1.2 Amount of substance

Question 1

Give the defnition for one mole

Answer 1

One mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

specifiy the particle e.g atom, molecule, ion…

Question 2

Give the definition for relative atomic mass

Answer 2

Relative atomic mass is the average mass of one atom compared to one twelfth the mass of one atom of carbon-12.

Question 3

Give the definition for relative atomic mass

Answer 3

Relative atomic mass is the average mass of one atom compared to one twelfth the mass of one atom of carbon-12.

Question 4

Give the definition for the relative molecular mass

Answer 4

Relative molecular mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12.

Question 5

Give the equation to calculate moles for pure solids, liquids and gases

Answer 5

moles = mass/Mr

mass = grams
moles = mol

Mr must be calcualted and quoted to 1dp

Question 6

Give the equation to calculate moles for gases

Answer 6

PV=nRT

pressure(P) = Pa
volume(V) = m^3
temperature(T) = K
n = mol
R = 8.31

celcius > kelvin +273

Question 7

Give the equation for calculating moles in solutions

Answer 7

concentration = moles/volume

concentration = mol dm^-3
volume = dm^3

cm^3 > dm^3 ÷ 1000
m^3 > dm^3 x 1000

Question 8

How do you know how many signifigant figures to give?

Answer 8

Give your answer to the same number of signifigant figures given in the question. If a mixture is given, use the smallest

Question 9

How is avagadro’s constant used to calculate the number of particles?

Answer 9

Number of particles = moles of substance x avagadro’s constant

Question 10

Give the equation for density and state when it can be used

Answer 10

Density = mass/volume

Density calculations are usually used with pure liquids to work out the mass from a measured volume. It can also be used with solids and gases.

Question 11

Give the definition for empirical formulae

Answer 11

An empirical formula is the simplest ratio of atoms of each element in the compound.

Question 12

Give the general method for calculating empirical formulae

Answer 12

• Divide each mass (or % mass) by the atomic mass of the element
• For each of the asnswers divide by the smallest one of thoes numbers
• Sometimes the numbers calculated will need to be multiplied to give whole(/almost whole) numbers
  these give your empirical formula

Question 13

Give the definition for molecular formula

Answer 13

A molecular formula is the actual number of atoms of each element in the compound

Question 14

What is a hydrated salt?

Answer 14

A hydrated salt conrains waters of crystalisation
e.g Cu(NO3)2 .6H2O
hydrated copper (II) nitrate (V)

Question 15

Give the method for removing waters of crystalisation with a cruciable

Answer 15

-Weigh an empty clean dry crucible and lid
- add 2g of calcium sulfate to the crucible and weigh again
heat strongly with a bunsen for a couple of minutes
- allow to cool and weigh crucible and contents again
-heat crucible again and reweigh until you reach a constant mass to ensure reaction is compleate

Question 16

State ways to improve accuracy by heating with a crucible

Answer 16

-the lid prevents loss of solid from the experiment but should be loose fitting to allow gas to escape
- small amounts of solid, such as 0.100g should not be used as the pecentage uncertinties in weighing would be too high
-large amounts such as 50g should also not be used as the decomposition is likely to be incompleate
-the crucible needs to be dry otherwise it would give an inacurate result. it would cause the loss of mass to be to large as water would be lost when heating

Question 17

What is the unit for concentration

Answer 17

Mol dm^-3

Question 18

What happens when ions dissociate in a solution?

Answer 18

When soluble ionic solids dissolve in water they will dissociate into separate ions. This can lead to the concentration of ions differing from the concentration of the solute

Question 19

How do you calculate the new concentration of a solution you have diluted ?

Answer 19

New diluted concentration = original concentration X original volume/ new diluted volume

Question 20

What is the ideal gas equation used for?

Answer 20

The ideal gas equation applies to all gases and mixtures of gases. If a mixture of gases is used the value n will be the total moles of all gases in the mixture.