Question

When 6M sodium hydroxide is added to an unknown white solid, the solid dissolves. What is a possible identity for this solid? The options include: Mg(OH)2, Al2(SO4)3, BaCO3, and AgBr. Which one would the solid be and why?

Answer 1

sodium hydroxide NaOH is a strong base and it will reacts easily with acids.

Mg(OH)₂ is also a base and not completely soluble in water rather it forms a suspension called as molk of magnesia, it will not react with NaOH.

Al₂(SO₄)₃ is a salt of strong acid H2SO4 and weak base Al(OH)3 hence its aqueous solution is acidic, it is a white crystalline solid, the balanced chemical reaction is as follows

Al₂(SO₄)₃ + 6NaOH → 2Al(OH)₃ + 3Na₂SO₄

Barium carbonate BaCO₃ is insoluble in water and is also a weak base (all carbonates are weak bases due to carbonate-bicarbonate equilibrium exist in aqueous solutions).

Silver bromide (AgBr) is a salt of strong acid HBr and weak base AgOH. As AgOH is unstable it converts into silver oxide as 2AgOH --> Ag₂O + H₂O. Silver oxide is Black/ brown colored compound.

Final Answer: Al₂(SO₄)₃

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