Moles and Mole Conversions

What is Avogadro's number?

• 6.022 x 10^23

• 9.80665

• 12.345

• 3.14159

Answer explanation

Avogadro's number is 6.022 x 10^23, which represents the number of atoms, ions, or molecules in one mole of a substance.

Calculate the molar mass of H2O.

• 20.00 g/mol

• 16.04 g/mol

• 18.02 g/mol

• 22.99 g/mol

Answer explanation

The molar mass of H2O is calculated by adding the atomic masses of its elements, which are 2(1.01) + 16.00 = 18.02 g/mol. Therefore, the correct answer is 18.02 g/mol.

How many moles are in 36 grams of water (H2O)?

• 10 moles

• 2 moles

• 0.5 moles

• 5 moles

Answer explanation

To find the moles in 36 grams of water, divide the given mass by the molar mass of water (18 grams/mole). 36 grams / 18 grams/mole = 2 moles.

What is the mass of 2 moles of carbon dioxide (CO2)?

• 88.02 g

• 72.03 g

• 26.04 g

• 44.01 g

Answer explanation

The molar mass of CO2 is 44.01 g/mol. Therefore, the mass of 2 moles of CO2 is 2 * 44.01 g = 88.02 g.

Convert 5 moles of oxygen (O2) to grams.

• 10 grams

• 50 grams

• 160 grams

• 200 grams

Answer explanation

To convert moles to grams, use the molar mass of oxygen (O2), which is 32 grams/mol. So, 5 moles of O2 is equal to 5 moles * 32 grams/mole = 160 grams.

Determine the number of moles in 100 grams of calcium carbonate (CaCO3).

• 2.5 moles

• 0.5 moles

• 1.5 moles

• 0.999 moles

Answer explanation

The molar mass of CaCO3 is 100.09 g/mol. Therefore, 100 grams of CaCO3 is equal to 1 mole (100g / 100.09g/mol = 0.999 moles). So, the correct answer is 0.999 moles.

Calculate the empirical formula of a compound that contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen.

• C2H3O2

• C3H4O3

• C4H5O4

• CH3O2

Answer explanation

The empirical formula is calculated by converting the percentages to moles and then dividing by the smallest number of moles. The correct empirical formula is C3H4O3.

What is the molar mass of the empirical formula CH2O?

• 44.01 g/mol

• 12.01 g/mol

• 18.02 g/mol

• 30.03 g/mol

Answer explanation

The molar mass of CH2O is calculated by adding the atomic masses of carbon, hydrogen, and oxygen, which gives 30.03 g/mol, making it the correct choice.

Convert 25 grams of sodium chloride (NaCl) to moles.

• 0.25 moles

• 0.75 moles

• 0.425 moles

• 0.125 moles

Answer explanation

To convert grams to moles, divide the given mass by the molar mass. The molar mass of NaCl is 58.44 g/mol. So, 25g / 58.44 g/mol = 0.425 moles.

If a compound has a molar mass of 180 g/mol and the empirical formula is CH2O, what is the molecular formula?

• CH4O2

• C3H6O3

• C2H4O2

• C6H12O6

Answer explanation

The molecular formula can be found by multiplying the subscripts in the empirical formula by a whole number to get the molar mass. In this case, the molecular formula is C6H12O6.