Lesson 20 – All about Glass
Things to do
1. Find the following lists from the passage and copy them
Everyday things made of glass
Ans: Light bulbs, bottles, jars, glasses, reading glasses, marbles, window panes, etc.
What you can do with hot liquid glass
Ans: We can pour hot liquid glass, mould it, roll it, press it or even blow it.
Names of colours
Ans: Blue, violet, turquoise, ruby red, pink, amber, orange, deep yellow, purple, amethyst, dark green, black, white.
2. Guess the meaning of the following words from the passage:
molten
Ans: heated to a very high temperature so that it can become liquid.
transparent
Ans: allowing you to see through.
impermeable
Ans: not allowing liquid gas to pass through.
impart
Ans: to pass something to somebody or something.
recyclable
Ans: something that can be recycled, i.e., used again after certain treatments.
3. Write short notes on the following:
(a) How glass is made
Ans: Glass is made by heating a mixture of clean white sand and chemicals like soda and lime. The mixture is heated in a furnace until it turns into hot liquid glass, and when it cools down, it becomes stiff and hard.
(b) How glass is shaped
Ans: Glass is shaped into different articles when it is still hot and soft. It can be poured into moulds, rolled out, floated on a bed of molten metal, blown into shapes, or even drawn out into fibres.
(c) Some properties of glass
Ans: Glass has many useful properties, as follows:
1. Glass is transparent; we can see through it.
2. It is strong and hard; we can put a lot of load on it.
3. It is impermeable; hence, it does not allow water or other liquids to pass through it.
4. It has no effect on water or food material stored in it, i.e., it does not smell or taste like them.
(d) Coloured glass
Ans: Ordinary glass is colourless, but it is possible to produce coloured and transparent glass by using different combinations of chemicals in the glass-making process. Glass can be given many beautiful colours like blue, violet, turquoise, ruby red, dark pink, amber, orange, deep yellow, purple amethyst, dark and even black, and white.
4. Find out how paper and plastic are recycled.
(a) Recycling of paper:
Ans: The process of paper recycling involves the collection of waste paper and then mixing it with water and chemicals to chemically break it down. First, these papers are chopped and heated so that they get converted into strands of cellulose. This mixture is also called pulp or slurry. It is then filtered to remove impurities, washed, de-inked, bleached, and mixed with water. This can then be used to make new papers.
(b) Recycling of plastics:
Ans: Before recycling, the plastics are collected and sorted based on their colors and types. They are shredded and washed to eliminate any impurities. The material is melted and extruded into small pellets. These small pellets are then used to make other plastic materials.