Class 9 Science · 42 questions · 42 with answers
Which of the following statements are true for pure substances? (i) Pure substances contain only one kind of particles (ii) Pure substances may be compounds or mixtures (iii) Pure substances have the same composition throughout (iv) Pure substances can be exemplified by all elements other than nickel
(b) (i) and (iii)
Rusting of an article made up of iron is called
(c) corrosion and it is a chemical change
A mixture of sulphur and carbon disulphide is
(d) homogeneous and does not show Tyndall effect
Tincture of iodine has antiseptic properties. This solution is made by dissolving
(d) iodine in alcohol
Which of the following are homogeneous in nature? (i) ice (ii) wood (iii) soil (iv) air
(c) (i) and (iv)
Which of the following are physical changes? (i) Melting of iron metal (ii) Rusting of iron (iii) Bending of an iron rod (iv) Drawing a wire of iron metal
(c) (i), (iii) and (iv)
Which of the following are chemical changes? (i) Decaying of wood (ii) Burning of wood (iii) Sawing of wood (iv) Hammering of a nail into a piece of wood
(a) (i) and (ii)
Two substances, A and B were made to react to form a third substance, A2B according to the following reaction 2 A + B → A2 B Which of the following statements concerning this reaction are incorrect? (i) The product A2B shows the properties of substances A and B (ii) The product will always have a fixed composition (iii) The product so formed cannot be classified as a compound (iv) The product so formed is an element
(c) (i), (iii) and (iv)
Two chemical species X and Y combine together to form a product P which contains both X and Y X+Y→P X and Y cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning the species X, Y and P are correct? (i) P is a compound (ii) X and Y are compounds (iii) X and Y are elements IS MATTER AROUND US PURE 13 16-04-2018 (iv) P has a fixed composition
(d) (i), (iii) and (iv)
Suggest separation technique(s) one would need to employ to separate the following mixtures.
(a) Mercury and water
(b) Potassium chloride and ammonium chloride
(c) Common salt, water and sand
(d) Kerosene oil, water and salt
Which of the tubes in Fig. 2.1
This question refers to a figure in the original PDF.
Hint— Look for the larger surface area. The presence of beads in tube (a) would provide a larger surface area for cooling.
Salt can be recovered from its solution by evaporation. Suggest some other technique for the same?
Crystallization
The ‘sea-water’ can be classified as a homogeneous as well as heterogeneous mixture. Comment. Fig. 2.1
This question refers to a figure in the original PDF.
Homogeneous— mixture of salts and water only Heterogeneous— contains salts, water, mud, decayed plant etc.
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.
Hint— Distillation, since acetone is more volatile it will separate out first.
What would you observe when
(a) a saturated solution of potassium chloride prepared at 60°C is allowed to cool to room temperature.
(b) an aqueous sugar solution is heated to dryness.
(c) a mixture of iron filings and sulphur powder is heated strongly.
Explain why particles of a colloidal solution do not settle down when left undisturbed, while in the case of a suspension they do.
Particle size in a suspension is larger than those in a colloidal solution. Also molecular interaction in a suspension is not strong enough to keep the particles suspended and hence they settle down.
Smoke and fog both are aerosols. In what way are they different?
Both fog and smoke have gas as the dispersion medium. The only difference is that the dispersed phase in fog is liquid and in smoke it is a solid
Classify the following as physical or chemical properties
(a) The composition of a sample of steel is: 98% iron, 1.5% carbon and 0.5% other elements.
(c) Metallic sodium is soft enough to be cut with a knife.
(b) Zinc dissolves in hydrochloric acid with the evolution of hydrogen gas.
(d) Most metal oxides form alkalis on interacting with water. 16-04-2018
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 100 mL of water, ‘B’ dissolved 50g of NaOH in 100g of water while ‘C’ dissolved 50g of NaOH in water to make 100 mL of solution. Which one of them has made the desired solution and why?
‘C’ has made the desired solution Mass of solute Mass by volume % = ×100 Volume of solution = ×100 = 50 % mass by volume
Name the process associated with the following
(a) Dry ice is kept at room temperature and at one atmospheric pressure.
(b) A drop of ink placed on the surface of water contained in a glass spreads throughout the water.
(c) A potassium permanganate crystal is in a beaker and water is poured into the beaker with stirring.
(d) A acetone bottle is left open and the bottle becomes empty. (e) Milk is churned to separate cream from it. (f) Settling of sand when a mixture of sand and water is left undisturbed for some time. (g) Fine beam of light entering through a small hole in a dark room, illuminates the particles in its paths.
You are given two samples of water labelled as ‘A’ and ‘B’. Sample ‘A’ boils at 100°C and sample ‘B’ boils at 102°C. Which sample of water will not freeze at 0°C? Comment.
Sample ‘B’ will not freeze at 0°C because it is not pure water. At 1 atm, the boiling point of pure water is 100°C and the freezing point of pure water is 0°C.
What are the favourable qualities given to gold when it is alloyed with copper or silver for the purpose of making ornaments?
Pure gold is very soft as compared to gold alloyed with silver or copper. Thus for providing strength to gold, it is alloyed.
An element is sonorous and highly ductile. Under which category would you classify this element? What other characteristics do you expect the element to possess?
This element is a metal. Other characteristics expected to be possessed by the element are–lustre, malleability, heat and electrical conductivity.
Give an example each for the mixture having the following characteristics. Suggest a suitable method to separate the components of these mixtures
(a) A volatile and a non-volatile component.
(b) Two volatile components with appreciable difference in boiling points.
(c) Two immiscible liquids.
(d) One of the components changes directly from solid to gaseous state. (e) Two or more coloured constituents soluble in some solvent.
Fill in the blanks
(a) A colloid is a ——— mixture and its components can be separated by the technique known as ———.
(b) Ice, water and water vapour look different and display different —— properties but they are ——— the same.
(c) A mixture of chloroform and water taken in a separating funnel is mixed and left undisturbed for some time. The upper layer in the separating funnel will be of——— and the lower layer will be that of ———.
(d) A mixture of two or more miscible liquids, for which the difference in the boiling points is less than 25 K can be separated by the process called———. IS MATTER AROUND US PURE 15 16-04-2018 (e) When light is passed through water containing a few drops of milk, it shows a bluish tinge. This is due to the ——— of light by milk and the phenomenon is called ——— . This indicates that milk is a ——— solution.
Sucrose (sugar) crystals obtained from sugarcane and beetroot are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.
It is a pure substance because chemical composition of sugar crystals is same irrespective of its source.
Give some examples of Tyndall effect observed in your surroundings?
Hint—Tyndall effect can be seen when light passes through a heterogeneous mixture. Example, when sunlight passes through the canopy of a dense forest.
Can we separate alcohol dissolved in water by using a separating funnel? If yes, then describe the procedure. If not, explain.
Hint— Water and alcohol are miscible. ANSWERS 97
On heating calcium carbonate gets converted into calcium oxide and carbon dioxide.
(a) Is this a physical or a chemical change?
(b) Can you prepare one acidic and one basic solution by using the products formed in the above process? If so, write the chemical equation involved.
Non metals are usually poor conductors of heat and electricity. They are non-lustrous, non-sonorous, non-malleable and are coloured.
(a) Name a lustrous non-metal.
(b) Name a non-metal which exists as a liquid at room temperature.
(c) The allotropic form of a non-metal is a good conductor of electricity. Name the allotrope.
(d) Name a non-metal which is known to form the largest number of compounds. (e) Name a non-metal other than carbon which shows allotropy. (f) Name a non-metal which is required for combustion.
Classify the substances given in Fig. 2.2 into elements and compounds Fig. 2.2 16-04-2018
This question refers to a figure in the original PDF.
Elements Compounds Cu CaCO3 Zn H2O F2 O2 Diamond (carbon)
Which of the following are not compounds?
Chlorine gas, Iron, Aluminium, Iodine, Carbon, Sulphur powder. Long Answer Questions
Fractional distillation is suitable for separation of miscible liquids with a boiling point difference of about 25 K or less. What part of fractional distillation apparatus makes it efficient and possess an advantage over a simple distillation process. Explain using a diagram.
The fractionating column packed with glass beads provides a surface for the vapours to collide and lose energy so that they can be quickly condensed and distilled. Also length of the column would increase the efficiency. Figure: Fractional distillation
Hint– (a) Homogenous mixture, because they have a uniform composition throughout (b) No, solid solutions and gaseous solutions are also possible. Examples brass and air (c) No, solution is a homogenous mixture of two or more substances
Iron filings and sulphur were mixed together and divided into two parts, ‘A’ and ‘B’. Part ‘A’ was heated strongly while Part ‘B’ was not heated. Dilute hydrochloric acid was added to both the Parts and evolution of gas was seen in both the cases. How will you identify the gases evolved?
Part A Fe (s) + S (s) Heat FeS (s) FeS + 2 HCl (aq) → FeCl2 + H2 S Part B Fe (s) + S (s)→ Mixture of iron filings and sulphur When dilute HCl is added to it Fe (s) + S (s) + 2 HCl (aq) → FeCl2 + H2 gas Sulphur remains unreacted H2S gas formed has a foul smell and on passing through lead acetate solution, it turns the solution black. Hydrogen gas burns with a pop sound.
A child wanted to separate the mixture of dyes constituting a sample of ink. He marked a line by the ink on the filter paper and placed the filter paper in a glass containing water as shown in Fig.2.3. The filter paper was removed when the water moved near the top of the filter paper.
This question refers to a figure in the original PDF.
Hint– (i) Three different bands will be observed. (ii) Chromatography (iii) To separate the pigments present in Chlorophyll.
A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumbler in the box as shown in the Fig.2.4. They were amazed to see that milk taken in the tumbler was Fig. 2.4 IS MATTER AROUND US PURE 17 16-04-2018 illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it?
This question refers to a figure in the original PDF.
(a) Explain why the milk sample was illuminated. Name the phenomenon involved.
(b) Same results were not observed with a salt solution. Explain.
(c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?
Classify each of the following, as a physical or a chemical change. Give reasons.
Hint—Physical changes —(a), (b), (e) Chemical changes— (c), (d)
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.
(a) Are the two solutions of the same concentration
(b) Compare the mass % of the two solutions.
You are provided with a mixture containing sand, iron filings, ammonium chloride and sodium chloride. Describe the procedures you would use to separate these constituents from the mixture?
Hint– Step-1 Separate iron filings with the help of a magnet Step-2 Sublimation of the remaining mixture separates ammonium chloride Step-3 Add water to the remaining mixture, stir and filter Step-4 The filtrate can be evaporated to get back sodium chloride.
Arun has prepared 0.01% (by mass) solution of sodium chloride in water. Which of the following correctly represents the composition of the solutions?
(c) 0.0l g of NaCl + 99.99g of water
Calculate the mass of sodium sulphate required to prepare its 20% (mass percent) solution in 100g of water? 16-04-2018
Let the mass of sodium sulphate required be = x g The mass of solution would be = (x +100) g x g of solute in (x + 100) g of solution 20% = ×100 x +100 20 x + 2000= 100 x 80 x = 2000 PNNN x = = 25 g C hapter 3 _lqucpq Multiple Choice Questions