Answer
See answer below.
Work Step by Step
a) $Mg(OH)_2+2\ HCl\rightarrow MgCl_2+2\ H_2O$
b) Number of moles of HCl:
$29.52\ mL\times0.500\ M=14.76\ mmol$
Number of moles of $CaCO_3$:
$550\ mg \div 100.09\ mg/mmol=5.50\ mmol$
From stoichiometry, the number of moles of the hydroxide:
$(14.8-2/1\times5.50)\ mmol\times1/2=1.88\ mmol$
$1.88\ mmol\times58.32\ mg/mmol=110.\ mg$
