Chemistry - Key Concepts

Question 1

What is Ar and Mr?

Answer 1

Ar = the atomic mass of an element
- (e.g the Ar of Carbon is 12)
Mr = the SUM of the atomic masses in a compound
- (e.g, CuBr₂ = 64 + (80x2) = 144)

Question 2

What is Avagadro’s Number?

Answer 2

The number of units in one mole of a substance

= 6.023 x 10²³

Question 3

What is the formula for calculating concentration?

Answer 3

Concentration (g/dm³) = mass of solute (g) / volume of solution (dm³)

Question 4

What is the relationship between mass, Ar/Mr and Moles?

Answer 4

mass (g) = Ar/Mr x moles

rearranged formulae:
mass / Ar or Mr = moles
(mass / moles = Ar or Mr)

Question 5

1dm³ = ? cm³

Answer 5

1dm³ = 1,000cm³

Question 6

What’s the difference between the molecular and empirical formula?

Answer 6

molecular = FULL amount of atoms in compound
e.g, C₆H₁₂O₆ (glucose)
empirical = shows simplest RATIO of atoms in compound
e.g, CH₂O (emp for glucose)