Formula Mass Calculations for Covalent and Ionic Compounds

Which statement best defines formula mass for a substance?

• Weight of a compound under standard gravity

• Sum of average atomic masses in formula

• Mass of one atom of the heaviest element

• Sum of measured masses from a single sample

For covalent compounds, what term is appropriately used for formula mass?

• Net mass of cations and anions

• Empirical mass of an array

• Ionic weight of the lattice

• Molecular mass of a single molecule

Which reason explains why ionic compounds usually avoid the term molecular mass?

• They lack average atomic masses

• They form extended ion lattices

• They have undefined atomic numbers

• They contain only neutral molecules

Using average atomic masses C=12.01, H=1.008, Cl=35.45, what is the molecular mass of CHCl3?

• 120.38 amu

• 106.35 amu

• 115.37 amu

• 119.37 amu

Which setup correctly expresses the calculation for CHCl3?

• 2(C)+2(H)+2(Cl)

• 1(C)+3(H)+1(Cl)

• 3(C)+1(H)+1(Cl)

• 1(C)+1(H)+3(Cl)

Tags

NGSS.MS-PS1-1

Aspirin has formula C9H8O4. Using C=12.01, H=1.008, O=16.00, which total is closest?

• 180.15 amu

• 176.09 amu

• 172.00 amu

• 184.21 amu

Ibuprofen molecules contain 13 C, 18 H, and 2 O. Which expression gives its molecular mass?

• 13(12.01)+18(1.008)+2(16.00)

• 9(12.01)+8(1.008)+4(16.00)

• 12(12.01)+18(1.008)+4(16.00)

• 13(1.008)+18(12.01)+2(16.00)

Sodium chloride consists of Na+ and Cl− in a 1:1 ratio. Which calculation yields its formula mass?

• Neutral Na minus ionic Cl

• 2(Na)+1(Cl) lattice masses

• 1(Na)+2(Cl) ionic masses

• 1(Na)+1(Cl) average masses

Tags

NGSS.MS-PS1-1

Why is it acceptable to use neutral atom average masses when computing ionic compound formula masses?

• Ions lack defined particle numbers

• Electron mass differences are negligible

• Neutral atoms have larger radii

• Bond energies cancel exactly

Which step is essential when summing to find a compound’s formula mass?

• Multiply each element’s average mass by its quantity

• Subtract the smallest mass from the largest

• Round each atomic mass to the nearest ten

• Divide total mass by Avogadro’s number