Question

unit review - matter and change
skip
compare the total mass of the
reactants to the total mass of the
products.
what choice demonstrates the law of
conservation of mass?
$165\\ \text{g}\\ \text{al(oh)}_3 \
ightarrow 102\\ \text{g}\\ \text{al}_2\text{o}_3 + 54\\ \text{g}\\ \text{h}_2\text{o}$
$500\\ \text{g}\\ \text{ag}_2\text{o} \
ightarrow 432\\ \text{g}\\ \text{ag} + 32\\ \text{g}\\ \text{o}_2$
$58\\ \text{g}\\ \text{mg(oh)}_2 \
ightarrow 40\\ \text{g}\\ \text{mgo} + 18\\ \text{g}\\ \text{h}_2\text{o}$
$401\\ \text{g}\\ \text{hg} + 32\\ \text{g}\\ \text{o}_2 \
ightarrow 440\\ \text{g}\\ \text{hgo}$

Explanation:

Step1: Calculate reactant mass (1st option)

$165\ \text{g}$

Step2: Calculate product mass (1st option)

$102\ \text{g} + 54\ \text{g} = 156\ \text{g}$

Step3: Calculate reactant mass (2nd option)

$500\ \text{g}$

Step4: Calculate product mass (2nd option)

$432\ \text{g} + 32\ \text{g} = 464\ \text{g}$

Step5: Calculate reactant mass (3rd option)

$58\ \text{g}$

Step6: Calculate product mass (3rd option)

$40\ \text{g} + 18\ \text{g} = 58\ \text{g}$

Step7: Calculate reactant mass (4th option)

$401\ \text{g} + 32\ \text{g} = 433\ \text{g}$

Step8: Calculate product mass (4th option)

$440\ \text{g}$

Step9: Match equal mass pairs

Identify where reactant mass = product mass

Answer:

C. $58\ \text{g Mg(OH)}_2
ightarrow 40\ \text{g MgO} + 18\ \text{g H}_2\text{O}$