Amount of a substance

Question 1

Empirical formula

Answer 1

The formula that represents the simplest whole number ratio of the atoms of each element in a compound

Question 2

Molecular formula

Answer 2

the formula that gives the actual number of atoms of each element in one molecule of a compound

Question 3

Spectator ions

Answer 3

Ions that are unchanged during a chemical reaction, that is, they do not take part in the reaction

Question 4

The number of moles in a given volume of solution - equation

Answer 4

number of moles in solution n =

concentration c (mol dm-3) x volume V (cm3)
over 1000

Question 5

percentage uncertainty

Answer 5

(uncertainty/vol) x 100

Question 6

Atom economy

Answer 6

Describes the efficiency of a chemical reaction by comparing the total number of atoms in the product with the total number of atoms in the starting materials

(% atom economy =mass of desired product) x 100
over total mass of reactants

to reduce waste, find a use for the waste product

Question 7

Percentage yield

Answer 7

The practical efficiency of the process

(actual mass / theoretical) x 100

Question 8

How can you measure mass accurately?

Answer 8

1. measure mass on 2 or 3 dp balance of a weighing bottle with required quantity of solid in it
2. empty mass into reaction vessel
3. reweigh empty weighing bottle
4. first reading - mass of empty weighing bottle gives the exact mass added