U1.4: The Mole

Question 1

Define the mole

Answer 1

A fixed number of particles and refers to the amount of substance, n.

Question 2

Define molar mass

Answer 2

Mass of one mole of a substance (g mol^-1)

Question 3

Define relative atomic mass

Answer 3

The average mass of all isotopes of an element compared to 1/12 the mass of the Carbon-12 atom

Question 4

Define molecular formula

Answer 4

The actual number of atoms in one mole of a substance

Question 5

Define empirical formula

Answer 5

the simplest formula of a substance

Question 6

Define what the excess reagent is

Answer 6

Reactant that will be first leftover after the limiting reagent’s all used up

Question 7

Define what the limiting reagent is

Answer 7

The reactant that’s first used up

Question 8

Formula to find the # of particles in 1 mole:

Answer 8

N = n x A
(# of particles = # of moles x avogadro’s constant)

Question 9

Formula to calculate moles

Answer 9

n = m / M
moles = mass / Molar mass

Question 10

What is the link between mass to moles to number of particles?

Answer 10

mass (g) —> divided by Mr –> moles (1 mole) —-> x6.02x10^23 —> # of particles

Question 11

Formula for % composition

Answer 11

(# of atoms of that element) x Ar / (relative molar mass of entire compound) x 100

Question 12

How to find empirical formula of a compound that was hydrated then heated?

Answer 12

1. Calculate m, M and n of the compound
2. Do the same for water
3. Find mole ratio
4. The EF would be _____.xH2O where x is a number from the ratio

Question 13

cm^3 —> dm^3?

Answer 13

Divide by 1000

Question 14

Formula for concentration (and units)

Answer 14

n(mol) = c (mol dm^-3) x v(dm^3)

Question 15

Formula for concentration ( in g dm^-3)

Answer 15

m(g) = c (g dm^-3) x v (dm^3)

Question 16

What to do when asked for concentration in mol dm^-3?

Answer 16

Use the formula n=cv

Question 17

What to do when asked for concentration in g dm^-3?

Answer 17

Use the formula m=cv

Question 18

What is concentration also known as?

Answer 18

The “molarity”

Question 19

How can molarity be shown as an answer?

Answer 19

With Square brackets […]
e.g.: [NaCl]: 1 mol dm^-3

Question 20

How to solve questions asking for mol of (element) atoms in ______ mol of (compound)

Answer 20

• find # of elements added together
• _____ mol x # of elements

and when asked for # of atoms of an element in the same type of question:
- at the end, do ans(6.02x10^23)