Chemistry
State one relevant reason for each of the following:
(i) Graphite anode is preferred to platinum in the electrolysis of molten lead bromide.
(ii) Soda lime is preferred to sodium hydroxide in the laboratory preparation of methane.
(iii) Hydrated copper sulphate crystals turn white on heating.
(iv) Concentrated nitric acid appears yellow, when it is left for a while in a glass bottle.
(v) Hydrogen chloride gas fumes in moist air.
Answer
(i) As graphite is unaffected by the reactive bromine vapours released at the anode hence, a graphite anode is preferred to platinum in the electrolysis of molten lead bromide.
(ii) Sodalime is preferred to sodium hydroxide in the laboratory preparation of methane since it is not deliquescent and does not attack glass.
(iii) The blue coloured hydrous copper sulphate changes to white anhydrous copper sulphate as the water of crystallization is removed on heating.
CuSO4.5H2O ⟶ CuSO4 + 5H2O
(iv) Pure nitric acid [HNO3] is colourless and unstable and decomposes slightly even at ordinary temperatures and in the presence of sunlight.
The decomposition results in formation of reddish brown nitrogen dioxide [NO2] which remains dissolved in the acid thus imparting a slight yellowish brown colour.
(v) Due to the high solubility of HCl gas, it fumes in moist air and forms a mist of droplets of HCl acid.
Related Questions
Write a balanced chemical equation for each of the following:
(i) Reaction of carbon powder and concentrated nitric acid.
(ii) Reaction of excess ammonia with chlorine.
(iii) Reaction of lead nitrate solution with ammonium hydroxide.
(iv) Producing ethane from bromo ethane using Zn/Cu couple in alcohol.
(v) Complete combustion of ethane.
(i) Draw the structural formula for each of the following:
- 2,2 dimethyl pentane
- methanol
(ii) Write the IUPAC name for the following compounds:
- acetaldehyde
- acetylene
Give one word or a phrase for the following statements:
(i) The chemical bond formed by a shared pair of electrons, each bonding atom contributing one electron to the pair.
(ii) Electrode used as cathode in electrorefining of impure copper.
(iii) The substance prepared by adding other metals to a base metal in appropriate proportions to obtain certain desirable properties.
(iv) The tendency of an atom to attract electrons to itself when combined in a compound.
(v) The reaction in which carboxylic acid reacts with alcohol in the presence of conc. H2SO4 to form a substance having a fruity smell.
Calculate:
(i) The amount of each reactant required to produce 750 ml of carbon dioxide, when two volumes of carbon monoxide combine with one volume of oxygen to produce two volumes of carbon dioxide.
2CO + O2 ⟶ 2CO2
(ii) The volume occupied by 80 g of carbon dioxide at STP.
(iii) Calculate the number of molecules in 4.4 gm of CO2.
[Atomic mass of C= 12, O=16]
(iv) State the law associated in question no. (f)(i) above.