AP Chemistry: Chemical Reactions & Stoichiometry 2

Question 1

How many moles of O2 are required to completely combust 2 mol of C3H8 (propane)?

Accepted Answer

10 mol

Answer

Balanced equation C3H8 + 5O2 -> 3CO2 + 4H2O needs 5 mol O2 per mol propane, so 2 mol needs 10 mol.

Question 2

What is the molar mass of calcium phosphate, Ca3(PO4)2?

Accepted Answer

310.18 g/mol

Answer

3(40.08) + 2(30.97) + 8(16.00) = 310.18 g/mol.

Question 3

In the reaction 2Al + 3Cl2 -> 2AlCl3, if 4 mol Al react, how many mol AlCl3 form?

Accepted Answer

4 mol

Answer

The Al:AlCl3 ratio is 2:2 (1:1), so 4 mol Al yields 4 mol AlCl3.

Question 4

Which quantity equals one mole of any substance?

Accepted Answer

6.022 x 10^23 representative particles

Answer

A mole is defined as 6.022 x 10^23 (Avogadro's number) of representative particles.

Question 5

What is the percent by mass of nitrogen in NH4NO3?

Accepted Answer

35.0%

Answer

Two N atoms (28.02 g) over molar mass 80.06 g gives about 35.0%.

AP Practice Test