NCERT Class 9 Science Chapter 2 Is matter arround us pure

Q1. Which separation technique will you apply for the separation of the following:

1. sodium chloride from a mixture containing sodium chloride and ammonium chloride
2. small pieces of metal in the engine oil of car
3. different pigments from an extract of flower petals
4. butter from curd
5. oil from water
6. tea leaves from tea
7. iron pins from sand
8. wheat grains from husk
9. fine mud particles suspended in water

Answer:

1. evaporation
2. sublimation
3. filteration
4. fractional distillation
5. chromatography
6. centrifugation
7. separating funnel
8. filtration
9. magnetic separation
10. winnowing
11. decantion

Q2. Write the steps you would use for making tea. Use the words- solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Answer:

1. Boil some water in a pan. Boiled water is the solvent.
2. Put tea and sugar. They are the solute here.
3. Sugar is soluble in water and will dissolve.
4. Tea leaves are insoluble and will not dissolve.
5. Put some milk and let the solution boil.
6. Put the solution through a strainer and the residue (tea leaves) will remain in the strainer. The tea (filtrate) will pass through the strainer.

Q3. Pragya tested the solubility of three different substances at different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of susbstances dissolved in 100 grams of water to form a saturated solution)

1. What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
2. Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperture. What would she observe as the solution cools? Explain.
3. Find the solubility of each salt at 293 K? Which salt has the highest solubility at this temperature?
4. What is the effect of change of temperature on the solubility of a salt?

Answer:

1. From the table above, we know that for getting a saturated solution of potassium nitrate at 313 K we require 62 grams of potassium nitrate for 100 grams of water. For 50 grams of water at 313 we will require 62/2 = 31 grams of potassium nitrate
2. At 353K , the solution will have 54 grams of potassium chloride. As the solution begin to cool the solubility decreases and at room temperature (293 K) only 35grams are required to produce a saturated solution. The extra potassium chloride will be start to appear and will settle down at the bottom.
3. Solubility of salt at 293K as per the table are given below:

            Potassium nitrate 32

            Sodium chloride 36

            potassium chloride 35

           Ammonium chloride 37

          It is clear from above data that Ammonium chlroide has the maximum solubility

      4. From the table given in the question, One can see that the solubility of salt increases as the      

          temperature increases.

 

Q4. Explain the following giving examples:

1. saturated solution
2. pure substance
3. colloid
4. suspension

Answer:

1. saturated solution is the one in which no more solute could be dissovled, keeping the temperature constant.example: At a constant temperature , lets say 25 ^{oc, we mix sodium chloride in 100 g of water and keep mixing the salt until no more salt dissolves. Then we will get saturated solution of sodium chloride at 25 oc.}
2. A pure substance is the one which always have the same colour, taste and texture at a constant temperature and pressure. Example Distilled water is a pure substance.
3. A colloidal solution is one which the size of particles lies between 1 nm and 100 nm. Example: Jelly
4. Suspension is a heterogenous mixture in which the solute particles stay suspended throughout the bulk of the medium. Example: chalk mixed with water, saw dust mixed with water.

Q5. Classify each of the following as homogenous or heterogenous mixture:

soda water, wood, air, soil,vinegar,filtered tea.

Answer:

Soda water - Homogeneous

Air - Heterogenous

wood - Heterogenous

soil - Heterogenous

vinegar- Homogeneous

filtered tea - Homogeneous

Q6. How would you confirm that a colourless liquid given to you is pure water?

Answer:

It could be confirmed by checking the boiling point of the colourless liquid. If the liquid boils at 100 oC then it is pure water. Presence of salts in the water pushes the temperature of the water.

Q7. Which of the following materials fall in the categories of a "pure substances" ?

Answer:

1. Ice - impure
2. Milk - impure
3. Iron - pure
4. Hydrochloric acid - pure
5. calcium oxide - pure
6. mercury - pure
7. brick - impure
8. wood - impure
9. air - impure

Q8. Identify the solutions among the following mixtures:

1. Soil
2. sea water
3. air
4. coal
5. soda water

Answer:

1. Soil - mixture
2. sea water - solution
3. air - mixture
4. coal - mixture
5. soda water - Solution

Q9. Which of the following will show "Tyndall effect"?

Answer:

1. Salt Solution
2. Milk
3. copper Sulphate solution
4. starch solution

Q10. Classify the following into elements, compounds abd mixtures:

answer:

1. sodium - element
2. soil -mixture
3. sugar solution -mixture
4. silver- element
5. calcium carbonate - compound
6. tin- element
7. silicon- element
8. coal- element
9. air-mixture
10. soap - compound
11. methane - compound
12. carbon dioxide - compound
13. blood-mixture

Q11. Which of the following are chemical changes?

1. growth of a plant
2. rusting of iron
3. mixing of iron fillings and sand
4. cooking of food
5. digestion of food
6. freezing of water
7. burning of a candle

Answer:

1. growth of a plant
2. rusting of iron - chemical change
3. mixing of iron fillings and sand
4. cooking of food- chemical change
5. digestion of food- chemical change
6. freezing of water
7. burning of a candle- chemical change

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