Question

dimensional analysis one step:
choose the correct fraction for the problem, then solve.
$\frac{1 \text{mol}}{6.02e23 \text{things}}$ or $\frac{1 \text{mol}}{\text{molar mass (g)}}$

1. 0.250 mol silver to atoms of silver

$\frac{0.250}{6.02×10^{23}} =$

1. $8.56 × 10^{-3}$ mol nacl to molecules nacl
2. 35.4 mol ca to grams of ca
3. 3.25g pb to mol pb
4. $4.96 × 10^{24}$ atoms au to mol au
5. $1.56 × 10^{23}$ molecules $o_2$ to mol $o_2$
6. 3.96 g $mg(oh)_2$ to mol $mg(oh)_2$

25

Explanation:

Step1: Moles to atoms (Avogadro's number)

$0.250\ \text{mol Ag} \times 6.02 \times 10^{23}\ \text{atoms/mol} = 1.51 \times 10^{23}\ \text{atoms Ag}$

Step2: Moles to molecules (Avogadro's number)

$8.56 \times 10^{-3}\ \text{mol NaCl} \times 6.02 \times 10^{23}\ \text{molecules/mol} = 5.15 \times 10^{21}\ \text{molecules NaCl}$

Step3: Moles to grams (molar mass Ca=40.08g/mol)

$35.4\ \text{mol Ca} \times 40.08\ \text{g/mol} = 1419\ \text{g Ca}$

Step4: Grams to moles (molar mass Pb=207.2g/mol)

$3.25\ \text{g Pb} \times \frac{1\ \text{mol}}{207.2\ \text{g}} = 0.0157\ \text{mol Pb}$

Step5: Atoms to moles (Avogadro's number)

$4.96 \times 10^{24}\ \text{atoms Au} \times \frac{1\ \text{mol}}{6.02 \times 10^{23}\ \text{atoms}} = 8.24\ \text{mol Au}$

Step6: Molecules to moles (Avogadro's number)

$1.56 \times 10^{23}\ \text{molecules }O_2 \times \frac{1\ \text{mol}}{6.02 \times 10^{23}\ \text{molecules}} = 0.259\ \text{mol }O_2$

Step7: Grams to moles (molar mass $\text{Mg(OH)}_2=58.32$g/mol)

$3.96\ \text{g Mg(OH)}_2 \times \frac{1\ \text{mol}}{58.32\ \text{g}} = 0.0679\ \text{mol Mg(OH)}_2$

Answer:

1. $1.51 \times 10^{23}$ atoms of silver
2. $5.15 \times 10^{21}$ molecules of NaCl
3. $1419$ grams of Ca
4. $0.0157$ mol Pb
5. $8.24$ mol Au
6. $0.259$ mol $O_2$
7. $0.0679$ mol $\text{Mg(OH)}_2$