Question 1

Explain the method that can be used for separating the following mixtures:(i) Sand and husk(ii) Wheat, sugar, and silk(iii) Water and petrol(iv) Rice and salt(v) Sand and salt.

Accepted Answer

(i) Mixture of sand and husk: Sand and husk can be separated by the method of winnowing.(ii) Mixture of wheat, sugar and silk: For separating silk from the mixture, we should follow the winnowing method because silk is lighter than the other two components and get separated. Wheat and sugar can be separated by sieving because their particles are of different sizes.(iii) Mixture of water and petrol: Water does not dissolve in petrol. So, it can be separated by the use of separating funnel.(iv) Mixture of rice and salt: Rice and salt can be separated by sieving.(v) Mixture of sand and salt: Sand and salt is mixed with water, salt dissolves in water and sand can be separated by sedimentation and decantation followed by filtration. After that using evaporation, common salt is separated.

Question 2

Describe the method of obtain salt from sea water.

Accepted Answer

Sea water contains many salts mixed in it. One of them is common salt, when sea water is allowed to stand in shallow pits, water gets evaporated by sunlight and slowly turns into water vapor. In a few days, the water evaporates completely leaving behind the solid salts. Common salt is then obtained from this mixture of salts by further purification.

Question 3

What is winnowing? Where is it used?

Accepted Answer

Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air. This process is used by farmers to separate lighter husk particles from heavier seeds of grain.

Question 4

A solution which contains maximum possible amount of solute at any given temperature is called a :

Accepted Answer

Solution which contains maximum possible amount of solute at any given temperature is called a saturated solution. At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution. In other words, when no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

Question 5

What happens when a saturated solution is cooled?

Accepted Answer

A solution that contains the maximum amount of solute at a given temperature is called a saturated solution, and the amount of solute present in a saturated solution at a given temperature is called solubility. Solubility is directly proportional to temperature. So, when temperature decreases (i.e., when the saturated solution is cooled), solubility also decreases. On cooling the saturated solution, its solubility decreases which result in the separation of some of the dissolved substance or solute in the solid crystal form.Therefore, the solution becomes supersaturated.

Question 6

The mixture of sand and iron can be separated from each other by using a magnet.

Accepted Answer

The mixture of sand and iron can be separated from each other by using a magnet. Iron gets attracted towards a magnet leaving behind the sand.

Question 7

Explain the method of separation of solid-liquid mixtures.

Accepted Answer

When the solid particles are large such that they cannot pass through the filter paper, solid and liquid mixtures are separated by the process of filtration. Sometimes the solid particles in a liquid are very small and can pass through a filter paper. For such particles, the filtration technique cannot be used for separation. Such mixtures are separated by centrifugation. So, centrifugation is the process of separation of insoluble materials from a liquid where normal filtration does not work well. The centrifugation is based on the size, shape, and density of the particles, viscosity of the medium, and the speed of rotation. The principle is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly.

Question 8

A sugar solution contains 20 g sugar in 100 ml of water but when 20 g more sugar was added to it, it dissolves in the water. The previous solution will be known as :I) saturated solutionII) unsaturated solutionIII) dilute solution

Accepted Answer

The amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution. It can dissolve more solutes. A solution in which some more solute could be dissolved without changing its temperature is called unsaturated solution.A concentrated solution is one that has a relatively large amount of dissolved solute. A dilute solution is one that has a relatively small amount of dissolved solute.Option B is correct.

Question 9

Name the technique to separate the following:(a) Cream from milk(b) Salt from water(c) Camphor from sand(d) Oil from water

Accepted Answer

a)The process of centrifugation is used in dairies to separate cream from milk. Centrifugation is a method for separating the suspended particles of a substance from a liquid in which the mixture is rotated at a high speed in a centrifuge machine.b)We can separate Salt and Water Using Distillation. We can boil or evaporate the water and the salt will be left behind as a solid. If we want to collect the water, we can use distillation. This works because salt has a much higher boiling point than water.c)We know that camphor is a sublime substance and sand is not a sublime substance. Thus we can separate camphor from sand by heating the mixture slowly (sublimation). The vapours of camphor should be then collected and cooled downd)Oil being lighter forms the top layer, while water being heavier forms the bottom layer. Oil can be separated by decantation. However, a more useful method for separating oil and water is with the separating funnel.

Question 10

The process of&#10;settling down of heavier, insoluble particles in an undisturbed&#10;mixture solution is called:

Accepted Answer

Sedimentation is a process in which the liquid is separated from the insoluble solid particles. In this process, the mixture of liquid and insoluble solid is placed in a container. Due to the gravity, the heavier solid particles get settled at the bottom of the container. These solid particles are called sediment.