S1.4: Counting Particles By Mass: The Mole

Question 1

What is avogadros constant?

Answer 1

N_A or L

The number of particles equivalent to the relative atomic mass or molecular mass of a substance in grams
-> applies to atoms, molecules, ions

Avogadros constant: 6.02 x 10^23

Question 2

What is a mole?

Answer 2

One mole of a substance contains the same number of fundamental units as there are atoms in exactly 12g (atomic number) of C-12

6.02 x 10^23 atoms of carbon-12 -> 12g

Atoms very small -> easier to ‘count’ them as moles
Measure in mole bu weighing mass of substance

Question 3

What is relative atomic mass?

Answer 3

The A_r of an element is the weight mean of the naturally occurring isotopes of the element relative to 1/12 of a C-12 atom
-> molecules (covalent)

A_r = weight average mass of one atom of an element/ 1/12 mass of one atom of C-12

Question 4

What is relative formula mass?

Answer 4

M_r is used for compounds containing ions
-> ionic compounds

Calculated the same way as relative molecular mass

Question 5

What is molar mass?

Answer 5

Mass of one mole of any substance = molar mass (M)

Units: g/mol

Question 6

Formula for moles

Answer 6

Moles=mass/molar mass

(Molar mass=A_r or M_r (g/mol))

Question 7

What is empirical formula?
(+how to find)

Answer 7

The simplest whole number ratio of atoms of each element in one molecule or formula unit of a compound

Calculated either by knowing:
Mass of each
Percentage composition (mass assumed at 100g)

Question 8

What is molecular formula?
(+how to find)

Answer 8

The formula that shows the number and type of each atom in a molecule

Can be found by dividing relative molecular mass/relative mass of empirical formula
Then multiply the empirical formula by this number

Question 9

What is concentration?

Answer 9

Concentration of solution:
Amount of solute dissolved in a solvent to make 1dm^3 of solution

1.00 molar solution -> 1 mol of solute with total volume 1dm^3 of solution

Units:
Mol/dm^3 or g/dm^3
or ppm (small concentrations usually pollutants)
-> 1 ppm -> mass of 1mg dissolved in 1dm^3 of water

Question 10

What is the definition of:
Solute
Solvent
Concentrated solution
Dilute solution

Answer 10

Solute -> substance that dissolves

Solvent -> often water

Concentrated solution -> high concentration of solute

Dilute solution -> low concentration of solute

Question 11

Equation for concentration

Answer 11

Concentration = number of moles or mass of solute/volume of solution

! Be careful with cm^3 or dm^3 !

Question 12

How much volume does 1 mole of gas take up?

Answer 12

Stp - 22.4 dm3

Rtp (room temp and pressure) - 24 dm3