Explain the following-(a) Iron articles are galvanised.
Ans:- To prevent from rusting iron particles are galvanized.
(b)Metals like Na, K, Ca and Mg are never found in their free state in nature.
Ans:- Na, K, Ca and Mg are alkali and alkaline earth metals. They are the most reactive metal and readily react with atmospheric oxygen and other gases. Therefore they are found in their free state in nature.
(c)Reactivity of Al decreases if it is dipped in HNO3.
Ans:- When aluminum is dipped in nitric acid, a layer of aluminium oxide is formed on the metal.This happens because nitric is a strong oxidizing agent. The layer of aluminum oxide prevents further reaction of aluminium. Due to this, the reactivity of aluminium decreases if it is dipped HNO3.
(d)Carbon can not reduce the oxides of Na or Mg.
Ans:- The oxides of highly reactive metals like Na, Mg are very stable and cannot be reduced by carbon as a reducing agent.
(e)NaCl is not a conductor of electricity in the solid state whereas it does not conduct electricity in aqueous solution as well as in molten state.
Ans:- This is because it dissociates into ions in its aqueous state.
An element A burns with golden flame in air. It reacts with another element B, atomic number 17 to give a product C on electrolysis gives a compound D and liberate hydrogen. Identify A, B, C and D. Also write down the equation for the reactions involved.
Ans:- A- Sodium (Na), B- Chlorine (Cl),C- Sodium Chloride (NaCl),D- hydrochloric acid(HCl). The reaction involves —>
2 Na + Cl2 —> 2NaCl; 2NaCl + 2 H2O —> 2NaOH + Cl2 + H2
Write a balanced equation for the reaction when-(i) Iron is heated strongly in the air.(ii) steam is passed over a red hot iron.(iii) Aluminium is treated with dilute hydrochloric acid.
Ans:-(i) 3Fe (s) + 2O2 (g) —> Fe3O4 (s)
(ii) 3Fe (s) + 4H2O (g) —> Fe2O4 (s) + 4H2 (g)
(iii) 2Al (s) + 6HCl (aq) —> 2AlCl3 (aq) + 3H2 (g)
Q.(a) What is the activity series of metals? Arrange the metals Zn, Mg, Al, Cu and Fe in decreasing order of reactivity. (b) What would you observe when you put (i) some zinc pieces into blue copper sulphate solution (ii) Some copper pieces into green ferrous sulphate solution. (c) Name a metal which combines with hydrogen gas.
(a)The arrangement of metals in a vertical column in the order of decreasing reactivities is called reactivity series of metals or activity series of metals. The decreasing order of reactivity series are-: Mg>Al>Zn>Fe>Cu
(b)(I)When we put zinc copper sulphate solution then the blue color of copper will fade (II)No change will be seen as copper is less reactive than iron.
(c)Sodium combines with hydrogen gas to give sodium hydride.
15. Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.
Ans:- (a)Steps involved in the extraction of less reactive metals like mercury:
(l)Roasting: Heating of metal sulphide in presence of excess of air to form metal oxide.
2HgS + 3O2 —(Roasting)—> 2HgO + 2SO2
(ll)Reduction: Metal oxide can be reduced to metal in the presence of a reducing agent at high temperature.
(b)Extraction of metals with medium reactivity like Zinc:
(l)Roasting: Heating of metal sulphide in the presence of excess of air to form metal oxide.
2 ZnS + 3O2 —> 2 ZnO + 2 SO2
(ll)Reduction: Metal oxide can be reduced to metal in the presence of a reducing agent like C or Al at high temperature.
What is Calcination? What type of ores are subjected to calcination? Write the chemical equation that takes place during the calcination of Limestone and Calamine.
Ans:- Calcination in the process in which a carbonate ore is heated strongly in the absence of air to convert it into metal oxide. Carbonate ores are subjected to calcination. Chemical Reaction:
Two ores A and B were taken on heating, ore A gives CO2 whereas B gives SO2. What steps will you take to convert them into metals?
Ans:- Since are A gives CO2 & B gives SO2.So ore A is a carbonate ore and ore B is a sulphide ore. Since A is a Carbonate Ore, it is first subjected to calcination followed by reduction.
As B is a sulphide ore, it is first subjected to roasting followed by reduction.
What are the constituents of solder alloy? Which property of solder makes it suitable for welding electrical wires?
Ans:- The constituents of solder alloy are lead and tin. Solder alloy has a low melting point but has excellent electrical conductivity, So it is used for soldering of electrical wires.
A non-metal A is an important constituent for 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?
Ans:- (l) A–>Carbon(C) , B –>Carbon monoxide(CO), C –>Carbon dioxide( CO2 )
(ll)Since the electronic configuration of carbon is 2,4. It is present in the 14th group of the periodic table.
Explain the methods of reducing oxides of the least reactive metals, moderate reactive metals and more reactive metals.
Ans:- The less reactive metals which are quite low in metal reactivity series are extracted by reduction of their oxides by heat alone.Eg:-Extraction of mercury from cinnabar.
The moderately reactive metals which are in the middle of the reactivity series are extracted by reduction of their oxides with Carbon, Aluminum, Sodium or Calcium.
The highly reactive metals (which are placed high up in the reactivity series) are extracted by electrolysis of their molten chlorides or oxides. An electrolytic reduction is brought about by passing an electric current through the molten salt.
Of the three metals X, Y and z. X reacts with cold water, Y reacts with hot water and Z with steam only. Identify X,Y and Z and also arrange them in order of increasing reactivity from their respective sulphide ores.
Ans:- X reacts with cold water. So the element is calcium.
Y reacts with hot water, so it is magnesium.
Z reacts with steam only, so it can be Iron.
Arranging in ascending order:-
A non-metal A which is the largest constituent of air, when heated with H2 in 1:3 ratio in presence of a catalyst (Fe) gives a gas B. On heating with O2 gas it gives an oxide. If this oxide is passed into the water in the presence of air it gives an acid D which acts as a strong oxidising agent. (a) Identify A, B, C and D (b) To which group of periodic table does this non-metal belong?
Ans:- N2 + 3 H2 —> 2NH3; N2 + 2 O2 —> 2NO2; 3NO2 + H2O —> 2 HNO3
A-Nitrogen gas, B-ammonia gas, C-Nitrogen dioxide, D-Nitric acid.
(b) The non-metal belongs to group 15 because it has 5 valance electron.