Electrolytes
Classify NaCl as a strong, weak, or nonelectrolyte.
NaCl is a strong electrolyte because it completely dissociates: NaCl → Na⁺ + Cl⁻.
Define molarity.
Molarity is the concentration of a solution expressed as the number of moles of solute per liter of solution.
Write the general form of a synthesis reaction.
A + B → AB
Are all nitrates soluble?
Yes, all nitrates are soluble in water.
Define oxidation.
Loss of electrons (increase in oxidation number).
Is acetic acid (CH₃COOH) a strong, weak, or nonelectrolyte?
Acetic acid is a weak electrolyte because it only partially ionizes in water, forming a small amount of H⁺ and CH₃COO⁻ ions.
How many moles are in 250 mL of 0.4 M NaOH?
0.4×0.250=0.10 molNaOH.
A double replacement reaction is a chemical reaction where two compounds exchange ions to form two new compounds, usually resulting in a precipitate, gas, or water.
Will AgCl form a precipitate?
Yes
Ag⁺ + Cl⁻ → AgCl (s).
Oxidation number of Cr in Cr₂O₇²⁻?
2x+(−14)=−2→x=+6.
When 0.050 moles of aluminum sulfate (Al₂(SO₄)₃) dissolves in water to make 1.0 L of solution, what is the total molar concentration of ions in the solution?
Aluminum sulfate dissociates as Al₂(SO₄)₃ → 2 Al³⁺ + 3 SO₄²⁻, producing 5 moles of ions per formula unit. Thus, 0.050 mol × 5 = 0.25 mol of ions total.
Dividing by 1.0 L gives an ion concentration of 0.25 M total ions in solution.
You have 2.0 M HCl and need 250 mL of 0.5 M HCl. What volume of stock is needed?
M1V1=M2V2→(2.0)V1=(0.5)(0.250)→V1=0.0625L=62.5mL.
Type of reaction: Cu + 2 AgNO₃ → 2 Ag + Cu(NO₃)₂.
Single replacement.
Solutions of potassium sulfate (K₂SO₄) and barium nitrate (Ba(NO₃)₂) are mixed.
Will a precipitate form? Write the balanced molecular and net ionic equations.
Barium sulfate is insoluble.
Molecular: K₂SO₄ (aq) + Ba(NO₃)₂ (aq) → 2 KNO₃ (aq) + BaSO₄ (s)
Net ionic: Ba²⁺ (aq) + SO₄²⁻ (aq) → BaSO₄ (s)
Precipitate: BaSO₄
Reaction type: Double-replacement
When solid magnesium reacts with aqueous copper(II) sulfate, what occurs?
A. Magnesium is reduced and copper is oxidized.
B. Copper is reduced and magnesium is oxidized.
C. No reaction occurs because both are metals.
D. The solution remains blue because Cu²⁺ ions do not change.
Correct Answer: B
Reaction: Mg(s) + CuSO₄(aq) → Cu(s) + MgSO₄(aq).
Magnesium (0 → +2) is oxidized, and copper (+2 → 0) is reduced (a single-replacement redox reaction).
Why is table sugar (C₁₂H₂₂O₁₁) a nonelectrolyte even though it dissolves in water?
Sugar is a nonelectrolyte because it dissolves as whole molecules and does not form ions in solution, so it cannot conduct electricity.
You have 12.0 M HCl. You first dilute 10.0 mL of this stock acid to 250.0 mL, and then take 25.0 mL of that solution and dilute it again to 500.0 mL.
What is the final molarity of HCl after both dilutions?
First dilution:
M₁V₁ = M₂V₂
(12.0)(10.0) = M₂(250.0) → M₂ = 0.480 M
Second dilution:
M₁V₁ = M₂V₂
(0.480)(25.0) = M₂(500.0) → M₂ = 0.0240 M
0.0240 M HCl after both dilutions.
Predict products: H₂SO₄ + Ba(OH)₂ → ?
BaSO₄ (s) + 2 H₂O
A solution of lead(II) nitrate (Pb(NO₃)₂) is mixed with potassium iodide (KI).
Predict the products and write the net ionic equation.
Lead(II) iodide is insoluble and forms a yellow solid.
Molecular: Pb(NO₃)₂ (aq) + 2 KI (aq) → PbI₂ (s) + 2 KNO₃ (aq)
Net ionic: Pb²⁺ (aq) + 2 I⁻ (aq) → PbI₂ (s)
Precipitate: PbI₂
In acidic solution, the following redox reaction occurs:
MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O
Which statement best describes what is happening?
A. Fe²⁺ is reduced and MnO₄⁻ is oxidized.
B. Both Fe²⁺ and MnO₄⁻ are oxidized.
C. Fe²⁺ is oxidized and MnO₄⁻ is reduced.
D. MnO₄⁻ acts as a reducing agent.
Correct Answer: C
Fe²⁺ → Fe³⁺ (oxidation),
Mn⁷⁺ → Mn²⁺ (reduction).
Thus Fe²⁺ is oxidized, MnO₄⁻ is reduced, and MnO₄⁻ is the oxidizing agent.
A 0.020 M solution of calcium phosphate, Ca₃(PO₄)₂, is prepared. Assuming complete dissociation (even though it is only slightly soluble), what is the total molar concentration of all ions in the solution?
Calcium phosphate dissociates as: Ca₃(PO₄)₂ → 3 Ca²⁺ + 2 PO₄³⁻. Each formula unit gives 5 ions total (3 + 2). For a 0.020 M solution: (0.020 mol/L) × 5 = 0.10 M total ions.
Thus, the solution would contain 0.060 M Ca²⁺, 0.040 M PO₄³⁻, and a total ionic concentration of 0.10 M if fully dissociated.
A student adds water to a 1.0 M NaOH solution until the volume doubles. The student then says, “The number of moles of NaOH has doubled.”
Is the student correct? Explain.
The student is incorrect.
When water is added, the volume increases but the moles of solute stay the same. Only the concentration decreases. Doubling the volume cuts the molarity in half to 0.50 M, but the total number of moles of NaOH remains constant because dilution never creates or destroys solute.
Aqueous ammonium sulfate [(NH₄)₂SO₄] is mixed with aqueous barium chloride (BaCl₂). Predict the products, write the balanced molecular, complete ionic, and net ionic equations, and identify the reaction type.
Predict products:
Exchange ions → BaSO₄ (insoluble) + 2 NH₄Cl (soluble).
Balanced molecular equation:
(NH₄)₂SO₄(aq) + BaCl₂(aq) → 2 NH₄Cl(aq) + BaSO₄(s)
Complete ionic equation:
2 NH₄⁺(aq) + SO₄²⁻(aq) + Ba²⁺(aq) + 2 Cl⁻(aq) → 2 NH₄⁺(aq) + 2 Cl⁻(aq) + BaSO₄(s)
Net ionic equation:
Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
Type of reaction:
Double replacement
When aqueous FeCl₃ is mixed with aqueous NaOH, a reaction occurs. Which of the following statements is correct?
A. No reaction occurs because all chlorides and hydroxides are soluble.
B. A brown precipitate of Fe(OH)₃ forms due to the reaction between Fe³⁺ and OH⁻ ions.
C. The reaction produces a colorless solution because Fe(OH)₃ is soluble in water.
D. The solution becomes acidic because OH⁻ ions are neutralized by Cl⁻ ions.
Correct Answer: B
FeCl₃(aq) + 3 NaOH(aq) → Fe(OH)₃(s) + 3 NaCl(aq).
Fe(OH)₃ is insoluble and forms a reddish-brown precipitate.
In a redox titration, 25.00 mL of 0.0200 M KMnO₄ solution is required to completely react with Fe²⁺ ions in an acidic solution according to the equation:
MnO₄⁻ + 5Fe²⁺ + 8H⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O
What is the molarity of Fe²⁺ in the solution if 50.00 mL of it was titrated?
A) 0.0100 M
B) 0.0500 M
C) 0.00400 M
D) 0.0200 M
Correct Answer: B
Moles of MnO₄⁻ = M × V = (0.0200 M)(0.02500 L) = 5.00 × 10⁻⁴ mol
From the balanced equation, 1 mol MnO₄⁻ reacts with 5 mol Fe²⁺ →
moles Fe²⁺ = (5)(5.00 × 10⁻⁴) = 2.50 × 10⁻³ mol
Molarity of Fe²⁺ = mol / L = (2.50 × 10⁻³) / 0.05000 = 0.0500 M
Explanation:
Each MnO₄⁻ ion oxidizes 5 Fe²⁺ ions to Fe³⁺.
Using stoichiometry and titration volume relationships gives 0.0500 M Fe²⁺.