Question

unit 5: mass-mole-atoms of elements
using avogadros number, determine the number of atoms in each of the following. also write the elements symbol. (ex: carbon = c)

1. 0.250 mol silver to atoms of silver
2. $8.56 \times 10^{-3}$ mol sodium to atoms of sodium
3. 35.4 mol bismuth to atoms of bismuth

determine the number of moles in each of the following. also write the name of the element.

1. $3.25 \times 10^{20}$ atoms pb to mol pb
2. $4.96 \times 10^{24}$ atoms au to mol au
3. $1.56 \times 10^{23}$ atoms sn to mol sn

use the molar mass of the element to convert from mol to g.

1. 0.375 mol calcium to g calcium
2. $8.56 \times 10^{-3}$ mol potassium to g potassium
3. 55 mol silicon to g silicon

Explanation:

Step1: Moles to atoms (Ag)

Use Avogadro's number $N_A = 6.022 \times 10^{23}\ \text{atoms/mol}$
$\text{Atoms of Ag} = 0.250\ \text{mol} \times 6.022 \times 10^{23}\ \text{atoms/mol}$

Step2: Moles to atoms (Na)

$\text{Atoms of Na} = 8.56 \times 10^{-3}\ \text{mol} \times 6.022 \times 10^{23}\ \text{atoms/mol}$

Step3: Moles to atoms (Bi)

$\text{Atoms of Bi} = 35.4\ \text{mol} \times 6.022 \times 10^{23}\ \text{atoms/mol}$

Step4: Atoms to moles (Pb)

Element: Lead (Pb)
$\text{Moles of Pb} = \frac{3.25 \times 10^{20}\ \text{atoms}}{6.022 \times 10^{23}\ \text{atoms/mol}}$

Step5: Atoms to moles (Au)

Element: Gold (Au)
$\text{Moles of Au} = \frac{4.96 \times 10^{24}\ \text{atoms}}{6.022 \times 10^{23}\ \text{atoms/mol}}$

Step6: Atoms to moles (Sn)

Element: Tin (Sn)
$\text{Moles of Sn} = \frac{1.56 \times 10^{23}\ \text{atoms}}{6.022 \times 10^{23}\ \text{atoms/mol}}$

Step7: Moles to mass (Ca)

Molar mass of Ca = $40.08\ \text{g/mol}$
$\text{Mass of Ca} = 0.375\ \text{mol} \times 40.08\ \text{g/mol}$

Step8: Moles to mass (K)

Molar mass of K = $39.10\ \text{g/mol}$
$\text{Mass of K} = 8.56 \times 10^{-3}\ \text{mol} \times 39.10\ \text{g/mol}$

Step9: Moles to mass (Si)

Molar mass of Si = $28.09\ \text{g/mol}$
$\text{Mass of Si} = 55\ \text{mol} \times 28.09\ \text{g/mol}$

Answer:

1. $1.51 \times 10^{23}$ atoms of Ag
2. $5.15 \times 10^{21}$ atoms of Na
3. $2.13 \times 10^{25}$ atoms of Bi
4. $5.40 \times 10^{-4}$ mol of Lead (Pb)
5. $8.24$ mol of Gold (Au)
6. $0.259$ mol of Tin (Sn)
7. $15.0$ g of Ca
8. $0.335$ g of K
9. $1545$ g (or $1.5 \times 10^3$ g) of Si