Molar Mass

What is the mass of one mole of aluminum?

• 27 g Al

  1 mol Al

• 13 g Al

  1 mol Al

• 54 g Al

  1 mol Al

• 14 g Al

  1 mol Al

Answer explanation

Find the molar mass of an element in the Periodic Table.

Remember, in addition to the atomic number, the Periodic Table includes the mass of each element. The mass will always be a decimal number.

Calculate the molar mass of KOH.

• 28 g KOH

  1 mol KOH

• 56 g KOH

  1 mol KOH

• 84 g KOH

  1 mol KOH

• 112 g KOH

  1 mol KOH

Answer explanation

To find the total mass of a compound, add the mass of each element in the compound.

Find the molar mass of KCl.

• 36.00 g KCl

  1 mol KCl

• 78.00 g KCl

  1 mol KCl

• 74.55 g KCl

  1 mol KCl

• 178.01 g KCl

  1 mol KCl

What is the molar mass of Cl₂?

• 17 g Cl₂

  1 mol Cl₂

• 35 g Cl₂

  1 mol Cl₂

• 70 g Cl₂

  1 mol Cl₂

• 89 g Cl₂

  1 mol Cl₂

Answer explanation

When an element is found more than once in the compound, multiply its mass by the number of times it is found in the compound.

Calculate the molar mass of Ba(C₂H₃O₂)₂

• 255.3 g Ba(C₂H₃O₂)₂

  1 mol Ba(C₂H₃O₂)₂

• 237.3 g Ba(C₂H₃O₂)₂

  1 mol Ba(C₂H₃O₂)₂

• 228.3 g Ba(C₂H₃O₂)₂

  1 mol Ba(C₂H₃O₂)₂

• 196.3 g Ba(C₂H₃O₂)₂

  1 mol Ba(C₂H₃O₂)₂

Answer explanation

When any part of a compound's chemical formula is surrounded by parenthesis, that means that those elements are in a group. That group of elements are found 2 or more times in the formula.

You must multiply the mass of each element in the parenthesis by the number found outside the parenthesis.

Then add that amount to the mass of the elements outside the parenthesis.

Tags

NGSS.HS-PS1-7

Calculate the molar mass for Al(OH)₃

• 78.0 g Al(OH)₃

  1 mol Al(OH)₃

• 72 g Al(OH)₃

  1 mol Al(OH)₃

• 28 g Al(OH)₃

  1 mol Al(OH)₃

• 25 g Al(OH)₃

  1 mol Al(OH)₃

Tags

NGSS.HS-PS1-7

Calculate the molar mass of NH₄NO₂

• 50 g NH₄NO₂

  1 mol NH₄NO₂

• 60 g NH₄NO₂

  1 mol NH₄NO₂

• 64 g NH₄NO₂

  1 mol NH₄NO₂

• 78 g NH₄NO₂

  1 mol NH₄NO₂

Answer explanation

Remember:

When there is no number after the element, that element exists only once in the formula.

When an element exists more than once in the formula, it will have a number written immediately to its right.

What is the molar mass of UF₆?

• 101 g UF₆

  1 mol UF₆

• 238 g UF₆

  1 mol UF₆

• 257 g UF₆

  1 mol UF₆

• 352 g UF₆

  1 mol UF₆

What is the percent composition of Mg in MgO?

• 60.3%

• 25.0%

• 80.5%

• 12.7%

Answer explanation

To find the percent composition of that element in the compound, follow these steps.

Step 1: Find the mass of the compound.

Step 2: Divide the mass of the element by the total mass of the compound.

What is the percent composition of Na in table salt (NaCl)?

• 39.3%

• 78.6%

• 10.6%

• 58.4%