C3 Amount Of Substance

Question 1

What’s avogadros constant

Answer 1

6.02 x 10^23 mol^-1

The number of atoms per mole of the C-12 isotope

Question 2

How to calculate the mass of 1 mole of the element

Answer 2

Mass of 1 mole = relative atomic mass in grams

Question 3

State Avogadro’s law

Answer 3

Under same temp and press, 1 mole of any gas would occupy the same volume.

Question 4

Define molar gas volume

Answer 4

Volume per mole of gas molecules at a stated temp & press

Question 5

Why do diff gas particles occupy the same volume

Answer 5

Gas particles are very spread out, hence individual differences has no effect.

Question 6

What are the ideal ways in which gases behave

Answer 6

They’re in continuous motion

No IMF’s experienced

Exert pressure when they collide with each other or container

No Ek is lost in collisions

When temp increases, Ek of gases also increase

Question 7

1 atm is equal to how many Pa

Answer 7

1atm =1.0133 bars 101325 Pa

Question 8

0*C is equal to how many kelvins

Answer 8

273K

Question 9

What doe conc of a solution mean

Answer 9

Amount of solute dissolved in 1 dm^3 of solvent

Question 10

What’s a standard solution

Answer 10

Solution of known conc

Question 11

What does percentage yield mean

Answer 11

Efficiency of which reactants are converted into products

Question 12

Reasons for not obtaining 100% yield

Answer 12

Reaction may be at equilibrium

Reactants may be impure

Side reactions could occur

Reactants/products may be left behind while transferring

Loss of products during separation & purification

Question 13

What does atom economy tell us about

Answer 13

Proportion of desired products compared with all the products formed in the reaction

Is a measure of how well atoms have been utilised

Question 14

Does 100% yield mean 100% atom economy

Answer 14

No

Even if all reactants are converted into products, not all products of reaction will be the required products

Question 15

Which type of reaction has 100% atom economy

Answer 15

Addition reactions

(2 or more reactants are combined to form a product)

Question 16

What’s the molecular formula

Answer 16

Number of atoms of each element in a molecule

Question 17

What is empirical formula

Answer 17

Simplest whole number ratio of atoms of each element in a compound

Question 18

What does hydrated and water of crystallisation mean

Answer 18

Water molecules are part of their crystalline structure

Question 19

What does anhydrous mean

Answer 19

Doesn’t contain water molecules

Question 20

What’s the method to find the formula of a hydrated salt

Answer 20

Weigh empty crucible

Add hydrated salt into weighed crucible

Weight crucible and hydrated salt

Using pipe clay triangle, support crucible containing hydrated salt on a tripod

Heat crucible & contents gently for about 1 min

Then heat it strongly for 3 more mins

Leave crucible to cool

Weight crucible and anhydrous salt

Question 21

What are the assumptions made when finding the formula of a hydrated salt

Answer 21

All water has been lost - only see surface of crystals, there could be water inside - solution = heat to constant mass

No further decomposition - difficult to judge if there’s no colour change

Question 22

what is molar gas volume at RTP

Answer 22

24.0 dm^3mol^-1

Question 23

Formulas to calculate volume of gas in dm3 and cm3

Answer 23

n = V/24.0 dm3

n= V/24000 cm3

Question 24

What are the assumptions for molecules making up an ideal gas

Answer 24

Random motion

Elastic collisions

Negligible size

No IMFs

Question 25

Ideal gas equation

Answer 25

pV = nRT

Question 26

Units are conversions for the ideal gas equation

Answer 26

p = Pa (pressure) kPa to Pa = x10^3

V = m^3 (volume) cm^3 to m^3 = x10^-6
dm^3 to m^3 = x10^-3

n = mol (amount of gas molecules)

R = 8.31 Jmol^-1K^-1 (ideal gas constant)

T = K (temperature) *C to Pa = +273

Question 27

Method to find relative molecular mass

Answer 27

Add sample of volatile (l) to small syringe via needle

Weigh small syringe

Inject sample into gas syringe through self sealing rubber cap

Reweigh small syringe to find mass of volatile (l) added to gas syringe

Place gas syringe in boiling water bath at 100*C

(l) vaporises producing a gas

Pressure is recorded

Question 28

Why is the theoretical yield hard to achieve

Answer 28

Reaction may not have gone to completion

Other reactions (side reactions) may have taken place alongside main reaction

Purification of product may result in loss of some product

Question 29

Formula for percentage yield

Answer 29

(Actual/theoretical) x 100%

Question 30

What is a limiting reagent

Answer 30

Reactant that’s not in excess

Used up first & stops reaction

In the 1:1 ratio It’s the reactant with higher moles