Spring Final Practice Assessment

How many formula units are in 2.5 moles of cesium sulfite, Cs₂SO₃?

• 345.89 formula units

• 864.73 formula units

• 1.51 x 10²⁴ formula units

• 2.41 x 10²³ formula units

How many molecules are in 9.0 grams of potassium nitrate, KNO₃?

• 2.95 x 10^²⁵ molecules

• 9.0 x 10^-1 molecules

• 1.5 x 10²³ molecules

• 5.36 x 10²² molecules

Find the molecular formula of a compound if the empirical formula is CH₂O and the molar mass is 120 g/mol.

• CH₂O

• C₈H₁₆O₈

• C₄H₈O₄

• C₆H₁₂O₆

What is the percent of calcium in calcium sulfate, CaSO₄?

• 29.4%

• 23.5%

• 47.0%

• 136.15%

What is the empirical formula for a compound that is 40.05% sulfur and 59.95% oxygen?

• SO

• SO₂

• SO₃

• SO₄

How many moles of Al2O₃ can be made from 3.5 moles of Al?

4 Al + 3 O₂ → 2 Al₂O₃

• 1.75 moles

• 2.63 moles

• 3.5 moles

• 7.0 moles

Use the balanced equation to answer the question: How many moles of Al are used to form 509.8 g of Al₂O₃?

4 Al + 3 O₂ → 2 Al₂O₃

• 0.4 mol Al

• 2.5 mol Al

• 5.0 mol Al

• 10.0 mol Al

Use the balanced equation to answer the question:

Given 345 g of aluminum, Al, and excess oxygen O₂ , how many grams of aluminum oxide, Al₂O₃ can be produced?

4 Al + 3 O₂ → 2 Al₂O₃

• 182.58 g Al2O3

• 306.89 g Al2O3

• 651.89 g Al2O3

• 732.84 g Al2O3

Four students are planning an experiment to determine the limiting reactant in the combustion of a cotton strip (C₆H₁₀O₅ ) using a Bunsen burner. Which student's argument is CORRECT?

C₆H₁₀O₅ + 6 O₂ → 6 CO₂ + 5 H₂O

• Student 1 argues that the oxygen is the limiting reactant because there is no combustion without oxygen.

• Student 2 argues that the oxygen is the limiting reactant because you will make the least moles of it compared to carbon dioxide.

• Student 3 argues that the cotton strip is the limiting reactant because when it has completely burned up, there will still be oxygen left over.

• Student 4 argues that there is no limiting reactant in the stated experiment.

Answer explanation

Limiting reactants are the reactant that will run out first.

In this case, cotton will completely burn up and there will be oxygen left over because there is plenty of oxygen in the environment.

Beakers 1 and 2 represent two different solutions. Using the solution models shown in the diagrams, determine which student's argument is CORRECT.

• Student A claims that beaker 1 is dissociation because it contains ionic molecules that break apart into charged particles.

• Student B claims that beaker 1 is dissociation because it contains covalent molecules that break apart into charged particles.

• Student C claims that beaker 2 is dissociation because it contains ionic molecules that stay together when dissolved.

• Student D claims that beaker 2 is dissociation because it contains covalent molecules that stay together when dissolved.

Answer explanation

Ionic compounds dissociate into ions which will solvate (the solvent particles will surround each ion) when placed in a polar solvent.

Covalent compounds will solvate, where the solvent particles with surround the solute particles.

The solvent and the solute must have the same polarity because like dissolves like.