NCERT Solutions for Class 9 Science Chapter 2
What is Matter?
The chapter Is Matter Around us Pure starts by defining matter. Everything that takes up space and has mass is considered matter. This includes solids, liquids, and gases.
Pure Substances vs. Mixtures:
- Pure Substances:
- These are substances with a fixed composition throughout.
- They consist of only one type of particle at the chemical level.
- Examples of pure substances include elements like iron (Fe) and compounds like water (H2O).
- Mixtures:
- Most of the matter around us is a mixture.
- Mixtures combine two or more pure substances that can be separated physically without changing their chemical properties.
- The composition of a mixture can vary.
There are two main types of mixtures:
- Homogeneous Mixtures:
- Also called solutions, these appear uniform throughout.
- The components are evenly distributed, and you can’t distinguish them by sight.
- Examples include sugar dissolved in water (solution) or air (a suspension of gases).
- Heterogeneous Mixtures:
- These have visibly distinguishable components.
- You can easily identify the different parts that make up the mixture.
- Examples include granite (contains different minerals) or salad (mixture of vegetables).
Separating Mixtures:
The chapter discusses various techniques used to separate mixtures into their component parts. These techniques rely on the physical properties of the components in the mixture. Some common separation methods include:
- Filtration: This technique is used to separate a solid from a liquid. A filter paper allows the liquid to pass through while trapping the solid particles.
- Evaporation: This method separates a dissolved solid from a liquid. The liquid is heated, resulting in its evaporation, while the solid remains unaffected.
- Distillation: This technique is used to separate liquids with different boiling points. The mixture is heated, and the lower boiling point liquid vaporizes first, condenses, and is collected.
- Chromatography: This is a more advanced technique used to separate a mixture of dissolved substances based on their different rates of travel across a specific medium.
Chemical vs. Physical Changes:
The chapter also introduces the concept of chemical and physical changes. A physical change modifies the outward appearance or state of matter without altering its chemical composition.Separating mixtures using the techniques mentioned above are all examples of physical changes. In contrast, a chemical change transforms one substance into a new substance with different properties. This typically involves breaking or forming new chemical bonds.
By understanding the concepts of pure substances, mixtures, and separation techniques, you’ll gain a foundational knowledge of how matter is composed and manipulated in the world around you.
NCERT Solutions for Class 9 Science Chapter 2
Q1. Which separation techniques will you apply for the separation of the following?
(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c) Small pieces of metal in the engine oil of a car.
(d) Different pigments from an extract of flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water.
Ans:
- Evaporation
- Sublimation
- Filtration
- Chromatography
- Centrifugation
- Separating funnel
- Filtration
- Magnetic separation
- Winnowing or sieving
- Sedimentation and filtration (or centrifugation)
Q2. Write the steps you would use for making tea. Use the words, solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Ans:
1. Boil water (solvent).
2. Add tea leaves (solute) and sugar (optional solute) to cup.
3. Pour hot water to dissolve (dissolve solutes).
4. Steep (allow solutes to dissolve further).
5. Remove the tea bag (filter) or strain (separate solutes from solution).
Q3. Pragya tested the solubility of three different substances at different temperatures and collected, the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).
(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to coo! at room temperature. What would she observe us the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt?
Ans:
a) Mass of Potassium Nitrate for Saturated Solution:
Assuming you have the data table and it shows the solubility of potassium nitrate at 313 K to be X grams per 100 grams of water, you can calculate the mass needed for 50 grams of water using a proportion:
(X grams) / (100 grams) = Needed mass / (50 grams)
Solve for “Needed mass” to find the amount of potassium nitrate required for a saturated solution in 50 grams of water.
(b) Cooling Saturated Potassium Chloride Solution:
When Pragya cools the saturated potassium chloride solution, the solubility of the salt will decrease. This means that the solution, which was originally saturated at 353 K, will become supersaturated at room temperature. As a result, some of the dissolved potassium chloride will come out of the solution and crystallize, forming a solid precipitate at the bottom of the container.
(c) Solubility at 293 K (Missing Information):
Without the data table, we cannot determine the solubility of each salt at 293 K. However, you can look for this information in the table once you have it. The salt with the highest value in grams per 100 grams of water at 293 K will have the highest solubility at that temperature.
(d) Effect of Temperature on Solubility:
In general, the solubility of most salts increases with increasing temperature. This means that more grams of the salt can dissolve in a given amount of water at a higher temperature. In Pragya’s case, the potassium chloride solution became supersaturated upon cooling because the solubility decreased at the lower temperature.
Q4. Explain the following giving examples:
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
Ans:
(a) Saturated solution: Maximum solute dissolved in solvent at a temperature (like a crowded bus). Ex: Sugary drink with undissolved sugar at the bottom.
(b) Pure substance: Only one type of particle, fixed composition (like a uniform element or compound). Ex: Gold (element), Water (compound).
(c) Colloid: Mixture with mid-sized particles scattering light (cloudy). Ex: Milk, Fog.
(d) Suspension: Visible solid particles in liquid that can settle (unstable). Ex: Sandy water, Mud.
Q5. Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air. soil, vinegar, filtered tea.
Ans: Homogeneous: Soda water, air, vinegar, filtered tea.
Heterogeneous: Wood, soil.
Q6. How would, you confirm that a colourless liquid given to you is pure water?
Ans: Boil the liquid: If it boils sharply at 100°C and conducts minimal electricity (needs a metre), it’s likely pure water. Not a foolproof test, but a good indication.
Q7. Which of the following materials fall in the category of a “pure substance”?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Back
(h) Wood
(i) Air.
Ans: Out of the options, pure substances are:
- (c) Iron (Fe)
- (e) Calcium oxide (CaO)
- (f) Mercury (Hg)
Q8. Identify the solutions among the following mixtures. (a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water.
Ans: Solutions: (b) Sea water, (c) Air, (e) Soda water.
Q9. Which of the following will show “Tyndall effect”? (a) Salt solution (b) Milk (c) Copper sulphate solution (d) Starch solution.
Ans: (b) Milk. Milk is a colloid that scatters light, causing the Tyndall effect.
Q10. Classify the following into elements, compounds and mixtures.
(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Tin
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood
Ans: Elements: (a) Na, (d) Ag, (f) Sn, (g) Si
Compounds: (e) CaCO3, (k) CH4, (l) CO2
Mixtures: (b) Soil, (c) Sugar solution, (h) Coal, (i) Air, (j) Soap, (m) Blood
Q11. Which of the following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle.
Ans: Chemical changes: (b) Rusting of iron, (d) Cooking of food, (e) Digestion of food, (g) Burning of a candle.
NCERT Solutions for Class 9 Science Chapter 2
FAQ’s
What topics are covered in Class 9 Science Chapter 2: “Is Matter Around Us Pure”?
Class 9 Science Chapter 2 explores the concept of purity in matter, covering topics such as types of mixtures, methods of separation, and the significance of pure substances in various applications.
How can NCERT solutions for Class 9 Science Chapter 2 help in understanding purity in matter?
NCERT solutions offer detailed explanations and analyses of concepts related to the purity of matter, helping students understand the properties of pure substances, methods of purification, and the importance of purity in daily life and industries.
Where can I find NCERT solutions for Class 9 Science Chapter 2?
NCERT solutions for Class 9 Science Chapter 2 can be found online or in study materials provided by educational platforms or institutes specializing in academic resources.
When should I refer to NCERT solutions for Class 9 Science Chapter 2?
NCERT solutions are beneficial for reinforcing learning, clarifying doubts, and preparing for exams. They can be used alongside regular study or as a revision tool before assessments to enhance understanding of purity in matter.
What specific examples are discussed in Class 9 Science Chapter 2 Is Matter Around us Pure regarding purity in matter?
Class 9 Science Chapter 2 discusses various examples of pure substances and methods of purification, such as distillation, filtration, and chromatography, offering insights into the importance of purity in everyday life and industries.
