GLASS-10th Science Notes

CHAPTER-11

Industrial Inorganic Chemistry

(A)GLASS

Text Book Question and Answers

I. Four alternatives are given to each of the following statement or question. Select the correct alternative.

1. The another name of flint glass is

(a)soda lime (b)potash lime (c)lead glass (d)borosilicate glass

Answer: (c)Lead Glass

2. During manufacture of glass, which material is used to increase the fusibility?

(a)soda (b)lime stone (c)sand (d)cullets

Answer: (d)Cullets

3. Glass will crack if it is suddenly heated or cooled, because of its____________

(a)bad conducting nature and high co-efficient of expansion (b) transparency

(c)plasticity (d)density

Answer: (a) bad conducting nature and high co-efficient of expansion

4. CaCo₃ + SiO₂ ----> _________

(a)CaO + SiCO₃ (b)CaSiO₃ + SiO₂ (c)CaSiO₂ + CaO (d)CaSiO₂ + CO₂

Answer: (d) CaSiO₂ + CO₂

5. Which type of glass is used to prepare lenses?

(a)lead glass (b)borosilicate glass (c)soda-lime glass (d)safety glass.

Answer: (a)Lead Glass

II. Fill in the blanks with suitable words

1. The decolourising substance Manganese dioxide

2. The raw materials are used in glass manufacture are soda, lime stone and Sand

III. Match the following

1. Yellow colour glass - Ferric Compound

2. Green colour glass - Chromium Compound and Ferrous

3. Blue colour glass - Cobalt Compound

4. Red colour glass - Cuprous Compound or Nickel Salts

IV. Answer the following

1. List any four properties of glass

a. They are chemically resistant.

b. Glass has a shining smooth surface which can be polished.

c. Glass can be moulded into different shapes conveniently

d. Glasses can be coloured

e. Glass is transparent

f. Glass can be altered suitably by including additives

g. The transparent nature can be made automatically adjustable to the intensity light.

h. Glass does not have a fixed melting point.

2. State uses of the following glasses (a) Borosilicate glass (b) lead glass

a. Borosilicate Glass: It is used extensively in industry for the preparation of pipelines, Superior laboratory apparatus.

b. Lead Glass: It is used widely for the manufacture of high optical purpose (like Lenses), neon sign tubing’s, cathode ray tubes, and electrical insulators.

3. Give reason

a. Annealing process is carried out in glass manufacture.

If glass allowed cooling rapidly, glass is being bad conductor of heat, the superficial layer cools down first leaving the interior portion in a state of stain. Owing to this unequal expansion, the articles are likely to crack into pieces. The process of gradual cooling of glass articles to room temperature is called annealing

b. Vinyl plastic is used in preparing safety glass

This is done so that glass becomes tough and when such a glass breaks, it does not fly into pieces as vinyl plastic holds back the broken pieces of glass

4. Write a note on optical fibre.

Optical fiber is a flexible, transparent fiber made up of very pure glass, not much wider than a human hair that acts as a wave guide or light pipe, to transmit light between the two ends.

Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. It is more advantageous to long distance communications, because light propagates through the fiber.

Addition Questions

1. What is glass?

Glass is an amorphous, transparent or translucent synthetic material which is essentially a super cooled mixture of silicates.

2. Why glass is called a super cooled liquid?

Glass appears like a solid and has many properties of solids. However, the molecules in glass are arranged randomly inside it which is similar to those of liquids. Hence, glass is called a super cooled liquid.

3. Name the Raw materials are used to manufacture of common glass

a. Soda ash (Na₂ CO₃)

b. Lime Stone (CaCO₃)

c. Sand (SiO₂)

d. Broken pieces of glass (up to 25%)

4. Why is scrap glass added along with the raw materials while manufacturing glass?

Scrap glass increases the fusibility of the materials and also serves to recycle glass. Therefore, scrap glass up to 25% is added along with the raw materials while manufacturing glass.

5. Name the homogenous mixture of Glass

Sodium silicate and Calcium silicate

6. Which compounds are used as special additive in glass manufacture to give colour glass

Metallic compounds

7. Explain the process of preparation of glass

a. Melting: Raw materials in proper proportions are mixed with cullets (glass pieces) are finely powdered and mixed. The intimate mixture is fused by heating it in a furnace, at high temperature (about 2073K) the charge melts and the following chemical reactions take place.

CaCO₃ + SiO₂ ------> CaSiO₃ + CO₂

Na₂CO₃ + SiO₂ ------> Na₂SiO₃ + CO₂

When all the carbon dioxide escapes out of the molten mass, decolourizers (such as manganese dioxides) are added to get away with ferrous compounds and carbon, if present if a coloured glass is desired, the colouring agents some namely metallic compounds are added at molten stage.

b. Shaping: Molten glass is then worked into articles of desired shaped by either blowing or moulding or pressing between rollers.

c. Annealing: the process of gradual cooling of glass articles to room temperature is called annealing.

d. Finishing: all glass articles after annealing are subjected to finishing processes such as cutting, grinding and polishing.

8. What are the compounds formed when (a) calcium carbonate reacts with silicon dioxide and (b) sodium carbonate reacts with silicon dioxide?

a) Calcium carbonate reacts with silicon dioxide to give calcium silicate and carbon dioxide gas,

b) Sodium carbonate reacts with silicon dioxide to give sodium silicate and carbon dioxide gas.

9. Name a decolourizer used while making glass.

Manganese dioxide is a decolourizer used while making glass.

10. Which are the three common ways of giving shape to molten glass?

Molten glass is given the desired shape either by blowing, moulding or by pressing between rollers.

11. What is meant by annealing of glass? Explain.

Glass articles become brittle when cooled suddenly. However, the brittleness can be avoided by slow cooling. The process of eliminating brittleness of glass by cooling it very slowly is called annealing.

12. Why is annealing process done during the manufacture of glass? Give reason.

Hot molten glass solidifies into a brittle material when it is cooled suddenly. In order to remove the brittleness, the glass is cooled slowly by a process called annealing. This process makes glass less brittle.

13. Write the limitations of glass

Glass is brittle and dense

Glass is heavy

Glass is cracks if it is suddenly heated or cooled.

Normal Glass is break when it is fall down

14. What is glass being replaced with now days?

Glass is being replaced by not so heavy and transparent polymers like Poly methyl methacrylate polymers, Scratches on this transparent polymer can be easily wiped out by Acetone. It is less brittle compared to glass.

15. Why Glass cracks if it is suddenly heated or cooled.

Due to rapid expansion and contraction along the hot region and cold region respectively

16. Write the types of glasses and its preparation and uses

a. Soda-Lime Glass

It is low it cost and relatively resistant to water, it melts easily

Use: it is widely used as window glass, electric bulbs, plate glass, bottles, jars, building blocks and cheaper table wares.

b. Potash lime/hard glass/Bohemian glass

This type of glass is prepared from silica (Sand), calcium carbonate and potassium carbonate. It possesses high melting point and it fuses with difficulty.

Use: potash lime type of glass is used for preparing chemical apparatus, combustion tubes.

c. Lead glass/Flint glass

This is made by using lead oxide instead of calcium oxide for fluxing together with silica.

Use: lead glass is used widely for the manufacture of high optical purposes (like lenses), neon sign tubing’s, cathode ray tubes, and electrical insulators.

d. Borosilicate glass/Pyrex glass/ Jena glass

This is the most common of the hard glasses used for commercial purposes. Such glasses virtually contain only silica and boron with a small amount of alumina and less alkaline oxides.

Use: borosilicate glass is used extensively in industry for the preparation of pipelines, superior laboratory apparatus.

e. Safety glass

This is made by sandwiching thin layer of synthetic vinyl plastic in between two or three flat sheets of glass and then it is subjected to slight pressure. It is then heated till the glass layers and plastic layers merge into on another. On cooling, the glass becomes quite tough. When such a glass breaks, it does not fly into pieces as the inner plastic layer tends to hold back the broken pieces of the glass.

Use: it is mostly used in automobile and aeroplane industries as wind shield.

17. State two important properties of potash-lime glass.

Potash-lime glass softens at high temperatures. It fuses with difficulty

18. Write the merits of optical fibres

a. Since optical fiber does not interact with air or water, it never corrodes.

b. Message reaches the destination much faster since photons transmit much faster than electrons.

c. Optic fibers can transmit more messages at once, compared to transmission by electron in a wire.

19. What is an optical fibre? What is it made of?

An optical fiber is a thin, transparent but flexible strand of glass which is used to transmit light between the two ends of the fiber. It is a kind of light pipe. '

An optical fiber is made of two types of materials. The inner part of the fibre is called core and the outer part is called clad. The outer layer has higher refractive index than the inner layer.