Chemical Reactions & Solutions

What is a precipitation reaction?

A reaction in which an insoluble solid (precipitate) forms, usually from two aqueous solutions.

What symbol tells you that a precipitate formed?

(s), meaning a solid formed.

Is AgNO₃(aq) + HCl(aq) → AgCl(s) + HNO₃(aq) a precipitation reaction?

Yes, because AgCl(s) is produced.

What type of reaction is Mg(s) + O₂(g) → MgO(s)?

Synthesis/combination, not precipitation.

What type of reaction is Zn + 2Ag⁺ → 2Ag + Zn²⁺?

Single-replacement and redox.

What is a double-displacement reaction?

Two ionic compounds exchange ions:

$$AB+CD\rightarrow AD+CB$$

What usually causes a double-displacement reaction to occur?

Formation of a precipitate, water, or gas.

What does oxidation mean?

Loss of electrons and usually an increase in oxidation state.

What does reduction mean?

Gain of electrons and usually a decrease in oxidation state.

What mnemonic helps you remember oxidation and reduction?

LEO says GER:

Loss of Electrons = Oxidation

Gain of Electrons = Reduction

What is a redox reaction?

A reaction where oxidation and reduction occur together.

How can you identify a redox reaction?

Check whether any element's oxidation state changes.

What happens to Mg in Mg + I₂ → MgI₂?

Mg goes from 0 → +2, so Mg is oxidized.

What happens to iodine in Mg + I₂ → MgI₂?

I goes from 0 → −1, so iodine is reduced.

In H₂O + CO → H₂ + CO₂, which substance is oxidized?

CO.

Carbon goes from +2 → +4.

How do you calculate the oxidation state of an element?

Assign the known oxidation states and make the total equal the overall charge.

What is oxygen's usual oxidation state?

−2.

What is hydrogen's usual oxidation state?

+1 when bonded to nonmetals.

What is the oxidation state of nitrogen in NO₂?

+4.

$N+2(-2)=0$ $N=+4$

What is nitrogen's oxidation state in HNO₃?

+5.

What is an acid according to Brønsted-Lowry?

An H⁺ donor.

What is a base according to Brønsted-Lowry?

An H⁺ acceptor.

What happens when NH₃ reacts with H₂O?

$$NH_3+H_2O\rightleftharpoons NH_4^++OH^-$$

NH₃ accepts H⁺ and acts as a base.

What does the double arrow (⇌) mean?

The reaction is reversible and can reach equilibrium.

What happens if NH₄⁺ and OH⁻ are mixed?

They can react to produce NH₃ and H₂O.

Are NH₄⁺ and OH⁻ produced in a 1:1 or 1:2 ratio in the NH₃ reaction?

1:1.

$$NH_3+H_2O\rightleftharpoons NH_4^++OH^-$$

Is NH₃ a strong or weak base?

Weak base.

What is a strong acid?

An acid that ionizes essentially completely in water.

What is a weak acid?

An acid that only partially ionizes in water.

Which acid from the test is weak?

HNO₂ (nitrous acid).

Which acids from the test are strong acids?

HBr, HClO₄, H₂SO₄, and HCl.

What is the difference between HNO₃ and HNO₂?

HNO₃ is a strong acid, while HNO₂ is a weak acid.

What is a solution?

A homogeneous mixture containing a solute and a solvent.

What is the solvent?

The substance that does the dissolving and is usually present in the greater amount.

What does "aqueous" mean?

Water is the solvent.

What is an electrolyte?

A substance that produces ions in water, allowing the solution to conduct electricity.

What is a strong electrolyte?

A substance that produces ions essentially completely in solution.

Are soluble ionic compounds strong electrolytes?

Generally, yes.

Example:

$$NaCl\rightarrow Na^++Cl^-$$

Can a molecular compound be an electrolyte?

Yes. Some molecular compounds ionize in water.

Example: HCl.

Is HCl an ionic compound?

No. HCl is molecular, but it is a strong electrolyte in water because it ionizes essentially completely.

What is a weak electrolyte?

A substance that produces ions only partially in water.

What is a nonelectrolyte?

A substance that does not produce ions in water.

Which compound in the test is a nonelectrolyte?

C₆H₈.

Is acetic acid a strong or weak electrolyte?

Weak electrolyte because it only partially ionizes.

What is a spectator ion?

An ion that is present but does not participate in the actual reaction.

What are the spectator ions when KOH reacts with Fe(NO₃)₃?

K⁺ and NO₃⁻.

What is the net ionic equation for KOH + Fe(NO₃)₃?

$$\boxed{Fe^{3+}(aq)+3OH^-(aq)\rightarrow Fe(OH)3(s)}$$

Why does Fe(OH)₃ form a precipitate?

Fe(OH)₃ is insoluble, so it forms a solid.

Which compound forms a precipitate in the test?

PbI₂.

What is the key solubility fact for PbI₂?

Most iodides are soluble, but PbI₂ is an important exception and forms a solid precipitate.