Hydrogen

(a) lighter

(b) sparingly

(c) pale blue, pop

(d) above, dilute acids

(e) metal, water

(f) hydrogen, oxygen

(g) simultaneously

(a) False
Corrected statement — Hydrogen molecule is divalent.

(b) False
Corrected statement — The removal of oxygen from a substance is called reduction.

(c) True

(d) True

(e) True

(f) False
Corrected statement — Hydrogen is combustible but it is non-supporter of combustion.

(g) False
Corrected statement — Hydrogen gas cannot be easily liquefied.

(a) H₂ + Cl₂ ⟶ 2HCl

(b) H₂ + S ⟶ H₂S

(c) Zn + 2HCl ⟶ ZnCl₂ + H₂

(d) CuO + H₂ ⟶ Cu + H₂O

(e) 3Fe + 4H₂O ⟶ Fe₃O₄ + 4H₂

(f) 2K + 2H₂O ⟶ 2KOH + H₂

(a) Hydrogen has high heat of combustion and is pollution free so it is used as a fuel. Liquid hydrogen is used as a rocket fuel.

(b) Though hydrogen is lighter than air it cannot be collected by downward displacement of air because a mixture of hydrogen and air can lead to an explosion so it is not safe to collect hydrogen gas by this method.

(c) A pop sound is produced when hydrogen gas is burnt because of the presence of impurities in it.

(d) Hydrogen gas is highly inflammable in nature, so it is replaced by helium for filling in weather forecasting balloons.

(e) Nitric acid is a strong oxidizing agent (even when it is dilute). It oxidises hydrogen gas converting it into water which defeats the purpose. Hence, nitric acid is not used for the preparation of hydrogen gas.

(a) Potassium, sodium

(b) Iron

(c) Oxidation

(d) Lead monoxide (PbO)

(a) Granulated zinc and dilute hydrochloric acid are the chemicals required to prepare hydrogen gas in the laboratory.

(b) Zn + 2HCl ⟶ ZnCl₂ + H₂ (g)

(c) Below diagram shows the laboratory preparation of Hydrogen gas:

(d) Hydrogen gas is collected by downward displacement of water as it is sparingly soluble in water. Though hydrogen gas is lighter than air, it is not collected by downward displacement of air as a mixture of hydrogen and air can lead to an explosion.

(a) Hydrogen gas is a non-supporter of combustion is shown by the following experiment:

1. Hold a hydrogen gas filled jar with its mouth downwards.
2. Placed a lighted candle and cover it with this jar.
3. The candle gets extinguished but the gas burns with a pop sound.

This shows that hydrogen gas is non-supporter of combustion but itself is combustible.

(b) Hydrogen gas is lighter than air is shown by the following experiment:

1. Take a delivery tube and place one of its ends in a liquid soap solution kept in a trough and other end inside a flat bottom jar.
2. In the flat bottom jar hydrogen gas is freshly prepared by the action of dilute hydrochloric acid on zinc granules.
3. Hydrogen gas enters the soap solution through delivery tube.
4. The soap bubbles containing hydrogen rise upward in the air.

The rising soap bubbles prove that hydrogen is lighter than air.

When hydrogen is passed over hot metallic oxides of copper, lead, iron, etc. it removes oxygen from them and thus reduces them to their corresponding metals. Hence, hydrogen acts as a good reducing agent.

When hydrogen gas is passed over heated copper oxide, copper oxide gets reduced to metallic copper by the removal of oxygen from it. The equation for the reaction is given below:

CuO + H₂ ⟶ Cu + H₂O

(a) Bosch process

(b) Equations for the reactions of Bosch process are:

Production of water gas:

$\underset{\text{hot coke}}{\text{C}} + \underset{\text{steam}}{\text{H}_2 \text{O}} \xrightarrow {1000\degree\text{C}} \underset{\text{water gas}}{(\text{CO} + \text{H}_2)} - \text{Heat}$

Reduction of steam by water gas:

$\underset{\text{water gas}}{(\text{CO}+\text{H}_2)} + \underset{\text{steam}}{\text{H}_2 \text{O}} \xrightarrow [\text{450\degree C}] {\text{Fe}_2\text{O}_3/ \text{Cr}_2\text{O}_3} \text{CO}_2 + 2\text{H}_2 + \text{Heat}$

(c) Hydrogen is separated from carbon dioxide by passing the mixture through water under pressure, where carbon dioxide gets dissolved leaving behind hydrogen. Carbon dioxide can also be separated by passing it through caustic potash (KOH) solution.

2KOH + CO₂ ⟶ K₂CO₃ + H₂O

Carbon monoxide is separated by passing through ammoniacal cuprous chloride in which carbon monoxide dissolves leaving behind hydrogen.

CuCl + CO + 2H₂O ⟶ CuCl.CO.2H₂O

The four uses of hydrogen are:

1. The oxy-hydrogen flame obtained by burning hydrogen and oxygen together has a very high temperature of about 2800°C - 3000°C. Hence it is used for cutting and welding of metals.
2. It is used as a fuel as hydrogen has high heat of combustion.
3. It is used for hydrogenation of vegetable oil.
4. It is used as a reducing agent in extraction of metals.

(a) Catalytic hydrogenation is a process by which hydrogen gas is passed through vegetable oils in the presence of a catalyst like Ni, Pt or Pd to convert the oils into vanaspati ghee.

(b) Oxidation is a chemical process that involves addition of oxygen to a substance or removal of hydrogen from a substance.

(c) Reduction is a chemical process that involves addition of hydrogen to a substance or removal of oxygen from a substance.

(d) Redox reactions are those in which reduction and oxidation both take place simultaneously i.e., one substance is reduced while the other gets oxidized.

hydrogen chloride

Reason — In diffused sunlight, hydrogen combines with equal volume of chlorine gas to form hydrogen chloride gas.

calcium

Reason — Calcium, sodium and potassium are highly active metals which reacts with cold water to produce hydrogen gas.

top

Reason — The metals are arranged in decreasing order of their reactivity in metal activity series, so more reactive metals are placed at the top of the series.

all of the above

Reason — Hydrogen is used in preparation of vanaspati ghee from liquid vegetable fats by catalytic hydrogenation process. It is used to produce chemicals like ammonia which is used as a fertilizer. When burnt with oxygen, it produces oxy-hydrogen flame.

combustible

Reason — Hydrogen is combustible in nature, burns with a pale blue flame but is a non-supporter of combustion.

carbon monoxide and hydrogen

Reason — Water gas is a mixture of carbon monoxide and hydrogen which is produced by passing steam over hot coke at 1000°C.

     $\text{C}+ \text{H}_2 \text{O} \xrightarrow {1000\degree \text{C}} \text({CO + H}_2) - \text{Heat}$