Chemistry U4 Test prep

Which equation correctly models how solid sodium carbonate (Na₂CO₃) dissociates when it is mixed with water?

A) Na₂CO₃(s)→ Na₂²⁺(aq) + CO₃^2-(aq)

B) Na₂CO₃(s)→ 2Na⁺(aq) + C(s) + 3O^2-(aq)

C) Na₂CO₃(s)→ 2Na⁺(aq) + CO₃^2-(aq)

D) Na₂CO₃(s)→ Na₂ (s) + C(s) + O₃(g)

C) Na₂CO₃(s)→ 2Na⁺(aq) + CO₃^2-(aq)

• Dissociation physically separates an ionic crystal lattice into its individual aqueous ions. The polyatomic carbonate ion (CO₃²⁻) stays intact, while the two sodium atoms become independent 1+ cations.

A student mixes equal volumes of 1.0 mol/L hydrochloric acid (HCl) and 1.0 mol/L sodium hydroxide (NaOH). What are the resulting products of this chemical process?

A) NaCl (aq) + H₂O(l)

B) Cl₂(g) + NaH(aq) + O₂(g)

C) HCIO(aq) + Na(s)

D) No reaction takes place

A) NaCl (aq) + H₂O(l)

Explanation: This is a classic strong acid-strong base neutralization reaction. The hydrogen ion (H⁺) and hydroxide ion (OH⁻) react to form liquid water, leaving aqueous sodium chloride salt in solution.

(Aluminum + Hydrochloric Acid Stoichiometry)

Solid aluminum metal reacts with aqueous hydrochloric acid. Write out:
a) Balanced molecular equation
b) Total ionic equation
c) Net ionic equation

A) 2Al(s) + 6HCl (aq)→ 2AlCl₃(aq) + 3H₂(g)

b) 2Al(s) + 6H⁺(aq) + 6Cl^-(aq)→ 2Al3+(aq) + 6Cl^-(aq) + 3H₂(g)

c) 2Al(s) + 6H⁺(aq)→ 2Al³⁺(aq) + 3H₂(g)

(Acid Dilution Calculation & Safety)

a) Calculate the final concentration when 25.0 mL of 12.0mol/L HCl is diluted to a volume of 500.0 mL
b) State the primary safety rule for diluting acids.

Use C₁V₁=C₂V₂:

(12.0 mol/L) x (0.0250L)= C₂ x (0.5000L)

C₂=0.300 mol/ 0.5000 L = 0.600 mol/L

b) Always Add Acid to water (AAA). Slowly pour concentrated acid into water while stirring. Never pour water into concentrated acid, or it can violently boil and splash acid out due to the highly exothermic reaction.

(Ion Concentrations in a Solution)

A 0.150 mol/L solution of iron (III) sulfate, Fe₂(SO₄)₃(aq), is prepared.

a) Write the dissociation equation.
b) Calculate [Fe³⁺].

c) Calculate [SO₄^2-].

a) Fe₂(SO₄)₃(s)→2Fe³⁺(aq) + 3SO₄^2-(aq)

b) [Fe³⁺]= 2 × 0.150 mol/L=0.300 mol/L

[SO₄^2-]= 3 × 0.150 mol/L= 0.450 mol/L

(Precipitation Net Ionic & Analysis)

Aqueous FeCl₃ reacts with dissolved aqueous H₂S to form a solid precipitate of iron(III) sulfide (Fe₂S₃).
a) Write the balanced molecular equation.
b) Write the net ionic equation.
c) Identify the spectator ions.

a) 2FeCl₃(aq) + 3H₂S(aq)→Fe₂S₃(s) + 6HCl(aq)

b) 2Fe³⁺(aq) + 3S^2-(aq)→ Fe₂S₃(S)

c) Spectator ions are Cl^-(aq) and H⁺(aq)

(Titration Math Step-by-Step)

A 25.00 mL sample of unknown H2SO4 requires an average volume of 20.00 mL of 0.150 mol/L NaOH to hit a pale pink endpoint. Find the molarity of the acid.

(H₂SO₄ + 2NaOH→ Na₂SO₄ + 2H₂O)

Find moles of base used:

ⁿNaOH=C X V= 0.150 mol/L x 0.02000L=0.00300 mol

use mole ratio (1 mol H₂SO₄ : 2 mol NAOH to find moles of acid;

n_acid= 0.00300 mol/2=0.00150 mol

Calculate the concentration of acid

C_acid= n/V= 0.00150 mol/0.02500L= 0.0600 mol/L