Matter in our surrounding Worksheet-6

Matter in our surrounding Worksheet-6

11. Are the melting point temperature of the solid state and the freezing point temperature of the liquid state of a substance different?

12. A substance is in liquid state at room temperature and changes into gas upon heating. What will you call its gaseous state?

13. When a crystal of copper sulphate is placed at the bottom of a beaker containing water, the colour of water slowly becomes blue, why ?

14. The boiling point of ethyl alcohol is 78°C. What is the corresponding temperature on kelvin scale?

15. Does the evaporation of a liquid occur only at a fixed temperature?

16. Does the temperature of liquid increase further when it starts boiling ?

17. How does pressure help in the liquefaction of a gas ?

18. When sugar is dissolved in water, there is hardly an increase in volume. Explain.

19. Arrange in the order indicated for solid, liquid and gas.

(i) effect of pressure - increasing order

(ii) interparticle spaces - decreasing order

(iii) tendency to flow - decreasing order

(iv) thermal expansion - increasing order,

20. Butter is generally wrapped in wet cloth during summer when refrigerator is not working. Explain.

21. Which of the following factor(s) is (are) responsible for the change of state of solid carbon dioxide into vapours ?

(a) Increase in pressure (b) Decrease in presssure

(c) Increase in temperature (d) Decrease in temperature

22. The diagram shows an experiment in which gases hydrogen and carbon dixide are placed in two jars as shown in the figure. If the lid separating the two jars be removed, what will the constituents in the gas jar A after a few minutes ?

(a) carbon dioxide only

(b) hydrogen only

(c) mixture of carbon dioxide and hydrogen

23. The graph alongside shows the heating curve for a pure substance. The temperature rises with time as the substance is heated:

(a) What is the physical state of the substance at the points A, B, C and D ?

(b) What is the melting point of the substance?

(c) What is its boiling point ?

(d) What happens to the temperature while the substance is changing state ?

(e) The substance is not water. How can you judge from the graph ?

24. Small quantities of water and ether are placed on the palms of both the hands. Which palm will experience more cooling?

Answer:

11. No, these are the same. For example, melting point of ice and freezing point of water are both 0°C or 273 K.

12. The gaseous state of the substance is called vapour. Gaseous state of a substance which exists as liquid also is known as vapour.

13. Copper sulphate on dissolution in water releases (Cu²⁺ ions) and SO₄^2– ions. Due to diffusion of Cu²⁺ ions the colour of water slowly becomes blue.

14. Temperature on kelvin scale = 78 + 273 = 351 K

15. No, the evaporation of a liquid occurs at all temperatures.

16. No, it does not because the energy supplied is absorbed as latent heat of vapourisation.

17. Increase in pressure helps in the liquefaction of a gas. Pressure varies inversely with volume. With the increase in pressure the volume of gas decreases. The particles or molecules of a gas come closer and closer. They ultimately condense and as a result, the gas liquefies or changes into the liquid state.

18. Particles or molecules of sugar (C₁₂H₂₂O₁₁) fill the Inter particle spaces in water(liquid state). That is why there is hardly any change in volume on dissolution of sugar in water.

19. (i) solid, liquid, gas (ii) gas, liquid, solid (in) gas, liquid, solid (iv) solid, liquid, gas.

20. In summer, the weather is a quite hot. As a result, water present in wet cloth will readily evaporate. Since cooling is caused during evaporation, the temperature of butter will get lowered. This will check the rancidity of butter or it will not give any foul odour.

21. The change of state can take place by decreasing the pressure and increasing the temperature. On decreasing the pressure volume will increase. On increasing temperature, molecules will gain energy and will start moving haphazardly thus changing the state of solid carbon dioxide.

22. (c) The gas jar A will contain both the gases carbon dioxide and hydrogen. Actually, the gas present in one jar will diffuse into the other jar and vice versa.

23. (a) At point A : The substance is in the solid state.

At point B: The substance has started melting. It exists both in the solid and liquid states.

At point C : The substance is in the liquid state.

At point D : The substance has started boiling. It exists both in the liquid and gaseous states.

(b) The melting point of the substance is 15°C.

(c) The boiling point of the substance is 110° C.

(d) The temperature remains the same during the change of state.

(e) Had substance been water, its melting point should have been 0⁰ C and boiling point 100º C. It is therefore not water.

24. The palm containing ether will experience more cooling. Actually ether is more volatile (Boiling point of ether is very less). Therefore, it will evaporate at a faster rate than water. Since cooling is always caused during evaporation, the palm containing ether will become cooler.