Science: The Mole and Avogadros Number Worksheet

Question 1

Define a mole in chemistry and state Avogadros number.

Accepted Answer

A mole is a counting unit used in chemistry to represent a very large number of particles. One mole contains 6.022 x 10^23 particles, which is called Avogadros number.

Question 2

How many atoms are in 2.0 moles of helium?

Accepted Answer

There are 1.204 x 10^24 atoms in 2.0 moles of helium. This is found by multiplying 2.0 moles by 6.022 x 10^23 atoms per mole.

Question 3

How many moles are represented by 3.011 x 10^23 molecules of oxygen gas, O2?

Accepted Answer

3.011 x 10^23 molecules of O2 is 0.500 moles. This is found by dividing 3.011 x 10^23 by 6.022 x 10^23.

Question 4

What is the molar mass of carbon dioxide, CO2?

Accepted Answer

The molar mass of CO2 is 44.01 g/mol. This is found by adding the mass of 1 carbon atom, 12.01 g/mol, and 2 oxygen atoms, 2 x 16.00 g/mol.

Question 5

How many grams are in 0.75 moles of sodium chloride, NaCl? Use a molar mass of 58.44 g/mol.

Accepted Answer

There are 43.83 grams in 0.75 moles of NaCl. This is found by multiplying 0.75 moles by 58.44 g/mol.

Question 6

How many moles are in 36.0 grams of water, H2O? Use a molar mass of 18.02 g/mol.

Accepted Answer

There are about 2.00 moles of water in 36.0 grams. This is found by dividing 36.0 grams by 18.02 g/mol.

Question 7

A sample contains 1.50 moles of magnesium atoms. How many atoms are present?

Accepted Answer

There are 9.03 x 10^23 magnesium atoms in the sample. This is found by multiplying 1.50 moles by 6.022 x 10^23 atoms per mole.

Question 8

A sample contains 4.50 x 10^24 atoms of aluminum. How many moles of aluminum atoms is this?

Accepted Answer

This sample contains about 7.47 moles of aluminum atoms. This is found by dividing 4.50 x 10^24 atoms by 6.022 x 10^23 atoms per mole.

Question 9

How many molecules are in 0.250 moles of methane, CH4?

Accepted Answer

There are 1.51 x 10^23 molecules in 0.250 moles of methane. This is found by multiplying 0.250 moles by 6.022 x 10^23 molecules per mole.

Question 10

What is the molar mass of calcium carbonate, CaCO3?

Accepted Answer

The molar mass of CaCO3 is 100.09 g/mol. This is found by adding calcium, 40.08 g/mol, carbon, 12.01 g/mol, and three oxygens, 48.00 g/mol.

Question 11

How many formula units are in 3.25 moles of calcium chloride, CaCl2?

Accepted Answer

There are 1.96 x 10^24 formula units in 3.25 moles of CaCl2. This is found by multiplying 3.25 moles by 6.022 x 10^23 formula units per mole.

Question 12

Explain why chemists use the mole instead of counting atoms or molecules one by one.

Accepted Answer

Chemists use the mole because atoms and molecules are far too small and numerous to count individually. The mole makes it possible to connect measurable amounts like mass to the number of particles in a sample.

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Science: The Mole and Avogadros Number

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