CBSE: CLASS-IX
SUBJECT : SCIENCE
TOPIC: IS MATTER AROUND US PURE? (PART-1)
These objective questions cover the essential
aspects of mixtures, solutions, and various separation methods used in science
and industry.
Objective Questions and Answers: is matter around us pure?
1. What is a mixture?
Answer: A mixture is a
combination of two or more substances where each substance retains its
individual properties. Mixtures can be homogeneous (uniform composition) or
heterogeneous (non-uniform composition).
2. Differentiate between homogeneous and heterogeneous mixtures with examples?
Answer:
Homogeneous Mixtures: Have
a uniform composition throughout. Example: Saltwater.
Heterogeneous Mixtures:
Have visibly distinct parts. Example: Sand and salt, oil and water.
Answer: A solution is a
homogeneous mixture of two or more substances. The substance present in a
larger amount is the solvent, and the substance present in a smaller amount is
the solute.
4. What are the properties of a solution?
Answer:
Homogeneous mixture.
·
Particles are
smaller than 1 nm and not visible to the naked eye.
·
Do not scatter
light (no Tyndall effect).
·
Solute particles
cannot be separated by filtration and do not settle over time.
5. What is the
difference between a dilute and a concentrated solution?
Answer: A dilute solution
has a relatively small amount of solute compared to the solvent, whereas a
concentrated solution has a larger amount of solute relative to the solvent.
6. Define saturated solution and its solubility.
Answer: A saturated
solution is one in which no more solute can be dissolved at a given
temperature. Solubility is the amount of solute that can be dissolved in a
solvent at a specific temperature to form a saturated solution.
7. What is a suspension?
Answer: A suspension is a
heterogeneous mixture where solid particles are dispersed in a liquid but are
large enough to settle over time. The particles can be seen with the naked eye
and scatter light.
8. Describe a colloidal solution and its properties.
Answer: A colloidal
solution is a heterogeneous mixture where the dispersed particles are smaller
than in suspensions but larger than in true solutions. They can scatter light
(Tyndall effect) but do not settle over time and cannot be separated by filtration.
9. What is the Tyndall effect?
Answer: The Tyndall effect
is the scattering of light by particles in a colloidal mixture, making the path
of light visible.
10.Differentiate between physical and chemical changes with examples.
Answer:
·
Physical Changes:
Do not alter the chemical composition of a substance. Example: Melting of
butter.
·
Chemical Changes:
Result in the formation of new substances with different properties. Example:
Burning of wood.
11. Classify the following
as chemical or physical changes:
o Cutting of trees:
Physical change
o Melting
of butter in a pan: Physical change
o Rusting
of almirah: Chemical change
o Boiling
of water to form steam: Physical change
o Passing
electric current through water and breaking it down into hydrogen and oxygen
gases: Chemical change
o Dissolving
common salt in water: Physical change
o Making
a fruit salad with raw fruits: Physical change
o Burning
of paper and wood: Chemical change
12. What is an element?
Answer: An element is a
basic form of matter that cannot be broken down into simpler substances by
chemical reactions.
13. Differentiate between an element and a compound.
Answer:
·
Element: A pure
substance that cannot be broken down further. Example: Iron.
·
Compound: A
substance composed of two or more elements chemically combined in fixed
proportions. Example: Water (H₂O).
14. What is the difference
between a mixture and a compound?
Answer:
·
Mixture: Contains
two or more substances physically combined and can have variable composition.
Components can be separated by physical methods.
·
Compound:
Contains two or more elements chemically combined in a fixed ratio and has a
fixed composition. Components can only be separated by chemical methods.
15. List the three methods
for expressing the concentration of a solution.
Answer:
·
Mass by mass
percentage
·
Mass by volume
percentage
·
Volume by volume
percentage
16. How would you classify
soda water, wood, air, soil, vinegar, and filtered tea?
Answer:
·
Soda water:
Homogeneous mixture
·
Wood:
Heterogeneous mixture
·
Air: Homogeneous
mixture
·
Soil:
Heterogeneous mixture
·
Vinegar:
Homogeneous mixture
·
Filtered tea:
Homogeneous mixture
17. What is the effect of
temperature on the solubility of salts?
Answer: Generally, the
solubility of most salts increases with temperature. However, this is not true
for all salts; for example, the solubility of sodium chloride remains almost
constant with temperature.
18. How would you confirm that a colourless liquid is pure water?
Answer: You can test the
boiling point and freezing point of the liquid. Pure water has a boiling point
of 100°C and a freezing point of 0°C at standard atmospheric pressure.
19. Explain the term “colloid” with examples.
Answer: A colloid is a
mixture where one substance is dispersed in another, and the particles are
small enough to remain suspended. Examples include milk (liquid in liquid) and
fog (liquid in gas).
20. Which separation techniques are suitable for the following mixtures:
·
Sodium chloride
from its solution in water: Evaporation or crystallization
·
Ammonium chloride
from a mixture containing sodium chloride: Sublimation
·
Small pieces of
metal in engine oil: Filtration
·
Different
pigments from an extract of flower petals: Chromatography
·
Butter from curd:
Centrifugation
·
Oil from water:
Separating funnel
·
Tea leaves from
tea: Filtration
·
Iron pins from
sand: Magnetic separation
·
Wheat grains from
husk: Sifting
·
Fine mud
particles suspended in water: Sedimentation and decantation or filtration
21. How would you design a
small-scale filtration plant?
Answer: Use an earthen pot
with layers of sand and pebbles to filter water. Water can be poured into the
pot, which passes through the layers, removing larger particles and impurities,
and the filtered water is collected at the bottom.
22. Find the concentration of a solution containing 40 g of common salt in 320 g of water in terms of mass by mass percentage.
Answer:
Mass of solution = 40 g
(salt) + 320 g (water) = 360 g
Mass percentage =
40 g360 g×100=11.1%\frac{40 \text{ g}}{360 \text{ g}} \times 100 =
11.1\%360 g40 g×100=11.1%
23. What happens when a
saturated solution is cooled slowly?
Answer: As a saturated
solution cools, it may become supersaturated if the temperature drop is
significant, causing the excess solute to crystallize out of the solution.
24. Classify the following as elements, compounds, and mixtures:
·
Elements: Sodium,
Silver, Tin
·
Compounds:
Calcium carbonate, Methane, Carbon dioxide
·
Mixtures: Soil,
Sugar solution, Air, Coal, Blood
25. Which materials are
pure substances?
Answer: Ice, Iron,
Hydrochloric acid, Calcium oxide, Mercury.
26. Identify the solutions among the following mixtures:
Answer: Sea water, Air,
Soda water.
27.Which of the following will show the Tyndall effect?
Answer: Milk, Starch
solution.
28.What are the components of a colloidal solution?
Answer: The dispersed
phase (particles) and the dispersion medium (substance in which particles are
suspended).
29.How are sol, solution, and suspension different from each other?
Answer:
·
Solution:
Homogeneous mixture with particles smaller than 1 nm, no Tyndall effect,
stable.
·
Suspension:
Heterogeneous mixture with visible particles, Tyndall effect, particles settle
over time.
·
Colloid:
Heterogeneous mixture with particles between 1 nm and 1000 nm, Tyndall effect,
particles do not settle.
30.Explain the difference
between elements and compounds using examples.
Answer: Elements are pure
substances like Iron (Fe) or Oxygen (O₂) that cannot be broken down further.
Compounds are substances like Water (H₂O) or Sodium chloride (NaCl) that are
made from two or more elements chemically combined in fixed proportions.
31.How does a separating funnel work to separate oil from water?
Answer: The separating
funnel separates immiscible liquids based on their density. Oil, being less
dense than water, will float on top, and after allowing the mixture to settle,
the oil can be drained from the top while the water remains at the bottom.
32.What is the principle behind using chromatography for separation?
Answer: Chromatography
separates components based on their different rates of movement through a
stationary phase due to differences in their affinity for the stationary phase
and the mobile phase.