Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in reaction mixture. He made the same observations when this element was treated with hydrochloric acid. Suggest how can he identify the produced gas. Write chemical equations for both the reactions.
The gas can be identified by bringing a burning matchstick near the reaction vessel; a pop sound is produced.
\( M + 2NaOH \rightarrow Na_2M O_2 + H_2 \)
\( M + 2HCl \rightarrow MCl_2 + H_2 \)
The element is a metal.
During extraction of metals, electrolytic refining is used to obtain pure metals. (a) Which material will be used as anode and cathode for refining of silver metal by this process? (b) Suggest a suitable electrolyte also. (c) In this electrolytic cell, where do we get pure silver after passing electric current?
(a) Anode: Impure silver
Cathode: Pure silver
(b) Electrolyte: Silver salt such as \( AgNO_3 \)
(c) Pure silver is obtained at the cathode.
Why should the metal sulphides and carbonates be converted to metal oxides in the process of extraction of metal from them?
It is easier to obtain metal from its oxide as compared with its sulphides and carbonates.
Generally, when metals are treated with mineral acids, hydrogen gas is liberated but when metals (except Mn and Mg) treated with \( HNO_3 \), hydrogen is not liberated. Why?
Because \( HNO_3 \) is a strong oxidising agent. It oxidises the \( H_2 \) produced to \( H_2O \).
Compound X and aluminium are used to join railway tracks. (a) Identify compound X. (b) Name the reaction. (c) Write down its reaction.
(a) X is \( Fe_2O_3 \)
(b) Thermite reaction
(c) \( Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + \text{Heat} \)
When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (Molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.
\( X = Na \)
\( Y = NaOH \)
\( Z = H_2 \)
Reaction: \( 2Na + 2H_2O \rightarrow 2NaOH + H_2 + \text{Heat} \)
A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.
X — Carbon
Y — Diamond
Z — Graphite
The following reaction takes place when aluminium powder is heated with \( MnO_2 \):
\( 3MnO_2(s) + 4Al(s) \rightarrow 3Mn(l) + 2Al_2O_3(l) + \text{Heat} \)
(a) Is aluminium getting reduced? (b) Is \( MnO_2 \) getting oxidised?
(a) No. Oxygen is added to aluminium; therefore, it is getting oxidised.
(b) No. Since manganese has lost oxygen, it is getting reduced.
What are the constituents of solder alloy? Which property of solder makes it suitable for welding electrical wires?
Solder is an alloy of lead and tin. Its low melting point makes it suitable for welding electrical wires.
A metal A, which is used in thermite process, when heated with oxygen gives an oxide B which is amphoteric in nature. Identify A and B. Write down the reactions of oxide B with HCl and NaOH.
A = Al
B = \( Al_2O_3 \)
\( Al_2O_3 + 6HCl \rightarrow 2AlCl_3 + 3H_2O \)
\( Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O \)
A metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved.
Metal: Mercury (Hg)
Ore: Cinnabar (HgS)
Reactions:
\( 2HgS + 3O_2 \xrightarrow{\text{Heat}} 2HgO + 2SO_2 \)
\( 2HgO \xrightarrow{\text{Heat}} 2Hg + O_2 \)
Give the formulae of the stable binary compounds that would be formed by the combination of following pairs of elements.
(a) Mg and N2
(b) Li and O2
(c) Al and Cl2
(d) K and O2
(a) \( Mg_3N_2 \)
(b) \( Li_2O \)
(c) \( AlCl_3 \)
(d) \( K_2O \)
What happens when
(a) \( ZnCO_3 \) is heated in the absence of oxygen?
(b) A mixture of \( Cu_2O \) and \( Cu_2S \) is heated?
(a) It undergoes calcination:
\( ZnCO_3 \xrightarrow{\text{Heat}} ZnO + CO_2 \)
(b) It undergoes auto-reduction forming copper and sulphur dioxide:
\( 2Cu_2O + Cu_2S \xrightarrow{\text{Heat}} 6Cu + SO_2 \)
A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming.
(a) Identify A, B and C.
(b) To which group of Periodic Table does A belong?
(a) A = Carbon, B = Carbon monoxide, C = Carbon dioxide
(b) A belongs to Group 14 of the Periodic Table.
Give two examples each of the metals that are good conductors and poor conductors of heat respectively.
Good conductors: Ag, Cu
Poor conductors: Pb, Hg
Name one metal and one non-metal that exist in liquid state at room temperature. Also name two metals having melting point less than 310 K (37°C).
Metal (liquid): Mercury (Hg)
Non-metal (liquid): Bromine (Br)
Metals with melting point less than 310 K: Caesium (Cs), Gallium (Ga)
An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved.
A = Ca
B = Ca(OH)2
C = CaO
\( Ca(s) + 2H_2O \rightarrow Ca(OH)_2(aq) + H_2(g) \)
\( Ca(OH)_2 \xrightarrow{\text{Heat}} CaO + H_2O \)
\( CaO + H_2O \rightarrow Ca(OH)_2 \)
An alkali metal A gives a compound B (molecular mass = 40) on reacting with water. The compound B gives a soluble compound C on treatment with aluminium oxide. Identify A, B and C and give the reaction involved.
A = Na
B = NaOH
C = NaAlO2
\( 2Na + 2H_2O \rightarrow 2NaOH + H_2 \)
\( Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O \)
Give the reaction involved during extraction of zinc from its ore by
(a) roasting of zinc ore
(b) calcination of zinc ore
(a) Roasting:
\( 2ZnS + 3O_2 \xrightarrow{\text{Heat}} 2ZnO + 2SO_2 \)
(b) Calcination:
\( ZnCO_3 \xrightarrow{\text{Heat}} ZnO + CO_2 \)
A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black coloured product. Identify M and the black coloured product and also explain the reaction of M with oxygen.
M = Cu
Black product = CuO
Reaction: \( 2Cu + O_2 \rightarrow 2CuO \)
An element forms an oxide \( A_2O_3 \) which is acidic in nature. Identify A as a metal or non-metal.
Since the oxide is acidic in nature, A is a non-metal.
A solution of \( CuSO_4 \) was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.
Iron is more reactive than copper. It displaces copper from copper sulphate solution and forms iron sulphate. The displaced copper deposits on the pot and iron dissolves gradually, forming holes.
\( Fe + CuSO_4 \rightarrow FeSO_4 + Cu \)