Separation of the Components of a Mixture

$7.$ How does this experiment illustrate the principle of conservation of matter?

$8.$ A mixture was found to contain $1\mathrm{.}05g$ of $Si{O}_2,0\mathrm{.}69g$ of cellulose, and $1\mathrm{.}82g$ of calcium carbonate. What percentage of calcium carbonate is in the mixture?

$9.$ How could you separate a mixture of acetone and $-$naphthol?

$10.$ How could you separate zinc chloride from $Si{O}_2?$

$11.$ A student found that her mixture was $13\%N{H}_{4}Cl,18\%$NaCl, and $75\%Si{O}_2.$ Assuming that her calculations are correct, what did she most likely do incorrectly in her experiment?

$12.$ Why is the NaCl extracted with water three times as opposed to only once?