Practice quiz: Molar mass and mole conversions

What is the molar mass of Al₂(CO₃)₃?

• 113.97 g/mol

• 137.99 g/mol

• 233.99 g/mol

• 185.99 g/mol

Answer explanation

To calculate molar mass:

1. Use the periodic table to find the atomic mass of each element in a particle.

2. Multiply each atomic mass by the number of atoms of each element in the particle.

3. 3. Find the sum, then change units to g/mol.

   Round to 2 decimal places (closest hundredth).

What is the molar mass of PbSO₄?

• 303.27 g/mol

• 255.27 g/mol

• 163.87 g/mol

• 372.27 g/mol

Answer explanation

To calculate molar mass:

1. Use the periodic table to find the atomic mass of each element in a particle.

2. Multiply each atomic mass by the number of atoms of each element in the particle.

3. 3. Find the sum, then change units to g/mol.

   Round to 2 decimal places (closest hundredth).

(Hint: write out how you would solve the problem first on paper before choosing an answer.) 

How would you set up the problem: if you have a sample of 2.50 g of sodium (Na), how many moles of Na do you have?

How would you set up the problem if you want to find the mass, in grams, of 0.55 moles of silicon?

How would you set up the problem if you have 3.80 moles of calcium (Ca), and you are trying to determine how many atoms of calcium you have?

Which of the following dimensional analysis setups will correctly convert 4.00x10²³atoms of cobalt to moles of cobalt? How many moles of colbalt are there?

• setup B : 0.664 mol Co

• setup A: 2.41x10⁴⁷mol Co

• setup A : 0.664 mol Co

• setup B: 2.41x10⁴⁷mol Co

Which of the following dimensional analysis setups will correctly convert 27.76 g of Li to atoms of Li?

• A

• B

• C

• D

How many formula units are in 2.5 moles of NaCl?

• 1.5 x10²⁴ formula units

• 1.5 formula units

• 4.2 formula units

• 4.2 x10^-24 molecules

Shivani measures out 6.0 moles of epsom salt (MgSO₄) to put in her bath. How many grams of MgSO₄ went in the bath?

• 3.6 x 10²⁴ g

• 720 g

• 0.050 g

• 340 g

How many molecules are there in 31.8 moles of water?

• 5.28 x 10^-23 molecules
• 1.91 x 10²⁵ molecules
• 5.28x 10-²⁵
• 1.91 x 10²²

Tags

NGSS.HS-PS1-7