CH110B

Chapter 4 Notes

How do the atoms and molecules come together so that their bonds can be broken and formed (the definition of a chemical reaction)? Solids are commonly made into solutions.

Electricity

The flow of charged particles

What enables this flow through a liquid?
The presence of charged particles, or IONS (CATION positive, ANION negative). (see Fig 4.2)

In a strong ELECTROLYTE, the solute is present almost entirely as ions.

In a NONELECTROLYTE, the solute exists almost entirely as NON-DISSOCIATED molecules.

A weak electrolyte exists as both ions and molecules in solution. There exists an EQUILIBRIUM between the molecules and ions. (see Fig 4.3)

Ion concentration

A strong electrolyte like 1 mole of NaCl would generate 1 mole of Na⁺ ions and 1 mole of Cl^- ions in solution. 1 mole of Na₂SO₄ would generate 2 moles of sodium ions and 1 mole of sulfate ions

Acids and bases

Strong acids and bases are strong electrolytes

We measure acid and base strength using a pH meter or an indicator (see Fig 4.4)

(Lab 3 in Ch111)

For a POLYPROTIC acid like H₂SO₄ the first ionization is generally stronger than the second

Acid plus base makes salt plus water- NEUTRALIZATION

A NET IONIC EQUATION shows only the particles undergoing change in the reaction
Ex- HCl(aq) + NaOH(aq) ------- NaCl(aq) + H₂O(l) FULL EQUATION
H⁺(aq) + Cl^-(aq) + Na⁺(aq) + OH^-(aq) ------ Na⁺(aq) + Cl^-(aq) + H₂O(l) IONIC EQUATION
H⁺(aq) + OH^-(aq) ------ H₂O(l) NET IONIC EQUATION

Titration- you will do this extensively in ch111

Experimental technique which allows you to determine concentration by employing reaction stoichiometry

The TITRANT is added to a flask of sample using a BURET

Precipitation reactions

When some cations and anions are combined a product which is insoluble in water sometimes results. The insoluble product is a PRECIPITATE. (see Fig 4.7 and 4.8 and 4.9)

The real world often believes in moderation, so very often, compounds are neither completely SOLUBLE nor completely INSOLUBLE- they may be SPARINGLY SOLUBLE

Oxidation states

An OXIDATION NUMBER represents the actual charge on a monoatomic ion or a hypothetical charge assigned to an atom in a molecule or polyatomic ion

Rules for determining OXIDATION STATES

For a neutral species, the sum of all the oxidation numbers is zero.

For a reaction, the sum of all the oxidation numbers of reactants must equal the sum of all the oxidation numbers of the products. (Conservation of charge.)

Group 1A metals have a charge of +1 in their compounds

Group 2A metals have a charge of +2 in their compounds

In binary compounds, the ox. no. of Group 7A elements is -1

In binary compounds, the ox. no. of Group 6A elements is -2

In binary compounds, the ox. no. of Group 5A elements is -3

In its compounds, the ox. no. of F is -1

In its compounds, the ox. no. of H is +1

In its compounds, the ox. no. of O is -2

WHY??? There exists a HYPERSTABILITY of an ion when it has as many electrons as its nearest noble gas element

For non-binary compounds, start with what you know and go from there. For example, in NO₃^-, since each oxygen is -2, the nitrogen must be +5 (see Fig 4.12)

In a RED-OX REACTION, oxidation states change (see Fig 4.10 and 4.11)

An element whose oxidation number increases (or becomes less negative) upon going from reactant to product is being OXIDIZED

An element whose oxidation number decreases (or becomes more negative) upon going from reactant to product is being REDUCED

The compound DOING the reducing is the REDUCING AGENT. Note that in DOING the reducing, the REDUCING AGENT gets OXIDIZED.

The compound DOING the oxidizing is the OXIDIZING AGENT. Note that in DOING the oxidizing, the OXIDIZING AGENT gets REDUCED.

In a red-ox reaction, BOTH the ATOMS and CHARGES must be balanced

A reactant that undergoes BOTH oxidation and reduction in the same reaction is involved in a DISPROPORTIONATION