Water reaches the maximum density at 4°C. The density of ice is lower than that of water. The molecules are in constant motion and the strong hydrogen bonding leads to the closed packing of water molecules.
The melting curve of water in the phase diagram has an unusual negative slope. When the pressure of water increases, its melting point decreases. This is because high pressure reduces the volume of water and this is achieved by changing ice to liquid water.
Water and hydrogen peroxide are poor electrical conductors as they can only slightly ionize in water.
2H2O(l) = H3O+(aq) + OH-(aq)
2H2O2 (aq) = H3O2+(aq) + HO2-(aq)
Water is also a good solvent due to its polar nature. It can dissolve many ionic substances by the solvation of ions in the solution. Moreover, it has a low viscosity and a high specific heat capacity. (4200 J kg-1 °C-1)
Hydrogen peroxide is miscible with cold water and is soluble in alcohol and ether. Although pure hydrogen peroxide is fairly stable, it decomposes into water and oxygen when heated above about 80°C
Occurrence and synthesis:
Water is a naturally occurring substance and most of the earth’s surface is sea. But water from sea is impure. To obtain pure water, simple distillation is practical.
Hydrogen peroxide can be prepared by autoxidation of 2-ethylanthraquinol.
Chemical properties:
Water is involved in many chemical reactions.
Reaction with metals: Water can react with reactive metals like potassium, sodium and calcium to forming metal hydroxide and hydrogen gas.
2K(s) + 2H2O(l) → 2KOH(aq) + H2 (g)
When water is in gaseous state, it can react with magnesium, aluminium, zinc and iron to form metal oxide and hydrogen gas.
Mg(s) + H2O(g) → MgO(s) + H2 (g)
Reaction with s-block metal hydrides: All s-block metal hydrides can react with water to form hydrides and hydrogen.
NaH(s) + H2O(l) → NaOH(aq) +H2 (g)
Reaction with ethane: Water can react with ethene to form ethanol which is catalytic hydration of ethene, for the preparation of ethanol in industries.
H3PO4
CH2=CH2 + H2O CH3CH2OH
300°C, 65 atm
Reaction with ester: Water can undergo a reversible reaction with ester to form alkanol and alkanoic acid.
CH3COOCH2CH3 + H2O = CH3COOH + CH3CH2OH
For hydrogen peroxide, it is readily decomposed into water and oxygen in the presence of MnO2 or catalase.
Catalase/MnO
2H2O2 (aq) 2H2O(l) + O2 (g)
Oxidizing property: Hydrogen peroxide is a powerful oxidizing agent which is readily reduced by the following half equation. The oxidation number of oxygen decreases from -1 to -2.
H2O2 (aq) + 2H+(aq) + 2e- → 2H2O(l)
For example, it can oxidize iodide ions to iodine.
H2O2 (aq) + 2H+(aq) +2I-(aq) → 2H2O(l) + I2 (aq)
Reducing property: Strong oxidants like permanganate ions will oxidize hydrogen peroxide into oxygen gas by the following half equation. The oxidation number of oxygen increases from -1 to 0.
2H2O2→ O2+ 2H + + 2e-
For example, it can reduce permanganate ions to manganese ion.
2MnO4-(aq) + 16H+(aq) + 10H2O2(aq) → 2Mn2+(aq) + 8H2O(l) + 5O2(g) + 10H+(aq)
Free Radical Addition: Hydrogen Peroxide can be used for the production of free radicals.
CH3CH=CH2 HBr/peroxide CH3CH2CH2Br
non-polar solvent
Importance:
Water is essential to our daily lives. It can act as a coolant in car engines for absorbing a large amount of heat with only a small rise in temperature. It can also used as solvent so as to dissolve many polar substances. It is an essential component in living things as it governs many cellular reactions inside our body and it is one of the raw materials in photosynthesis.
Hydrogen peroxide can act as an additive for the polymerization of organic compounds. Farmers can also spray dilute hydrogen peroxide to increase the crop yields. It is even required for the production of thyroid hormone and sexual hormones and help regulate the amount of oxygen getting to our cells. It is used in fuels for rockets and torpedoes and used as a bleaching agent for textiles, e.g., wool and silk, and in paper manufacture. It is also used in chemical manufacture.
End of the Essay