Quantitative Chemistry: Avogadro's Constant 2 (NOT DONE)

Question 1

1 mole is this number…

60200000000000000000000000
=
Avogadro’s constant
=
6.02 x 10↑23

Answer 1

1 mole is this number…

60200000000000000000000000
=
Avogadro’s constant
=
6.02 x 10↑23

Question 2

Calculate the number of atoms in 48g of magnesium. Ar Mg = 24

Answer 2

To calculate the number of atoms in a sample we first must calculate the number of moles in the sample. And to do this we use the equation:

Number of moles = mass (g) / relative atomic mass Ar

number of moles = 48 / 24

number of moles = 2 moles of Mg
▼
number of atoms = 2 x 6.02 x 10↑23
▼
number of atoms = 1.204 x 10↑24

remember that one mole is Avogadro’s constant: 6.02 x 10↑23

Question 3

Calculate the number of atoms in 28g of lithium. Ar Li = 7

Answer 3

To calculate the number of atoms in a sample we first must calculate the number of moles in the sample. And to do this we use the equation:
Number of moles = mass (g) / relative atomic mass

number of moles = 28 / 7

remember that one mole contains Avogadro’s constant: 6.02 x 10↑23 so to calculate the number of atoms in four moles we do:

number of moles = 4
▼
number of atoms = 4 x 6.02 x 10↑23
▼
number of atoms = 2.408 x 10↑24

Question 4

Calculate the number of atoms in 56g of calcium oxide. Ar Ca = 40 Ar = 16

CaO

Answer 4

First, we must calculate the relative formula mass of CaO which is
1 x 40 = 40
1 x 16 = 16
Mr: 40 + 16 =56

To calculate the number of atoms in a sample we first must calculate the number of moles in the sample. And to do this we use the equation:
Number of moles = mass (g) / relative formula mass

number of moles = 56 / 56 = 1

Number of molecules in one mole = 6.02 x 10↑23
▼
number of atoms in one mole = 2 x 6.02 x 10↑23
▼
number of atoms = 1.204 x 10↑24

Question 5

Calculate the number of atoms in 54g of water. Ar H = 1, Ar O = 16

Answer 5

First we’ve got to calculate the number of moles of water molecules and to do this we need to know the relative formula mass for water. Number of moles = mass (g) / relative formula mass Mr

54 / 18 = 3 moles of water

Number of molecules in one mole = 6.02 x 10↑23
▼
however, we have three moles of water so we must do 3 x 6.02 x 10↑23 which is 1.806 x 10↑24.
▼
the number of atoms in 3 moles = 3 x 1.806 x 10↑24 = 5.148 x 10↑24

Because each water molecule contains three atoms, we multiply the number of molecules by three to find the number of atoms.

Question 6

Magnesium has an atomic mass of 24g. Calculate the number of atoms in 24g of magnesium. Mg = 24

Answer 6

1 = 24 / 24

1 x 6.02 x 10↑23 =

6.02 x 10↑23