Topic 2 - Atoms, Molecules and Stoichiometry

Question 1

Unified atomic mass unit

Answer 1

Is 1/12 the mass of a carbon-12 atom.

Question 2

Relative Atomic Mass (Ar) of an element

Answer 2

Is the weighted average of the masses of its isotopes relative to 1/12 of the mass of a carbon-12 atom.
- This is for monatomic elements.

Question 3

Relative Molecular Mass (Mr)

Answer 3

Is the weighted average of the masses of the molecules of a compound relative to 1/12 of the mass of a carbon-12 atom.
- This is for covalent molecules.

Question 4

Relative Isotopic Mass

Answer 4

The mass of the isotope relative to 1/12 of the mass of a carbon-12 atom.
- This is for isotopes of an atom.

Question 5

Relative Formula Mass (Mr)

Answer 5

The weighted average of the masses of the formula units relative to 1/12 of the mass of a carbon-12 atom.
- This is for any compound (ionic or covalent).

Question 6

Mole

Answer 6

The amount of substance which contains the same number of particles as there are atoms in exactly 12g of carbon-12.

It is the amount of substance that contains 6.022x10^23 atoms, ions or molecules (particles).

Question 7

Avogadro’s Constant

Answer 7

The number of atoms in one mole of a carbon-12 atom.
- Which is 6.022 x10^23

Question 8

Limiting Reagent

Answer 8

It is the reactant, in a particular experiment, that governs the maximum amount of product that can be formed.
- The smallest number of moles on the reagent side, using the mole ratio.

Question 9

Percentage Yield

Answer 9

Is the percentage of the theoretical yield achieved in practice by dividing the actual yield by the predicted yield of a product.
- This is how much product is made in an incomplete reaction, compared to how much could be made if the reaction was 100% complete.

Question 10

Percentage Purity

Answer 10

Is the actual mass reacted divided by the initial mass used expressed as a percentage of a reactant.
- This is how pure a reagent is.

Question 11

Empirical Formula

Answer 11

Shows the simplest whole number ratio of atoms present in a substance.

Question 12

Molecular Formula

Answer 12

Shows the actual number of atoms of each element present in a substance.

Question 13

Nitrate (V)

Answer 13

NO3-

Question 14

Nitrate (III)

Answer 14

NO2-

Question 15

Sulfate (VI)

Answer 15

SO4 2-

Question 16

Sulfate (IV)

Answer 16

SO3 2-

Question 17

Phosphate (V)

Answer 17

PO4 3-

Question 18

Phosphate (III)

Answer 18

PO3 3-

Question 19

Number of Particles =

Answer 19

Number of Moles x A.C. (6.022 x10^23)

Question 20

Number of Moles =
(Equation for Mass)

Answer 20

mass / Mr

mass - g

Question 21

Number of Moles =
(Equation for Solutions)

Answer 21

Concentration / Volume

conc. - moldm^ -3
volume - dm^3

Question 22

Number of Moles =
(Equation for Gases)

Answer 22

Volume / 24

24rtp - room temp. and pressure
volume - dm^3