2. Atoms, molecules and stoichiometry

Question 1

What is the unified atomic mass unit?

Answer 1

1/12 the mass of a carbon-12 atom

Question 2

What is Relative Atomic Mass?

Answer 2

the average mass of an atom of an element compared to 1/12 of a carbon-12 atom.

(can be applied to relative molecular/isotopic/formula mass)

Question 3

What is avogadro’s constant?

Answer 3

6.022 x 10^23

Question 4

Formula for Nitrate Ion

Answer 4

NO3 -

Question 5

Formula for Carbonate Ion

Answer 5

CO3 2-

Question 6

Formula for Sulphate Ion

Answer 6

SO4 2-

Question 7

Formula for Hydroxide Ion

Answer 7

OH -

Question 8

Formula for Ammonium Ion

Answer 8

NH4 +

Question 9

Zinc Ion

Answer 9

Zn 2+

Question 10

Silver Ion

Answer 10

Ag +

Question 11

Bicarbonate Ion

Answer 11

HCO3 -

Question 12

Phospate Ion

Answer 12

PO4 3-

Question 13

Define empirical formula

Answer 13

The simplest whole number ratio of the atoms in a compound.

Question 14

Define molecular formula

Answer 14

The ratio of each atom in a compound

Question 15

Define anhydrous and hydrated

Answer 15

Anhydrous: substance that contains no water
Hydrated: substance that contains water

Question 16

What is water of crystallisation?

Answer 16

Water molecules bonded into the crystal structure.
Eg. CaSO4 · 2H20

Question 17

How to calculate percentage yield?

Answer 17

(actual yield or percent yield/theoretical yield) x 100

Question 18

Concentration formula

Answer 18

c = m/v
m= mol or mass
v= volume

Question 19

How much space does 1 mol of gas take up at room temperature?

Answer 19

24dm3

also known as the molar gas volume

Question 20

What is the limiting reagent

Answer 20

The reactant that is completely used up in a reaction.

Determines the maximum amount of product formed.

Question 21

What is the excess reagent?

Answer 21

The reactant that is not completely used in a reaction (still has left over/unreacted substance).