Calculations using Moles and the Avogadro Constant

Question 1

what is a mole

Answer 1

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

Question 2

if you have 1 mole of oxygen,16g and one mole of hydrogen, 1g, how do the number of atoms present differ

Answer 2

they both have the same number of atoms for those masses

Question 3

what does that then imply about the differences in mass between an atom of hydrogen and oxygen

Answer 3

that an atom of oxygen has a mass 16 times more than that of 1 atom of hydrogen

Question 4

what is avogadros constant

Answer 4

6.02x10^23

Question 5

what is the symbol used for the constant

Answer 5

L

Question 6

what does that number actually mean, using hydrogen as an example

Answer 6

• it tells us the number the number of atoms of an element that make up 1 mole of it
• for example, 6.02x10^23 hydrogen atoms make up 1 mole of hydrogen, which is 1 gram
• the same for oxygen, where 6.02x10^23 of its atoms have a mass of 16g, equating to what we call 1 mole of it

Question 7

what does the symbol n mean

Answer 7

the amount of substance in moles

Question 8

how many moles of 1 gram of an oxygen atom are there

Answer 8

• moles = mass / Mr

- 1 / 16 = 0.0625 moles

Question 9

how would this number differ if you had 1 gram of oxygen gas or ozone molecules

Answer 9

• the number of moles would get smaller
• as the mass remains the same but the Mr of the substances increases
• as oxygen gas is O2 which = 32g for 1 mole
• and ozone molecules are O3 = 48gmol-1

Question 10

although we know that moles = mass / Mr, what is the fancy way of writing it

Answer 10

• amount of substance in moles = mass in grams / molar mass

- or n = m / M

Question 11

how many H20 molecules are there in 1.25g of water

Answer 11

• youre gonna need the constant for this so you need to work out the number of moles
• moles = mass / Mr
• 1.25 / 18 = 0.0694 moles
• 6.02x10^23 x 0.0964 = 4.18x10^22

Question 12

what can avogadros constant be used to calculate if you have the amount in moles of a substance

Answer 12

number of atoms, ions, molecules, electrons and other species

Question 13

what is the definition of avogadros constant

Answer 13

the number of atoms of carbon-12

- in exactly 12g of it