# Learning Objectives: To be able to calculate M r values from A r values.

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Learning Objectives: To be able to calculate M r values from A r values

Masses of Molecules Example H 2 contains 2 x hydrogen atoms. Hydrogen atoms have a relative mass of 1, so H 2 has a relative mass of: HHHH mass = 1 mass = 1 H 2 2 x 1 = 2g

Masses of Molecules Example CO 2 contains 1 x carbon atom and 2 x oxygen atoms. carbon atoms have a relative mass of 12, and oxygen atoms have a relative mass of 16. The sum is:(1 x 12) + (2 x 16) = 12 + 32 = 44g COO 16 12 16

Calculate the M r values of the following: N 2 Al 2 O 3 NH 3 CaCO 3 H 2 ONaNO 3 MgONH 4 NO 3 NaOHCuSO 4 Na 2 OFe 2 O 3 C 2 H 6 HNO 3 H 2 SO 4 F 2 O 28 Reset 17 18 40 62 30 98 102 100 85 80 160 63 54 Show instructions Hide instructions Click on compounds to reveal answer Click on the large Periodic Table to shrink it Click on the Periodic Table to enlarge it

Extension Activity (find the Mr of these compounds) Mg(OH) 2 (NH 4 ) 2 SO 4 Fe(OH) 3 1 x Mg + 2 x O + 2 x H = 24 + (2 x 16) + (2 x 1) = 58 1 x Fe + 3 x O + 3 x H = 56 + (3 x 16) + (3 x 1) = 107 2 x N + 8 x H + 1 x S +4 x O = (2 x 14) + (8 x 1) + 32 + (4 x 16) = 132 Show Answer

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