INDUSTRIAL PREPARATION OF HYDROGEN

SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY CLASS: SS 2

SCHEME OF WORK

WEEK 2

SUB TOPIC 2: INDUSTRIAL PREPARATION OF HYDROGEN

Hydrogen can be prepared

PERIOD 2: LABORATORY AND INDUSTRIAL PREPARATION OF HYDROGEN.

Laboratory preparation of hydrogen:

Hydrogen is liberated when active metals react with dilute mineral acid, water or steam.e.g action of zinc on H₂SO₄

Zn_(s) + H₂SO_4(aq) ZnSO_4 (aq) +H_2 (g)

The hydrogen gas is dried by passing it through Calcium chloride. The apparatus is set up as shown below.

Dilute hydrochloric acid can also be used in place of H₂SO_4. Magnesium and iron can be used in the place of zinc.

Zn_(s) + 2HCl _(aq) ZnCl_{2 (aq)} + H_{2 (g)}

Mg_(s) + H₂SO_4 (aq) MgSO_4(aq) + H_2 (g)

Dilute trioxonitrates (v) acid is never used in the preparation of hydrogen because of its strong oxidizing property and it produces water instead of hydrogen on reaction with metals. However, very dilute trioxonitates (v) acid give out hydrogen on reaction with Magnesium.

Hydrogen can also be prepared in the laboratory in the following ways,

1. By the action of Sodium hydroxide on zinc metal or aluminium.

Zn_(s) + 2NaOH_(aq) Na₂ZnO_2(s) + H_2(g)

2Al_(s) + 2NaOH_(aq) + 2H₂O_(l) 2NaAlO_2(s) + 3H_2 (g)

1. Action of steam on heated metals e.g. Iron, Magnesium.

3Fe_(s) + 4H₂O_(g) → 2NaOH_(aq) + H_2(g)

PREPARATION OF DRY HYDROGEN

The hydrogen gas produced in the first method of flask containing concentrated tetraoxosulphate (vi) acid or anhydrous calcium (ii) chloride as d drying agents.industrially by different methods. These methods are as follows;

From water gas; in this case, water gas and excess stream are passed over a catalyst such as Iron (III) oxide, Fe₂O₃ at a temperature of 723k. The products are hydrogen and carbon (iv) oxide as shown in the equation below.

CO_(g) + H_{2 (g)} + H₂O ⇌ CO_{2 (g)} +2H_{2 (g)}

It is a reversible reaction. CO₂ is dissolved in water under pressure of 30atm or absorbed by caustic soda, leaving hydrogen in good yield. This is Bosch process.

H₂O_(l) + CO_{2( g)} H₂CO_3(aq)

METHOD 2

From natural gas. E.g methane – when natural gas is heated to a temperature of 1000 [thermal cracking] hydrogen is produced as shown in the equation below

CH_4(g) 2H_2(g) + C_(s)

Methane [CH₄] is one of the main constituents of natural gas.

METHOS 3 – FROM HYDROCARBONS

When hydrocarbon e.g methane or propane mixed with steam it is heated to a temperature of 800 in the presence of nickel catalysts, CO(g) and H₂(g) are produced.

CH_4(g) + H₂O_(g) CO_(g) + 3H_2(g)

The mixture of carbon (ii) oxide and hydrogen gas is called synthestic gas. The mixture of [CO_(g) + H_2(g) is reacted with more steam

CO_(g) + H_2(g) + H₂O_(g) ⇋ CO_2(g) + 2H_2(g)

The CO_2(g) is removed by absorption in water or any alkali such as Sodium hydroxide [NaOH] solution.

METHOD 4 – FROM COAL

Here, steam is passed over red-hot coal to obtain water gas[CO + H₂]:

C_(s) + H₂O_(g) CO_(g) + H_2(g)

The water gas [CO + H₂] is reacted with more steam in the presence of nickel or platinum catalyst to produce CO_(g) + H_2(g) + H₂O_(g) ⇋ CO_2(g) + 2H_2(g)

METHOD 5- FROM ELECTROLYSIS OF BRINE

Hydrogen is obtained as a by- production in the electrolysis of brine for the large scale production of Sodium hydroxide and Chlorine H₂ can also be produced by electrolysis of acidified water

EVALUATION

1. What do you observe when a piece of sodium is placed on the surface of water?
2. With equations only, describe at least two more methods of laboratory preparation of hydrogen.
3. What the precaution that one must take while preparing Hydrogen.
4. With equations only describe the preparation of hydrogen from hydrocarbons.