TOPIC 1; Stoichiometric Relationships

Question 1

Kinetic-molecular theory

Answer 1

describes the differences in the properties of solids, liquids, and gases on the basis
of the different kinetic energies of the particles.

Question 2

• The molar mass (M)

Answer 2

• The molar mass (M) is the relative mass expressed in g and has units of g mol–1.

Question 3

relative atomic mass (Ar)

Answer 3

relative atomic mass (Ar) of an element is the average mass of an atom according to relative abundances
of its isotopes, on a scale where the mass of one atom of 6
12C is 12 exactly. It has no units.

Question 4

relative molecular mass (Mr)

Answer 4

is the sum of the relative atomic masses of the atoms in the molecular formula.

Question 5

Titration

Answer 5

Titration is a chemical technique in which one solution is used to analyse another solution to find its
concentration or amount.

Question 6

Concentration

Answer 6

Concentration is the amount of solute in a known volume of solution. It can be expressed either in g dm–3 or
mol dm–3. Concentration in mol dm−3
is often represented by square brackets around the substance:
[solute] (mol dm−3) = nsolute (mol)/Vsolution (dm3)

Question 7

• Density

Answer 7

mass/volume

Question 8

A solution

Answer 8

• A solution is a homogeneous mixture of a liquid (the solvent) with another substance (the solute). The solute
can be solid, liquid, or gas but the solvent is generally a liquid.

Question 9

STP

Answer 9

STP for gases is standard temperature (0 °C or 273 K) and pressure (100 kPa).

Question 10

Number of mol

Answer 10

= volume/molar volume

Question 11

Avogadro’s law

Answer 11

Avogadro’s law states that equal volumes of different gases contain equal numbers of particles at the same
temperature and pressure.

Question 12

Temperature

Answer 12

Temperature (in K) is a measure of the average kinetic energy of the particles. Particles have minimum kinetic
energy at absolute zero (0 K).

Question 13

The ideal gas equation:

Answer 13

PV = nRT
• R = 8.31 J K–1 mol–1, T must be in K.
• T in k (C + 273)

Question 14

Percentage yield

Answer 14

(experimental yield/theoretical yield) × 100%

Question 15

SL unit of temperature

Answer 15

The kelvin is the SI unit of temperature: T (K) = T (°C) + 273

Question 16

fixed mass of an ideal gas at constant T

Answer 16

P = k1/V (k1 constant)

Question 17

Compounds

Answer 17

Compounds contain a fixed ratio of atoms of different elements and have different properties from their
component elements.

Question 18

Mixtures

Answer 18

Mixtures contain more than one element or compound that are not chemically combined.

Question 19

The molar mass (M)

Answer 19

is the relative mass expressed in g and has units of g mol–1.

Question 20

Number of mol

Answer 20

= mass/molar mass: n = m/M

Question 21

Number of particles

Answer 21

Number of particles = number of mol × Avogadro’s constant: N = nL