Pre-AP CHEM Unit 5 Days 3-4 Review NEW

What is the percent of oxygen by mass in a pure sample of sodium nitrate?

• 13%

• 56%

• 18%

• 28%

The molar mass of potassium fluoride, KF, is 58.1g/mol

The molar mass of potassium carbonate, K₂CO₃, is 138.2g/mol

The molar mass of potassium nitrate, KNO₃, is 101.3g/mol

Which of the following shows the correct percent by mass?

I) KF, 67% potassium

II) K₂CO₃ 28% potassium

III) KNO₃ 39% potassium

• I, II, and III

• II and III only

• I and III only

• III only

A substance has a molar mass of 60 g/mol with 40.0 percent carbon, 6.7 percent hydrogen, and 53.3 percent oxygen. What is its empirical formula?

• C₂H₄O₂ 
• C₂H₂O₄
• CHO₂ 
• CH₂O

An elemental analysis of compound X shows that the mass percentage composition of the compound is 26.86% C and 2.239% H, with the remainder being oxygen. A mass spectrum of X yields a molar mass of 90.0 g/mol. Write the molecular formula of X.

• CHO₂
• C₂H₂O₄
• C₂H₂O
• CH₂O 

Tags

NGSS.HS-PS1-1

A hydrocarbon (an organic compound containing only C and H) is found to be 7.74% H. If the molecular weight is known to be between 70 and 85 amu, find the molecular formula.

• C₆H₁₀
• C₅H₁₂
• C₆H₁₂
• C₆H₆

Which of the following could NOT be an empirical formula.

• CH₄

• CH

• C₂H₆

• CH₆