Amount of a Substance

Question 1

how to calculate moles

Answer 1

moles = mass / Mr

Question 2

state avogadro’s law

Answer 2

under the same temperature and pressure, one mole of any gas would occupy the same volume

Question 3

how much volume does a gas occupy at room temp and presssure

Answer 3

24dm3 or 24000cm3

Question 4

how to calculate moles using gas volume

Answer 4

moles = volume (cm3) / 24000

moles = volume (dm3) / 24

Question 5

what is the ideal gas equation

Answer 5

pV = nRT
pressure x volume = number of moles x gas constant x temperature

Question 6

1 atm = how many pascals??

Answer 6

1 atm = 101325 Pa

Question 7

0 degrees celcius = how many Kelvin

Answer 7

273 K

Question 8

how to calculate moles when concentration and volume are given

Answer 8

moles = conc x vol

Question 9

what is a standard solution

Answer 9

a solution of known concentration

Question 10

steps to prepare a standard solution

Answer 10

1. weigh the solute using the weigh by difference method
2. in a beaker dissolve the solute using the solvent
3. pour the solution into a volumetric flask
4. rinse the beaker using the solution and add it to the flask
5. add solvent to the flask carefully until it reaches the graduation line
6. mix the solution thoroughly to ensure complete mixing

Question 11

what does percentage yield mean?

Answer 11

the efficiency of which reactants are converted into products

Question 12

what are the reasons for not obtaining 100% yield

Answer 12

• reaction may be at equilibrium
• the reactants may be impure
• side reactions could happen
• reactants or products may be left behind whilst transferring
• loss of products during separation and purification

Question 13

how to calculate percentage yield

Answer 13

actual amount of product / theoretical amount of product x 100

Question 14

what does atom economy tell us

Answer 14

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

Question 15

how to calculate atom economy

Answer 15

Mr of desired product / sum of the Mr’s of all products
x100

Question 16

what type of reaction has 100% atom economy

Answer 16

addition reactions

Question 17

define relative atomic mass

Answer 17

average mass of an atom compared to C-12 on a scale in which an atom of C-12 has a mass of 12

Question 18

what is a hydrated compound

Answer 18

a compound that contains water of crystallisation

Question 19

how do you write a chemical formula for hydrated compounds

Answer 19

the waters of crystallisation are separated by a dot.

CuSO4 . 5H2O

Question 20

what is a compound called when it doesnt have any waters of crystallisation

Answer 20

anhydrous compound

Question 21

how do you convert a compound from hydrated to anhydrous?

Answer 21

heating the hydrated salt

Question 22

how do you calculate the degree of hydration (the number infront of the H2O)

Answer 22

• the mass of the hydrated salt must be measured before heating
• the salt is then heated until it reaches a constant mass
• the two mass values can be used to calculate the number of moles of water in the hydrated salt