atomic mass and the mole concept · 2020. 8. 5. · mole concept p. 245. mol is the si unit for...

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