Acid and bases - part 1.

Define molecular compunds!

Molecular compounds always contain two non-metals, NH3, CO2 etc. In oher words : they are easy to identify. They do not conduct electricity when dissolved in H2O because they are not formed by two ions of opposite charge.

Define ionic compounds!

They are compounds held together by ionic bonds, formed between ions of opposite charges. You probably all know this, but a good rule of thumb is that the cation is usually a metal!

What defines the Brœnstedt acid/base theory?

It is the classic definition of acids as proton donors and bases as proton acceptors. For instance : H₂SO₄ is an acid. It loses its proton to water and is thus transformed into its conjugate base : HSO4-.

Describe the Lewis-theory!

It is a WIDER definition of acids and bases and goes beyond simple proton transfer. Thus other substances than proton acceptors and donors can be denoted as acids or bases according to the Lewis theory, as it focuses on electron pair donations and acceptations.

A Lewis acid ACCEPTS an electron pair! (ACCEPT and ACID = two A:s!)

A Lewis base accordingly donates an electron pair! For instance a Lewis base may give an electron pair to a proton that accepts it - and a covalent bond is formed.

Every Brœnstedt base is a Lewis base, but not every Lewis base is a Brœnstedt base. For instance : CO is a Lewis base, because it donates an electron pair to certain METALS. But it is NOT a Brœnstedt base, since it does not accept protons.

Many nonmetal oxides are...?

Lewis acids. They react with water and accepts the electron pair of the oxygen in the H2O molecule. The product is a Brœnstedt acid!

What defines an acidic oxide?

As in the example above, it is a molecular oxide that reacts with water to form a Brœnstedt acid. Acidic oxides may also react with Brœnstedt bases, forming H₂O and salt.

Define a basic oxide!

It is a ionic compound. It reacts with water to create Brœnstedt bases. It may also react with acids, thus forming salt and H₂O.

Summary :

Acidic oxides are?

Molecular compunds!

They react with?

H₂O and the result is a Broensted acid as in the example below :

CO₂ + H₂O → H₂CO₃

Or with...?

A base with a salt + H₂O as a result! See example below :

CO₂ + 2NaOH → Na₂CO₃ + H₂O

Basic oxides are?

Ionic compounds!

They react with?

H₂O and the result is a Broensted base as in the example below :

CaO + H₂O → Ca(OH)₂

So now that's that. But whatabout oxides formed by the metalloids?

These elements form amphoteric oxides; that is they can react with both bases and acids.

Examples below :

Al₂O₃ + 6 HCl → 2 AlCl₃ + 3 H₂O

or

Al₂O₃ + 2 NaOH + 3H₂O → 2[NaAl(OH)₄]

Several of the d-element also form amphoteric oxides.

Write the two different equilibria between HCO₃^- and H₂O!

1. When HCO₃^- acts as an acid : HCO₃^- + H₂O → CO₃^2- + H3O⁺

2. When HCO₃^- acts as a base : HCO₃^- + H₂O → H₂CO₃ + OH^-

State wether the following oxides are acidic, basic or amphoteric! BaO, SO₃, As₂O₃, Bi₂O₃?

BaO = basic

SO₃ = acidic

As₂O₃ = amphoteric

Bi₂O₃ = basic

The easiest way to solve the question above is of course by looking at the periodic table.

More to come, bitches! Love/A