Formulae for ionic compounds

2 marks · Easy

Calculate the correct formula for the ionic compound made from barium ions and hydroxide ions. Show your working.

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Show answer

Ba(OH)2

Also accept: Ba(OH)2

Common mistakes: BaOH2; Ba2OH

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Marking points

M1 · 1 mark · Identifies Ba$^{2+}$ and OH$^{-}$; shows process of balancing charges.

A1 · 1 mark · Correct formula, including use of brackets: Ba(OH)$_2$ (follow-through)

Worked solution

Barium is in Group 2, so Ba$^{2+}$; hydroxide is OH$^-$.

Two hydroxide ions are needed to balance one Ba$^{2+}$.