Equations

Question 1

How do you work out moles of a solid?

Answer 1

n = m / mr

• n - moles
• m - mass (g)
• mr - molar mass/relative molecular mass (g mol^-1)

Question 2

How do you work out moles of a liquid?

Answer 2

n = c x v

• n - moles
• c - concentration (mol dm^-3)
• v - volume (dm³)

x 1000

dm³ <———-> cm³

^{÷ 1000}

Question 3

How do you work out moles of a gas?

Answer 3

n = v / 24

n - moles

v - volume (dm³)

24 - molar gass volume (dm³mol^-1)

• applicable at 298K and 1atm

Question 4

What is the ideal gas equation?

Answer 4

pV = nRT

p - pressure (Pa)

V - volume (m³)

n - moles

R - gas constant, 8.314

T - temperature (K) or (ºC + 273)

Question 5

What is Avogadro’s Constant?

Answer 5

6.02 x 10²³

Question 6

How do you work out moles from number of particles?

Answer 6

n = number of particles ÷ (6.02 x 10²³)

Question 7

How do you work out number of atoms?

Answer 7

number of particles = moles x (6.02 x 10²³)

• make sure if the particles are molecules that you multiply the total number by the number of atoms in that particle
• E.g. H₂S = 30 particles –> 30 x 3 = 90 atoms