Is Matter Around Us Pure CBSE Class 9 Chemistry Worksheets Set 04

Questions with Answers

Question 1. How will you convert one form of matter into another? Take water as an example.
Answer:
Water can be changed between its three states by changing temperature.
Ice (solid) melts to water (liquid) at its melting point, 0 °C. Water boils to steam (gas) at its boiling point, 100 °C when heat is supplied.
The reverse changes happen on cooling: steam condenses to water, and water freezes to ice at 0 °C. Gases can also be liquefied by cooling and applying pressure.
In simple words: Heating and cooling change matter from one state to another.

Teacher's Note:
1. Melting, boiling, condensation and freezing are physical changes.
2. The composition of water stays the same in all three states.

Question 2. What are fluids?
Answer:
Substances which can flow are called fluids. Liquids and gases flow easily because their particles are free to move over one another, so both are fluids.
In simple words: Liquids and gases can flow.

Teacher's Note:
1. Solids do not flow.
2. Fluids take the shape of their container.

Question 3. Name the three states of carbon dioxide.
Answer:
Carbon dioxide is a gas at room temperature. Under pressure and on cooling it becomes a liquid, and on strong cooling it forms a white solid called dry ice, which sublimes on warming.
In simple words: Gas (CO₂), liquid CO₂ and solid dry ice.

Teacher's Note:
1. Dry ice changes directly from solid to gas.
2. It is used to keep ice cream cold.

Question 4. Gases can be compressed but liquids and solids cannot. Why?
Answer:
Gas particles are far apart, so there is a lot of empty space between them, and pressure can push them closer. In liquids and solids the particles are already almost touching, so there is almost no space left to squeeze.
In simple words: Gases have large gaps between particles; solids and liquids have almost none.

Teacher's Note:
1. LPG and CNG are gases compressed into cylinders.
2. Compressibility shows that matter is made of particles with space between them.

Question 5. How will you classify matter on the basis of shape?
Answer:
A solid has a definite shape and a fixed volume. A liquid has no definite shape but a fixed volume and takes the shape of its container. A gas has neither a fixed shape nor a fixed volume and fills the whole container.
In simple words: Solids keep their shape, liquids take the shape of the vessel, gases fill it completely.

Teacher's Note:
1. Volume of a liquid is fixed.
2. Shape depends on how strongly the particles attract each other.

Question 6. Compare the densities of a solid, a liquid and a gas.
Answer:
Density is the mass per unit volume. A solid has the particles packed closest, so a high density. A liquid has a slightly lower (medium) density. A gas has particles far apart, so it has the lowest density.
In general density of solid > liquid > gas (water and ice are an exception: ice floats on water).
In simple words: More particles in a given volume means a higher density.

Teacher's Note:
1. Density = mass / volume.
2. Ice is less dense than water.

Question 7. How will you distinguish a mixture from a compound?
Answer:
A mixture has components in any proportion, which keep their own properties and can be separated by physical methods such as filtration, sublimation or a magnet. There is no energy change when it is made.
A compound has elements combined in a fixed ratio by mass, its properties differ from those of its elements and it can be broken into elements only by chemical methods. Heat or light is usually given out or taken in when it is formed.
Example: iron filings and sulphur form a mixture (a magnet removes the iron); heating them together gives iron sulphide, a compound that the magnet does not attract.
In simple words: A mixture can be separated physically; a compound cannot.

Teacher's Note:
1. Compounds have fixed composition.
2. Iron and sulphur show both.

Question 8. Classify as an element, compound or mixture: iron, well water, chalk, ink, coin, tungsten filament, graphite, carbon dioxide, water, gunpowder, steel, diamond, paint.
Answer:
Elements: iron, tungsten, graphite, diamond.
Compounds: carbon dioxide, water and chalk (mainly calcium carbonate).
Mixtures: well water, ink, coin (an alloy), gunpowder, steel (an alloy), paint.
In simple words: Elements have one kind of atom; compounds have fixed combinations; the rest are mixtures.

Teacher's Note:
1. Graphite and diamond are both carbon.
2. Alloys are mixtures of metals.

Question 9. Name a liquid metal. Also name a liquid non-metal.
Answer:
Mercury is a liquid metal at room temperature (caesium and gallium melt close to room temperature). Bromine is a liquid non-metal.
In simple words: Mercury and bromine are the two elements liquid at room temperature.

Teacher's Note:
1. Most metals are solids.
2. Bromine is a red-brown liquid.

Question 10. Using electrical properties, how will you distinguish a metal from a non-metal?
Answer:
Metals are good conductors of electricity; non-metals are poor conductors (insulators). Graphite, a non-metal, is an exception because it conducts electricity.
Test: connect the substance in a circuit with a cell and bulb. If the bulb glows, it is a metal.
In simple words: Metals conduct, non-metals mostly do not.

Teacher's Note:
1. Graphite conducts electricity.
2. Conduction is due to free electrons.

Question 11. Explain a metalloid with a suitable example.
Answer:
A metalloid shows some properties of metals and some of non-metals. For example, arsenic and antimony conduct electricity like metals, exist in allotropic forms like non-metals, and form oxides that react with both acids and alkalis (amphoteric).
Silicon and germanium are other metalloids.
In simple words: Elements in between metals and non-metals.

Teacher's Note:
1. Metalloids are semiconductors.
2. Examples: boron, silicon, germanium, arsenic, antimony.

Question 12. What are the main differences between metals and non-metals?
Answer:
Metals: shiny, hard, malleable and ductile, good conductors of heat and electricity, generally high melting points, form basic oxides.
Non-metals: dull, brittle if solid, poor conductors (except graphite), low melting points, form acidic or neutral oxides, and many exist as gases or molecules with several atoms.
In simple words: Metals shine, conduct and can be beaten into sheets; non-metals do not.

Teacher's Note:
1. Most metals are solids at room temperature.
2. Metal oxides are basic; non-metal oxides are acidic.

Question 13. Name the lightest and heaviest metals, and the lightest non-metal.
Answer:
Lithium is the lightest metal (lightest solid) and osmium is the densest (heaviest) metal, with density about 22.6 g per cm³. The lightest non-metal is hydrogen, followed by helium.
In simple words: Lightest metal lithium; heaviest osmium; lightest non-metal hydrogen.

Teacher's Note:
1. Density is mass per unit volume.
2. Mercury is a heavy liquid but not the densest metal.

Question 14. What are the advantages of using symbols for elements?
Answer:
Symbols are easy and short to write, they are the same all over the world, and they are used to write formulae and chemical equations. A symbol stands for one atom of the element and for one mole (its atomic mass in grams).
In simple words: Symbols are short, universal and used in equations.

Teacher's Note:
1. Co is cobalt while CO is carbon monoxide.
2. The first letter is capital, the second small.

Question 15. Give the characteristic properties of a solution. Give three examples.
Answer:
A solution is a homogeneous mixture: it looks the same throughout. The solute particles are too small to be seen even with a microscope, they pass through filter paper, do not settle on standing and do not scatter a beam of light.
Examples: sugar in water, salt in water, soda water, air, brass.
In simple words: A uniform mixture with very small particles.

Teacher's Note:
1. No Tyndall effect in a solution.
2. Solute and solvent can be solid, liquid or gas.

Question 16. What is a suspension? Give two examples.
Answer:
A suspension is a heterogeneous mixture in which solid particles large enough to be seen are spread through a liquid but not dissolved. The particles settle on standing, are stopped by filter paper and scatter light.
Examples: muddy water, chalk powder in water, flour in water.
In simple words: A mixture with large particles that settle down.

Teacher's Note:
1. Suspensions can be separated by filtration.
2. Particles are bigger than 10⁻⁴ cm.

Question 17. What are the characteristics of a colloidal solution? Name a few natural colloids.
Answer:
A colloid is heterogeneous but looks uniform. Particle size is 10⁻⁷ to 10⁻⁵ cm; the particles are not visible to the eye, pass through filter paper, do not settle and scatter a beam of light (Tyndall effect).
Natural colloids: milk, blood, fog, clouds, butter, jelly, smoke.
In simple words: Particles in between a solution and a suspension in size, which scatter light.

Teacher's Note:
1. Colloids are stable.
2. Tyndall effect identifies them.

Question 18. Distinguish between a solution, a suspension and a colloid.
Answer:
1. Solution: homogeneous, particles smaller than 10⁻⁷ cm, stable, passes through filter paper, no Tyndall effect.
2. Suspension: heterogeneous, particles larger than 10⁻⁴ cm, unstable (settles), does not pass through filter paper, scatters light.
3. Colloid: heterogeneous, particles between 10⁻⁷ and 10⁻⁵ cm, stable, passes through filter paper, scatters light (Tyndall effect).
In simple words: The three differ mainly in particle size and stability.

Teacher's Note:
1. Size: solution < colloid < suspension.
2. Tyndall effect separates colloids from true solutions.

Question 19. By visual observation, how will you distinguish a true solution from a colloid?
Answer:
Pass a narrow beam of light through each in a dark room. A colloid scatters the light and the path of the beam is seen as a bright track (Tyndall effect), but a true solution does not scatter light, so the beam is not visible inside it.
In simple words: A colloid shows a visible beam of light and a solution does not.

Teacher's Note:
1. The effect is visible from the side.
2. Starch solution shows it; salt solution does not.

Question 20. Define (a) solvent, (b) solute.
Answer:
(a) Solvent: the component of a solution which is present in the larger amount and in which the other component dissolves (for example water in salt solution).
(b) Solute: the component present in the smaller amount which dissolves in the solvent (for example salt).
In simple words: The solvent dissolves; the solute is dissolved.

Teacher's Note:
1. Both can be solid, liquid or gas.
2. Water is called the universal solvent.