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Q 1.
Choose amphoteric oxides from the following: Na2O, ZnO, Al2O3,
SO2.
Solution
Amphoteric
oxides = ZnO, Al2O3
Q 2.
Ionic compounds dissolve in water. Explain.
Solution
Ionic
compounds dissolve in water because water is a polar compound, it decreases the
electrostatic forces of attraction, resulting in free ions in aqueous solution.
Hence they dissolve.
Q 3.
Why is gold mixed with other metals for making jewellery? Name two metals mixed
with gold.
Solution
Gold
is a malleable metal and is extremely soft. So, mixing it with other metals
makes it stronger for its use in making jewellery. Commonly used metals to mix
with gold while making jewellery are copper and silver.
Q 4.
Why is carbon not used for reducing aluminium from aluminium oxide?
Solution
Because
aluminium has greater affinity for oxygen than for carbon, therefore carbon
cannot reduce alumina (Al2O3) to aluminium.
Q 5.
Why are metals good conductor of electricity?
Solution
The
metals are good conductors of electricity because they have free mobile
electrons which can move easily through the metal and conduct electricity.
Q 6.
What is aqua regia?
Solution
Aqua
regia is the freshly prepared mixture of concentrated hydrochloric acid and
concentrated nitric acid in the ratio 3:1. It can even dissolve metals like
gold and platinum.
Q 7.
How will you prove that a given salt is a carbonate of a metal?
Solution
To
the salt, add few drops of dilute HCl or H2SO4, if
colourless gas is evolved with brisk effervescence and when the gas is passed
through lime water and if lime water turns milky, then the gas is CO2 and
salt is carbonate of the metal.
Q 8.
State any two properties of alloys in comparison to the constituent metals.
Solution
1.
Alloys are stronger than the metals from which they are made. 2. Alloys are
more resistant to corrosion.
Q 9.
What is 'corrosion'? Name the compound formed when: (i) silver corrodes
(ii) copper corrodes
Solution
When
the surface of a metal is exposed to air, moisture or any other substance
around it, the metal is said to corrode, and the phenomenon is known as
corrosion. (i) Silver sulphide (ii) Basic Copper carbonate (mixture of
copper carbonate and copper hydroxide).
Q 10.
Answer the following question: (i) Are all pure liquids bad conductors of
electricity? Justify your answer with one example. (ii) Why ionic compounds are
always hard? (iii) Name the cathode and anode in the electrolytic refining of
copper.
Solution
(i)
No, all pure liquids are not bad conductors of electricity. There are many pure
liquids which are good conductors of electricity. For example, solutions of
acids like sulphuric acid, nitric acid are good conductors of electricity. (ii)
Ionic compounds are hard solids because they have strong electrostatic forces
of attraction between their ions, which cannot be separated easily. (iii)
Cathode: A thin strip of pure copper metal Anode:
A thick block of impure copper metal
Q 11.
Metals high up in the reactivity series cannot be obtained from their compounds
by heating with carbon. Why?
Solution
Carbon
cannot reduce the oxides of sodium and aluminium because these are highly
reactive metals; have more affinity towards oxygen than carbon.
Q 12.
Define corrosion. What is the condition required for corrosion to take place?
Solution
Corrosion
is the eating away of metals by the action of air, water, acids present on its
surface. Corrosion requires presence of air and water.
Q 13.
Name the metal which has very low melting point and can melt with the
heat of your palm.
Solution
Gallium
and Cesium have very low melting points.
Q 14.
Why ionic compounds are soluble in polar solvents and insoluble in non-polar
solvents?
Solution
Ionic
compounds are soluble in polar solvents and insoluble in non-polar solvents.
Polar solvents like water decrease the electrostatic forces of attraction,
resulting in free ions in aqueous solution. Hence, ionic compounds dissolve in
polar solvents. Non-polar solvents like kerosene, benzene are not capable of
dissolving ionic solids since they can not decrease the forces of attraction
between the ions.
Q 15.
Why do silver articles become black after some time when exposed to air?
Solution
Silver
articles get tarnished by reacting with atmospheric air to form black coating
of silver sulphide.
Q 16.
What is sonority?
Solution
When
we strike a metal, it produces a metallic pop sound. This property of metals is
called sonority.
Q 17.
What is the total number of ions produced by one molecule of Na2O
and MgBr2 in their aqueous solution?
Solution
The
total number of ions produced by one molecule of Na2O in its aqueous
solution is 3. The total number of ions produced by one molecule of MgBr2 in
its aqueous solution is 3.
Q 18.
What do you understand by enrichment of ores?
Solution
Ores
mined from the earth are usually combined with impurities. These impurities
must be removed from the ore before the extraction of metal. The removal of
impurities from the ore depends on the difference in physical and chemical
properties of impurities and metals. This method of removal of impurities from
metal ore is called enrichment of ores.
Q 19.
Define: (i) Minerals (ii) Ores (iii) Gangue
Solution
(i)
Minerals: The naturally occuring compounds of metals which are generally mixed
with other matter such as soil, sand, limestone and rocks are known as
minerals. (ii) Ores : The minerals from which metals are extracted commercially
at a comparatively low cost and with minimum effort are called ores. (iii)
Gangue : The earthly impurities including silica, mud etc. associated with the
ore are called gangue.
Q 20.
"All ores are minerals but all mineral are not ores". Justify the
statement with examples.
Solution
All
ores are minerals while all minerals are not ores as some of them might have a
large amount of unwanted substances such as sand, stones and earthly
impurities. For example: Aluminium occurs in earth's crust in the form of two
minerals bauxite and clay. Out of these, aluminium can be easily and profitably
extracted from bauxite only. So, we can infer that bauxite is an ore of
aluminium.On the other hand, it has not been possible to obtain aluminium from
clay by some easy and cheap method. So, clay remains only as mineral and not as
ore of aluminum.
Q 21.
Name two allotropes of carbon. Which is the hardest natural substance known?
Solution
The
two allotropes of carbon are diamond and graphite. Diamond is the hardest
natural substance.
Q 22.
What makes aluminium resistant to further corrosion? How can we improve it?
Solution
Aluminium
develops a thin layer of aluminium oxide when exposed to air. This aluminium
oxide prevents it from further corrosion. This can be improved further by
making the oxide layer thicker.
Q 23.
What is percentage of gold in 18 carat gold?
Solution
18
carat gold contains 75% gold and remaining 25% is copper and silver.
Q 24.
State two physical properties of gold which are of extreme use to jewellers.
Solution
Ductility
and lustre are the properties of gold which makes it useful in making
jewellery.
Q 25.
Define an amalgam. How are amalgams important to us?
Solution
A
mixture or an alloy of mercury with a number of metals or alloys such as sodium
as well as with some non-metals is known as amalgam. Uses: 1. Sodium is highly
reactive metal and therefore it is difficult to transport. To lower its
reactivity, it is mixed with mercury. 2. Dental amalgam is a mixture of mercury
and a silver-tin alloy and is used for fillings in teeth.
Q 26.
What are the four main steps involved in metallurgy?
Solution
The
main steps involved in metallurgy are- 1)
Extraction of ore. 2) Crushing and grinding of
ore. 3) Concentration or enrichment of ore.
4) Extraction of metal from concentrated ore.
Q 27.
Name any two metals that occur free in nature.
Solution
The
two metals that occur free in nature are gold and silver.
Q 28.
Give an example of a metal which is the best conductor of heat.
Solution
Silver
is the best conductor of heat.
Q 29.
"The way metals like sodium, magnesium and iron react with air and water
is an indication of their relative positions in the reactivity series". Is
this statement true? Justify your answer with examples.
Solution
The
statement is correct because they react with air and water at different rates
and in different conditions. While sodium reacts spontaneously and violently
with air and cold water, magnesium reacts with air less vigorously and with
water when heated. Iron reacts with air very slowly and reacts with steam to
form iron oxide and hydrogen being the least reactive among sodium, magnesium
and iron.
Q 30.
Make a distinction between metals and non - metals with respect to the nature
of their oxide.
Solution
Metallic
oxides are basic but few are amphoteric. Non-metallic oxides are acidic but
some are neutral.
Q 31.
Describe tin plating and chromium plating. What kind of materials are protected
using these methods?
Solution
Tin
and chromium metals are resistant to corrosion. So, a thin layer of tin metal
(or chromium metal) is deposited on iron and steel objects by electroplating to
protect these objects from rusting. Tin plating is used for tiffin boxes
because it is non-poisonous and hence does not contaminate the food kept in
them. Chromium plating is done on taps, bicycle handle bars and car bumpers
made of iron and steel to protect them from rusting and give them a shiny
appearence.
Q 32.
What are alloys? How are they made? Name the constituents and uses of brass,
bronze and solder.
Solution
Alloys
are homogeneous mixtures of two or more metals or a metal and a non metal. They
are prepared in the following ways: (i) Melting the primary metal. (ii)
Dissolving the other elements in a definite proportion and then cooling them to
room temperature. Constituents and uses of the alloys are: 1. Brass: It is an
alloy of copper and zinc Uses: In making utensils and
scientific instruments. 2. Bronze: It is an alloy of copper and tin
Uses: In making statues and medals. 3. Solder: It is an
alloy of lead and tin Uses: In soldering (welding)
electrical wires together.
Q 33.
Name a non-metal which is lustrous and a metal which is non-lustrous.
Solution
(a)
Non-metal which is lustrous = Iodine (I) (b) Metal which is non-lustrous =
Sodium (Na)
Q 34.
How do various metals occur in nature?
Solution
Most
of the metals are reactive so, they occur in combined state in the form of
their oxides, carbonates, halides, sulphides, suphates etc. For example, sodium
and potassium occur mainly as their chlorides, calcium and magnesium as
carbonates, aluminium as its oxide while zinc, lead, copper are found as
sulphides. Metals which have low chemical reactivity are found in free state.
e.g. gold, platinum.
Q 35.
Differentiate metals and non-metals on the basis of their physical properties.
Solution
Metals
Non-metals Metals are good conductors of heat and electricity. Non-metals are
bad conductors of heat and electricity. Metals are malleable that is they can
be beaten into sheets. Non-metals are not malleable. Metals are ductile that is
they can be drawn into wires. Non-metals are not ductile. Metals are sonorous.
Non-metals are not sonorous. Metals have high tensile strength due to
high attraction between molecules. Non-metals have low tensile strength
due to low attraction between molecules. Metals have high density. Non-metals
have low density.
Q 36.
An element X forms an oxide which turns red litmus blue. Identify whether X is
a metal or non-metal.
Solution
X
is a metal since metal oxides are basic in nature.
Q 37.
Give reason : (i) A magnesium ribbon should be cleaned before burning it in
air. (ii) The blue colour of copper sulphate solution changes when iron nails
are dipped in it.
Solution
(i)
Magnesium ribbon should be cleaned before burning it in air to remove the layer
of basic magnesium carbonate or magnesium oxide from its surface. (ii)
The colour of blue copper sulphate changes due to displacement reaction in
which a more reactive iron has displaced less reactive copper from its
solution.
Q 38.
In the formation of a compound XY, atom 'X' gives one electron to an atom of
'Y'. What is the nature of bond in XY?
Solution
Nature
of the bond will be ionic. Ionic bonds are formed by the transfer of electrons
from one atom to another.
Q 39.
Name any one metal which is found in its free state in nature.
Solution
Metal
which is found in its free state in nature - Gold or Platinum.
Q 40.
State the constituents of solder and their percentage composition. Which
property of solder makes it suitable for welding electrical wires?
Solution
The
constituents of Solder - Lead (Pb), Tin (Sn). It contains 50% lead and 50% tin.
Being a low melting solid, it is used for soldering electrical wires together.
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