2.1.6 Amount of Substance and the Mole

Question 1

What is the unit for mole, what what does it mean?

Answer 1

Mol: the unit for amount of substance;

Question 2

What is the unit for molar mass?

Answer 2

gmol^-1;

Question 3

What is ‘n’?

Answer 3

A quantity for the amount of substance for counting atoms - this is what Avogadro’s constant (determined after he died) does;

Question 4

What is the Avogadro constant?

Answer 4

N(small)A, is the number of particles per mole of the carbon-12 isotope, 6.02x10^23mol^-1 (3sf);

Question 5

Define amount of substance.

Answer 5

1. The QUANTITY that has moles as its unit;

2. ‘Amount of substance’ is a way of counting atoms.

Question 6

Define a mole.

Answer 6

1. The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the C-12 isotope.
2. This means that in 12g of C-12 contains 6.02x10^23 atoms. Each sample of 1mol of any substance will contain this many atoms.
3. We need to utilize moles because all atoms have different sizes.

Question 7

Define molar mass.

Answer 7

M, is the mass per mole of substance. The units for it are gmol^-1;

Question 8

How should one work our the mass of one mole of a substance? Eg: what would the mass of two moles of Carbon?

Answer 8

1. It is the RAM of the substance in grams. This is gives:
   Mass = mol x Mr - therefore the unit for Mr is g/mol (for them to cancel).
   THIS IS USED IN SOLIDS ONLY
2. 24g, because one mol weighs 12g - so two weighs twice that.

Question 9

How should one find the mass volume of a substance?

Answer 9

1. Measure the mass of a vessel;
2. Take this away from the final combined mass of the vessel and the substance;
   OR
3. ‘zero’ the display;
4. Add the substance, to record its mass directly.

Question 10

How should one more accurately measure the mass of a substance, to within 0.00001g?

Answer 10

Wih the aid of an analytical balance: these have doors on them that keep airflow away from the substance being weighed,to minimize random errors.

Question 11

Produce three examples which moles apply to. What is important to bear in mind here?

Answer 11

1. Amount of atoms (C,eg)
2. Amount of molecules (Cl2, eg)
3. Amount of ions (OH^- ions, eg);
   Bear in mind: that it is important to state the CHEMICAL FORMULA to which an amount of substance refers:
   1mol of oxygen could mean 1mol of O, or one mol of O2 (it can be read as either molecules, or atoms).

Question 12

What can molar mass be applied to?

Answer 12

Any chemical substance (elements, molecules or ions)

Question 13

C has an atomic mass of 12, what is its molar mass?

Answer 13

M(C)= 12.0 = 12.0gmol^-1

Question 14

What is M(CO2) asking?

Answer 14

1. The molar mass of CO2;
2. This would give:
3. 0+(16.0*2) - 44.0gmol^-1;

Question 15

By what formula are mass, he no of moles and molar mass linked? Produce a unit for each variable.

Answer 15

Mass(g)= No of moles(mol)*molar mass(gmol^-1)
OR
m=nM