Lakhmir Singh and Manjit Kaur ICSE Class 7 Chemistry Chapter 3 Elements, Compounds and Mixtures
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Board | ICSE |
Class | 7 |
Subject | Chemistry |
Chapter | 3 |
Chapter Name | Elements, Compounds and Mixtures
|
Author | Lakhmir Singh and Manjit Kaur |
Objective Type Questions
A) Choose the correct Option
1) Option D – Lemonade
2) Option D – All of these
3) Option D – Compound
4) Option B – Fractional Distillation
5) Option A – Filtration and Evaporation
6) Option C – Separation Funnel
7) Option D – Chromatography
B) Fill in the blanks
1) Pure
2) Four
3) Fractional Distillation
4) Mass
5) Separating funnel
6) Distillation.
7) Boiling point
8) Fractional distillation
9) Evaporation
10) Sublimation
C) Write T for true and F for false statements
1) False
2) False
3) True
4) True
5) True
6) True
7) True
D) Identify the elements and compounds in the following list and write them in the correct column.
H2, O2, N2, CuSO4, HCI, Cl2, NO2, Br2, Fe, CuS, NaCl, FeO, K, ZnCl2, NH3, CaO, Al, H₂O, FeS, MgO
Elements | Compounds |
H2 | Cuso4 |
O2 | HCl |
N2 | NO2 |
Cl2 | CuS |
Br2 | NaCl |
Fe | FeO |
K | ZnCl2 |
Al | NH3 |
CaO | |
H2O | |
FeS | |
MgO |
E) Give two examples of each:
1) Solid + Solid Mixture
i) Salt and sand mixture
ii) Bronze
2) Solid + Liquid Mixture
i) Sugar and water mixture
ii) Sand and water mixture
3) Liquid + Liquid (miscible) mixture
i) Milk and Water mixture
ii) Petrol and kerosene mixture
4) Liquid + Liquid (immiscible) mixture
i) Water and kerosene mixture
ii) Petrol and water mixture
Subjective Type Questions
F) Answer the following questions in short
1) Some of the characteristics of elements
i) Elements are made of only one kind of elements.
ii) Elements cannot be split into more simple elements by any physical or chemical processes.
iii) Different elements have different properties.
iv) The atoms found in an element cannot be found in any other elements in that specific arrangement.
v) Elements can exist in all three of the states which are solid, liquid and gaseous.
2) Some of the characteristics of compounds are given below
i) The property of a compound will be different from the elements it is made with.
ii) It is possible to break down a compound into elements by only using chemical processes.
iii) Energy will definitely be released or absorbed while the formation of a new compound.
iv) Compounds can be made of two or more than elements.
3)
Mixtures | Compounds |
1) The constituents of mixtures can easily be separated by physical process like filtration and evaporation. | 1) To break the compounds into its elements chemical processes are necessary. |
2) The properties of the constituents can be seen in the mixture. | 2) The properties of the compounds are different than that of the elements they are made of. |
3) There is no fixed proportion of the constituents in the mixture. | 3) The constituents are present in the compound have fixed proportion by mass. |
4) A mixture cannot be denoted by a formula. | 4) All Compounds have their unique formula. |
5) Mixtures do not have a fixed boiling point, melting point, freezing point etc. | 5) Compounds do have specific boiling points, melting points and freezing points. |
4) There can be multiple reasons why separation of mixtures can be required. Some of the reasons are
i) To get rid of undesirable component from the mixture.
ii) To get rid of harmful component present in the mixture.
iii) To achieve higher purity levels in mixture.
iv) To get a useful component present in the mixture.
5) Fractional distillation is separation method for separating two miscible liquids having boiling points separated by 25°C from a mixture.
Fractionating column is a long vertical glass tube filled with glass beads. It is used in the separating process. In the tube different temperature zones are created. At the top lowest temperature and at the bottom highest temperature zones are created. By using this two liquids are separated.
6) Chromatography is a technique that is used to separate two or more solids dissolved in a solution in very small quantities.
Chromatography is used in forensic science to detect and identify traces of substances like poison in stomach and bladder.
7)
a) Evaporation: Evaporation is a process in which liquid turns into vapour. This is used to separate solids dissolved in liquids.
b) Sublimation: In this process solids turn directly into vapours when heated.
c) Miscible liquids: These are the liquids that get mixed together in all proportions and form a single layer when mixed.
d) Immiscible liquids: These are the liquids that do not get mixed together and form separate layers when mixed.
e) Homogeneous mixture: These are the mixtures in which substances are mixed together completely and get become indistinguishable.
f) Heterogeneous mixture: These are the mixtures in which substances don’t get mixed uniformly throughout the mixture.
G) Answer the following questions in details.
1)
a) (i) Elements are substances that are made of only one kind of atom. Name of two elements are Hydrogen and oxygen.
(ii) Compounds are substance made of one or more elements in a fixed proportion by mass. Name of two compounds are water and carbon dioxide.
(iii) Mixtures are made by mixing two or more pure substances without any fixed proportion. Name of two mixtures are salt-water and brass.
b)
Elements | Compounds | Mixtures |
Gold | Sand | Marble |
Diamond | Petroleum | Air |
Graphite | Common Salt | Brass |
Chalk | Sea water |
2)
a) In homogeneous mixtures substances are completely mixed and cannot be distinguished separately. On the other hand in heterogeneous mixtures the substances does not get mixed uniformly throughout the mixture. This is the main difference between homogeneous and heterogeneous mixtures.
b)
Homogeneous Mixture | Heterogeneous Mixture |
Soda-water | Wood |
Air | Soil |
Vinegar | Petrol, water mixture |
Alcohol water mixture | Chalk and water mixture |
Sugar and water mixture | |
Copper Sulphate solution |
3)
a) Based on the properties elements are classified into four groups; metal, non-metal, metalloids and noble or inert gases.
Metals are solid materials which are good conductor of heat and electricity. Iron and Gold are example of metals.
Non-Metals are mostly liquid or gaseous in nature and does not have metallic attributes in them. Oxygen and Clorine are example of non-metals.
Metalloids are elements that show properties of both metals and non-metals. Boron and silicon are example of metalloids.
b)
Metals | Non-metals | Metalloids |
Mercury | Diamond | Silicon |
Sodium | Sulphur | Germanium |
Magnesium | Iodine | Boron |
Copper | Carbon | |
Helium |
4)
a) The difference between element and compound
Element | Compound |
1) Elements are made of only one kind of atoms. | 1) Compounds are made from two or more kind elements. |
2) Elements cannot be broken into more simple substances. | 2) Compounds can be broken into elements by chemical processes. |
b) The difference between distillation and fractional distillation.
Distillation | Fractional distillation. |
1) Distillation is a process used to separate liquids from non-volatile solids mixture or solution. | 1) Fractional distillation is a process used to separate miscible liquids from mixture. |
2) It involves two processes which are evaporation and condensation. | 2) In this process miscible liquids with a difference in boiling points of less than 25°C are separated by boiling the mixture through fractionating column and condensing the vapour. |
c) The difference between sublimation and evaporation
Sublimation | Evaporation |
1) In sublimation solid turns directly into vapour upon heating. | 1) In evaporation Liquid turns into vapour. |
2) This process occurs only in a few substances which makes it a rare process. | 2) This is a very common process for most of the liquids. |
Picture Based Questions
1) To separate ammonium chloride from a mixture of ammonium chloride and sodium chloride a sublimation process is used.
First the mixture of ammonium chloride and sodium chloride is taken in a china dish. Then the dish is covered with an inverted funnel. The tail of the funnel is plugged with cotton. Then the dish is heated on burner. Now we can see that the white fumes starting to come out of the mixture. The fumes can be seen getting condensed on the cooler parts of the funnel. After some time only sodium chloride is left on the china dish. The ammonium chloride can be seen on the cooler upper parts of the funnel.
Ammonium chloride is a sublime element so it turns into gaseous form when heated. It turns into fume and gets solidified on contact with the cooler parts of the funnel. On the other hand Sodium chloride or common salt is not sublime so it does not get evaporated upon heating and stay in the dish.
Chapter 2: Physical and Chemical Changes
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