15) How many grams are in 2.3times 10^-4 moles of calcium phosphate, Ca_(3)(PO_(3))_(2) 16) How many moles are in 3.4times 10^-7 grams of silicon dioxide, SiO_(2)

15) To find the number of grams in $2.3\times 10^{-4}$ moles of calcium phosphate, $Ca_{3}(PO_{3})_{2}$, we need to calculate the molar mass of the compound first.<br /><br />The molar mass of calcium phosphate is calculated by adding the molar masses of each element in the compound:<br />- Calcium (Ca): 40.08 g/mol<br />- Phosphorus (P): 30.97 g/mol<br />- Oxygen (O): 16.00 g/mol<br /><br />So, the molar mass of calcium phosphate is:<br />$Ca_{3}(PO_{3})_{2} = 3 \times 40.08 + 2 \times (30.97 + 3 \times 16.00) = 310.18$ g/mol<br /><br />Now, we can calculate the number of grams in $2.3\times 10^{-4}$ moles of calcium phosphate:<br />$2.3\times 10^{-4}$ moles $\times$ 310.18 g/mol = 0. grams<br /><br />Therefore, there are 0.0714 grams in $2.3\times 10^{-4}$ moles of calcium phosphate, $Ca_{3}(PO_{3})_{2}$.<br /><br />16) To find the number of moles in $3.4\times 10^{-7}$ grams of silicon dioxide, $SiO_{2}$, we need to calculate the molar mass of the compound first.<br /><br />The molar mass of silicon dioxide is calculated by adding the molar masses of each element in the compound:<br />- Silicon (Si): 28.09 g/mol<br />- Oxygen (O): 16.00 g/mol<br /><br />So, the molar mass of silicon dioxide is:<br />$SiO_{2} = 28.09 + 2 \times 16.00 = 60.09$ g/mol<br /><br />Now, we can calculate the number of moles in $3.4\times 10^{-7}$ grams of silicon dioxide:<br />$\frac{3.4\times 10^{-7}}{60.09}$ moles = $5.65\times 10^{-9}$ moles<br /><br />Therefore, there are $5.65\times 10^{-9}$ moles in $3.4\times 10^{-7}$ grams of silicon dioxide, $SiO_{2}$.