons.
Reason (R) : Hydrogen is lighter than air.
(a) Both A & R are true - and R is the correct explanation of A.
(b) Both A & R are true - but R is not the correct explanation of A.
(c) A is true - but R is false
(d) A is false - but R is true.
Answer: (b) Both A & R are true - but R is not the correct explanation of A.

7. Vegetable oils turn to semi solid fats, by absorption of hydrogen on the surface of a certain metals like - palladium. The phenomenon takes place due to, or by -
(a) Hydrogenation (b) Oxidation (c) Occlusion (d) Reduction
Answer: (c) Occlusion

8. In the reaction - 2H₂S + SO₂ → 2H₂O + 3S, the reaction takes place by -
(a) Removal of oxygen from a compound (b) Addition of hydrogen to a compound (c) Removal of electronegative element (c) Removal of hydrogen from a compound
Answer: (c) Removal of hydrogen from a compound

9. Redox reactions involve:
(a) Loss or gain of electrons, in the substance involved in the reaction.
(b) Oxidation of one substance, only in the reaction.
(c) Reduction of one substance, only in the reaction.
(d) Gain of electropositive radical, by one substance only in the reaction.
Answer: (a) Loss or gain of electrons, in the substance involved in the reaction.

1. Hydrogen is placed above Lithium [Li] in group 1 or above Fluorine [F] in group 17 - but not above beryllium [Be] in group 2 or oxygen [O] in group 16. Give reasons.
Hydrogen has one valence electron and loses it to form a +1 ion, making it comparable to Group 1 metals like Lithium. It also requires just one electron to complete its shell, similar to Group 17 halogens like Fluorine. It does not possess 2 valence electrons like Beryllium (Group 2), nor does it require 2 electrons like Oxygen (Group 16).

2. The reaction - of iron with steam is reversible, but of zinc with steam is not. Give reasons.
Iron reacts with steam to form magnetic oxide of iron (Fe₃O₄) and hydrogen. If the hydrogen is not allowed to escape, it can reduce the heated iron oxide back to iron and steam. Zinc forms zinc oxide (ZnO), which is stable under these specific conditions and is not easily reduced by hydrogen, hence the reaction is not reversible.

3. In the laboratory preparation - of hydrogen by the action of dilute acids on metals - reaction 'A' is used but reaction 'B' is not. Give reasons. A: Zn + HCl [dil.] → ; B: Pb + HNO₃ [dil.] →
Reaction A uses dilute HCl, which acts smoothly on zinc to liberate hydrogen. Reaction B uses dilute HNO₃, which is a powerful oxidizing agent and immediately oxidizes the liberated hydrogen gas into water.

4. 'Magnesium reacts with very dil. nitric acid at low temperatures liberating hydrogen.' Give reasons.
When nitric acid is highly dilute and kept at low temperatures, its oxidizing action is greatly reduced. Therefore, highly active magnesium reacts with it simply by displacing hydrogen.

5. In the laboratory preparation - of hydrogen from Zn & dil. HCl, the hydrogen is collected & then tested only after all the air in the apparatus is allowed to escape - give reasons.
A mixture of hydrogen and air forms a highly explosive mixture. If the gas is collected and ignited while air is still in the apparatus, a severe explosion could occur.

6. In the reaction in the Bosch process - for the manufacture of hydrogen the reaction is -
CO + H₂ + H₂O → (450°C / Fe₂O₃) CO₂ + 2H₂ + Δ
(a) State which substance is oxidised & which is reduced.
Carbon monoxide (CO) is oxidized to Carbon dioxide (CO₂). Water/steam (H₂O) is reduced to Hydrogen (H₂).
(b) To separate CO₂ from unreacted CO - state why the mixture is not dissolved in water under normal atmospheric pressure, but in water subjected to high pressure.
Carbon dioxide is significantly more soluble in water under high pressure (around 30 atmospheres), making the separation process highly efficient.
(c) The reason for adding chromic oxide to iron [III] oxide, in the reaction.
Chromic oxide acts as a promoter, meaning it enhances the catalytic efficiency of the Iron [III] oxide catalyst.

7. In extraction of metals - hydrogen reduces oxides of metals, e.g. Zn, Fe & Cu but not oxides of K, Na, & Ca to free metals.
K, Na, and Ca are highly active metals (placed above hydrogen in the activity series); their oxides are extremely stable and possess high affinity for oxygen, so hydrogen cannot reduce them. Zn, Fe, and Cu are less active, and their oxides can be successfully reduced by hydrogen.

8. Is the conversion of potassium iodide to iodine - a reduction or an oxidation reaction. Give reasons.
It is an oxidation reaction. The iodide ion (I^-) loses electrons to become an iodine molecule (I₂). According to the electronic concept, the loss of electrons is defined as oxidation.

9. In the reaction 2FeCl₃ + H₂S → 2FeCl₂ + 2HCl + S - H₂S acts as a reducing agent. Give reasons.
Hydrogen sulphide provides hydrogen to chlorine, and simultaneously removes the electronegative element (chlorine) from Iron [III] chloride, reducing it to Iron [II] chloride.

1. Ca(OH)₂ + H₂
C : cold water

2. MgO + H₂
E : boiling water

3. Fe₃O₄ + H₂
G : steam

4. Al₂(SO₄)₃ + H₂
A : dilute acid

5. NaAlO₂ + H₂
D : conc. alkali

1. MgCl₂ ← HCl → FeCl₂.
Mg + 2HCl → MgCl₂ + H₂
Fe + 2HCl → FeCl₂ + H₂

2. KAlO₂ ← KOH → K₂ZnO₂.
2Al + 2KOH + 2H₂O → 2KAlO₂ + 3H₂
Zn + 2KOH → K₂ZnO₂ + H₂

3. ZnO ← H₂O → Fe₃O₄
Zn + H₂O → ZnO + H₂
3Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂

4. CO + H₂ ← H₂O → CO₂ + H₂
C + H₂O → CO + H₂
CO + H₂ + H₂O → CO₂ + 2H₂

5. NH₃ ← H₂ → H₂S
N₂ + 3H₂ ⇌ 2NH₃
H₂ + S → H₂S

1. Nitric acid in the dilute form is not used in the laboratory preparation of hydrogen from metals.
It acts as a strong oxidizing agent and oxidizes the liberated hydrogen gas to form water.

2. Granulated zinc is preferred to metallic zinc in the preparation of hydrogen using dilute acid.
Granulated zinc contains traces of impurities (like copper), which have a catalyzing effect and safely enhance the speed of the chemical reaction.

3. Hydrogen and alkali metals of group 1 [IA] react with copper [II] oxide to give copper.
Both hydrogen and alkali metals act as strong reducing agents, successfully reducing the less active metal oxide (CuO) to pure metallic copper.

4. Hydrogen is collected by the downward displacement of water and not air even though - it is lighter than air.
Hydrogen forms a highly explosive mixture with air, so displacing air poses a huge risk. Since it is nearly insoluble in water, it can be collected safely by the downward displacement of water.

5. A mixture of hydrogen and chlorine can be separated by passage through a porous pot.
Hydrogen diffuses much faster than chlorine through the porous pot because it is considerably lighter (less dense), thereby allowing separation.

1. A metal below iron but above copper in the activity series of metals which has no reaction with water.
Lead (Pb).

2. A metal which cannot be used for the preparation of hydrogen using dilute acids.
Lead (Pb).

3. The salt formed when aluminium reacts with potassium hydroxide, during the preparation of hydrogen from alkalis.
Potassium aluminate (KAlO₂).

4. A gaseous reducing agent which is basic in nature.
Ammonia (NH₃).

5. A compound formed between hydrogen and an element from group 17 [VIIA] - period 3.
Hydrogen chloride (HCl).

1. The element placed below hydrogen in group 1 [IA]. [Na, Li, K, F].
Li

2. The element other than hydrogen, which forms a molecule containing a single covalent bond. [Cl, N, O]
Cl

3. The element, which like hydrogen has one valence electron. [He, Na, F, O]
Na

4. The element, which like hydrogen is a strong reducing agent. [Pb, Na, S, Cl]
Na

5. The element which forms a diatomic molecule. [C, Br, S, P]
Br

1. State what is added through the thistle funnel 'Y'.
Dilute hydrochloric acid or dilute sulphuric acid.

2. State what difference will be seen if pure zinc is added in the distillation flask 'X' instead of granulated zinc.
The reaction will be extremely slow due to the absence of trace impurities that normally act as a catalyst.

3. Name a solution which absorbs the impurity - H₂S.
Lead nitrate solution.

4. State why hydrogen is collected after all the air in the apparatus is allowed to escape.
To prevent the formation of an explosive hydrogen-air mixture which might explode upon accidental ignition.

5. Name a gas other than hydrogen collected by the same method.
Oxygen (or Nitrogen).