Structure 1.4 - 1.5 definitions review (IB HL Chemistry)

Relative Atomic Mass

The mass of an atom is measured on a relative scale

• The reference point of the scale is the carbon-12 isotope. It is

considered the standard with 12 units.

• The relative atomic mass (Ar) is the weighted average of one atom of

the element

Relative Formula Mass (Mr)

• The sum of the weighted average of the masses of the atoms in a

formula unit relative to one-twelfth of an atom of carbon-12.

• It does not have units

Components of a Solution

Solvent: A substance that has other substances dissolved in it (Does the dissolving).

Solute: Other substances present in a solution (Dissolve in solvent).

Hydrates

A hydrated salt is a compound that contains a fixed ratio of water

molecules within the crystalline structure of the compound. This water

of crystallization can be driven off by heating, resulting in an anhydrous

salt.

Titration

Titration is a laboratory procedure used to determine the

concentration of solution using a standardized solution (a.k.a. a

a solution whose concentration is known.)

• Titrant: solution of known concentration in the burette

• Sample: solution of unknown concentration in the flask

How Titrations Work

A base with known concentration is slowly added to the acid solution until all of the acids have been neutralized. At this endpoint, the solution changes color. The volume of base needed to reach the endpoint is used to calculate the concentration of the acid.f

Standard Solution

• A solution of known concentration

Ideal Gases

An ideal gas consists of moving particles with...

a) negligible volume

b) no interparticle forces. All collisions between particles are

considered elastic.

Ideal Gases vs Real Gases

Real gases deviate from the ideal gas model, particularly at low

temperatures and high pressures

As pressure increases...

• the gas occupies less space, and the particles occupy a greater

proportion of the space ∴ Their volume is no longer negligible

• the volume decreases, the particles approach one another and

attractive forces increase between particles

Ideal Gases vs Real Gases

Real gases deviate from the ideal gas model, particularly at low temperatures and high pressures

• At low temperatures, the kinetic energy of the particles decreases, and the strength of the interparticle forces increase

Molar Volume of an Ideal Gas

The molar volume of a gas is a constant at a specific temperature and pressure. At STP (standard temperature and pressure) one mole of a gas has a volume of 22.7 dm3 mol-1 (this number is in the data booklet)

@STP

T = 273 K (0°C)

P = 100 kPa

Solutions

A solution is a homogenous mixture of at least two substances in one

phase (the components are uniformly mixed giving an appearance that

there is one visible “part”.)

• Solutions can be solids, liquids, or gases

Boyle’s Law

The volume of a gas is always the same as the volume of the container

because particles spread fully….

• Pressure results from particles colliding with the walls of a container

• Pressure increases when the frequency or energy of collisions increases

Boyle’s Law: the pressure of a gas is inversely proportional to its volume

If the temperature is held constant, increasing volume of a fixed mass of

gas decreases its pressure

Charles’s law

The volume of a gas is directly proportional to its absolute temperature (a.k.a temperature in kelvin).

Gay-Lusaac’s Law

As Temperature increase…

• Kinetic energy of particles increases

• Particles move faster and collide with the walls of the container more frequently and with higer energy

• The pressure of a gas is directly proportional to absolute temp

Empirical formula

The empirical formula of a compound gives the simplest ratio of each

element present in that compound.

• Formulas of all ionic compounds are empirical

Molecular formula

The molecular formula gives the actual number of atoms of each

element present in a molecule. It is a multiple of the empirical formula.

• i.e Glucose CH20 & C6H12O6

Mole Definition

Mole definition: mass of a substance that contains as many particles

as there are atoms in 12 g of carbon 12