Calculations using moles and the Avogadro constant

Question 1

a mole is

Answer 1

the amount of substance that contains the same number of particles as the number of carbon atoms in exactly 12g of the C-12 isotope.

Question 2

atoms are

Answer 2

very tiny particles that cannot be seen by the human eye

Question 3

sand is made of

Answer 3

the silicon and oxygen compound SiO2

Question 4

the Avogadro constant is

Answer 4

the scaling-up factor from atoms to grams,

6.02 x 10(23) mol-1

Question 5

relative atomic masses are used to

Answer 5

compare the relative masses of atoms

Question 6

in a water molecule, the oxygen atom has a mass that is

Answer 6

16 times the mass of a hydrogen atom

Question 7

the number of oxygen atoms in 16.0g of oxygen is the same as the number of

Answer 7

hydrogen atoms in 1.0g of hydrogen

Question 8

The symbol L is used for

Answer 8

the Avogadro constant

Question 9

the Avogadro constant is represented using the symbol

Answer 9

L

Question 10

how many atoms of He are in 4.0g of helium?

Answer 10

6.02 x 10(23)

Question 11

there are…………. atoms of Na in 23.0g of sodium

Answer 11

6.02 x 10(23)

Question 12

you can use the mole to count

Answer 12

atoms, molecules, ions, electrons and other species

Question 13

when using moles, it is important to include the

Answer 13

exact description of the species being referred to

Question 14

one mole of water has mass

Answer 14

18.0g

Question 15

when talking of the mass of one mole of oxygen or hydrogen (for example), it depends on whether you are referring to

Answer 15

atoms or molecules

Question 16

the symbol…..is used for the amount of substance inmol

Answer 16

n

Question 17

it is good practice to refer to both

Answer 17

the formula and name when using moles, e.g.
the amount, in moles, of O in 16.0g of oxygen atoms is (1mol)
the amount, in moles, of O2 in 16.0g of oxygen molecules is (0.5mol)

Question 18

the equation for calculating moles is

Answer 18

amount of substance= mass in grams / molar mass

n= m/M

Question 19

when working with L in calculations, you can be asked to

Answer 19

calculate the number of particles in a given mass of a substance
calculate the mass of a given number of particles of a substance

Question 20

the steps you would go through when calculating the number of H2O molecules in 1.25g of water are:

Answer 20

1) calculate the mol
n= m/M so n= 1.25 / 18 = 0.0694mol
2) calculate the number of molecules
L x 0.0694 = 4.18 x 10(22)

Question 21

L =

Answer 21

6.02 x 10(23)

Question 22

the mass of 100 million atoms of gold can be calculated by

Answer 22

1) n = 100,000,000 / 6.02 x 10(23) = 1.66 x 10(-16) mol

2) m= 1.66 x 10(-16) x 197.0 = 3.27 x 10(-14) g of gold