Atomic mass and the mole conceptp. 245

MOL is the SI unit for amount of substance(amount of matter).

There are 6,02 x 1023 atoms in 12 g of carbon-12.

Avogadro’s constant (NA)

One mole is the amount of matter containing the same number of particles as there are atoms in 12 g of carbon-12.

Avogadro’s number, NA, is the number of particles (atoms, molecules, formula units) present in one mole (NA = 6,023 x 1023 mol-1).

One mole of atoms is 6,02 x 1023 atoms

One mole of ions is 6,02 x 1023 ions

One mole of molecules is 6,02 x 1023 molecules

How many atoms are in 1 mole of argon atoms?

6,02 x 1023 atoms

How many molecules are in 1 mole of HCℓ molecules?

6,02 x 1023 molecules

How many atoms are in 1 mole of HCℓ molecules?

2 x 6,02 x 1023 atoms

How many hydrogen atoms are in 1 mole of HCℓ molecules?

6,02 x 1023 H atoms

How many chlorine atoms are in 1 mole of HCℓ molecules?

6,02 x 1023 Cℓ atoms

How many chlorine molecules are in 1 mole of Cℓ2 molecules?

6,02 x 1023 Cℓ2 molecules

How many chlorine atoms are in 1 mole of Cℓ2 molecules?

2 x 6,02 x 1023 Cℓ atoms

How many water molecules are in 1 mole of H2O molecules?

6,02 x 1023 H2O molecules

How many atoms are in 1 mole of H2O molecules?

3 x 6,02 x 1023 atoms

How many H atoms are in 1 mole of H2O molecules?

2 x 6,02 x 1023 H atoms

How many O atoms are in 1 mole of H2O molecules?

6,02 x 1023 O atoms

Relative atomic mass is the mass of an atom ona scale where a carbon-12 atom has a mass of 12.No unit.

Molar mass is the mass of one mole of a substance measured in g·mol-1.

Homework

p. 249

nos. 2, 6.1, 6.2, 6.3, 7, 8

2. What are the approximate relative atomic masses (Ar) of the following atoms?

HydrogenCalciumHeliumIronCopperChlorine

14045663,535,5

6.1 Calculate the relative molecular formula mass (Mr) of the following substances:

C2H6

Mr(C2H6) = (2 x 12) + (6 x 1)= 30

6.2 Calculate the relative molecular formula mass (Mr) of the following substances:

Na2SO3

Mr(Na2SO3) = (2 x 23) + (32) + (3 x 16)= 126

6.3 Calculate the relative molecular formula mass (Mr) of the following substances:

K2Cr2O7

Mr(K2Cr2O7) = (2 x 39) + (2 x 52) + (7 x 16)= 294

7. Nitrogen forms a compound with molecular formula NxO4. The relative molecular mass of the compound is 92. What is the ...

(1) value of x? (2) correct formula for NxO4?

Mr(NxO4) = (x x 14) + (4 x 16) = 9214x + 64 = 92

14x = 28x = 2

Thus: N2O4

8. Four nitrogen atoms have the same mass as one formula unit of the ionic substance XO. Which element is X on the Periodic Table?

Mr(XO) = (x x 1) + (1 x 16) = (4 x 14)x + 16 = 56

x = 40

Thus: Element X is Ca → CaO