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MODULE • Chemistry Form 4

RELATIVE MOLECULAR MASS (RMM) / RELATIVE FORMULA MASS (RFM)
JISIM MOLEKUL RELATIF (JMR) / JISIM FORMULA RELATIF (JFR)

The average mass on one atom of the element / Jisim purata satu molekul
1 RMM / JMR =
1 × The mass of an atom of carbon-12 / Jisim satu atom karbon-12
12
2 RMM is obtained by adding up the RAM of all the atoms that are present in the molecule.
JMR diperoleh dengan menambahkan JAR semua atom yang terdapat dalam satu molekul.
Molecular substance Molecular formula Relative molecular mass
Bahan molekul Formula molekul Jisim molekul relatif

Oxygen / Oksigen O 2 × 16 = 32
2
Water / Air H O 2 × 1 + 16 = 18
2
Carbon dioxide / Karbon dioksida CO 12 + 2 × 16 = 44
2
Ammonia / Ammonia NH 14 + 3 × 1 = 17
3
[Relative atomic mass / Jisim atom relatif : O = 16, H = 1, C = 12, N = 14]
3 For ionic substances, RMM is replaced with Relative Formula Mass (RFM).
Untuk sebatian ion, JMR digantikan dengan Jisim Formula Relatif (JFR).

Substance Chemical formula Relative molecular mass
Bahan Formula kimia Jisim formula relatif

Sodium chloride / Natrium klorida NaCl 23 + 35.5 = 58.5

Potassium oxide / Kalium oksida K O 2 × 39 + 16 = 94
2
Copper(II) sulphate / Kuprum(II) sulfat CuSO 64 + 32 + 4 × 16 = 160
4
Ammonium carbonate / Ammonium karbonat (NH ) CO 2 [14 + 4 × 1] + 12 + 3 × 16 = 96
4 2 3
Aluminium nitrate / Aluminium nitrat Al(NO ) 27 + 3 [14 + 3 × 16] = 213
3 3
Calcium hydroxide / Kalsium hidroksida Ca(OH) 40 + 2 [16 + 1] = 74
2
Lead(II) hydroxide / Plumbum(II) hidroksida Pb(OH) 207 + 2 [16 + 1] = 241
2
Hydrated copper(II) sulphate / Kuprum(II) sulfat terhidrat CuSO 5H O 64 + 32 + 4 × 16 + 5 [2 × 1 + 16] = 250
4 2
[Relative atomic mass / Jisim atom relatif : Na = 23, Cl = 35.5, K = 39, O = 16, Cu = 64, S = 32, N = 14, H = 1, C = 12, Al = 27,
Ca = 40, Pb = 207]
(i) The formula of metal oxide of M is M O . Its relative formula mass is 152. What is the relative atomic mass of
2
3
metal M?
Oksida logam M mempunyai formula M O . Jisim formula relatif ialah 152. Apakah jisim atom relatif logam M?
2 3
M = RAM for M
2M + 3 × 16 = 152
M = 52
(ii) Phosphorus forms a chloride with a formula PClx. Its relative molecular mass is 208.5. Calculate the value of x.
Fosforus membentuk sebatian klorida dengan formula PClx. Jisim molekul relatifnya adalah 208.5. Hitungkan nilai x.
[Relative atomic mass / Jisim atom relatif : P = 31, Cl = 35.5]
31 + x × 35.5 = 208.5
35.5x = 208.5 – 31
35.5x = 177.5
x = 5

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02-Chem F4 (3P).indd 24 12/9/2011 5:59:05 PM