What is the molar mass of Oxygen, O₂?

Use the periodic table on the STAAR reference material to help.

A. 16.0 g/mol
Incorrect. Oxygen in a diatomic element, so you need to multiply by two.

B. 48.0 g/mol
Incorrect. Oxygen in a diatomic element, so you need to multiply by two. You multiplied by three.

C. 3.20 g/mol
Incorrect. Check your decimal placement.

D. 32.0 g/mol
Correct! The molar mass is 32.0 g/mol.

Calculate the molar mass of K₂CrO₄.

Use the periodic table on the STAAR reference material to help.

A. 178.2 g/mol
Incorrect. You only accounted for three of the four oxygen atoms.

B. 155.1 g/mol
Incorrect. You only accounted for one of the potassium atoms.

C. 194.2 g/mol
Correct!

D. 142.0 g/mol
Incorrect. You forgot to include the mass of chromium.

How many grams are in two moles of calcium carbonate, CaCO₃?

Use the periodic table on the STAAR reference material to help.

A. 100.1 grams
Incorrect. This is the number of grams in one mole.

B. 200.2 grams
Correct! The molar mass of calcium carbonate is 100.1, and since you have two moles, the total would be 200.2 grams.

C. 176.2 grams
Incorrect. You forgot to include the mass of carbon.

D. 168.2 grams
Incorrect. You forgot to include one of the oxygen atoms.

How many grams are in 1.85 moles of ammonium nitrate, NH₄NO₃?

Use the periodic table on the STAAR reference material to help.

A. 80.0 grams
Incorrect. This is the mass of one mole of ammonium nitrate. The question asked for the grams of 1.85 moles.

B. 148.0 grams
Correct! The molar mass of ammonium nitrate is 80.0 g/mol. When you multiply the molar mass by 1.85 moles, you get 148 grams.

C. 122.1 grams
Incorrect. You forgot to include one of the nitrogen atoms when you calculated the molar mass.

D. 118.4 grams
Incorrect. You forgot to include one of the oxygen atoms when you calculated the molar mass.

If we had one mole of carbon-12, how many atoms would we have?

A. 12
Incorrect. One mole of carbon would have a mass of 12.

B. 6
Incorrect. Carbon has an atomic number of six.

C. 6.03 × 10²³
Correct! This is Avogadro’s number and represents the number of particles in one mole of an element.

D. 602.0
Incorrect. What is Avogadro’s number?