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Science Answer the questions.[Che-2M]

Is Matter Around Us Pure · CBSE STD 9 (CBSE - English Medium). 126 questions.

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Answer the questions.[Che-2M]

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Question 12 Marks
You have been given a suspension and a solution. How could you tell the difference between them by their appearance?
Answer
Both the given solutions will be kept stationary in different beakers for some time. The beaker in which the dissolved particles settle down after some time is a suspension and another one is a solution.
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Question 22 Marks
You are provided with a solution of salt in water in one jar and mixture of salt and sand in other. Can you state one property in which they resemble and differ from one another.
Answer
  1. Both are mixtures and a physical change is taking place.
  2. Salt in water do not show tyndall effect whereas sand in water shows tyndall effect.
  3. Salt in water is a homogenous whereas sand in water is heterogeneous.
  4. After mixing their chemical composition remains the same.
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Question 32 Marks
You are given two samples of water labelled as ‘A’ and ‘B’. Sample ‘A’ boils at 100°C and sample ‘B’ boilsa 102°C. Which sample of water will not freeze at 0°C? Comment.
Answer
Sample ‘B’ will not freeze at 0°C because may contain impurities. At 1 atm, the boiling point of pure water is 100°C and the freezing point of pure water is 0°C.
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Question 42 Marks
You are given two liquids, one a solution and the other a compound. How will you distinguish the solution from the compound?
Answer
Evaporate both the liquids separately. A pure compound will evaporate completely, leaving no residue whereas solution will not be evaporated completely, i.e. some residue will be left behind.
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Question 52 Marks
Write two applications of centrifugation techniques.
Answer
Application of centrifugation are:
  1. Used in diagnostic laboratories for blood and urine test.
  2. Used in dairies and home to separate butter from cream.
  3. Used in a washing machines to squeeze out water from wet clothes.
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Question 62 Marks
Why is sodium a metal whereas carbon non-metal?
Answer
Metal is a electron donor or it have the tendecy to donate electrons but non metal are the substancses which accepts a electron.
Sodium have one electron in it's valence she'll there for it have the tendecy to loose on electron and it's a metal but carbon have 4 electron in valence shell and it's have a greater affinity to accept electron to complete the order rule.
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Question 72 Marks
Why direct heating of ink is avoided, during separation of ink?
Answer
If ink is heated directly at high temperatures, the dye may get decomposed. and we could not be able to separate the ink components so a water bath is used for evaporation process.
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Question 82 Marks
Which of the two will scatter light: soap solution or sugar solution? Why?
Answer
Soap solution will scatter light because in true solution i.e. sugar solution, the solute particles are so small that they cannot scatter light rays while in soap solution particles are big enough to scatter light.
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Question 92 Marks
Which of the following materials fall in the category of a “pure substance”?
  1. Ice.
  2. Milk.
  3. Iron.
  4. Hydrochloric acid.
  5. Calcium oxide.
  6. Mercury.
  7. Brick.
  8. Wood.
  9. Air.
Answer
A pure substance contains only one kind of pure matter and its composition is the same throughout. Mixtures are constituted by more than one kind of pure substance.A pure substance cannot be separated into other kinds of matter by any physical process.Whatever the source of a substance may be, it will always have the same characteristic properties. Therefor as per the description of pure substance above, the following materials fall in the category of a “pure substance”:
  1. Ice.
  1. Iron.
  2. Hydrochloric acid.
  3. Calcium oxide.
  4. Mercury.
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Question 102 Marks
Which of the following can be separated by using a separating funnel and which cannot be separated by using a separating funnel?
  1. Water and kerosene mixture.
  2. Water and acetone mixture.
Give reasons for your answer.
Answer
  1. Water and kerosene mixture can be separated by using a separating funnel because these are immiscible liquids and they have different densities.
  2. Water and acetone mixture cannot be separated by by using a separating funnel because these are miscible liquids.
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Question 112 Marks
Which of the following are physical changes and which are chemical changes?
  1. Burning of a magnesium wire.
  2. Freezing of water.
  3. Rusting of iron.
  4. Glowing of an electric bulb.
Answer

  1. Burning of magnesium wire: Chemical change.

  2. Freezing of water: Physical change.

  3. Rusting of iron: Chemical change.

  4. Glowing of electric bulb: Physical change.

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Question 122 Marks
Which of the following are physical changes and which are chemical changes?
Burning of candle wax, Melting of candle wax, Mixing of iron filings and sand, Burning of wood, Breaking a piece of chalk, Burning a piece of paper, Cutting a piece of paper.
Answer

  • Physical change: Melting of candle wax, mixing of iron filings and sand, breaking a piece of chalk, cutting a piece of paper.

  • Chemical change: Burning of candle wax, burning of wood, burning of piece of paper.

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Question 132 Marks
Which of the following are not compounds?
  1. Chlorine gas
  2. Potassium chloride
  3. Iron
  4. Iron sulphide
  5. Aluminium
  6. Iodine
  7. Carbon
  8. Carbon monoxide
  9. Sulphur powder
Answer
These are not compounds:
  1. Chlorine gas
  1. Iron
  1. Aluminium
  1. Iodine
  1. Carbon
  1. Sulphur powder
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Question 142 Marks
Which of the following are chemical changes?
  1. Growth of a plant.
  2. Rusting of iron.
  3. Mixing of iron filings and sand.
  4. Cooking of food.
  5. Digestion of food.
  6. Freezing of water.
  7. Burning of a candle.
Answer
Following are Chemical changes.
  1. Growth of a plant.
  2. Rusting of iron.
  3. Cooking of food.
  4. Digestion of food.
  5. Burning of a candle.
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Question 152 Marks
Which of the following are chemical changes and which physical? Give reason.
  1. A glass bottle breaking.
  2. Coal burning in air.
  3. Making a cake.
  4. Wool being knitted into a sweater.
Answer

  • Chemical change: Coal burning in air, making of cake.

  • Physical change: A glass bottle breaking, wool beging knitted into a sweater.

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Question 162 Marks
What would you observe when:
A saturated solution of potassium chloride prepared at 60°C is allowed to cool to room temperature.
Answer
When a saturated solution of potassium chloride prepared at 60°C is allowed to cool at room temperature, crystals of potassium chloride will be formed.
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Question 172 Marks
What would you observe when:
An aqueous sugar solution is heated to dryness.
Answer
Initially, sugar will obtained as water will get evaporated. But on dry heating sugar gets charred and it turns black.
$\text{C}_{12}\text{H}_{22}\text{O}_{11}\xrightarrow{\ \ \ {\Delta}\ \ \ }12\text{C}+11\text{H}_2\text{O}\uparrow$
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Question 182 Marks
What would you observe when:
A mixture of iron filings and sulphur powder is heated strongly.
Answer
The black coloured compound, iron sulphide is formed when a mixture of iron filings and sulphur powder is heated strongly.
$\text{Fe}\ \ \ \ \ \ \ \ \ \ +\ \ \ \ \ \ \ \ \ \text{S}\ \ \ \ \ \ \ \ \ \ \ \ \xrightarrow{\ \ \\ \ \ \ \ \ \ {\Delta}\ \ \ \\ \ \ \ \ \ \ \ \ }\ \ \ \ \ \ \text{FeS}\\^\text{Iron fillings}\ \ \ \ \ ^\text{Sulphur powder}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Iron sulphide}$
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Question 192 Marks
What will happen if a saturated solution is: (i) heated, and (ii) cooled?
Answer
If a saturated solution is heated to a higher temperature, then it becomes unsaturated. If a saturated solution is cooled to a lower temperature, then some of its dissolved solute will separate out in the form of solid crystals.
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Question 202 Marks
What will be the residue left on the watch glass on heating blue ink in it?
Answer
A way to separate the coloured compounds in a mixture. Ink is not a pure substance. It is a mixture of some coloured components (solid) in water (liquid). The activity is aimed to demonstrate the process to separate the components of ink. When we heat the ink on a watch glass, water present in is evaporated and a solid residue is left which is actually the coloured component due to which ink has some colour.
The purpose of taking ink on watch glass is because we do not want to heat ink directly. If it is heated directly then we will not be able to get the solid residue.Solid will also decompose if ink is heated directly so the purpose of separation will not be fulfilled. Thus ink is taken in a watch glass which is kept over a beaker containing water. Beaker is heated so that ink is indirectly heated.
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Question 212 Marks
What volume of ethyl alcohol and water must be mixed together to prepare 250ml of 60% volume by volume solution of alcohol in water.
Answer
60% by volume of alcohol solution means, each 100ml of solution will have 60ml ethyl alcohol.
So, 250ml of solution will have
$=\Big(\frac{60}{100}\Big)\times250=150\text{ml}$ of ethyl alcohol 
Hence in a 250ml solution of 60% by volume of alchohol and water, alcohol should be 150ml and water should be 100ml.
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Question 222 Marks
What should be the boiling point (°C) for the separation of two miscible liquids by fractional distillation?
Answer
A mixture of two miscible liquids can be separated by the process of fractional distillation. The separation of two liquids by fractional distillation depends on the difference in their boiling points.
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Question 232 Marks
What is the need to heat solution?
Answer
If the temperature is too low (below 55 degrees celsius), the interaction between the oxalate and the potassium permanganate will move too slow as to be used as a practical lab experiment. Above 60 degrees celsius, oxalate acid begins to decompose, so its important to stay in this range. 
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Question 242 Marks
What is the name of the clear liquid formed when a solid dissolves in a liquid?
Answer
Dissolution of a solid in liquid form a homogenous mixture called solution. Solution is clear in nature as the solid particles (solute) in a solution are very small and get completely dissolved in the liquid (solvent).
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Question 252 Marks
What is the major difference between a solution and an ordinary mixture?
Answer
Mixtures are generally heterogeneous in which there is a boundary separation between different substituents. Solutions are homogeneous mixtures in which no separation is visible between different materials.
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Question 262 Marks
What is the effect of temperature on the solubility of solids in liquids?
Answer
The solubility of solids in liquids increases on increasing the temperature and decreases on decreasing the temperature.
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Question 272 Marks
What is the difference between solutions and colloids?
Answer
A solution is a homogeneous mixture of two or more substances whereas a colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions.
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Question 282 Marks
What is the difference between colloids and suspensions?
Answer
A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions whereas a suspension is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it.
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Question 292 Marks
What is the difference between a pure substance and a mixture? Give one example in each case.
Answer
Pure substance: Matter that has the same composition and properties throughout is called a substance.
Eg: Pure water is a pure substance. It consist of only water molecules. 
Mixture: It is the combination of two or more pure substances where each substance retains its own identity.
Eg: Alcohol-water mixture, both co-exist together.
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Question 302 Marks
What is the concentration of a solution which contains 16g of urea in 120g of solution?
Answer
Given mass of urea = 16g
And, mass of solution = 120g
So,
Concentration of solution $=\frac{\text{Mass of solute}}{\text{Mass of solution}}\times100$
Concentration of solution $=\frac{16}{120}\times100=13.33\%$
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Question 312 Marks
What is the composition (in per cent) of brass alloy?
Answer
Brass is an alloy made primarily of copper and zinc. The proportions of the copper and zinc are varied to yield many different kinds of brass. Basic modern brass is 67% copper and 33% zinc. However, the amount of copper may range from 55% to 95% by weight, with the amount of zinc varying from 5% to 40%
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Question 322 Marks
What is meant by man-made elements?
Answer
A Complete List of Man-made Synthetic Elements, man-made or “Synthetic elements are unstable chemical elements and they are not naturally found on the earth. These elements are synthesized in the laboratory”. These elements are formed by taking other elements in very small amounts and accelerating them in a particle accelerator to extremely high speeds and then crashing them into each other.
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Question 332 Marks
What is meant by (i) homogeneous mixtures, and (ii) heterogeneous mixtures? Give two examples of homogeneous mixtures and two of heterogeneous mixtures.
Answer
  1. Homogeneous mixtures: Those mixtures in which the substance are completely mixed together and are indistinguishable from one another, are called homogeneous mixtures.

Example: Sugar solution, copper sulphate solution.

  1. Heterogeneous mixtures: Those mixtures in which the substances remain separate and one substance is spread throughout the other substance as small particles, droplets or bubbles, are called heterogeneous mixtures. 

Example: Starch solution, soap solution.

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Question 342 Marks
What is meant by a substance?
Answer
A pure substance is the one that consists of a single type of particles, i.e., all constituent particles of the substance have the same chemical nature. Pure substances can be classified as elements or compounds.
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Question 352 Marks
What is meant by a solution? Give two examples of solutions.
Answer
A solution is a homogeneous mixture of two or more substances.
Example: Salt solution, metal alloys.
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Question 362 Marks
What is chlorination?
Answer
Chlorination is one of many methods that can be used to disinfect water. It is a chemical disinfection method that uses various types of chlorine or chlorine-containing substances for the oxidation and disinfection of what will be the potable water source.
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Question 372 Marks
What is a suspension? Give two examples of suspensions.
Answer
A suspension is a heterogeneous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it.
Example: Muddy-water, Milk of magnesia.
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Question 382 Marks
What is a physical change? Give two examples of physical changes.
Answer
The change in which no new substance is formed is called a physical change.
Example: Melting of candle wax, mixing of iron filings and sand.
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Question 392 Marks
What is a mixture? Give two example of mixtures.
Answer
Mixtures: A mixture is a substance which consists of two or more elements or compounds not chemically combined together.
Examples: Air, gun powder.
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Question 402 Marks
What is a colloid? Give two examples of colloids (or colloidal solutions).
Answer
A colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and those in suspensions.
Example: Soap solution, milk.
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Question 412 Marks
What is a chemical change?
Give two examples of chemical changes.
Answer
The change in which new substance is formed is called a chemical change.
Example: Burning of candle wax, burning of wood.
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Question 422 Marks
What do you understand by aerosol?
Answer
An aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. Aerosols can be natural or anthropogenic. Diseases can also spread by means of small droplets in the breath, also called aerosols (or sometimes bioaerosols).
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Question 432 Marks
What do you observe in the china dish during crystallization?
Answer
Crystallisation is the process of slow precipitation of solid crystals of a substance from a concentrated homogeneous solution. It is basically a separation method in which a substance is transferred from the liquid (i.e. solution) phase to the solid state. Thus during crystallisation, the substance is obtained in pure crystalline form in china dish which has no impurity. 
When formation of crystals take place in china dish, we observe that all crystals of different compounds looks different. Some crystals are needle shaped, some are cube shaped and some are hair like which are extremely fine. There are many different forms of crystals. You will learn about them in higher grades. 
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Question 442 Marks
What are the two types of pure substance? Give one example of each type.
Answer
Two types of pure substances:

  1. Pure substance made up of same kind of atoms.

Example: Sulphur.

  1. Pure substance made up of same kind of molecules.

Example: Water.

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Question 452 Marks
What are the three groups into which all the elements can be divided? Name two elements belonging to each group.
Answer
All the elements can be divided into following three groups:
  • Metals: Iron and copper.
  • Non-metals: Carbon and sulphur.
  • Metalloids: Boron and silicon.
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Question 462 Marks
What are the metalloids?
Answer
Along the border between nonmetals and metals are seven elements called metalloids. The metalloids have some characteristics of both metals and nonmetals. All are solids at room temperature. They are brittle, hard, and somewhat reactive. The most common metalloid is silicon (Si). The most useful property of the metalloids is their varying ability to conduct electricity. Whether or not a metalloid conducts electricity can depend on temperature, exposure to light, or the presence of small amounts os impurities. Semiconductors are substances that can conduct electricity under some conditions but not under other conditions.
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Question 472 Marks
What are the favourable qualities given to gold when it is alloyed with copper or silver for the purpose of making ornaments?
Answer
Pure gold (24-carat gold) is very soft. It is alloyed with silver or copper to impart strength while making ornaments. An alloy that contains 20 parts of gold and 4 parts of silver is called a 20-carat gold.
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Question 482 Marks
What are 'suspended particles'?
Answer
Suspended solids (SS) is the amount of tiny solid particles that remain suspended in water and act as a colloid. The measurement of suspended solids is one way of gauging water quality.
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Question 492 Marks
What are solute and solvent in aerated drinks?
Answer
There is no solute and solvent in aerated drinks because it is a colloid and for colloid the solute is called dispersed phase and the solvent is called dispersion medium, and the dispersed phase in aerated drink is carbon dioxide and dispersion medium is water.
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Question 502 Marks
The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare a 50% (mass by volume) solution of sodium hydroxide (NaOH). ‘A’ dissolved 50g of NaOH in 100mL of water, ‘B’ dissolved 50g of NaOH in 100g of water while ‘C’ dissolved 50g of NaOH in water to make 100mL of solution. Which one of them has made the desired solution and why?
Answer
Student 'C' has made the desired solution.
$\text{Mass by volume%}=\frac{\text{Mass of solute}}{\text{Volume of solution}}\times200$
$=\frac{50\text{g}}{100\text{ml}}\times100=50\%\text{mass by volume}$
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