Relative atomic masses and common molar masses — Relative atomic masses and common molar masses

SECTION NOTES: MUST-KNOW CHEMISTRY

RELATIVE ATOMIC MASSES AND COMMON MOLAR MASSES

1. RELATIVE ATOMIC MASSES (VALUES USED IN CALCULATIONS)

Z	Symbol	Element	A_r
1	H	Hydrogen	1
2	He	Helium	4
3	Li	Lithium	7
4	Be	Beryllium	9
5	B	Boron	11
6	C	Carbon	12
7	N	Nitrogen	14
8	O	Oxygen	16
9	F	Fluorine	19
10	Ne	Neon	20
11	Na	Sodium	23
12	Mg	Magnesium	24
13	Al	Aluminium	27
14	Si	Silicon	28
15	P	Phosphorus	31
16	S	Sulfur	32
17	Cl	Chlorine	35.5
18	Ar	Argon	40
19	K	Potassium	39
20	Ca	Calcium	40
21	Sc	Scandium	45
22	Ti	Titanium	48
23	V	Vanadium	51
24	Cr	Chromium	52
25	Mn	Manganese	55
26	Fe	Iron	56
27	Co	Cobalt	59
28	Ni	Nickel	59
29	Cu	Copper	63.5
30	Zn	Zinc	65
31	Ga	Gallium	70
32	Ge	Germanium	73
33	As	Arsenic	75
34	Se	Selenium	79
35	Br	Bromine	80
36	Kr	Krypton	84

Other heavy elements often met:

2. READY-MADE MOLAR MASSES (g/mol)

Formula	Name	M (g/mol)
H₂O	Water	18
CO₂	Carbon dioxide	44
CO	Carbon monoxide	28
NH₃	Ammonia	17
CH₄	Methane	16
O₂	Oxygen	32
N₂	Nitrogen	28
Cl₂	Chlorine	71
SO₂	Sulfur dioxide	64
SO₃	Sulfur trioxide	80
NO₂	Nitrogen dioxide	46
HCl	Hydrogen chloride	36.5
HNO₃	Nitric acid	63
H₂SO₄	Sulfuric acid	98
H₃PO₄	Phosphoric acid	98
CH₃COOH	Ethanoic (acetic) acid	60
NaOH	Sodium hydroxide	40
KOH	Potassium hydroxide	56
Ca(OH)₂	Calcium hydroxide	74
NaCl	Sodium chloride	58.5
KCl	Potassium chloride	74.5
CaCl₂	Calcium chloride	111
CaCO₃	Calcium carbonate	100
Na₂CO₃	Sodium carbonate	106
NaHCO₃	Sodium hydrogencarbonate	84
CaO	Calcium oxide	56
MgO	Magnesium oxide	40
Al₂O₃	Aluminium oxide	102
Fe₂O₃	Iron(III) oxide	160
CuO	Copper(II) oxide	79.5
CuSO₄	Copper(II) sulfate	159.5
CuSO₄·5H₂O	Copper(II) sulfate pentahydrate	249.5
KMnO₄	Potassium permanganate	158
K₂Cr₂O₇	Potassium dichromate	294
AgNO₃	Silver nitrate	170
NH₄Cl	Ammonium chloride	53.5
(NH₄)₂SO₄	Ammonium sulfate	132
Na₂S₂O₃	Sodium thiosulfate	158
C₂H₅OH	Ethanol	46
C₆H₁₂O₆	Glucose	180
C₁₂H₂₂O₁₁	Sucrose	342
C₂H₄	Ethene	28
C₃H₈	Propane	44
C₄H₁₀	Butane	58
C₈H₁₈	Octane	114
CO(NH₂)₂	Urea	60

3. SHORTCUTS

Water of crystallisation adds 18 g/mol for each H₂O: CuSO₄ 159.5 → CuSO₄·5H₂O 249.5.

Moles: $n = \dfrac{m}{M}$, and for gases $n = \dfrac{V}{22.4\ \text{dm}^3}$ at s.t.p.

Percentage of an element = (mass of that element in one mole ÷ M) × 100.