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CTEVT Chemistry Note : Inorganic Chemistry(I) : Hydrogen and Water.

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CHAPTER-1  : HYDROGEN

Symbol : H

Atomic Number : 1

Atomic weight : 1.008

Electronic configuration : 1s1
Laboratory preparation of hydrogen gas :

Hydrogen is prepared in the laboratory by the action of the dilute hydrochloric acid or dilute sulphuric acid on granulated zinc.

Granulated zinc is taken in woulf’s bottle and all the apparatus are fitted as shown in fig. When dil. H2SO4 is poured through thistle funnel, reaction between Zn and H2SO4 takes place to produce hydrogen gas which is collected in a gas jar by downward displacement of water.

Hydrogenation reaction : (Preparation of Vanaspati ghee) :

When vegetable oil is heated with hydrogen gas in presence of Ni, Pt or Pd, vegetable ghee is formed. This process is called hydrogenation or hardening of vegetable oil.

Different forms of hydrogen :
  1. Molecular hydrogen
  2. Atomic hydrogen
  3. Nascent hydrogen

 1. Molecular hydrogen : Ordinary hydrogen gas which consists of diatomic molecules in which two H atoms are combined together by a covalent bond is known as molecular hydrogen. Due to high H-H bond energy ( 104 KCalmol-1), molecules of hydrogen is very stable. It does not reacts under ordinary conditions.

 2. Nascent hydrogen : (nascent=newly born) : The atomic hydrogen which is produced during the chemical reaction is called nascent hydrogen.

It is more reactive than ordinary hydrogen molecule. Thus nascent hydrogen is powerful reducing agent than ordinary hydrogen. Following reactions support this statement:       

i. Reduction of potassium permanganate: When molecular hydrogen gas is passed through acidified KMnO4, the pink colour of KMnO4 does not change.

But when a piece of zinc is treated with acidified KMnO4, it’s pink colour is discharged. This is because nascent hydrogen produced from the reaction between zinc and H2SO4 reduces KMnO4 into MnSO4 salt.

ii.Reduction of potassium dichromate: When molecular hydrogen gas is passed through acidified K2Cr2O7, the orange colour of K2Cr2O7 does not change.

But when a piece of zinc is treated with acidified K2Cr2O7, it’s orange colour changes to light green. This is because nascent hydrogen produced from the reaction between zinc and H2SO4 reduces K2Cr2O7 into Cr2(SO4)3 salt.

iii.Reduction of ferric chloride: When molecular hydrogen gas is passed through ferric chloride, the yellowish brown(orange) colour of ferric chloride does not change.

But when a piece of zinc is treated with acidified FeCl3, its colour changes to pale green.

Ortho and Para hydrogen :

Hydrogen molecule in which two hydrogen atoms have same nuclear spin (parallel nucleus spin) is called ortho hydrogen and hydrogen molecule in which two hydrogen atoms have opposite nuclear spin( anti-parallel nucleus spin) is called para hydrogen.

           ( Parallel spin)                 ( Opposite spin)

Therefore, in ortho hydrogen two nuclei spin in the same direction and resultant nuclear spin is high but in para hydrogen, two nuclei spin in opposite direction and the resultant nuclear spin is zero. Hence, para hydrogen has lower internal energy than the ortho hydrogen.

Differences between ortho and para hydrogen :

 Ortho hydrogen

             Para hydrogen
  1. Hydrogen molecule in which two hydrogen atoms have same nuclear spin is called ortho hydrogen.
  2. It is more stable at room temperature.
  3. 75% of total hydrogens are ortho at room temperature.
  4. It’s % can be increased by increasing temperature.
  1. Hydrogen molecule in which two hydrogen atoms have opposite nuclear spin is called para hydrogen.
  2. It is very stable at very low temperature(273K)
  3. 25% of total hydrogen are para at room temperature.
  4. It’s % can be increased by decreasing temperature.
Isotopes of Hydrogen :

Isotopes are the atoms of the same element having same atomic number but different mass number. There are three isotopes of hydrogen:

  1. Protium or ordinary hydrogen
  2. Deuterium or heavy hydrogen
  3. Tritium or radioactive hydrogen.

   

       Name

Protium

Deuterium

Tritium

Symbol

Atomic no.(Z)

Mass no.(A)

Protons

Neutrons

Electrons

1H or H

1

1.007

1

0

1

2H or D

1

2.0014

1

1

1

3H or T

1

3.017

1

2

1

Naturally occurring hydrogen contains about 99.985% of proton, 0.014% of deuterium and 0.001 % of tritium.

CHAPTER – 2  : WATER

Classification of water :

Depending upon the nature of salts(mineral substances) present in the water and its behavior towards soap, water is classified into two types.

Types of Hardness : The hardness of water is of two types:

Q) Explain the causes of permanent/temporary hardness of water.

Removal of hardness of water :

1. Removal of temporary hardness of water :

By boiling : When temporary hard water containing bicarbonates of magnesium and calcium is boiled, these are converted to the insoluble carbonates which settle down. These residues are removed by filtration, and then the filtrate becomes soft water.

2. Removal of permanent hardness of water :

i) By the addition of washing soda ( Na2CO3. 10 H2O) :

When hard water is treated with sodium carbonate ( washing soda), the insoluble carbonates of Ca and Mg are obtained which are removed by filtration, then the filtrate becomes soft water.

ii) By Permutit Process (Ion exchange method) : – – – – – – {Very imp.}

In this method, hard water is passed through a bed of a special material called zeolite, which has the property of removing calcium and magnesium from the water and substituting sodium in their place by ion exchange. {This method is applied to remove both temporary and permanent hardness of water at the same time. }

Permutit is a complex compound which occurs naturally but may also be synthesized. The common artificial zeolite is permutit i.e. sodium aluminium silicate (Na2Z , where, Z = Al2Si2O8.xH2O)

A tall cylindrical vessel fitted with two inlets and two outlets is filled with sand at its bottom and permutit above the sand as shown in figure. When hard water containing CaSO4, CaCl2, MgSO4 or MgCl2 is passed into the vessel through the inlet, sodium ion of the permutit is exchanged by Ca++ or Mg++ ions of hard water to produce insoluble calcium or magnesium aluminum silicate. Thus hard water rising above gets softened and goes out through outlet provided at the top of the vessel.

Regeneration of permutit: After some time, the whole Na2Z gets changed into MgZ and CaZ, and further reaction stops. The exhausted permutit is treated with 10% NaCl solution, original permutit is regenerated. The 10% NaCl solution is passed into cylinder through second inlet and waste products are removed through second outlet provided at the bottom of the vessel.

Advantages and disadvantages of hard water :

The advantages of hard water :

  1. Hard water is good for making our bones and teeth stronger when we drink it.
  2. Hard water tastes better than soft water.
  3. Hard water is generally safer for drinking than soft water.
  4. Hard water does not dissolve lead, and as a result of this it does not lead to lead poisoning if lead pipes are used in transferring the water into households.

The disadvantages of hard water :

  1. Since hard water does not give lather easily with soap, it wastes more soap when it is used in washing. It therefore is not economical to be used in washing.
  2. It is not advisable to use hard water in washing white fabrics since it tends to stain white fabrics by making them appear grey.
  3. Hard water forms annoying lime scales (a hard crust) in containers such as kettles, pots, pipes, etc.
Drinking Water :

Meaning of drinking water:

Water used for drinking purposes should fulfill the following conditions:

  1. It should be colourless and free from any foul smell.
  2. It should be free from any germs, bacteria, algae and fungi which cause diseases.
  3. It should contain small quantities of calcium salts dissolved in it.
  4. It should be free from dissolved salts like nitrites, nitrates and ammonium salts.
Methods for purification of drinking water :
  1. Boiling : Boiling water is the cheapest and safest method of purifying water for household purposes. To be effective, the water must be boiled for 5 to 10 minutes. It kills all bacteria, spores, cysts, ova, etc and yields sterilized water. Boiling also removes temporary hardness of water. Water should be boiled in the same container in which it is to be stored to avoid contamination during storage.
  2. Filtration : Water can be purified on a small scale by filtering through ceramic filters. Filter candles of the fine type usually remove bacteria found in drinking water, but not the filter-passing viruses. Filter candles should be cleaned by scrubbing with a hard brush under running water and boiled at least once a week.

Since filtration does not deplete all the mineral salts, water that has been filtered is considered healthier compared to water purified using other methods.

       3. Using chemical disinfectants: eg.

    1. By using bleaching powder
    2. By using chlorine solution
    3. By using iodine
    4. By using ozone

Chlorination : Chlorine is a powerful chemical that has been in use for many years to treat water for household purposes. Chlorination is an cheap and effective water purification method that kills bacteria, germs, parasites and other disease-causing organisms found in ground or tap water. Water can be purified using chlorine tablets or liquid chlorine. However, caution should be taken when using chlorine liquid or tablets to treat drinking water. For example, people suffering from thyroid problems should talk to a medical practitioner before using chlorinated water. When using chlorine tablets, it is important to apply them in heated water, as they dissolve well in water that is at 21 degree Celsius or higher.

Solvent property of water :

Water is also called universal solvent because it dissolves many substances than any other solvent does. Water dissolves many inorganic as well as polar organic compounds. It dissolves ionic and covalent compound in different way.

 1. Ionic compounds : Water has very high value of dielectric constant( i.e. ~82).It means the electrostatic force of attraction existing between the ions in the crystal lattice is weakened nearly 82 times .So, when ionic compound is added to water, they are first dissociated by water into their respective ions. The ions are then surrounded with water molecules by forming ion-dipole interactions. For example, if the ionic compound is NaCl then,

Fig. Hydration of sodium chloride.

2. Covalent compounds : Some polar covalent compounds like alcohol, ammonia, amines, carboxylic acids, etc. are soluble in water because water molecule interacts with the functional group of these compounds by forming intermolecular hydrogen bond.

For example, if the covalent compound is alcohol then,

Heavy Water :

Deuterium oxide (D2O) is called heavy water. It’s molecular weight is 20.

Uses: 1) It is used as moderator and coolant in nuclear reactors.

          2) It is used as a tracer in metabolic process.

         3) It is used in the preparation of heavy hydrogen.

See next chapters ⇒

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