Consider the following statements related to the glass: 1.The addition of lime makes the glass fluid and suitable for blowing. 2.Excess of soda increases the safety. 3.Silica is used in the form of pure quartz. Which of the above statements are correct?
- A2 and 3 only
- B1 and 2 only
- C1, 2 and 3
- D1 and 3 onlyCorrect
Solution
Concept
Each raw material in glass (silica, soda, lime) has a specific role. Too much soda makes glass weak against weather.
Step-by-step solution
1. Statement 1: Lime (CaO) is added to soda glass. Standard texts say it makes the glass fluid and suitable for blowing. It also makes glass durable and insoluble. So statement 1 is correct. 2. Statement 2: Soda is a flux and lowers the melting point. Excess soda makes glass soluble and easily attacked by moisture and air, so durability and safety go down. So statement 2 is wrong. 3. Statement 3: Silica is the main glass former. It is used as pure quartz or clean white sand. So statement 3 is correct. 4. Correct statements are 1 and 3, so the answer is D.
Explanation
Silica is the main ingredient and is taken as pure quartz or white sand. Lime helps the melt become fluid for blowing and gives durability. Excess soda makes glass weak and easily attacked by weather, so it does not increase safety.
Why the other options are wrong
A: Statement 2 is wrong and statement 1 is missing. B: Statement 2 is wrong. C: All three are not correct because statement 2 is wrong.
Shortcut
Excess of any alkali (soda or potash) is always bad for durability. Remove any option that has statement 2.
Common mistake
Thinking more soda means a better or safer glass. Excess soda actually makes glass soluble and weak.
Correct answer: D) 1 and 3 only