Understanding
Metals and Non – metals
Q1. Name the following:
1. Metal which forms an amphoteric
oxide?
Ans. Aluminium.
2. An alloy of copper and zinc.
Ans. Brass
3. A compound which is added to lower
the fusion temperature of an electrolytic bath in extraction of aluminium.
Ans. Cryolite.
4. A metal which does not react with
cold water but reacts with steam.
Ans. Aluminium.
5. A common ore of aluminium.
Ans. Bauxite.
Q2. From the list of characteristic given below select the
five which are relevant to metals and their compounds.
1. Ductile
2. Conduct electricity
3. Acidic oxide.
4. Discharged at anode basic oxides.
5. Brittle
6. (1,2,3) valence electrons.
7. Discharged at cathode.
8. (5,6,7) valence electrons.
9. Occurring in solid or gaseous state.
10. Basic oxides.
Ans. Characteristic of metals are:
1. Ductile
2. Conduct of electricity.
3. Basic oxides
4. (1,2,3) valence electrons.
5. Discharged at cathode.
Q3. Name one metal each occurring as,
1. A sulphide.
Ans. Copper
2. A carbonate
Ans. Zinc
3. An oxide
Ans. Aluminium
Q4. Explain the following terms.
1. Minerals: - The naturally occurring compounds
of metals along with other impurities are known as minerals.
2. Gangue: - Ores contain metal compounds with
some of the impurities like soil, sand, rocky material etc. These impurities
are called as gangue.
3. Ores: -The minerals from which metals are
extracted profitably and conveniently are called ores.
4. Metallurgy: - The process used for extraction of
metals in their pure form from their ores is called metallurgy.
5. Roasting: - The sulphide ores are first
converted into oxides by heating strongly in excess of air. This process is
called as roasting.
Q5. Give scientific reasons for the following.
1. Sodium is stored under kerosene.
Ans.
i.
Sodium
is a highly reactive metal.
ii.
Sodium
reacts with oxygen in air at room temperature to form, sodium oxide.
iii.
Therefore,
it catches fire and starts burning when open in the air.
iv.
Hence,
sodium is stored under kerosene to prevent its reaction with oxygen, moisture
and carbon dioxide.
2. Gold and silver are used to make
jewellery.
Ans.
i.
Gold
and silver are highly inactive metals. Therefore, they do not undergo corrosion
due to attack by moisture and atmospheric gases.
ii.
Gold
and Silver are very shiny metals (lustrous).
iii.
They
are used to make jewellery because of its bright shiny surface and high
resistance to corrosion.
3. Calcium floats over water during the
reaction with water.
Ans.
i.
Calcium
reacts with water less vigorously so that the heat evolved is not sufficient
for the hydrogen formed, to catch fire.
ii.
Instead,
calcium starts floating because the bubbles of hydrogen gas formed stick to the
surface of the water calcium.
4. Ionic compounds have high melting and
boiling points
Ans.
i.
Ionic
compounds are solids and hard due to strong force of attraction between
positive and negative ions in their molecules.
ii.
A
considerable amount of energy is required to break the strong inter molecular
attraction.
iii.
Hence
ionic compounds have high melting and boiling points.
5. Tarnished copper utensils are cleaned
with lime juice or tamarind.
Ans.
i.
When
copper utensils are exposed to moist air, they get tarnished or corroded due to
the formation of green copper carbonate.
ii.
When
these tarnished vessels are rubbed with lime juice or tamarind the weak acids
present in them dissolve the green copper carbonate and original shine returns.
Q6. Sudha dipped a copper coin in a solution of silver nitrate. After some time
she saw the silver shine on the coin. Why? Give the balanced chemical equation
for the same.
Ans.
1. Copper is more reactive than silver.
Hence displacement reaction occurs.
2. When copper coin is dipped in silver
nitrate solution forming copper nitrate and silver metal.
3. A shining white deposit of silver
metal is formed on copper coin. Hence she saw a silver shine on the copper
coin.
Balanced equation:-
2AgNO3(ag) +
Cu(s) → Cu(NO3)2(ag) + 2Ag(s)
Q7. Metal A has electronic configuration of 2,8,1 and metal B
has 2,8,8,2 which is more reactive. Identify these metals and vie their
reactions with dil HCl.
Ans. Metal A is Sodium (Na) : 2,8,1
Metal B is Calcium (Ca) : 2,8,8,2.
Metal A (Sodium) is more reactive than metal B (Calcium).
Reaction: -
i.
Sodium
metal reacts violently with dilute hydrochloric acid to form sodium chlorides
and hydrogen.
2Na(a) + 2HCl(aq)
→ 2NaCl(aq) + H2(g)
ii.
Calcium
reacts less vigorously to form calcium chloride and hydrogen.
Ca + 2HCl → CaCl2 + H2
Q8. To obtain (zinc) Zn from zinc sulphide two chemical
reaction are involved
Write the equations for A and B.
Ans. Equation for A:
Roasting is the process in which a sulphide ore is strongly heated in
the presence of air to convert it into metal oxide.
Equation for B : Zinc metal is extracted by the reduction of its
oxide with carbon (or coke). Thus, when, Zinc oxide is heated with carbon, Zinc
metal is produced.
Q9. Translate the following statements into chemical equation
and then balance them.
1. When steam is passed over aluminium.
Ans. Aluminium reacts
with steam to form aluminium oxide and hydrogen gas.
2. Extraction of copper from its sulphide
ore.
Ans.
i.
The
concentrated copper sulphide ore is roasted in air when a part of copper
sulphide is oxidized to copper oxide.
ii.
Copper
oxide formed above reacts with the remaining copper sulphide to form copper
metal and sulphur dioxide.
3. Thermit reaction.
Ans. Iron oxide reacts
with aluminium to give iron and aluminium oxide evolving lot of heat.
4. When magnesium reacts with hot water.
Ans. Magnesium reacts
with hot water to form magnesium hydroxide and hydrogen.
5. What
happens when aluminium oxide dissolves in aqueous sodium hydroxide?
Ans. Aluminium oxide
being amphoteric in nature dissolves in aqueous sodium hydroxide to form water
soluble sodium aluminate.
Q10. In the extraction of aluminium
1. Name the process of concentration of
Bauxite.
2. Write the cathode reaction in
electrolytic reduction of alumina.
3. Write the function and formula of
cryolite in the extraction of aluminium.
4. Write an equation for the action of heat
on aluminium hydroxide.
5. Draw the diagram of extraction of
aluminium.
6. Why is it necessary to replace anodes
time to time?
7. What happens when aluminium ore is heated
with concentrated caustic soda. Write the balanced chemical equation for the
same.
Ans.
i.
The
process of concentration of Bauxite is done by Bayer’s Process.
ii.
The
positively charged aluminium ions (Al3+) are attracted to the cathode
(negative electrode). The aluminium ions accept electrons from the cathode and
get reduced to form aluminium atoms (or aluminium metal).
Cathode reaction :
iii.
Alumina
has a very high melting point (>20000C). Cryolite lowers the
fusion temperature from 20000C to 10000C and enhances
conductivity.
Chemical formula of cryolite:
iv.
Equation:
v.
Diagram
vi.
As
the anode gets oxidized during the electrolysis of alumina. It has to be
replaced from time to time.
vii.
When
aluminium or is heated with caustic soda
solution under high pressure for 2 to 8 hours
at
water
soluble sodium aluminate is formed.
Q11. Write two methods of preventing rusting of iron.
Ans.
i.
The
most common method of preventing the rusting of iron is to coat its surface
with paint or apply grease, oil or varnish.
ii.
Rusting
of iron can be prevented by galvanization. The process of depositing a thin
layer of Zinc metal on Iron objects is called galvanization.
Q12. What is an alloy? Give two examples with their chemical
composition.
Ans. An alloy is a homogenous mixture of two or more metals or a
metal and a non – metal in definite proportion.
Eg.
i.
Brass
– copper and zinc.
ii.
Stainless
steel – iron, nickel and chromium.
Q13. Arrange the following metals in the decreasing order of
chemical reactivity, Cu, Mg, Fe, Na, Ca, Zn.
Ans. The arrangement of metals in the decreasing order of their
chemical reactivity are Na > Ca > Mg > Zn > Fe > Cu.
Q14. Explain the formation of an ionic compound between metal
and a non – metal by transfer of electrons with Mg as the metal and Cl as a non
– metal to illustrate your answer.
Ans. Magnesium is a metal whereas chlorine is a non – metal.
Magnesium reacts with chlorine to form an ionic compound magnesium chloride.
The atomic number of magnesium is 12, so its electronic
configuration is 2,8,2. It has 2 valance electrons. A magnesium atom donates
its 2 valence electrons (to two chlorine atoms) and forms a stable magnesium
ion,
The atomic number of chlorine is 17,
and its electronic configuration is 2,8,7. Chlorine atom has 7 valance
electrons, so it requires only 1 more electrons to complete its octet. Since,
one magnesium atom donates 2 electrons, so, two chlorine atoms take these two
electrons and form two chloride ions.
The positively charged magnesium ions and negatively charged
chloride ions are held together by electrostatic force of attraction to form
magnesium chloride
compound.
Q15. An element x on reacting oxygen forms an oxide X2O.
This oxide dissolves in water and turns red litmus blue. State whether element
X is a metal or a non – metal. Explain with proper example.
Ans.
The element X is very likely to be a non – metal because most of the oxides of
non – metals are acidic and are soluble in water.