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Science Answer the questions.[Che-3M]

Is Matter Around Us Pure · CBSE STD 9 (CBSE - English Medium). 53 questions.

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Question 13 Marks
You are provided with soda water, milk and muddy water. How can you differentiate between them in terms of:
  1. Homogeneity.
  2. Filtration.
  3. Tyndall effect.
Answer
S.NoPropertySoda waterMilkMuddy water
a.HomogeneityHomogeneousHeterogeneousHeterogeneous
b.FiltrationCannot be separatedCannot be separatedCannot be separated
c.Tyndall effectDoes not showShowsShows
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Question 23 Marks
Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Answer
First, water is taken as a solvent in a saucer pan. This water (solvent) is allowed to boil. During heating, milk and tea leaves are added to the solvent as solutes. They form a solution. Then, the solution is poured through a strainer. The insoluble part of the solution remains on the strainer as residue. Sugar added to the filtrate, which dissolves in the filtrate. The resulting solution is the required tea.
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Question 33 Marks
Write a method to separate a mixture of sand and potash alum.
Answer
Potash alum is soluble in water whereas sand is insoluble in water. The difference in their solubility is used to separate them. The mixture of sand and potash alum is dissolved in water, then it is filtered with the help of filter paper. Sand remains as residue on the filter paper while potash alum solution is obtained as filtrate. The filtrate is then evaporated to get crystals of potash alum.
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Question 43 Marks
While diluting a solution of salt in water, a student by mistake added acetone (boiling point 56°C). What technique can be employed to get back the acetone? Justify your choice.
Answer
Acetone is soluble in water, a homogeneous mixture is obtained and hence separation by separating funnel cannot be used. Acetone can be get back by simple distillation because the difference in the boiling points of acetone and water is more than 25°C.
Boiling point of acetone — 56°C
Boiling point of water — 100°C
In distillation flask, acetone will boil at 56°C and change into vapours and can be collected in flask after condensation.
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Question 53 Marks
Which separation techniques will you apply for the separation of the following? 
  1. The different pigments from an extract of flower petals.
  2. Butter from curd.
  3. Oil from water.
  4. Tea leaves from tea.
  5. Iron pins from sand.
  6. Wheat grains from husk.
  7. Fine mud particles floating in water.
Answer
  1. Different pigments from an extract of flower petals.
  2. Butter from curd Centrifugation.
  3. Oil from water Using separating funnel.
  4. Tea leaves from tea Filtration.
  5. Iron pins from sand Magnetic Separation.
  6. Wheat grains from husk Winnowing.
  7. Fine mud particles suspended in water Centrifugation.
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Question 63 Marks
Which method is better for recovering sugar from sugar solution: evaporation or crystallization? Give reason for your answer.
Answer
Crystallisation is better method for recovering sugar from sugar solution than evaporation because:
  1. Sugar decomposes or get charred on heating to dryness during evaporation. There is no such problem in crystallization.
  2. The soluble impurities do not get removed in the process of evaporation. But such impurities get removed in crystallization.
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Question 73 Marks
What type of mixtures are separated by the technique of crystallisation?
Answer
The crystallisation method is used to purify solids.
Crystallisation is a separation technique that is used to separate. a solid that has dissolved in a liquid and made a solution. The solution is warmed in an open container, allowing the solvent to evaporate, leaving a saturated solution. A solution that has as much solid dissolved in it.
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Question 83 Marks
What is the distillation process? What kind of mixture can be separated by distillation?
Answer
Distillation is a process employed to obtain pure liquid from its solution. It can be defined as the conversion of impure liquid into vapours by evaporation and then condensation of the vapours to get pure liquid. This method is generally used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and their boiling points are quite different (more than 25-30°C).
For example: if you heat salt water the water in the solution will boil before the salt.
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Question 93 Marks
What is meant by (i) elements (ii) compounds, and (iii) mixtures? Write down the names of two elements, two compounds and two mixtures.
Answer
  1. Elements: An element is a substance which cannot be split up into two or more simpler substances by the usual chemical methods of applying heat, light or electricity.

Examples: Hydrogen, Oxygen.

  1. Compounds: A compound is a substance made up of two or more elements chemically combined in a fixed proportion by mass.

Examples: Sodium chloride, calcium carbonate.

  1. Mixtures: A mixture is a substance which consists of two or more elements or compounds not chemically combined together.
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Question 103 Marks
What is chromatography? State its two applications.
Answer
Chromatography is a technique of separating two or more dissolved solids which are present in a solution in very small quantities. Its two applications are:
  1. Chromatography is used to separate solutions of coloured substances (dyes and pigments).
  2. Chromatography is used to separate small amounts of products of chemical reactions.
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Question 113 Marks
What is a physical change? Give an example of physical change.
Answer
A change which occurs without a change in the composition and chemical nature of the substance is called a physical change. It means that there is a change only in the physical properties of the substance. Properties like colour, hardness, rigidity, fluidity, density, melting point and boiling point are known as physical properties.
Examples of physical changes include crushing a can, melting an ice cube, and breaking a bottle.
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Question 123 Marks
What are (i) metals (ii) non-metals, and (iii) metalloids? Give two examples each of metals, non-metals and metalloids.
Answer
  1. METALS: A metal is an element that is malleable, ductile and conducts electricity.

Example: Iron, Copper.

  1. NON-METALS: A non metal is an element that is neither malleable, nor ductile and does not conducts electricity.

Example: Carbon, Sulphur.

  1. METALLOIDS: The elements which show some properties of metals and some other properties of non-metals are called metalloids.

Example: Boron, Silicon, Helium, Magnesium, Copper.

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Question 133 Marks
To make a saturated solution, 36g of sodium chloride is dissolved in 100g of water at 293K. Find its concentration at this temperature.
Answer
Mass of solute (sodium chloride) = 36g
Mass of solvent (water) = 100g
Mass of solution = Mass of solute + Mass of solvent
= 36g + 100g = 136g
$\text{Concentration}=\frac{\text{Mass of solute}}{\text{Mass of solution}}\times100$
$=\frac{36}{136}\times100=26.47\%$
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Question 143 Marks
The solubility of potassium nitrate at 20°C is 32g per 100g of water. How much salt is required to prepare 66g of its saturated solution?
Answer
16g is required to prepare 66gram of saturated solution.
Explanation:
Here solute is potassium nitrate.
Solubility of potassium nitrate.
= 32g per 100g of water.
At maximum solubility the solution will be saturated.
Total mass of the solution when saturated = Mass of the solute + mass of water.
= 32 + 100 = 132g
At saturated solution, 132g of the solution will have 32g of the solute.
At saturated solution, 66g of the solution will have $\frac{32\text{g}}{132\text{g}}\times66\text{g}$
= 16g of the solute.
Thus 16g of potassium nitrate is required to prepare 66gram of saturated solution.
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Question 153 Marks
The ‘sea-water’ can be classified as a homogeneous as well as heterogeneous mixture. Comment.
Answer
Sample of sea-water collected from the surface of sea, Sea water can be considered as a homogeneous mixture when it has salts and water only. Sample of sea-water collected from deep sea, Sea water will be a heterogeneous mixture when the sample is collected from deeper layers and it contains salts, water, mud, decayed plant, etc.
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Question 163 Marks
The boiling points of two liquids A and B are 61°C and 111°C respectively. How will you separate this mixture?
Answer
For separating A and B, simple distillation is used. When mixture is heated to 61°C, vapours of A rise in the flask, pass through condenser and collect as distillate in the receiver. Liquid B has higher boiling liquid so it remains in the distillation flask.
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Question 173 Marks
State three reasons why you think air is a mixture and water is a compound.
Answer
Air is a mixture because:
  1. Air can be separated into its constituents like oxygen, nitrogen, etc. by physical process of fractional distillation.
  2. Air shows the properties of all the gases present in it.
  3. Liquid air does not have a fixed boiling point.
Water is compound because:
  1. Water cannot be separated into its constituents, hydrogen and oxygen by physical methods.
  2. Heat and light are given out when water is prepared by burning hydrogen in oxygen.
  3. Water has standard b.p. of 100°C under standard atmospheric pressure.
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Question 183 Marks
State the principle of centrifugation. Give its two applications.
Answer
The principle of centrifugation is that the denser particles are forced to settle at the bottom yhile the lighter particles stay at the top vhen spun rapidly.
APPLICATIONS:
  1. Used in dairy to separate butter from cream.
  2. Used for blood and urine test.
  3. Used in vashing machine to squueze out vater from clothes.
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Question 193 Marks
Non metals are usually poor conductors of heat and electricity. They are non-lustrous, non-sonorous, non-malleable and are coloured.
  1. Name a lustrous non-metal.
  2. Name a non-metal which exists as a liquid at room temperature.
  3. The allotropic form of a non-metal is a good conductor of electricity. Name the allotrope.
  4. Name a non-metal which is known to form the largest number of compounds.
  5. Name a non-metal other than carbon which shows allotropy.
  6. Name a non-metal which is required for combustion.
Answer
  1. Iodine is a lustrous non-metal.
  2. Bromine is a non-metal which exists as a liquid at room temperature.
  3. Graphite is the allotropic form of carbon and it is a good conductor of electricity.
  4. Carbon is a non-metal which is known to form the largest number of compounds.
  5. Phosphorus is a non-metal other than carbon which shows allotropy.
  6. Oxygen is a non-metal which is required for combustion.
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Question 203 Marks
Name the process associated with the following:
Milk is churned to separate cream from it.
Answer
This process is centrifugation. Milk is put in a closed container in big centrifuge machine. When machine is switched on, milk is rotated at a very high speed. Due to this, milk separates into ‘cream’ and ‘skimmed milk’. The cream being lighter, floats over the skimmed milk and then can be removed.
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Question 213 Marks
Name the different types of solutions. Give one example of each.
Answer
Types of solution:

  1. Solid in solid.

Example: Brass.

  1. Solid in a liquid.

Example: Tincture of iodine.

  1. Liquid in liquid.

Example: ethanoic acid.

  1. Gas in a liquid.

Example: CO2 in water.

  1. Gas in gas.

Example: Air.

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Question 223 Marks
Mention the three characteristics of a mixture.
Answer
The three characteristics of a mixture:
  1. Mixture are both homogenous and hetrogenous.
  2. Mixture are soluble in water.
  3. Mixture is the type of impure matter.
  4. They can be mixed in any ratio.
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Question 233 Marks
Melting of wax is a physical change but burning of wax is a chemical change. Explain.
Answer
Melting of wax is a physical change but burning of a candle is a chemical change. In melting of wax, only the state of wax changes from solid to liquid. It is a reversible reaction and no new substance is formed.... Burning of wick is achemical change as it involves combustion.
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Question 243 Marks
List the points of differences between homogeneous and heterogeneous mixtures.
Answer
A homogeneous mixture is a mixture having a uniform composition throughout the mixture. For example: salt in water, sugar in water, copper sulphate in water
A heterogeneous mixture is a mixture having a non-uniform composition throughout the mixture. For example: sodium chloride and iron fillings, salt and sulphur, oil and water.
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Question 253 Marks
Is air a mixture or a compound? Give three reasons for your answer.
Answer
Air is a mixture because:
  1. Air can be separated into its constituents like oxygen, nitrogen, etc. by physical process of fractional distillation.
  2. Air shows the properties of all the gases present in it.
  3. Liquid air does not have a fixed boiling point.
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Question 263 Marks
In what respects does a true solution differ from a colloidal solution?
Answer
A true solution does not scatter a beam of light passing through it but a colloidal solution scatters a beam of light passing through it and renders its path visible. A true solution is a homogeneous mixture of two or more substances whereas a colloidal solution is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions and is a heterogeneous mixture.
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Question 273 Marks
Identify colloids and true solutions from the following.
  1. Vinegar.
  2. Muddy water.
  3. Mist.
  4. Aluminium paint.
Answer

  1. Vinegar: True solutions are vinegar.

  2. Mist: Colloidal solution (Liquid droplets dispersed in gas).

  3. Muddy water: Colloidal solution (solid material dispersed in liquid).

  4. Aluminium paint: Colloidal solution (solid material dispersed in liquid).

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Question 283 Marks
How would you obtain sodium chloride from a mixture of sodium chloride and sulphur without using water?
Answer
Sulphur is soluble in carbon disulphide whereas sodium chloride is insoluble in carbon disulphide. The mixture of sulphur and sodium chloride is shaken with carbon disulphide. Sulphur dissolves in carbon disulphide whereas sodium chloride remains un-dissolved. The solution is then filtered, sodium chloride is obtained as residue. On evaporating the filtrate, carbon disulphide solvent is eliminated and solid sulphur remains behind.
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Question 293 Marks
How will you separate water from mustard oil?
Answer
The mixture of mustard oil and water is put in separating funnel and allowed to stand for some time. The mixture separates into two layers according to the densities of water and mustard oil. Water is heavier than mustard oil. So, water forms lower layer while mustard oil forms upper layer. On opening the stop clock of separating funnel, the lower layer of water comes out first and collected in beaker leaving behind mustard oil.
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Question 303 Marks
How will you separate iron pins from sand?
Answer
Mixture of iron pins and sand can be separated by using magnet. A horse-shoe magnet is moved on the surface of the mixture. The iron pins are attracted by the magnet, they cling to the poles of the magnet and get separated. This process is repeated a number of times till complete separation of iron pins is achieved.
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Question 313 Marks
How will you separate a mixture of sodium chloride and sand?
Answer
Sodium chloride is soluble in water whereas sand is insoluble in water. The difference in their solubility is used to separate them. The mixture of sand and sodium chloride is dissolved in water, then it is filtered with the help of filter paper and remains as residue on the filter paper while sodium chloride solution is obtained as filtrate .The filtrate is then evaporated to get crystals of sodium chloride.
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Question 323 Marks
How will you separate a mixture of iron filings and sulphur powder without using carbon disulphide?
Answer
Mixture of iron filings and powdered carbon can be separated by using magnet. A horse-shoe magnet is moved on the surface of the mixture. The iron filings are attracted by the magnet, they cling to the poles of the magnet and get separated. This process is repeated a number of times till complete separation of iron filings is done.
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Question 333 Marks
How will you separate a mixture of iron filings and powdered carbon?
Answer
Mixture of iron filings and powdered carbon can be separated by using magnet. A horse-shoe magnet is moved on the surface of the mixture. The iron filings are attracted by the magnet, they cling to the poles of the magnet and get separated. This process is repeated a number of times till complete separation of iron filings is done.
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Question 343 Marks
How will you separate a mixture of cooking oil (groundnut oil) and water?
Answer
The mixture of cooking oil (groundnut oil) and water is put in separating funnel and allowed to stand for some time. The mixture separates into two layers according to the densities of water and groundnut oil. Water is heavier than groundnut oil. So, water forms lower layer while groundnut oil forms upper layer. On opening the stop clock of separating funnel, the lower layer of water comes out first and collected in beaker leaving behind groundnut oil.
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Question 353 Marks
How is scrap iron separated from a heap of waste materials in factories?
Answer
In factories, scrap iron is separated from the heap of waste materials by using big electromagnets fitted to a crane. When a crane fitted with a powerful electromagnet is lowered on to the heap of waste materials, then the scrap iron objects present in the heap cling to the electromagnet. The crane is then moved up and away to drop these scrap iron objects at a separate place.
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Question 363 Marks
How is cream separated form milk?
Answer
Centrifugation is used to separate cream from milk. Milk is a suspension of tiny droplets of oil in a watery liquid. It is put in closed container in a big centrifuge machine. When machine is switched on, milk is rotated at very high speed in its container. The cream being lighter floats over the skimmed milk and then can be removed.
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Question 373 Marks
Give an example in which physical and chemical changes take place together.
Answer
Physical changes in burning candle On heating, candle's wax melts, it is a physical change. Since, it again turns into solid wax on cooling. The change is reversible. Chemical changes in burning candle The wax near to flame burns and gives new substances like carbon dioxide, carbon soot, water vapours, heat and light. Cooking of food, boiling of eggs are examples of both physical and chemical changes. In both cases, the physical appearance of the substances change and new substances are formed.
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Question 383 Marks
Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.
Answer
In a suspension, the size of the particles is relatively larger than that in a colloidal solution. Also, the molecular interaction in a suspension is not strong enough to keep the particles suspended. Hence the particles settle down when the suspension is left undisturbed for some time. On the other hand, the molecular interaction in a colloidal solution (like milk) is strong enough and does not allow the particles to settle down.
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Question 393 Marks
Explain the following giving examples.
Suspension.
Answer
Suspensions are heterogeneous mixtures. The solute particles in this mixture remain suspended throughout the bulk of the medium. The particles can be seen with naked eyes. Suspension shows the Tyndall effect. The solute particles settle down when the mixture is left undisturbed. This means that suspensions are unstable. Suspensions can be separated by the method of filtration. For example, mixtures of chalk powder and water, wheat flour and water.
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Question 403 Marks
Explain the following giving examples.
Saturated solution.
Answer
A saturated solution is a solution in which the maximum amount of solute has been dissolved at a given temperature. The solution cannot dissolve beyond that amount of solute at that temperature. Any more solute added will settle down at the bottom of the container as a precipitate.
Suppose 500g of a solvent can dissolve a maximum of 150g of a particular solute at 40°C. Then, the solution obtained by dissolving 150g of that solute in 500g of that solvent at 300K is said to be a saturated solution at 300K.
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Question 413 Marks
Explain the following giving examples.
Colloid.
Answer
A colloid is a heterogeneous mixture. The size of the solutes in this mixture is so small that they cannot be seen individually with naked eyes, and seems to be distributed uniformly throughout the mixture. The solute particles do not settle down when the mixture is left undisturbed. This means that colloids are quite stable. Colloids cannot be separated by the process of filtration. They can be separated by centrifugation. Colloids show the Tyndall effect. For example, milk, butter, foam, fog, smoke, clouds.
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Question 423 Marks
Explain how, impure copper sulphate can be purified by crystallization.
Answer
Impure copper sulphate is dissolved in minimum amount of water in a china dish to make copper sulphate solution. It is then filtered to remove insoluble impurities. Now, copper sulphate solution is heated gently on a water bath to evaporate water and a saturated solution is obtained. Then heating is stopped and saturated solution of copper sulphate is allowed to cool slowly. Crystals of pure copper sulphate will be formed leaving behind impurities. These crystals are then separated and dried.
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Question 433 Marks
During an experiment the students were asked to prepare a 10% (Mass/ Mass) solution of sugar in water. Ramesh dissolved 10g of sugar in 100g of water while Sarika prepared it by dissolving 10g of sugar in water to make 100g of the solution.
  1. Are the two solutions of the same concentration.
  2. Compare the mass % of the two solutions.
Answer
  1. No, the two solutions do not have the same concentration.
  2. Mass percentage of solution prepared by Ramesh $=\frac{\text{mass of solute}}{\text{mass of solution}}\times100$

$=\frac{\text{mass of solute }\times100}{\text{mass of solute }+\text{ mass of solvent}}$

$=\frac{10\text{g}}{(10\text{g}+100\text{g})}\times100$

$=\frac{100}{11}=9.09\%$

Mass percentage of solution prepared by sarika $=\frac{10}{100}\times100=10\%$

The solution prepared by Ramesh has less percentage (9.09%) by mass than that of Sarika (10%)

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Question 443 Marks
Draw a flow diagram of the processes involved in obtaining gases like nitrogen, oxygen and argon from air.
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Question 453 Marks
Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer
A homogeneous mixture is a mixture having a uniform composition throughout the mixture. For example, mixtures of salt in water, sugar in water, copper sulphate in water, iodine in alcohol, alloy, and air have uniform compositions throughout the mixtures.
On the other hand, a heterogeneous mixture is a mixture having a non-uniform composition throughout the mixture. For example, composition of mixtures of sodium chloride and iron fillings, salt and sulphur, oil and water, chalk powder in water, wheat flour in water, milk and water are not uniform throughout the mixtures.
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Question 463 Marks
Describe a method for separating a mixture of iron filings and sulphur powder other than that by using a magnet.
Answer
Sulphur is soluble in carbon disulphide whereas iron filing is insoluble in carbon disulphide. The mixture of sulphur and iron filing is shaken with carbon-di-sulphide. Sulphur dissolves in carbon disulphide whereas iron filings remain un-dissolved. The solution is then filtered, iron filing is obtained as residue. On evaporating the filtrate, carbon disulphide solvent is eliminated and solid sulphur remains behind.
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Question 473 Marks
Define solubility. How does solubility of a solid in water change with temperature?
Answer
Solubility: Amount of a substance (called the solute) that dissolves in a unit volume of a liquid substance (called the solvent) to form a saturated solution under specified conditions of temperature and pressure. Solubility is expressed usually as moles of solute per 100 grams of solvent.
For many solids dissolved in liquid water, the solubility increases with temperature. The increase in kinetic energy that comes with higher temperatures allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions.
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Question 483 Marks
Define distillation. What types of liquids (substances) can be separated by this process?
Answer
Distillation is a process employed to obtain pure liquid from its solution. It can be defined as the conversion of impure liquid into vapours by evaporation and then condensation of the vapours to get pure liquid. This method is generally used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and their boiling points are quite different (more than 25 - 30°C).
For example: if you heat salt water the water in the solution will boil before the salt.
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Question 493 Marks
Classify the following as physical or chemical changes:
  1. Cooking of food.
  2. Boiling of water.
  3. Cutting of trees.
  4. Dissolving salt in water.
  5. Digestion of food.
  6. Melting of ice.
Answer

  1. Cooking of food: Chemical change.

  2. Boiling of water: Physical change.

  3. Cutting of trees: Physical change.

  4. Dissolving salt in water: Physical change.

  5. Digestion of food: Chemical change.

  6. Melting of ice: Physical change.

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Question 503 Marks
Calculate the mass of water and mass of glucose required to make 250g of 40% solution of glucose.
Answer
We know that,
Mass percent $=\frac{\text{mass of solute}}{\text{mass of solution}}$
Here mass of solution = 250g
Mass of solute = X
Mass percent = 40
Hence 40% $=\frac{\text{x}}{250}$
Therefore X = 100g
Hence amount of solute needed to make 250g of 40% solution is 100g
As we know mass of solution = mass of solute + mass of solvent,
Therefore mass of solute = 250g – 100g
Hence the mass of solute = 150g
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