JEE Main 2023 · 8 April · evening · Single correct · +4 / −1
For a good quality cement, the ratio of lime to the total of the oxides of Si, Al and Fe should be as close as to :
- (a) 3
- (b) 2
- (c) 1
- (d) 4
Answer and solution
Answer (b) 2
Solution
Chemistry ma’am · 3 steps
In good cement, lime outweighs all the other oxides together, by about two to one.
- Typical composition. Portland cement is mostly lime, CaO, at 50–60%. The rest is mainly silica, SiO₂ (20–25%), alumina, Al₂O₃ (5–10%), and a little ferric oxide, Fe₂O₃ (1–2%).
- Compare the two parts. The three oxides of Si, Al and Fe add up to roughly 26–37%. Lime at 50–60% is close to twice that total.
CaO/(SiO₂ + Al₂O₃ + Fe₂O₃) ≈ 2
- So. For good quality cement this ratio should be as close as possible to 2, which is option (b). Too much lime makes the cement crack on setting, and too little makes it weak.
The idea to keep. Remember two cement ratios: lime to (silica + alumina + iron oxide) close to 2, and silica to (alumina + iron oxide) between 2.5 and 4. Do not mix them up.
Answer from the NTA final answer key. Solution by PrepWiser.