Question

multiple choice 2 points
the amount of sand recovered from 10g of original sample was 7.0g. what proportion of the original sample is sand?
140%
70%
30%
43%

multiple choice 2 points
the initial mass of sample was 2.79g. if the amount of nacl(s), sio2(s), and caco3(s) recovered was 2.65g, what is the percent recovery?
95%
5%
14%
105%

multiple choice 2 points
which step in the procedure required digestion?
evaporation of water from nacl(aq).
drying sio2(s) in the oven.
treating the sand/calcium carbonate mixture with hcl
precipitation of caco3(s) with k2co3(aq)

Explanation:

6.

Step1: Recall proportion formula

Proportion = $\frac{\text{amount of sand}}{\text{original sample amount}}\times100\%$

Step2: Substitute values

$\frac{7.0}{10}\times 100\%=70\%$

Step1: Recall percent - recovery formula

Percent recovery = $\frac{\text{mass recovered}}{\text{initial mass}}\times 100\%$

Step2: Substitute values

$\frac{2.65}{2.79}\times 100\%\approx95\%$

Digestion in chemistry often involves using a strong acid to break down a solid sample. Treating the sand/calcium carbonate mixture with HCl is a digestion - like process as HCl can react with calcium carbonate to dissolve it.

Answer:

B. 70%

7.