GSEB Solutions for Class 7 Science and Technology – Properties of Water (English Medium)
GSEB SolutionsMathsScience
Exercise 29:
Solution 1(a):
Taste of water: Tasteless
Colour of water: Colourless
Smell of water: No smell
Solution 1(b):
Solid wax sinks into its liquid form.
Solution 1(c):
Ice floats on water.
Exercise 30:
Solution 1(a):
Ice floats on water. Solid form of water is ice, which is lighter than the liquid form of water. As ice is lighter than water, it floats.
Exercise 31:
Solution 1(a):
In the electrolysis of water, on passing electricity through water, gases starts collecting on both the poles.
Solution 1(b):
In electrolysis of water, on passing electricity through water, gases starts collecting on both the poles. The test-tube consisting cathode (negatively charged electrode) contains more gas.
Solution 1(c):
When a lighted match stick is brought near the test tube containing hydrogen gas, the gas burns with a pop sound.
Solution 1(d):
The gas at the positive pole supports the incense trick in smoking.
Exercise 32:
Solution 1(a):
| Things dissolving in water | Things not dissolving in water |
| milk | sand |
| Common salt | oil |
| sugar | |
| alum |
Exercise 34:
Solution 1:
| Name of the sample water, which forms more foam. | Name of the sample water, which forms less foam. |
| Distilled water | Sea-water |
Exercise 36:
Solution 1(a):
On filtering muddy water, visible impurities get stuck on the cotton cloth. The filtrate in the test-tube is clearer than the water in the first test-tube.
Exercise 37:
Solution 1(a):
On moving alum in the filtered water, insoluble impurities get settled down.
Exercise 38:
Solution 1(a):
Keep a bowl in the middle of the vessel. Pour salt-water in the vessel in such a way that the bowl is not immersed in it. Cover the vessel by a plastic sheet and tie it with a string. Put a stone on the plastic in such a way that it is exactly above the bowl. Now, keep this vessel in the sun for two to three hours. Distilled water will get collected in the middle bowl.
Solution 1(b):
The mark of ice level is higher than the mark of liquefied water.
Exercise 39:
Solution 1(a):
The density of ice is less than the density of liquefied water, hence the water get expanded on freezing.
Solution 1:
| Solvent | Soluble | Solution |
| Water | Common salt | Solution of common salt |
| Sugar | Solution of sugar | |
| Alum |
Solution 2.1:
In modern times, we use R.O. Plant (Reverse Osmosis Plant). It is a process of separating the dissolved salts from a liquid. In this plant, water is passed through a membrane made of small nets with a very high pressure and the dissolved salts are removed. The surplus water containing all salts is left to go out. Now, the water with no salt is allowed to pass through ultraviolet rays and the microorganisms are made inactive and the water thus obtained, is proper for drinking.
Also, in big cities, water-purification plants are used.
Solution 2.2:
In our school, the arrangement to purify drinking water is as given below:
- Water is made germfree by adding bleaching powder or chlorine tablets.
- Then, water is passed through R. O. Plant and then collected in the overhead tank.
- This germfree water is then filled in the water cooler.