Mole Money, Mole Problems
Breaking Bad…
The Mole Must Go On
The Last Reactant Standing
Great Expectations (Low Yields)
It's Complicated (Chemically)
100
If you know the number of moles of an element, how do you calculate the number of atoms?
Multiply the number of moles by Avogadro’s number (6.022 × 10²³ atoms/mol)
100
What is the difference between a coefficient and a subscript in a chemical formula or equation?
A coefficient tells us how many molecules or formula units there are. A subscript tells us how many atoms of an element are in each molecule or formula unit.
100
Why must a chemical equation be balanced before we use it for stoichiometry calculations?
The coefficients provide the mole ratios between reactants and products. Without a balanced equation, those ratios may be incorrect.
100
What is a limiting reactant, and why is it important in a chemical reaction?
The limiting reactant is the reactant that gets used up first. It determines the maximum amount of product that can form.
100
What is the difference between theoretical yield and actual yield?
Theoretical yield is the maximum amount of product predicted by stoichiometry. Actual yield is the amount of product obtained experimentally.
100
What is the molarity of a solution containing 0.250 mol of NaCl dissolved in enough water to make 500.0 mL of solution?
0.500 M
200
How do you find the number of oxygen atoms present in 1 mole of Al₂(SO₄)₃?
Each formula unit contains 12 oxygen atoms (3 × 4). Multiply 12 by Avogadro’s number.
200
Which of these substances are strong acids: HBr, HF, HNO₃, H₃PO₄, and HClO₄?
HBr, HNO₃, and HClO₄.
200
Balance the following chemical equation:
Al + O₂ → Al₂O₃
4Al + 3O₂ → 2Al₂O₃
200
If a reaction requires 2 moles of hydrogen for every 1 mole of oxygen, which reactant is limiting when you have 3 moles of H₂ and 2 moles of O₂?
H₂ is the limiting reactant. The 3 moles of H₂ require only 1.5 moles of O₂.
200
A reaction has a theoretical yield of 25.0 g, but only 20.0 g of product is collected. What is the percent yield?
80.0%
200
Which of the following substances are strong electrolytes, weak electrolytes, or nonelectrolytes?
HCl, CH₃COOH, NaOH, CH₃OH
HCl — Strong electrolyte
CH₃COOH — Weak electrolyte
NaOH — Strong electrolyte
CH₃OH — Nonelectrolyte
300
How many moles of water (H₂O) are in 13.5 g of water?
0.749 mol H₂O.
300
Why is HF considered a weak acid even though HCl, HBr, and HI are strong acids?
The H–F bond is unusually strong, so HF only partially ionizes in water.
300
Using the balanced equation below, how many moles of NH₃ can be produced from 2.50 mol of N₂ if H₂ is in excess?
N₂ + 3H₂ → 2NH₃
5.00 mol NH₃
300
2Al + 3Cl₂ → 2AlCl₃
If you have 4.00 mol of Al and 4.00 mol of Cl₂, which reactant is limiting?
Cl₂. Reacting all 4.00 mol of Al would require 6.00 mol of Cl₂.
300
A student starts with 12.0 g of Mg, which reacts with excess oxygen to produce MgO. What is the theoretical yield of MgO?
19.9 g MgO
300
You dilute 25.0 mL of 2.00 M KNO₃ to a final volume of 100.0 mL. What is the new molarity?
0.500 M
400
A compound has an empirical formula of CH₂O and a molar mass of approximately 90.1 g/mol. What is its molecular formula?
C₃H₆O₃.
400
Classify each substance as a strong electrolyte, weak electrolyte, or nonelectrolyte: NaCl, CH₃COOH, and CH₃OH.
NaCl — Strong electrolyte
CH₃COOH — Weak electrolyte
CH₃OH — Nonelectrolyte
400
Magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen gas.
Write the balanced chemical equation.
Mg + 2HCl → MgCl₂ + H₂
400
For the reaction below, which reactant is limiting if 5.00 g of H₂ reacts with 20.0 g of O₂? How many grams of the excess reactant remain?
2H₂ + O₂ → 2H₂O
Limiting reactant: O₂
Excess reactant: H₂
H₂ remaining: 2.48 g
400
A reaction produces 18.5 g of product with a percent yield of 74.0%. What was the theoretical yield?
25.0 g
400
When aqueous solutions of BaCl₂ and Na₂SO₄ are mixed, what precipitate forms? Write the balanced molecular equation and the net ionic equation.
BaSO₄(s) is the precipitate.
500
How many oxygen atoms are present in 0.250 mol of Ca(NO₃)₂?
Avogadro’s number - 6.022 × 10²³
9.03 × 10²³ oxygen atoms
500
A compound contains 52.2% carbon, 13.1% hydrogen, and 34.7% oxygen by mass. What is its empirical formula?
Assume 100 g, convert each element's mass to moles, then divide all mole amounts by the smallest to obtain the ratio 2:6:1
500
Calcium carbonate decomposes when heated, producing calcium oxide and carbon dioxide.
If 15.0 g of CaCO₃ decomposes completely, how many grams of CO₂ are produced?
6.60 g CO₂.
CaCO₃ → CaO + CO₂
500
Magnesium reacts with oxygen to produce magnesium oxide.
If 6.00 g of Mg reacts with 5.00 g of O₂, which reactant is limiting, and how many grams of MgO can form?
Mg is limiting, and 9.95 g of MgO can form.
500
Aluminum reacts with excess chlorine gas to produce aluminum chloride.
If 5.40 g of Al reacts and 21.0 g of AlCl₃ is collected, what is the percent yield?
78.7%
500
