Mole Word Problems
The recommended daily allowance of selenium in your diet is 6.97x10-7 mole. How many atoms of selenium is this?

A bracelet containing 0.200 mol metal is 75% gold. How many atoms of gold are in the bracelet?

Which has more atoms, 10.0 g C or 10.0 g of Ca? How many atoms does each contain?
A mixture contains 0.250 mol Fe and 1.20 g C. What is the total number of atoms in the mixture?

Air contains several gases. Argon makes up 0.934% of the air. If a person takes a breath that contains 0.600 g of air, calculate the number of argon atoms inhaled.

A chemist needs 0.015 mol of iodine crystals, I2, for an experiment. What mass of iodine crystals should the student obtain?

BONUS PROBLEM
One atom of an unknown element has a mass of 6.66x10-23 g. What is the identity of this element?

As we know that 1 mole of any substance contains exactly 6.022 × 10²³ particles which is also called as Avogadro's Number. So in order to calculate the number of particles (atoms) contained by 6.97 × 10⁻⁷ moles of Se, we will use following relation,

Moles = Number of Atoms ÷ 6.022 × 10²³ Atoms.mol⁻¹

Solving for Number of Atoms,

Number of Atoms = Moles × 6.022 × 10²³ Atoms.mol⁻¹

Putting values,

Number of Atoms = 6.97 × 10⁻⁷ mol × 6.022 × 10²³ Atoms.mol⁻¹

Number of Atoms = 4.19 × 10¹⁷ Atoms

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Q: A bracelet containing 0.200 mol metal is 75% gold. How many atoms of gold are in the bracelet?

Answer:

9.033 × 10²² Atoms of Gold

Solution:

As we know that 1 mole of any substance contains exactly 6.022 × 10²³ particles which is also called as Avogadro's Number. So in order to calculate the number of particles (atoms) contained by 0.200 moles of Au, we will use following relation,

Moles = Number of Atoms ÷ 6.022 × 10²³ Atoms.mol⁻¹

Solving for Number of Atoms,

Number of Atoms = Moles × 6.022 × 10²³ Atoms.mol⁻¹

Putting values,

Number of Atoms = 0.200 mol × 6.022 × 10²³ Atoms.mol⁻¹

Number of Atoms = 1.20 × 10²³ Atoms

For 75%,

Number of Atoms = 1.20 × 10²³ Atoms × 0.75

Number of Atoms = 9.033 × 10²² Atoms of Gold

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Q: Which has more atoms, 10.0 g C or 10.0 g of Ca? How many atoms does each contain?

Answer:

Carbon has greater number of Atoms.

Solution:

Data Given:

Mass of Carbon = 10 g

M.Mass of Carbon = 12.01 g.mol⁻¹

Mass of Calcium = 10 g

M.Mass of Calcium = 40.08 g.mol⁻¹

Step 1: Calculate Moles of Carbon as,

Moles = Mass ÷ M.Mass

Putting values,

Moles = 10 g ÷ 12.01 g.mol⁻¹

Moles = 0.8326 mol

Step 2: Calculate number of Carbon atoms,

As 1 mole of any substance contains 6.022 × 10²³ particles (Avogadro's Number) then the relation for Moles and Number of Carbon atoms can be written as,

Moles = Number of C Atoms ÷ 6.022 × 10²³ Atoms.mol⁻¹

Solving for Number of C atoms,

Number of C atoms = Moles × 6.022 × 10²³ Atoms.mol⁻¹

Putting value of moles,

Number of C atoms = 0.8326 mol × 6.022 × 10²³ Atoms.mol⁻¹

Number of C atoms = 5.01 × 10²³ C atoms

Step 3: Calculate Moles of Calcium as,

Moles = Mass ÷ M.Mass

Putting values,

Moles = 10 g ÷ 40.08 g.mol⁻¹

Moles = 0.25 mol

Step 4: Calculate number of Calcium atoms,

As 1 mole of any substance contains 6.022 × 10²³ particles (Avogadro's Number) then the relation for Moles and Number of Calcium atoms can be written as,

Moles = Number of Ca Atoms ÷ 6.022 × 10²³ Atoms.mol⁻¹

Solving for Number of Ca atoms,

Number of Ca atoms = Moles × 6.022 × 10²³ Atoms.mol⁻¹

Putting value of moles,

Number of Ca atoms = 0.25 mol × 6.022 × 10²³ Atoms.mol⁻¹

Number of Ca atoms = 1.50 × 10²³ C atoms

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Q: A mixture contains 0.250 mol Fe and 1.20 g C. What is the total number of atoms in the mixture?

Answer:

2.10 × 10²³ Atoms in Mixture

Solution:

Atoms in Fe:

As we know that 1 mole of any substance contains exactly 6.022 × 10²³ particles which is also called as Avogadro's Number. So in order to calculate the number of particles (atoms) contained by 0.25 moles of Fe, we will use following relation,

Moles = Number of Atoms ÷ 6.022 × 10²³ Atoms.mol⁻¹

Solving for Number of Atoms,

Number of Atoms = Moles × 6.022 × 10²³ Atoms.mol⁻¹

Putting values,

Number of Molecules = 0.25 mol × 6.022 × 10²³ Atoms.mol⁻¹

Number of Molecules = 1.50 × 10²³ Atoms of Fe

Atoms in C:

Step 1: Calculate Moles of Carbon as,

Moles = Mass ÷ M.Mass

Putting values,

Moles = 1.20g ÷ 12.01 g.mol⁻¹

Moles = 0.0999 mol

Step 2: Calculate number of Carbon atoms,

As 1 mole of any substance contains 6.022 × 10²³ particles (Avogadro's Number) then the relation for Moles and Number of Carbon atoms can be written as,

Moles = Number of C Atoms ÷ 6.022 × 10²³ Atoms.mol⁻¹

Solving for Number of C atoms,

Number of C atoms = Moles × 6.022 × 10²³ Atoms.mol⁻¹

Number of C atoms = 0.0999 × 6.022 × 10²³ Atoms.mol⁻¹

Number of C atoms = 6.01 × 10²² C Atoms

Total Number of Atoms:

= 6.01 × 10²² C Atoms + 1.50 × 10²³ Atoms of Fe

= 2.10 × 10²³ Atoms in Mixture

Remaining answers are attached.