Chem Math & Gas Properties

Determine the molar mass of Na₂O₂.

• 55 g/mol

• 4 g/mol

• 78 g/mol

• 39 g/mol

Answer explanation

Na: 2 x 23 = 46

O: 2 x 16 = 32

46+32 = 78

Which equation represents a conservation of atoms?

• 2Fe + 2O₂ → Fe₂O₃

• 4Fe + 3O₂ → 2Fe₂O₃

• 2Fe + 3O₂ → Fe₂O₃

• 4Fe + 2O₂ → 2Fe₂O₃

The coefficients in a balanced chemical equation

represent

• the mole ratios of the substances in the reaction

• the total number of electrons in the reaction

• the mass ratios of the substances in the reaction

• the total number of elements in the reaction

What is the total mass in grams of 0.75 mole of SO₂?

• 16 g

• 24 g

• 32 g

• 48 g

Answer explanation

# mol = given/GFM

Which sample of gas at STP has the same number of

molecules as 6 liters of Cl₂(g) at STP?

• 3 moles of O₂(g)

• 3 liters of O₂(g)

• 6 liters of N₂(g)

• 6 moles of N₂(g)

Given the reaction:

2Al + 3H₂SO₄ → 3H₂ + Al₂(SO₄)₃

The total number of moles of H₂SO₄ needed to react

completely with 5.0 moles of Al is

• 5.0 moles

• 7.5 moles

• 9.0 moles

• 2.5 moles

What is the molecular formula of a compound with an empirical formula of CH and a molecular mass of 78?

• C₆H₆

• C₄H₁₀

• C₂H₂

• CH

What is the empirical formula of a compound that has

a carbon-to-hydrogen ratio of 2 to 6?

• C₆H₂

• C₃H

• CH₃

• C₂H₆

What is the percent by mass of hydrogen in NH₃

(formula mass = 17.0)?

• 82.4%

• 5.9%

• 21.4%

• 17.6%

Balance the following:

_C₂H₂ + _O₂ → _CO₂ + _H₂O

What is the sum of the coefficients?

• 7

• 11

• 13

• 26