Mole Concepts
What is molarity?
The number of moles in a solute dissolved in a litre of solution.
What is percent composition?
The percent by mass of each element in a compound. (mass of element ÷ molar mass of compound) × 100
What does a balanced chemical equation tell us about moles?
The coefficients give the mole ratio of reactants and products
What are the units for molarity (M)?
Moles of solute per liter of solution (mol/L)
According to Arrhenius, what does an acid produce in water?
An acid produces H⁺ (hydrogen ions) in water
What is dimensional analysis?
Using conversion factors to convert measurements from one unit to another
What is an empirical formula?
The simplest whole-number ratio of atoms in a compound
In the reaction 2H₂ + O₂ → 2H₂O, how many moles of water form from 4 moles of H₂?
4 mol H₂ × (2 mol H₂O / 2 mol H₂) = 4 mol H₂O
What is a solution? Give one example.
A homogeneous mixture of solute dissolved in solvent. Example: saltwater, HCl(aq)
As pH decreases, what happens to the concentration of hydrogen ions (H+)?
The concentration of hydrogen ions increases
Convert 2.5 moles of CO₂ to grams. (Molar mass of CO₂ = 44 g/mol)
2.5 mol × 44 g/mol = 110 g
Find the percent composition of carbon in CO₂. (C = 12, O = 16)
(12 / 44) × 100 = 27.3% carbon
What is percent error and how is it calculated?
% error = |experimental − theoretical| / theoretical × 100. Measures the accuracy of a result.
Calculate the molarity of a solution made by dissolving 2.0 mol NaCl in 500 mL of solution.
M = 2.0 mol / 0.500 L = 4.0 M
A solution has [H⁺] = 1×10⁻³ M. What is the pH, and is it acidic or basic?
pH = −log(1×10⁻³) = 3; acidic (pH < 7)
How many moles are in 11.2 L of any gas at STP?
0.500 mol (22.4 L = 1 mol at STP)
A compound is 40.0% C, 6.7% H, and 53.3% O. Find the empirical formula.
C:3.33, H:6.64, O:3.33 → ratio 1:2:1 → empirical formula: CH₂O
How many grams of H₂O are produced from 4.0 g of H₂? (2H₂ + O₂ → 2H₂O, H₂ = 2 g/mol, H₂O = 18 g/mol)
4.0g ÷ 2 g/mol = 2 mol H₂ → 2 mol H₂O × 18 = 36 g H₂O
Using M₁V₁ = M₂V₂, find the final volume when 25 mL of 6.0 M HCl is diluted to 0.50 M.
(6.0)(25) = (0.50)(V₂) → V₂ = 300 mL
What are the formulas and the relationship between pH and pOH? (Hint: Logs & they add up to something)
pH = -log[H+]
pOH = -log[OH-]
They add up to 14
A sample of nitrogen gas occupies 5.60 L at STP. How many molecules of N₂ are present?
0.250 mol × 6.022×10²³ = 1.506×10²³ molecules
A compound has empirical formula CH₂O and molar mass 180 g/mol. What is the molecular formula?
Empirical mass = 30 g/mol; 180/30 = 6 → molecular formula: C₆H₁₂O₆
How many liters of O₂ at STP are needed to completely react with 5.0 g of C? C + O₂ → CO₂, C = 12 g/mol
5.0/12 = 0.417 mol C → 0.417 mol O₂ × 22.4 L = 9.3 L O2
How many mL of 2.0 M NaOH are needed to react with 40 mL of 1.5 M H₂SO₄? (2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O)
mol H₂SO₄ = 0.040 × 1.5 = 0.060 mol → needs 0.120 mol NaOH → 0.120/2.0 = 0.060 L = 60 mL
Name a compound that acts as a Brønsted-Lowry base but not an Arrhenius base in aqueous solution?
NH3