Chem 1411 Unit 3 Exam

What three roles do greenhouse gases play in Earth’s energy balance?

They allow sunlight in, warm Earth’s surface, and trap some outgoing heat.

Since 1860, by how much has the average atmospheric temperature risen?

About 0.8 °C (1.4 °F).

What percent rise in atmospheric CO₂ has occurred since 1860?

Approximately 37 %.

Define a physical change.

A change that alters only state or appearance without changing composition.

Give an example of a physical change involving water.

Boiling water (liquid → gas) without changing H₂O molecules.

Define a chemical change.

A change that alters the composition of matter by rearranging atoms to create new substances.

Why is rusting iron a chemical change?

Fe atoms react with O₂, forming a new compound, Fe₂O₃.

Which of the following is a chemical change: evaporation of rubbing alcohol, burning lamp oil, or frost formation?

Burning lamp oil.

What information does a chemical equation provide?

Formulas, states, relative quantities of reactants/products, enabling mass calculations.

State the law that underlies balancing equations.

Law of conservation of mass.

What is stoichiometry?

The numerical relationship between quantities of reactants and products in a reaction.

Write the balanced combustion equation for butane (C₄H₁₀).

2 C₄H₁₀ + 13 O₂ → 8 CO₂ + 10 H₂O.

In balancing, which atoms should generally be balanced last?

Free elements (uncombined).

How many moles of CO₂ form from 22.0 mol of C₈H₁₈?

176 mol CO₂ (using 2 mol C₈H₁₈ : 16 mol CO₂).

Outline the mass-to-mass stoichiometry path.

Mass A → moles A → moles B (using ratio) → mass B.

Define limiting reactant.

The reactant completely consumed first, limiting product amount.

Define theoretical yield.

Maximum product mass predicted from the limiting reactant.

Define actual yield.

Product mass actually obtained in the experiment.

Give the percent yield formula.

(Actual yield / Theoretical yield) × 100 %.

What reactant limits pizza production if sauce allows only 3 pizzas but crust allows 4 and cheese 5?

Tomato sauce (limiting reactant).

General products of a hydrocarbon combustion.

CO₂, H₂O, and heat (if complete).

Write the balanced combustion of CH₃OH.

2 CH₃OH + 3 O₂ → 2 CO₂ + 4 H₂O.

Alkali metal reaction with water general form.

2 M + 2 H₂O → 2 M⁺ + 2 OH⁻ + H₂↑

What strong reaction may occur when alkali metals contact water?

Highly exothermic reaction producing H₂ gas that can ignite.

General reaction of halogen with hydrogen.

H₂ + X₂ → 2 HX.

Define solution.

A homogeneous mixture of solute (minor) in solvent (major).

Differentiate dilute vs concentrated solution.

Dilute: small solute relative to solvent; Concentrated: large solute amount.

Give molarity formula.

M = moles solute / liters solution.

How many moles of solute are in 0.500 L of 2.00 M NaCl?

1.00 mol NaCl.

State the dilution equation.

C₁V₁ = C₂V₂ (or M₁V₁ = M₂V₂).

How many liters of 0.125 M NaOH contain 0.255 mol NaOH?

2.04 L.

Define electrolyte.

Substance that forms conducting solutions by producing ions in water.

Distinguish strong vs weak electrolyte.

Strong: nearly 100 % dissociation into ions; Weak: partial dissociation.

Is sugar (C₁₂H₂₂O₁₁) an electrolyte?

No, it is a nonelectrolyte (dissolves as molecules).

Give one solubility rule for nitrates.

All NO₃⁻ salts are soluble.

What precipitate forms when KI(aq) mixes with Pb(NO₃)₂(aq)?

PbI₂(s) (yellow).

Write the net ionic equation for K₂SO₄ + 2 AgNO₃.

2 Ag⁺ + SO₄²⁻ → Ag₂SO₄(s).

Spectator ions definition.

Ions unchanged on both sides of a complete ionic equation.

General net ionic equation for strong acid-strong base reaction.

H⁺ + OH⁻ → H₂O.

What is the equivalence point in titration?

Point at which moles acid = moles base.

Indicator purpose in titration.

Substance that changes color near the equivalence point.

Arrhenius definition of acid.

Produces H⁺ in aqueous solution.

Arrhenius definition of base.

Produces OH⁻ in aqueous solution.

Name HF(aq).

Hydrofluoric acid.

Change the ion name nitrate to its oxyacid.

HNO₃, called nitric acid.

Write the net ionic equation for HI + Ba(OH)₂.

H⁺ + OH⁻ → H₂O (spectators removed).

Give an example of a gas-evolution intermediate product that decomposes.

H₂CO₃ → H₂O + CO₂(g).

What gas forms when sulfide reacts with acid?

H₂S gas.

Define oxidation in terms of electrons.

Loss of electrons (increase in oxidation state).

Define reduction in terms of electrons.

Gain of electrons (decrease in oxidation state).

In 2 Na + Cl₂ → 2 NaCl, which is oxidized?

Na is oxidized to Na⁺.

Assign oxidation state to oxygen in H₂O₂.

−1 (peroxide exception).

Sum of oxidation states in a neutral compound equals _.

0.

Rule for oxidation state of Group 1A metals in compounds.

+1.

Is precipitation reaction always formed when two ionic solutions mix?

No; if both products are soluble, no reaction occurs.

Write the balanced molecular equation: K₂CO₃ + NiCl₂.

K₂CO₃ + NiCl₂ → NiCO₃(s) + 2 KCl(aq).

Explain limiting reactant concept using pizza ingredients.

Ingredient yielding the fewest pizzas limits production, analogous to limiting reactant in chemical reactions.

Percent yield definition.

Ratio of actual yield to theoretical yield times 100 %.

General combustion reactant and products.

Fuel + O₂ → oxides (CO₂, H₂O) + energy.

Give molar ratio for balanced octane combustion (2 C₈H₁₈).

2 C₈H₁₈ : 25 O₂ : 16 CO₂ : 18 H₂O.

What does a solubility table order predict?

Relative tendency of metals to be oxidized (activity series).

Activity series rule for spontaneous reaction.

A metal higher in series will reduce ions of metals below it.

Does Cu metal reduce Mg²⁺ ions spontaneously?

No, because Cu is below Mg in activity series.

Define reducing agent.

Substance that donates electrons and is oxidized.

Define oxidizing agent.

Substance that accepts electrons and is reduced.

General alkali metal + halogen reaction.

2 M + X₂ → 2 MX (metal halide).

Solution stoichiometry conceptual path for volume-to-volume problems.

Volume A → moles A (M) → moles B (ratio) → volume B (M).

What volume of 0.150 M KCl reacts with 0.150 L 0.175 M Pb(NO₃)₂?

0.350 L KCl needed.

Strong acids list four examples.

HCl, HBr, HI, HNO₃, H₂SO₄ (first proton), HClO₄ (any four).

Weak acid example used in lecture.

Acetic acid, HC₂H₃O₂.

Write net ionic equation for HC₂H₃O₂ + OH⁻.

HC₂H₃O₂ + OH⁻ → H₂O + C₂H₃O₂⁻.

Calculate molarity: 25.5 g KBr in 1.75 L.

0.120 M KBr.

How to prepare 1.00 L of 1.00 M NaCl.

Dissolve 58.44 g NaCl, add water to 1 L mark.

Define spectator ion.

Ion that remains aqueous and unchanged during reaction.

Example of nonelectrolyte solution.

Sugar dissolved in water.

What happens at equivalence point in acid-base titration?

Stoichiometric amounts of H⁺ and OH⁻ have reacted.

Give oxidation state of nitrogen in NO₃⁻.

+5.

Gas-evolution reaction type producing SO₂ gas.

Sulfite + acid producing H₂SO₃ intermediate → SO₂ + H₂O.

Equation for NaHCO₃ with HCl.

NaHCO₃ + HCl → NaCl + H₂O + CO₂↑

Why are ionic solids insoluble like AgCl not electrolytes?

They do not dissociate; ions remain locked in solid lattice.

Define hydration of ions.

Process where water molecules surround and insulate dissolved ions.

Why does H₂O have partial charges?

Uneven electron distribution; O electronegative, creates δ− at O and δ+ at H.

Example of polyprotic acid.

H₂SO₄ (diprotic).

Which solution classification has all ions written separately in ionic equations?

Strong electrolyte aqueous solutions.

Percent yield if theoretical 52.9 kg Ti and actual 42.8 kg.

81 % (42.8 / 52.9 × 100).

Oxidation state change indicates what?

Transfer (complete or partial) of electrons.

Net ionic for precipitation of Mg(OH)₂ from KOH + Mg(NO₃)₂.

Mg²⁺ + 2 OH⁻ → Mg(OH)₂(s).

Describe strong vs weak acid dissociation.

Strong: nearly 100 % ionization; weak: small fraction ionizes.

Name H₂SO₄.

Sulfuric acid.

Name H₂SO₃.

Sulfurous acid.

Give formula for perchloric acid.

HClO₄.

OH⁻ concentration comes from what in NH₃ solution?

NH₃ pulling H⁺ from water: NH₃ + H₂O ↔ NH₄⁺ + OH⁻ (weak).

Solubility rule for OH⁻ salts.

Generally insoluble except with Li⁺, Na⁺, K⁺, NH₄⁺; Ca²⁺, Sr²⁺, Ba²⁺ slightly soluble.

When balancing equations, why clear fractional coefficients?

To achieve whole-number stoichiometric coefficients.

Gas formed in reaction of ammonium salt with base.

NH₃ gas.

Define combustion reaction.

Rapid oxidation with O₂ producing heat and light.

Net ionic for AgNO₃ + NaCl.

Ag⁺ + Cl⁻ → AgCl(s).

Purpose of activity series table.

Predict spontaneity of metal displacement redox reactions.

Is CaCO₃ + CO₂ → CaCO₃ redox?

No, oxidation states unchanged.

In titration problem: 12.54 mL 0.100 M NaOH titrates 10.00 mL HCl. What is HCl molarity?

0.125 M HCl.