Question

Equimolar solutions of the following compounds are prepared separately in water. Which will have the lowest pH value ?

• A. $BeCl_2$
• B. $SrCl_2$
• C. $CaCl_2$
• D. $MgCl_2$

Answer 1

Answer: (A)

$BeCl_2$

Answer 2

Metal halide on hydrolysis with water form corresponding hydroxides.
The basic strength of hydroxide increases as we move down in a group. This is because of the increase in size which results in decrease of ionization energy which weakens the strength of $M - O$ bonds in $MOH$ and thus increases the basic strength.
$\underset{\text{Amphoteric}}{{Be(OH)2}}$ $\quad$ $\underset{\text{Weak base}}{{Mg(OH)2}}$
${Ca(OH)2}$ $\underset{\text{Strong base}}{{Sr(OH)2}}$ ${Ba(OH)2}$
Hence, ${Ba(OH)2}$ will have lowest pH.