Carbon Dioxide

Occurrence

Free, 20% in air, and 0.04% dissolved in water

Preparation

Lab method

1.        By heating a metal carbonate

CaCO₃ Δ→ CaO + CO_2↑

ZnCO₃ Δ→ ZnO + CO_2↑

CuCO₃ Δ→ CuO + CO_2↑ (bluish-green to black)

Sodium and potassium carbonates do not decompose on heating. Sodium carbonate may give off water vapor.

               Na₂CO₃ · 10H₂O → Na₂CO₃ + 10H₂O

2.        By adding hydrochloric acid to calcium carbonate

CaCO₃ + 2HCl →  CaCl₂ + H₂O + CO_{2 ↑}

(Other acids, like sulphuric acid are not preferred because calcium carbonate gets coated by another calcium salt, rendering it passive)

The gas is collected under air.

               NaHCO₃ + HCl →  NaCl + H₂O + CO_{2 ↑}

               2NaHCO₃ Δ→ Na₂CO3 + H₂O + CO_2↑

               Ca(HCO₃)₂ Δ→ Ca₂CO3 + H₂O + CO_2↑

Industrial method

Steam is passed over heated coke. The reaction produces hydrogen and carbon monoxide. This water gas, if passed with excess steam over a catalyst, iron (III) oxide, forms carbon dioxide and hydrogen.

C + H₂O → CO + H₂

CO + H₂ + H₂O → CO₂ + 2H₂

Properties

Physical

1.        It is a colorless, odorless, tasteless acidic gas.

2.        It is slightly soluble in water. (It can be dried using P₂O₅)

Chemical

1.        It does not support combustion, and it does not burn. However, magnesium burns in CO₂ to form its oxide and carbon.

2Mg + CO₂ → 2MgO + C

               Sodium and potassium also burn, but later form carbonates.

4Na + CO₂ → 2Na₂O + C

4K + CO₂ → 2K₂O + C

Na₂O + CO₂ → Na₂CO₃

K₂O + CO₂ → K₂CO₃

2.        It neutralizes alkalies.

CO₂ + 2KOH → K₂CO₃ + H₂O

CO₂ + 2NaOH → Na₂CO₃ + H₂O

CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

Uses

1.        In fire extinguishers – formed by the action of sulphuric acid on sodium hydrogen carbonate.

2.        Used as a refrigerant – dry ice.

3.         Is a leavening agent – baking soda, sodium bicarbonate and an acid in dry form react.

4.        In soft drinks, dissolved and under pressure.

Hydrogen

Occurrence

In water, organic compounds, etc.

Preparation

Lab method

1. Action of active metals on water.

2Na + 2H₂O → 2NaOH + H_2↑

2K + 2H₂O → 2KOH + H_2↑

Ca + 2H₂O → Ca(OH)₂ + H_2↑

2. Action of less active metals on steam –

Zn + H₂O → ZnO + H_2↑

Mg + H₂O → MgO + H_2↑

Over red hot iron, steam forms hydrogen

3Fe + 4 H₂O → Fe₃O₄ + 4H_2↑

3. From acids

Zn + H₂SO₄ → ZnSO₄ + H_2↑

Zn + 2HCl → ZnCl₂ + H_2↑

                    The intensity with which metals displace hydrogen from acids depends on a series

K, Ca, Na,	Mg, Al, Zn, Fe,	Ni, Sn, Pb,	H,	Cu, Hg, Ag, Au, Pt
Displace hydrogen  violently	Displace hydrogen  vigorously	Displace hydrogen quietly		Do not displace hydrogen

4. From alkalies

Zn + 2NaOH → Na₂ZnO₂ + H_2↑

Zn + 2KOH → K₂ZnO₂ + H_2↑

2Al + 2NaOH + 2H₂O → 2NaAlO₂ + 3H_2↑

2Al + 2KOH + 2H₂O → 2KAlO₂ + 3H_2↑

The gas is dried by CaCl₂

Industrial method

1. Steam is passed over heated coke to produce water gas.

               C + H₂O → CO + H_2↑

Water gas and excess steam are passed over a catalyst, iron (III) oxide.

               CO + H₂ + H₂O → CO₂ + 2H_2↑

Carbon dioxide is absorbed by caustic soda or potash to obtain hydrogen.

2. If water is electrolyzed, hydrogen can be collected at the cathode.

Properties

Physical

1. It is a colorless, odorless gas.
2. It is 0.069 times as heavy as air.
3. It is almost insoluble in water.
4. B.P = -253°C, M.P. = -259.4°C.
5. Noble metals readily absorb hydrogen when finely divided.

Chemical

1. It is combustible, but does not support combustion.

2H₂ + O₂ → 2H₂O

2. Hydrogen and chlorine react explosively in direct sunlight.

H₂ + Cl₂ → 2HCl

3. If hydrogen is passed through boiling sulfur, it forms hydrogen sulfide

H₂ + S → H₂S

4. Combines with nitrogen in the presence of catalysts to form ammonia.

N₂ + 3H₂ → 2NH₃

5. It reduces metal oxides

H₂ + CuO → H₂O + Cu

H₂ + PbO → H₂O + Pb

Fe₂O₃+ 3H₂ → 3H₂O + 2Fe

Uses

1. As a fuel – in rockets, in torches. In electric arcs, it absorbs energy to split to atoms, and outside the arc it forms molecules releasing energy.
2. In self-lighting jets – hydrogen is absorbed by finely divided metals, and heat is released, which is used to ignite fuel.
3. In meteorological balloons.
4. In the presence of catalysts, it is used to make petrol from coal.
5. In the extraction of metals

WO₃ + 3H₂ → W + 3H₂O

6. Hydrogenation of oils – If heated with oils to 150° - 200°C at 5 atmos. pressure in the presence of nickel, oils are hydrogenated to a semi-solid state.
7. To make ammonia and hydrochloric acid by the direct combination of elements.

Quicklime

Coal and limestone are heated in a furnace. Quicklime is formed, but it contains ash. To get ash-free quicklime, limestone is heated with producer gas.

Uses

1.        To make slaked lime and limewater.
CaO + H₂O → Ca(OH)₂

2.        To dry ammonia.

3.        To produce limelight, an intense white light created by heated CaO.

4.        To make mortar. A thick paste of slaked lime, 3-4 parts sand, is used as mortar. On drying, CaO remains, which reacts with carbon dioxide to form calcium carbonate.
Ca(OH)₂ → CaO + H₂O
CaO + CO₂ → CaCO₃

Oxygen

Occurrence

1.      In air, 21% by volume.

2.      In water, 89%, and dissolved in it.

3.      In metal and non-metal oxides.

Preparation

Lab method

1.      Heating of metal oxides

2Ag₂O Δ→ 4Ag + O_2↑

2HgO Δ → 2Hg + O_2↑

2Pb₃O₄ Δ → 6PbO + O_2↑

2PbO₂ Δ → 2PbO + O_2↑

2.      Heating hydrogen peroxide
2H₂O₂ Δ (MnO₂) → 2H₂O + O_2↑

3.      Heating of potassium chlorate
2KClO₃ Δ → 2KCl + 3O₂

4.      Reaction of water and sodium peroxide.
2Na₂O₂ + H₂O → 4NaOH + O_2↑

Industrial

1.      From air – dust is removed by filters, CO₂ is removed by potassium hydroxide and water is removed by a drying agent. Air is liquefied by compression and cooling. When warmed, liquid nitrogen boils away first (-196°C) and liquid oxygen next (-183°C). It is stored in cylinders.

2.      From water – the electrolysis of water yields oxygen at the anode.

Properties

Physical

1.      It is a colorless, odorless, tasteless, neutral gas.

2.      It is slightly soluble in water, and slightly heavier than air.

3.      It boils at -183°C.

Chemical

1. It does not burn, but supports combustion.
2. It forms oxides.
1. Acidic oxides – or acid anhydrides, combine with water to form acids.

S + O₂ → SO₂ then SO₂ + H₂O → H₂SO₃

C + O₂ → CO₂ then CO₂ + H₂O → H₂CO₃

4P + 5O₂ → 2P₂O₅ then P₂O₅ + 3H₂O → 2H₃PO₄

These react with bases:

SO₂ + NaOH → Na₂SO₃ + H₂O

CO₂ + NaOH → Na₂CO₃ + H₂O

P₂O₅ + 6NaOH → 2Na₃PO₄ + 3H₂O

2. Basic oxides – are oxides of metals – they react with acids

MgO + H₂SO₄ → MgSO₄ + H₂O

Fe₂O₃ + 6HCl → 2FeCl₃ + 3H₂O

CaO + H₂SO₄ → CaSO₄ + H₂O

Some basic oxides react with water to form alkalis

K₂O + H₂O → 2KOH

Na₂O + H₂O → 2NaOH

CaO + H₂O → Ca(OH)₂

3. Neutral oxides – for example, H₂O, CO, NO, etc.
4. Amphoteric oxides – act as both acids and bases.

ZnO + H₂SO₄ → ZnSO₄ + H₂O

ZnO + 2NaOH → Na₂ZnO₂ + H₂O

3.  Oxygen oxidizes lower oxides                    

2NO + O_{2 (Pt)}→ 2NO₂
2SO₂ +  O₂ → 2SO₃
2CO + O₂ → 2CO₂

4.  Oxidation

2H₂S + 3O₂ → 2H₂O + 2SO₂

CH₄ + 2O₂ → CO₂ + 2H₂O

2ZnS + 3O₂ → 2ZnO + 2SO₂

4NH₃ + 5O_{2 (Pt, 800°C)} → 4NO + 6H₂O

Confirmatory Tests

1. It rekindles a glowing splint
2. In contact with colorless nitric oxide, it produces reddish-brown fumes of nitrogen dioxide
3. It is absorbed by a solution of pyrogallol, which turns brown

Uses

1. For respiration
2. In medicine
3. In oxy-acetylene torch
4. In iron and steel production, to remove impurities
5. In explosives
6. In rockets, liquid oxygen is used for combustion

Carbon Monoxide

Carbon monoxide is formed by the incomplete oxidation of carbon. It is found in petrol fumes.

Preparation

Lab method

1.        Concentrated sulphuric acid is added to oxalic acid and heated. Dehydration occurs, and a mixture of carbon dioxide and carbon monoxide is formed.
Carbon monoxide is collected by the downward placement of water.
H₂C₂O₄ Δ (Conc. H₂SO₄) → H₂O + CO₂ + CO 
Carbon dioxide is absorbed by potassium hydroxide solution.
KOH + CO₂ → KHCO₃

2.         Concentrated sulphuric acid is added to formic acid and heated. Dehydration occurs, and the carbon monoxide formed is collected over water.
H · COOH Δ (Conc. H₂SO₄) → H₂O + CO

Sodium formate can also be used – first formic acid is liberated, then it is dehydrated

H · COONa + H₂SO₄ → NaHSO₄ + H · COOH
H · COOH Δ (Conc. H₂SO₄) → H₂O + CO

These preparations should be carried out in fume cupboards.

Properties

Physical

1. It is a colorless, odorless and tasteless gas.
2. It is slightly soluble in water.
3. It is highly poisonous.
4. Boiling point -192°C
5. Melting point -207°C

Chemical

1. It is a neutral oxide of carbon.
2. It is a stable compound.
3. It does not support combustion, but is combustible.

               2CO + O₂ → 2CO₂ + 135400 cal.

4. It reduces metal oxides at high temperatures.

               PbO + CO → Pb + CO₂

               CuO  + CO → Cu + CO₂

               Fe₂O₃ + 3CO → 2Fe + 3CO₂

5. It combines with chlorine in sunlight and in the presence of charcoal.

               CO + Cl₂ → COCl₂ carbonylchloride (phosgene)

6. At 200°C and 6-10 atmos. it combines with sodium hydroxide.

               NaOH + CO → H · COONa

7. It forms an addition product with copper (I) chloride in HCl or ammonia solution.

               CuCl + CO + 2H₂O → CuCl · CO · 2H₂O

8.  
1. With hydrogen, at 300°C, and over nickel, it forms methane.

  300°C, Ni

                                 CO + 3H₂ →  CH₄ + H₂O

2. With hydrogen, at 400°C, and zinc and chromium oxides it forms methyl alcohol.

                              CO + 2H₂ →  CH₃OH

Uses

1. As a fuel – producer of water gas
2. To manufacture phosgene, sodium formate, and methyl alcohol

Efflorescent, Deliquescent, and Hygroscopic Substances

1.      In efflorescence, the vapor pressure of the hydrated salt is greater than the vapor pressure of water vapor in the atmosphere. The salt tries to equalize pressure but, in view of the size of the atmosphere, this can never be achieved, and so it passed to a lower hydrate or the anhydrous salt, with a lower vapor pressure.

Na₂CO₃ · 10H₂O → Na₂CO₃ · H₂O + 9H₂O

2.      In deliquescence, the vapor of the salt hydrate (and its saturated solution) is less than the vapor pressure of water vapor in the atmosphere. The salt tries to equalize pressures by absorbing water from the atmosphere, forming eventually an unsaturated solution.

MgCl₂, 6 H₂O, P₂O₅, NaOH

It should be remembered that the water vapor present in the atmosphere is not constant, varying from day to day and especially from summer to winter. Hence, there is a possibility that certain compounds may be either efflorescent or deliquescent depending on the season or the locality.
Ordinary common salt is not deliquescent but because of MgCl₂ which is an impurity, it dissolves and forms a solution in rainy reason and becomes deliquescent.

Calcium chloride is sprinkled on the road to remove dust as it absorbs moisture and forms a saturated solution by dissolving in it. It is used as a dehydrating agent. The term deliquescent is used for solids only.

3.      A hygroscopic substance (e.g. conc. H₂SO₄, CuO) absorbs water from the atmosphere without forming a solution.
Human hair is hygroscopic.
H₂SO₄ is not deliquescent but it is hygroscopic and used as a dehydrating agent.

Drying Apparatus

To Dry	Drying Agent	Apparatus
Gas	·            Conc. H2SO4 ·        P2O5 ·        CaCl2	Woulfe’s bottle
Gas	·        P2O5 ·            CaCl2 ·        CaO	Drying Tower
Gas	·        (Salt and ice) Freezing mixture	U tube
Liquid	·        Conc. H2SO4	Bottle
Solid	·        Silica gel ·        CaO ·        Anhydrous CaCl2	Dessicator
Solid	·        Conc. H2SO4	Bottle

Crystals

A solid bounded by plain surfaces having definite geometrical shapes. In nature, crystals are found as minerals, for example, ruby, diamond, graphite, etc. These crystals have beautiful color due to impurities or traces of water present in them.

Making Crystals

_1.           Dissolving a solid in water or any other solvent and then evaporating the liquid. For example, salt, nitre, alum in water. Sulfur in carbon disulphide or carbon tetrachloride CCl₄, iodine in petrol or benzene or spirit.

_2.           By melting a solid and allowing it to cool properly. For example, prismatic sulfur.

_3.           By sublimation. For example, iodine and ammonium crystals.

_4.           By subjecting a solid to great heat and pressure. For example, diamond and graphite. The cost is prohibitive as artificial diamond is more costly than natural diamond.

Water of Crystallization

Some solids while crystallizing out from solution unite with a definite quantity of H₂O known as water of crystallization/ hydration. This water of crystallization can be driven out by heating the crystal to 100°C, and may be condensed and tested. Such crystals lose their crystalline structure and become anhydrous.

Water of crystallization is the number of molecules of water combined it a loose chemical combination which on heating on exposure to air is partly on fully given off by a hydrated salt.

Hydrated Salts

A hydrated salt is a substance which contains water of crystallization which on exposure to air or heat becomes anhydrous by giving off partly or fully its water of crystallization.

Hydrated Salt	Chemical Formula	Common Name
sodium carbonate	Na2CO3 · 10H2O	washing soda
sodium sulphate	Na2SO4 · 10H2O	Glauber’s salt
copper sulphate	CuSO4 · 5H2O	blue vitriol
ferrous sulphate	FeSO4 · 7H2O	green vitriol
zinc sulphate	ZnSO4 · 7H2O	white vitriol (H2SO4 is called oil of vitriol)
cobalt chloride	CoCl2 · 6H2O
barium chloride	BaCl2 · 2H2O
calcium chloride	CaCl2 · 6H2O
magnesium sulphate	MgSO4 · 7H2O	Epsom salt

Crystals without Water of Crystallization – Anhydrous

Anhydrous Salt	Chemical Formula
sodium chloride (common salt)	NaCl
nitre	KNO3
potassium chromate	K2C5O7
potassium chloride	KCl