Question 1:
Which of
the following pairs will give displacement reactions?
(a) NaCl
solution and copper metal
(b) MgCl2
solution and aluminium metal
(c) FeSO4
solution and silver metal
(d) AgNO3
solution and copper metal.
(d) AgNO3 solution and copper metal
Question 2:
Which of
the following methods is suitable for preventing an iron frying pan
from rusting?
(a) Applying
grease
(b) Applying
paint
(c) Applying
a coating of zinc
(d) all of
the above.
(We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed.)
Question 3:
An element
reacts with oxygen to give a compound with a high melting point. This
compound is also soluble in water. The element is likely to be
(a) calcium
(b) carbon
(c) silicon
(d) iron
Question 4:
Food cans
are coated with tin and not with zinc because
(a) zinc
is costlier than tin.
(b) zinc
has a higher melting point than tin.
(c) zinc
is more reactive than tin.
(d) zinc
is less reactive than tin.
Question 5:
You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals
and non-metals?
(b) Assess the usefulness of these tests in distinguishing between
metals and non-metals.
(a) With the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non-metal. Similarly, we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.
(b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved in these tests.
Question 6:
What are
amphoteric oxides? Give two examples of amphoteric oxides.
Those oxides that behave as both acidic and basic oxides are called amphoteric oxides.
Examples: aluminium oxide (Al2O3), zinc oxide (ZnO)
Question 7:
Name two
metals which will displace hydrogen from dilute acids, and two metals
which will not.
Metals that are more reactive than hydrogen displace it from dilute acids. For example: sodium and potassium. Metals that are less reactive than hydrogen do not displace it. For example: copper and silver.
Question 8:
In the
electrolytic refining of a metal M, what would you take as the anode,
the cathode and the electrolyte?
In the electrolytic refining of a metal M:
Anode → Impure metal M
Cathode → Thin strip of pure metal M
Electrolyte → Solution of salt of the metal M
Question 9:
Pratyush
took sulphur powder on a spatula and heated it. He collected the
gas evolved by inverting a test tube over it, as shown in figure
below.
(a) What
will be the action of gas on
(i) dry litmus paper?
(ii) moist litmus paper?
(b) Write
a balanced chemical equation for the reaction taking place.
(a) (i) There will be no action on dry litmus paper.
(ii) Since the gas is sulphur dioxide (SO2), it turns moist blue litmus paper to red because sulphur dioxide reacts with moisture to form sulphurous acid.
(b)
Question 10:
State two ways to prevent the rusting of iron.
Two ways to prevent the rusting of iron are:
(i) Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
(ii) Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.
Question 11:
What type of oxides are formed when non-metals combine with oxygen?
Non-metals combine with oxygen to form acidic oxides.
For example:
Question 12:
Give
reasons
(a) Platinum,
gold and silver are used to make jewellery.
(b) Sodium,
potassium and lithium are stored under oil.
(c) Aluminium is a highly reactive metal, yet it is used to make
utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides
during the process of extraction.
(a) Platinum, gold, and silver are used to make jewellery because they are very lustrous. Also, they are very less reactive and do not corrode easily.
(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water. Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.
(c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides.
Question 13:
You must
have seen tarnished copper vessels being cleaned with lemon or
tamarind juice. Explain why these sour substances are effective in
cleaning the vessels.
Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.
Question 14:
Differentiate between metal and non-metal on the basis of their
chemical properties.
Metal
|
Non-metal
|
| Metals are electropositive. | Non-metals are electronegative. |
They
react with oxygen to form basic oxides. These have ionic bonds. |
They
react with oxygen to form acidic or neutral oxides. These have covalent bonds. |
They
react with water to form oxides and hydroxides. Some metals react
with cold water, some with hot water, and some with steam. |
They do not react with water. |
They
react with dilute acids to form a salt and evolve hydrogen gas.
However, Cu, Ag, Au, Pt, Hg do not react. |
They do not react with dilute acids. These are not capable of replacing hydrogen. |
They
react with the salt solution of metals. Depending on their
reactivity, displacement reaction can occur. |
These react with the salt solution of non-metals. |
They
act as reducing agents (as they can easily lose electrons). |
These
act as oxidising agents (as they can gain electrons). |
Question 15:
A man went
door to door posing as a goldsmith. He promised to bring back the
glitter of old and dull gold ornaments. An unsuspecting lady gave a
set of gold bangles to him which he dipped in a particular solution.
The bangles sparkled like new but their weight was reduced
drastically. The lady was upset but after a futile argument the man
beat a hasty retreat. Can you play the detective to find out the
nature of the solution he had used?
He must have dipped the gold metal in the solution of aqua regia − a 3:1 mixture of conc. HCl and conc. HNO3. Aqua regia is a fuming, highly corrosive liquid. It dissolves gold in it. After dipping the gold ornaments in aqua regia, the outer layer of gold gets dissolved and the inner shiny layer appears. That is why the weight of gold ornament reduced.
Question 16:
Give
reasons why copper is used to make hot water tanks and not steel (an
alloy of iron).
Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water.
That is why copper is used to make hot water tanks, and not steel.