amount of substance

Question 1

what is molar mass?

Answer 1

the mass in grams off 1 mole of a substance

Question 2

what is the term ‘amount of substance’?

Answer 2

measured in moles

Question 3

what is Avagadro’s constant?

Answer 3

6.02x10^23 atoms in a mole

Question 4

what is molar gas volume?

Answer 4

one mole of a gaseous substance occupies 24 dm^-3

Question 5

what is the empirical formula?

Answer 5

the simplest whole number ratio of atoms in an element

Question 6

what is the molecular formula?

Answer 6

the number and type of atoms of each element in a molecule

Question 7

what does anhydrous mean?

Answer 7

contains no water

Question 8

what does hydrated mean?

Answer 8

contains water

Question 9

what is ‘water of crystallisation’?

Answer 9

the water molecules in a hydrated salt

Question 10

how do you calculate the formula of a hydrated salt via percentage/mass composition?

Answer 10

use the mass of water to find the simplest whole no. ratio

Question 11

how do you calculate the formula of a hydrated salt via experimentation?

Answer 11

1. weigh the empty crucible and then the hydrated salt
2. heat the crucible
3. reweigh

Question 12

what are the problems with experimental formulae of hydrated salts?

Answer 12

1. we assume all the water has been lost-should heat to a constant mass
2. we assume there is no further decomposition

Question 13

how do you find N in solution?

Answer 13

N=CV

Question 14

what is a standard solution?

Answer 14

a solution of known concentration. made by dissolving an exact mass of solute in a solvent and making it up to an exact volume.

Question 15

what is the ideal gas equation?

Answer 15

pV = nRT

Question 16

what assumptions are made in the ideal gas equation?

Answer 16

1. random motion
2. elastic collision
3. negligible size
4. no intermolecular forces

Question 17

what do the letters in the real gas equation mean?

Answer 17

p = pressure (Pa)
V = volume (m^3)
n = moles (mol)
R = ideal gas constant 8.31 jmol^-1K^-1
T = temperature (K)

Question 18

what is stoichiometry?

Answer 18

the ratio of moles of each substance in a chemical equation

Question 19

why is 100% percentage yield so hard to achieve?

Answer 19

1. the reaction may be reversible
2. the reactants may contain impurities
3. there may be by-products
4. reactants/products may be left in the apparatus
5. product lost during separation/filtration

Question 20

what is the % yield calculation?

Answer 20

actual yield/theoretical yield

Question 21

what is atom economy?

Answer 21

the proportion of products formed that are actually useful

Question 22

what is the calculation for atom economy?

Answer 22

molecular mass of desired product/Mr of all products

Question 23

why is a high atom economy beneficial for sustainability?

Answer 23

1. makes better use of finite resources

2. reduces the need to process waste products