The Mole (pg 124)

Question 1

What do the name ‘The Mole’ mean, in terms of chemistry?

Answer 1

The mole is simply the name given to an amount of a substane.

(its just a number)

Question 2

What is the Avogardro Constant?

Answer 2

it is the number of Atoms, Molecules or ions in a mole of the given substance

It is the proportionality factor that relates the number of sonstituent particles (usually molecules, atoms or ions), in a sample with the amount of substance in that sample.

Question 3

One mole of any substance is just an amount of that substance that contains an Avogadro number of particles, give an example?

Answer 3

6.02 x 10²³ particles. The particles could be atoms, molecules, ions or electrons of that substance

Question 4

Why is the Avogardro constant such a silly long number and with a 6 at the front?

Answer 4

The answer is that the mass of that number of atoms or molecules of ay substance is exactly the same number of grams as the relative atomic mass. (Ar) or relative formular mass (Mr) of the element or compound.

so one mole of atoms or molecules of any substance will have a mass in grams equal to the relative formlar mass (Ar or Mr) for that substance.

Question 5

Carbon has an Ar of 12. What mole does it weigh?

Answer 5

So one mole of carbon weighs exactly 12g.

Question 6

Nitrogen gas, N2 has an M of 28 (2x14), so what is the mole?

Answer 6

One mole of N2 weighs exactly 28g

Question 7

Carbon Dioxide,CO2, has an Mr of 44 (12+ [2x16]), what is the weight in mole?

Answer 7

one mole of CO2 weighs exactly 44g

Question 8

So if 12g of carbon, or 28g of N2, or 44g of Co2 all weigh this in mole, what do this mean?

Answer 8

This means they all contain the same number of particles, namely one mole or 6.023 x 10²³ atome or molecules

Question 9

How many moles are there in 66g of carbon dixoide (CO2)? how is this calculated?

Answer 9

1. Calculate the M of the carbon dioxide

Mr of CO2 = 12 + (16 x 2) = 44

2. Use the formula below to find out how many moles there are.

No. of moles = Mass (g) ÷ Mr = 66 ÷ 44 = 1.5 mol (mol is the symbol for the unit Moles)

Number of moles = mass in g (of an element or compound)
_________________________________
Mr (of the element or compound)

Question 10

What is a Formula triangle?

Answer 10

You can rearange the equation using the formula triangle. You could use it to find the mass of a known number of moles of a substance, or to find the Mr of a substance from a known mass and number of moles. Just cover up the thing you want to find with your finger and write down what’s left showing.

Example:

What mass of carbon is there in 4 moles of carbon dioxide?

There are 4 moles of carbon in 4 moles of CO2, (cover up ‘mass’ in the formula triange), this leave you with ‘no. of moles x Mr. So the mass of 4 moles of carbon = 4 x 12 = 48g

see diagram on page 124.

Question 11

Calculate the number of moles in 90g of water (H2O). Ar (O) = 16, Ar(H) = 1?

Answer 11

Mr of H2O = 16 ÷ (2x1) = 18

number of moles = mass ÷ Mr
number of moles = 90g ÷ 18 = 5 moles

Question 12

Calculate the mass of 0.20 mol of postssium bromide (KBr). Ar(K)=39, Ar(BR) =80

Answer 12

Mr of KBr = 39 + 80 = 119

mass = number of moles x Mr
mass = 0.20 x 119 = 24g