May Exam Review: Honors

The molar mass of CO2 is

• 12

• 16

• 32

• 44

Answer explanation

use atomic mass from periodic table

carbon = 12. oxygen = 16

12+16+16 = 44

What is the total mass of oxygen in 1.0 mole of Fe2O3?

• 112

• 56

• 16

• 48

Answer explanation

the compound contains 3 oxygen. 16x3 = 48

What is the total number of moles of oxygen atoms in Fe2(SO4)3?

• 2

• 3

• 4

• 12

Answer explanation

there are 3 sets of the polyatomic ion with 4 oxygen atoms each. 3x4 = 12

A sample of a compound contains 40.1 grams calcium, 12.0 grams carbon, and 48.0 grams oxygen. What is the correct mole ratio and formula?

• 40.1 : 12.0 : 48.0

  Ca40C12O48

• 1 : 1: 2

  CaCO2

• 1: 3 : 1

  CaC3O

• 1 : 1 : 3

  CaCO3

Answer explanation

40.1 grams calcium = 1 mole calcium

12.0 grams carbon = 1 mole carbon

48.0 grams oxygen = 3 moles oxygen (48/16)

Ca 1

C 1

O 3

How many moles are in a 50.6 grams sample of KNO3? (molar mass = 101.06)

• 50.6 moles

• 0.250 moles

• 2.00 moles

• 0.500 moles

Answer explanation

52.6 grams divided by the molar mass (101.06) = 0.500

What is the total number of atoms in a 30 gram sample of neon?

(molar mass = 20.18g and 6.02*10^23 atoms per mole)

• 2.5 * 10^-24

• 20.18 atoms

• 6.0 * 10^23 atoms

• 8.9 * 10^23 atoms

Answer explanation

begin with 30 grams of neon. Divide by molar mass (20.18) and then multiply by Avogadro's number

What is the percent by mass of oxygen in water (H2O)?

• 0.111

• 11.1%

• 0.889%

• 88.9%

Answer explanation

H2O has a mass of 18 grams. Oxygen is 16/18, or approximately 89% of the mass.

What molecule has an empirical formula of CH2, but molar mass of 28 grams?

• C2H

• C4H8

• CH4

• C2H4

What is the formula of a compound that contains 30.4% nitrogen and 69.6% oxygen by mass?

• N2O3

• N2O5

• NO

• NO2

Answer explanation

use molar mass to find moles of each element, and then see it is a 1:2 ratio

30.4 grams N = 2.2 moles N

69.6 grams O = 4.4 moles O

NO2

Which is the correctly balanced equation showing the combustion of magnesium to form magnesium oxide (hint: magnesium forms +2 ion, oxygen forms -2 ion)?

• Mg + O2 --> MgO

• Mg + O2 --> MgO2

• 2 Mg + O2 --> 2 MgO

• Mg + 2 O2 --> MgO4

Answer explanation

magnesium oxide is MgO. number of magnesium atoms is two on both sides of the equation and number of oxygen atoms on both sides of the equation is 2