A silicon chip has a mass of 5.68mg. If 100g of Si has 1mol of Si, how many silicon atoms are present?

The given mass of the silicon chip is $5.68 \text{ mg}$. There are $1000 \text{ mg}$ in $1 \text{ g}$.

$$5.68 \text{ mg Si} \times \frac{1 \text{ g}}{1000 \text{ mg}} = 0.00568 \text{ g Si}$$

The molar mass of silicon (Si) is $28.09 \text{ g/mol}$.

$$0.00568 \text{ g Si} \times \frac{1 \text{ mol Si}}{28.09 \text{ g Si}}$$

Avogadro's number states that there are $6.022 \times 10^{23}$ atoms in $1 \text{ mol}$ of any substance.

$$\left(0.00568 \text{ g Si} \times \frac{1 \text{ mol Si}}{28.09 \text{ g Si}}\right) \times \frac{6.022 \times 10^{23} \text{ atoms Si}}{1 \text{ mol Si}}$$

Combine the terms:

$$\text{Number of atoms} = \frac{5.68 \times 1 \times 6.022 \times 10^{23}}{1000 \times 28.09 \times 1}$$ $$\text{Number of atoms} = \frac{34.20536 \times 10^{23}}{28090}$$ $$\text{Number of atoms} = \frac{3.420536 \times 10^{24}}{28090}$$ $$\text{Number of atoms} \approx 0.00012177 \times 10^{24}$$ $$\text{Number of atoms} \approx 1.2177 \times 10^{20}$$

Rounding to three significant figures, which is consistent with the given mass:

$$\text{Number of atoms} \approx 1.22 \times 10^{20} \text{ atoms}$$

The number of silicon atoms present is $1.22 \times 10^{20} \text{ atoms}$.