Maharashtra State Board
Standard VII – Science
Chapter 14 – Elements, Compounds and Mixtures
Textbook Solutions
1. Who are my companions?
| Group ‘A’ | Group ‘B’ |
|---|---|
| (i) Stainless steel | (a) Non-metal |
| (ii) Silver | (b) Compound |
| (iii) Bhajani mixture for milling | (c) Mixture |
| (iv) Salt | (d) Element |
| (v) Coal | (e) Alloy |
| (vi) Hydrogen | (f) Metal |
Ans:
| Group ‘A’ | Group ‘B’ |
|---|---|
| (i) Stainless steel | (e) Alloy |
| (ii) Silver | (f) Metal |
| (iii) Bhajani mixture for milling | (c) Mixture |
| (iv) Salt | (b) Compound |
| (v) Coal | (a) Non-metal |
| (vi) Hydrogen | (d) Element |
2. Write the names of elements from the following symbols
Zn, Cd, Xe, Br, Ti, Cu, Fe, Si, Ir, Pt
| Symbol | Element |
|---|---|
| Zn | Zinc |
| Cd | Cadmium |
| Xe | Xenon |
| Br | Bromine |
| Ti | Titanium |
| Cu | Copper |
| Fe | Iron |
| Si | Silicon |
| Ir | Iridium |
| Pt | Platinum |
3. What are the molecular formulae of the following compounds?
Hydrochloric acid, sulphuric acid, sodium chloride, glucose, methane.
| Compound | Molecular Formula |
|---|---|
| Hydrochloric acid | HCl |
| Sulphuric acid | H₂SO₄ |
| Sodium chloride | NaCl |
| Glucose | C₆H₁₂O₆ |
| Methane | CH₄ |
4. Give scientific reasons.
(a) Buttermilk is churned to get butter.
Churning is one of the methods of separation. In buttermilk, small particles of butter are spread throughout the liquid. When buttermilk is churned, these particles come together and form a lump of butter due to centrifugal force. Therefore, buttermilk is churned to obtain butter.
(b) In chromatography, the ingredients of a mixture rise up to a limited height when water rises up to the upper end of the paper.
Chromatography is a method used to separate the components of a mixture. The separation depends on the solubility of substances in the solvent and their ability to stick to the filter paper. Since these properties are different for different substances, each component rises only up to a certain height.
(c) A wet cloth is wrapped around a water storage container in summer.
The water present in the wet cloth evaporates during summer. During evaporation it absorbs heat from the water container. As a result the water inside the container becomes cooler.
5. Explain the difference
(a) Metals and Non-metals
| Metals | Non-metals |
|---|---|
| Metals have lustre. | Non-metals do not have lustre. |
| Good conductors of heat and electricity. | Poor conductors of heat and electricity. |
| Usually high density. | Usually lower density. |
| Mostly solid at room temperature. | May exist as solids or gases. |
(b) Mixtures and Compounds
| Mixtures | Compounds |
|---|---|
| Formed by mixing substances. | Formed by chemical combination of elements. |
| Properties remain unchanged. | Properties are different from elements. |
| Separated by physical methods. | Separated by chemical methods. |
(c) Atoms and Molecules
| Atoms | Molecules |
|---|---|
| Smallest particle of an element. | Formed by combination of atoms. |
| Usually cannot exist independently. | Can exist independently. |
| Combine to form molecules. | Can be broken into atoms. |
6. Write answers to the following questions in your own words
(a) How are the components of mixtures separated by simple methods?
- Filtering – separates insoluble substances from liquids.
- Sieving – separates particles of different sizes.
- Hand picking – removes unwanted materials.
- Winnowing – separates lighter particles using wind.
- Magnetic separation – removes iron particles using a magnet.
(b) Which elements, compounds and mixtures do we use in daily life?
Elements:
Metals – Iron, gold, silver, copper
Non-metals – Carbon, oxygen, hydrogen, nitrogen
Compounds:
Salt, sugar, water
Mixtures:
Soap, steel, brass, 22-carat gold
Metals – Iron, gold, silver, copper
Non-metals – Carbon, oxygen, hydrogen, nitrogen
Compounds:
Salt, sugar, water
Mixtures:
Soap, steel, brass, 22-carat gold
(c) Where do we use centrifugation in everyday life?
- Drying clothes in a washing machine.
- Separating cream from milk.
- Removing water from washed vegetables.
- Separating butter from curd.
(d) Where are distillation and separating funnel used?
Distillation: Used to separate dissolved substances from liquids such as separating salt from seawater.
Separating Funnel: Used to separate immiscible liquids such as kerosene and water.
Separating Funnel: Used to separate immiscible liquids such as kerosene and water.
(e) What precautions should be taken?
- The distillation apparatus should be set up properly.
- The distillation flask should be heated carefully.
- The stopcock of the separating funnel should be handled carefully.
- Check the stopcock properly to avoid leakage.