quantitive chemistry

Question 1

why is there sometimes a change in mass in an experiment even though no atoms are created or destroyed?

Answer 1

a gas may have been produced and escaped, this can usually be identified by bubbles

Question 2

rfm x moles =

Answer 2

mass

Question 3

how many atoms in one mole?

Answer 3

6.02 x 10^23

Question 4

what do the big numbers in symbol equations show?

Answer 4

the ratio in which the reactants react

Question 5

what is a limiting reactant, what does it do, how do we work it out and what is a reactant in excess?

Answer 5

the reactants that are used up first
they dictate how much product can be made
it is the reactant that can’t live up to it’s ratio
the other reactant is in excess, the one that is greater than its ratio if the limiting reactant is at its ratio

Question 6

concentration x volume =

Answer 6

number of moles or mass ( depending on the units )

Question 7

what is 24cm^3 in dm^3?

Answer 7

0.024 ( divide by 1000 )

Question 8

vol of a gas =

Answer 8

24dm^3 x number of moles

Question 9

how do you work out percentage yield?

Answer 9

actual mass / theoretical mass x 100

Question 10

why should we only make as much as we need ( 3 ) ?

Answer 10

don’t waste resources
don’t waste money
less pollutants like CO2, CH4 or SO2 ( acid rain )

Question 11

why might the theoretical mass not equal the actual mass (3)?

Answer 11

• the reaction may not go to completion if it is reversible
• some of the product may be lost when it is separated from the 
reaction mixture
• some of the reactants may react in ways different to the 
expected reaction. 


Question 12

atom economy =

Answer 12

relative formula mass of desired product / total rfm of reactants x 100

Question 13

how are the particles arranged in a gas?

Answer 13

well separated in a random arrangement

Question 14

when working out the mass, mol or rfm of a substance which must follow the ratio?

Answer 14

the mol, if the equation in 2:1 the moles must also be in a 2:1