Question

unit exam - matter and change
compare the total mass of the reactants to the total mass of the products.
what choice demonstrates the law of conservation of mass?
$23\\ \text{g}\\ \text{na}_2\text{co}_3 + 1\\ \text{g}\\ \text{h}_2\text{o} + 28\\ \text{g}\\ \text{co}_2 \
ightarrow 84\\ \text{g}\\ \text{nahco}_3$
$55\\ \text{g}\\ \text{mn} + 32\\ \text{g}\\ \text{o}_2 \
ightarrow 85\\ \text{g}\\ \text{mno}$
$78\\ \text{g}\\ \text{k} + 71\\ \text{g}\\ \text{cl}_2 \
ightarrow 149\\ \text{g}\\ \text{kcl}$
$56\\ \text{g}\\ \text{fe} + 16\\ \text{g}\\ \text{o}_2 \
ightarrow 88\\ \text{g}\\ \text{feo}$

Explanation:

Step1: Calculate reactant mass (Option1)

$23\ \text{g} + 1\ \text{g} + 28\ \text{g} = 52\ \text{g}$

Step2: Compare to product mass (Option1)

$52\ \text{g}
eq 84\ \text{g}$

Step3: Calculate reactant mass (Option2)

$55\ \text{g} + 32\ \text{g} = 87\ \text{g}$

Step4: Compare to product mass (Option2)

$87\ \text{g}
eq 85\ \text{g}$

Step5: Calculate reactant mass (Option3)

$78\ \text{g} + 71\ \text{g} = 149\ \text{g}$

Step6: Compare to product mass (Option3)

$149\ \text{g} = 149\ \text{g}$

Step7: Calculate reactant mass (Option4)

$56\ \text{g} + 16\ \text{g} = 72\ \text{g}$

Step8: Compare to product mass (Option4)

$72\ \text{g}
eq 88\ \text{g}$

Answer:

C. $78\ \text{g K} + 71\ \text{g Cl}_2
ightarrow 149\ \text{g KCl}$