Q: Which equation correctly represents the calculation for the mass of sodium in 15 g of $$\mathrm{NaCl}$$?

$$15\ \mathrm{g}\ \mathrm{NaCl}\ \times\ \dfrac{1\ \mathrm{mol}\ \mathrm{NaCl}}{58.44\ \mathrm{g}\ \mathrm{NaCl}}\ \times\ \dfrac{1\ \mathrm{mol}\ \mathrm{Na}}{1\ \mathrm{mol}\ \mathrm{NaCl}}\ \times\ \dfrac{22.99\ \mathrm{g}\ \mathrm{Na}}{1\ \mathrm{mol}\ \mathrm{Na}}$$

Q: A nutritionist wants to know how much sodium is in 5 g of table salt ($$\mathrm{NaCl}). $$What is the correct calculation?

$$5\ \mathrm{g}\ \mathrm{NaCl}\ \times\ \dfrac{1\ \mathrm{mol}\ \mathrm{NaCl}}{58.44\ \mathrm{g}\ \mathrm{NaCl}}\ \times\ \dfrac{1\ \mathrm{mol}\ \mathrm{Na}}{1\ \mathrm{mol}\ \mathrm{NaCl}}\ \times\ \dfrac{22.99\ \mathrm{g}\ \mathrm{Na}}{1\ \mathrm{mol}\ \mathrm{Na}}$$

Question 1

A student wants to find the mass of sodium present in 15 g of sodium chloride ($$\mathrm{NaCl}). $$Which sequence of conversion factors should be used to solve this problem?

Accepted Answer

Convert grams of $$\mathrm{NaCl} to $$moles of $$\mathrm{NaCl}$$, then moles of $$\mathrm{NaCl} to $$moles of $$\mathrm{Na}$$, then moles of $$\mathrm{Na} to $$grams of $$\mathrm{Na}.$$

Question 2

What is the molar mass of sodium chloride ($$\mathrm{NaCl}$$)?

Accepted Answer

$$58.44\ \mathrm{g/mol}$$

Question 3

Given 15 g of $$\mathrm{NaCl}$$, how many moles of $$\mathrm{NaCl}$$ does this represent? Use the molar mass $$58.44\ \mathrm{g/mol}.$$

Accepted Answer

$$0.257\ \mathrm{mol}$$

Question 4

In the compound $$\mathrm{NaCl}$$, what is the mole ratio of sodium to sodium chloride?

Accepted Answer

1:1

Question 5

If you have $$0.257\ \mathrm{mol} of$$ $$\mathrm{NaCl}$$, how many grams of sodium ($$\mathrm{Na}) $$are present? (Atomic mass of $$\mathrm{Na} is$$ $$22.99\ \mathrm{g/mol})$$

Accepted Answer

$$5.91\ \mathrm{g}$$

Question 6

Which of the following best describes the process used to determine the mass of sodium in a sample of sodium chloride?

Accepted Answer

Stoichiometric conversion using molar mass and mole ratios

Question 7

A patient is prescribed a low-sodium diet. If they consume 15 g of $$\mathrm{NaCl}$$, how much sodium have they ingested?

Accepted Answer

$$5.91\ \mathrm{g}$$

Question 8

Which equation correctly represents the calculation for the mass of sodium in 15 g of $$\mathrm{NaCl}$$?

Accepted Answer

$$15\ \mathrm{g}\ \mathrm{NaCl}\ 	imes\ \dfrac{1\ \mathrm{mol}\ \mathrm{NaCl}}{58.44\ \mathrm{g}\ \mathrm{NaCl}}\ 	imes\ \dfrac{1\ \mathrm{mol}\ \mathrm{Na}}{1\ \mathrm{mol}\ \mathrm{NaCl}}\ 	imes\ \dfrac{22.99\ \mathrm{g}\ \mathrm{Na}}{1\ \mathrm{mol}\ \mathrm{Na}}$$

Question 9

If a chemist needs to isolate sodium from sodium chloride, which property of sodium chloride is most useful for calculating the amount of sodium present?

Accepted Answer

Molar mass of sodium chloride

Question 10

A sample contains 29.22 g of $$\mathrm{NaCl}. $$How many grams of sodium does it contain? (Molar mass of $$\mathrm{NaCl} is$$ $$58.44\ \mathrm{g/mol}$$, atomic mass of $$\mathrm{Na} is$$ $$22.99\ \mathrm{g/mol})$$

Accepted Answer

$$11.46\ \mathrm{g}$$

Question 11

Which of the following is a correct step in converting grams of a compound to grams of a constituent element?

Accepted Answer

Divide by the molar mass of the compound to get moles, use the mole ratio, then multiply by the atomic mass of the element.

Question 12

If you have 100 g of $$\mathrm{NaCl}$$, what is the mass of sodium present? (Molar mass of $$\mathrm{NaCl} is$$ $$58.44\ \mathrm{g/mol}$$, atomic mass of $$\mathrm{Na} is$$ $$22.99\ \mathrm{g/mol})$$

Accepted Answer

$$39.34\ \mathrm{g}$$

Question 13

Which of the following is NOT a necessary conversion when finding the mass of an element in a compound?

Accepted Answer

Grams of compound directly to grams of element without using mole ratios

Question 14

A nutritionist wants to know how much sodium is in 5 g of table salt ($$\mathrm{NaCl}). $$What is the correct calculation?

Accepted Answer

$$5\ \mathrm{g}\ \mathrm{NaCl}\ 	imes\ \dfrac{1\ \mathrm{mol}\ \mathrm{NaCl}}{58.44\ \mathrm{g}\ \mathrm{NaCl}}\ 	imes\ \dfrac{1\ \mathrm{mol}\ \mathrm{Na}}{1\ \mathrm{mol}\ \mathrm{NaCl}}\ 	imes\ \dfrac{22.99\ \mathrm{g}\ \mathrm{Na}}{1\ \mathrm{mol}\ \mathrm{Na}}$$

Question 15

Why is it important to use the mole ratio when converting from a compound to a constituent element?

Accepted Answer

Because the number of moles of each element in a compound is determined by the chemical formula.

Question 16

A chemist has 50 g of $$\mathrm{NaCl}. $$How many grams of sodium are present? (Molar mass of $$\mathrm{NaCl} is$$ $$58.44\ \mathrm{g/mol}$$, atomic mass of $$\mathrm{Na} is$$ $$22.99\ \mathrm{g/mol})$$

Accepted Answer

$$19.66\ \mathrm{g}$$

Question 17

Which step is missing if a student calculates the number of moles of $$\mathrm{NaCl}$$ but does not find the mass of sodium?

Accepted Answer

Multiplying by the atomic mass of sodium

Question 18

If a sample contains $$0.5\ \mathrm{mol} of$$ $$\mathrm{NaCl}$$, how many grams of sodium does it contain?

Accepted Answer

$$11.50\ \mathrm{g}$$

Relating Mass of a Compound to Mass of a Constituent Element: Sodium in Sodium Chloride

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