14-
Elements, Compounds and Mixtures
Q. 1. Match the columns :
Answer
(1)
Stainless steel - Alloy
(2) Silver - Metal
(3) Bhajani mixture for milling - Mixture
(4) Salt - Compound
(5) Coal - Element
(6) Hydrogen - Non-metal
Q. 2. Write
the names of elements from the following symbols:
Zn, Cd, Xe,
Br, Ti, Cu, Fe, Si, Ir, Pt.
Ans.
|
No |
Symbol |
Element |
|
1. |
Zn |
Zinc |
|
2. |
Cd |
Cadmium |
|
3. |
Xe |
Xenon |
|
4. |
Br |
Bromine |
|
5. |
Ti |
Titanium |
|
6. |
Cu |
Copper (Cuprus) |
|
7. |
Fe |
Iron (Ferrum) |
|
8. |
Si |
Silicon |
|
9. |
Ir |
Iridium |
|
10. |
Pt |
Platinum |
Q. 3. What are the molecular
formulae of the following compounds?
Compound Ans.
(1) Hydrochloric acid HCI
(2) Sulphuric acid H2SO4
(3) Sodium chloride NaCl
(4) Glucose
C6H12O6
(5) Methane CH4
Q. 4. Explain the difference:
(1) Metals
and Non-metals.
Metals Non-metals
1. Metals have lustre. 1. Non-metals do not have lustre
. 2. Metals are malleable 2.
Non-metals are not malleable
3. Metals are ductile 3. Non-metals are not ductile.
4. Metals are good conductors of heat 4. Non-metals are not good conductors
of heat
and electricity. and
electricity.
5. At normal
temperature, metals are in 5. At normal temperature, non-metals
are
solid state. either
in solid state or in gaseous state.
(Exception
Mercury) (Exception
: Bromine – in liquid form)
6. Normally metals have high density. 6. Normally non-metals have less density.
e.g., Gold,
silver, mercury e.g.,
Oxygen, hydrogen.
(2) Compounds and mixtures.
Ans. Compounds Mixtures
1. A compound is made of two or more 1. A
mixture is obtained by just mixing two
elements chemically combined in a fixed or more substances in any proportion.
proportion
2. A compound can be further subdivided 2. A
mixture can be further subdivided into into simpler substances by chemical simpler
substances by simple physical
means only. processes.
3. The properties of a compound are entirely 3. The constituents of a mixture retain their
different from the properties of its original properties. e.g.,
air, sea water. constituents.
e.g., common
salt, sugar, water.
(3) Atom and molecule.
Ans. Atom Molecule
1. An atom is smallest particle in an element 1.
Molecules are formed by the combination
that has the properties of the element of two or more atoms.
2. It is not possible to breakdown the atom 2. Molecules can be subdivided to individual
further retaining the properties of the atoms.
e.g., Water molecule can further
element. divided
into oxygen and hydrogen atoms.
3. The atoms are bonded together in a 3.
When similar molecules combine together
in any numbers, a simple product is
formed.
4. An atom
is not stable by itself.
4. A molecule is usually stable
to exist itself.
(4)Separation by distillation
and by separating funnel :
Ans. Separation by distillation Separation
by separating funnel
1.For separation
of solutes from the 1. For separation of two immiscible
liquids
solution, the method of distillation is the method of separating funnel is used.
used.
2. Heat is given during the separation. 2. Heat is not given during the process
Q. 5. Write answers to the the following
questions.
(1) How are the components of mixtures separated
by simple methods? OR
Straining
(filtering), sifting, picking, sorting, winnowing, combing with a magnet and
sublimation are simple and easy methods for separation. Which ingredients, from
which mixtures could be separated by using these methods?
Ans. There
are various methods to separate the mixtures. Some of these are used in our
daily life such as straining (filtering), sifting, picking, sorting, winnowing,
combing with a magnet and sublimation.
(1) Filtering or
straining : To separate insoluble substances from the solution, we use the method of filtering.
(2) Sifting
is done to separate solids of various sizes. The larger particles and the
smaller particles can be separated by sitting,
(3) Picking
and sorting : By this method, a substances that are needed/or not needed are
separated out.
(4) Winnowing:
The substances which are lighter in weight and those that are unwanted are
removed from the mixture. The grains in the farm are particularly cleaned by
the process of winnowing.
(5) Combing
with a magnet: If there is adulteration of semolina with iron, the magnet is
combed through it for removing these iron particles. The mixture that contains iron
particles is specially combed with a magnet.
(2) In everyday life, where and for what purpose do we
use centrifugation?
Ans. Use of
centrifuge machine is never done in our common house-hold work. By using method
of centrifugation the particles of smaller size are separated due to
centrifugal force. Based on this principle, we use stirrer for making
buttermilk from yoghurt. The stirrer helps to separate particles of butter from
the suspension of the buttermilk. Due to centrifugal force, the particles of
butter aggregate and are thus easily removed.
(3) Where are the methods of separation by distillation and by separating
funnel used? Why?
Ans. (1) Distillation : Distillation is the separation method used to
separate impurities or dissolved salts from the solution. By this method, the
solute and the solvent are separated. For removing salt from sea water,
distillation method is used. This helps in making potable water from sea water.
(2) Using separating funnel : When two liquids in a mixture which are immiscible
with each other are to be separated, the method using separating funnel is
used. This can be used for separation of mixture of kerosene and water
(4) Which precaution will you take while using the methods of distillation
separation by separating funnel?
Ans. In the
method of distillation, the entire apparatus should be properly set up. The distillation flask should be carefully heated.
The condenser tube should be properly
cooled.
In the separating funnel
experiment care should be taken to well manipulate the stopcock.
The malfunctioning stopcock many a times releases the
liquids inadvertently. The separation of lower phase liquid should be done with precision by opening and closing the stopcock.
Q 6. Give scientific reasons :
(1) Buttermilk is churned to get butter.
Ans.
Churning is one of the method of separation. The particles of butter are all
spread out in the buttermilk. By stirring they aggregate due to centrifugal
force and form one solid lump. To separate the butter, the buttermilk is
therefore churned.
(2) In Chromatography,
the ingredients of a mixture rise up to a limited height when water rises up to
the upper end of the paper.
Ans In chromatography method, two mutually opposite
properties of substances are used
These are
(1) the solubility of the substance in the solvent that moves up and (2) the ability
of the substance to stick to the stationary filter paper. These properties are
different for different substances. Since water is a solvent, it rises rapidly
across the chromatography filter paper. But the solutes will not rise with that
speed. Therefore, the ingredients of a mixture rise up to a limited height when
water rises up to the upper end of the paper.
(3) A wet cloth is wrapped around a
water storage container in summer.
Ans. The
moisture in the wet cloth evaporates during summer season. During its evaporation
it absorbs some amount of heat from the water storage container. The water inside
the container thus becomes cooler. Hence, a wet cloth is wrapped around a water
storage container in summer.
(4) Which elements (metals and
non-metals), compounds and mixtures do we
use in our
day-to-day life?
Ans. Elements : Metals - iron, gold, silver, copper.
Non-metals - Carbon, oxygen, hydrogen, nitrogen.
Compounds : Sugar, salt, oil
Mixtures : Soap, alloys like steel, brass, 22 carat gold
