Matter-Nature and its Behaviour (Short Answer Type Questions)

Question 1. Classify the following substances as elements,compounds and mixtures.

(i) Gasoline

(ii) Tap water

(iii) Distilled water

(iv) Milk

(v) Air

(vi) Sand

(vii) Diamond

(viii)Wood

(ix) Brass.

Answer.

(i) Mixture (Homogeneous)

(ii) Mixture (Homogeneous)

(iii) Compound

(iv) Mixture (Heterogeneous)

(v) Mixture (Heterogeneous)

(iv) Mixture (Heterogeneous)

(vii) Elements

(viii) Mixture (Heterogeneous)

(ix) Mixture (Heterogeneous)

Question 2. How would you separate the following mixture?

(i) salt and water

(ii) glass powder and iron filings

Answer.

(i) By distillation, salt remains as residue. In case of insoluble salt we can use filtration.

(ii) By magnetic separation. Iron filings are attracted by magnet.

 

Question 3. Classify the following into elements and compounds:

copper, iron sulphide, washing soda, tungsten, graphite, iron.

Answer.

Copper – element

Iron sulphide – compound

Washing soda – compound (it is sodium carbonate)

Tungsten – element

Graphite – element (it is carbon)

Iron – element

Question 4. Which method is used to separate two immiscible liquids?

Answer.

A separating funnel is used for this purpose.

Question 5. Which method is used to separate salt from sea water?

Answer.

Evaporation

Question 6. Which of the following mixtures are homogeneous ?

(a) wood

(b) tap water

(c) soil

(d) cloud

(e) smoke

Answer.

Cloud and tap water are homogeneous mixtures. Others are heterogeneous mixtures.

Question 7. Which of the following mixtures is homogeneous and why ?

Ethyl alcohol and water

Or

Oil and water

Answer.

Ethyl alcohol and water mixture is considered as homogeneous mixture because in such a mixture there is no boundary of separation between two component (i.e. ethyl alcohol and water) and it exists in a single phase.

In case of oil and water mixture we can see the boundary of separation between oil and water and there are two separate layers, one of water and other of oil so it is heterogeneous mixture.

Question 8. Which one shows Tyndall effect and why? True solution or colloidal solution.

Answer.

Tyndall effect is shown by colloidal solution. This is because of the size of colloidal particles (l nm to 100 nm) which can scatter the light falling on them. In true solution the size of particle is very small and they fail to scatter the light falling on them.

Question 9. How do fog differ from clouds ?

Answer.

Both fog and clouds are liquid in gas type of colloids. They differ in the fact that clouds are formed in the upper atmosphere but fog is formed in this region of atmosphere that is close to earth.

Question 10. Explain the cleansing action of soap.

Answer.

The dust particles present on oil drops sticking to clothes can not be easily removed by washing with water because water and oil do not form stable emulsion. Soap plays the role of emulsifier and helps in formation of a stable emulsion between water and oil. In this way soap helps in cleasing.

Question 11. Will the solubility of common salt in water decrease or increase with increase in
temperature? Explain your answer.

Answer.

Solubility of common salt in water increases with increase of temperature. The dissolution of common salt in water is accompanied by absorption of heat (i.e. it is endothermic). Due to endothermic nature the solubility increases with increase in temperature.

Question 12. If we add little amount of a solute to some solution (of same solute) provided to us and the solute remains undissolved. What does it indicate ?

Answer.

It indicates that the solution provided to us is saturated solution.

Question 13. What will happen if a saturated solution is

(a) heated

Answer (a). It becomes unsaturated.

(b) cooled

Answer (b). Some solute gets deposited at the bottom of solution.

Question 14. If we mix mustard oil with water, what type of colloidal solution is formed ?

Answer.

An oil in water type of colloidal solution is formed. Such type of colloidal solution is called emulsion.

Question 15. Why are the metals good conductors of electricity ?

Answer.

In metals we find that mobile electrons are present and it accounts for the high electrical conductivity of metals.

Question 16. What is meant by a non-aqueous solution ? Give one example.

Answer.

A solution in which the solvent is not water is called a non-aqueous solution, e.g., A solution of iodine (solute) in carbon tetrachloride (solvent).

Question 17. What is the volume % age of a solution prepared by mixing 100 ml of alcohol and 400 ml of water?

Answer.

Question 18. Classify the following as water-in-oil or oil-in water type of emulsion. milk, vanishing cream, cold cream, butter

Answer.

Milk—-oil-in-water

Vanishing cream —- oil-in-water

Cold cream —– water-in-oil

Butter —– water-in-oil

Question 19. What is the name given to a class of colloidal solution to which butter belongs ? Explain.

Answer.

Butter belongs to a colloidal solution in which dispersion medium is liquid and dispersed phase is solid. Such a colloidal solution is called a gel. When butter is pressed we find that drops of liquid come out. It shows the butter is a gel.

Question 20. Sometimes we refer to alloys as substitution solids. Why ?

Answer.

Alloys contain two or more metals and have a variable composition so they are homogeneous mixtures, e.g., brass contains copper and zinc. In brass, copper is a crystalline solid i.e. in copper atoms are closely packed to form a crystal lattice. When brass is formed some of these atoms of copper have been replaced by atoms of zinc (i.e. zinc atoms have substituted some copper atoms) and due to this brass is considered as substitution solid solution.

Question 21. Discuss the function of fractionating column in fractional distillation.

Answer.

The fractionating column obstructs the upward movement of vapours of the liquids and helps in absorptions of heat energy released by high boiling liquid to be¹ taken up by low boiling liquid. Due to this the lower boiling liquid remains in vapour phase and the high boiling liquid condenses to liquid phase and this condensed liquid falls back in the distillation flask. In this way fractionating column helps in the separation of two liquids.

Question 22. Explain Brownian movement.

Answer.

The zigzag motion of colloidal particles is called Brownian movement. This type of motion is due to moving molecules of dispersion medium constantly with colloidal particles. During collisions, molecules of dispersion medium import momentum to colloidal particles. You must have seen dust particles in a beam of sunlight coming through a slit in a dark room, which keeps on moving in zigzag path. It is used to determine Avogadro’s number.

Question 23. Explain why, water is a compound and not a mixture?

Answer.

Water is considered as a compound because

(i) Water cannot be separated into its constituents, hydrogen and oxygen, by t he physical methods) such as filtration, evaporation, distillation, sublimation, magnet, etc.)

(ii) The properties of water are entirely different from those of its constituents, hydrogen ad oxygen. For example, water is a liquid whereas hydrogen and oxygen and gases, water does not burn whereas hydrogen burns, water does not support combustion whereas oxygen supports combustion.

Question 24. Describe how you would prepare 100 g of a solution that is 0.5% phenolphthalein by mass.

Answer.

Since the solute (phenolphthalein) is a solid, the solution is percent by mass. Mass percent means the number of grams of solute per 100 g of solution,

mass percent = (mass of solute/mass of solution) 100%

mass of solute = mass percent mass of solution/100%

=0.5%x 100g/100% = 0.5g

Since the total mass of the solution equals 100 g, the remaining 99.5 g of the solution is water. To prepare the solution, dissolve 0.5 g phenolphthalein in 99.5 g distilled water.

Question 25. A solution contains 50 ml of alcohol mixed with 150 ml of water. Calculate the concentration of this solution.

Answer.

This solution contains a liquid solute (alcohol) mixed with a liquid solvent (water), so we have to calculate the concentration of this solution in terms of volume percentage of solute (alcohol). Now, we know that: Concentration of solution

 

 

Here, volume of solute (alcohol) = 50 ml And, volume of solvent (water) = 150 ml

So, volume of solution = Volume of solute + Volume of solvent

= 50+150 = 200 ml

Now, putting these values of’ volume of solute’ and ‘volume of solution’ in the above formula we get: Concentration of solution

Question 26. In terms of physical properties, what is there about mixtures that makes it possible to separate out the components?

Answer.

The components of a mixture are not chemically combined; therefore, the individual chemical and physical properties of the two components remain individual and unique, allowing for easy separation based on these properties. Separating a mixture can be likened to separating two different colored marbles from ajar.

Question 27. How does a gas differ from a liquid with respect to each of the following properties: (a) density, (b) compressibility, (c) ability to mix with other substances of the same phase to form homogeneous mixtures ?

Answer.

(a) A gas is much less dense than a liquid.

(b) A gas is much more compressible than a liquid.

(c) All mixtures of gases are homogenous. Similar liquid molecules form homogeneous mixtures, while very dissimilar molecules form heterogeneous mixtures.

Question 28. What are the advantage of chromatography as a method of separation of components of a mixture ?

Answer.

Main advantages of chromatography are :

(i) Only a small quantity of sample is required,

(ii) The constituents retain their individual characteristics during the process,

(iii) The process can be used for separation of constituents even if they have very similar chemical properties.