Chem - quantitive chem!!!

Question 1

what is the atom economy?

Answer 1

an indication of the amount of starting material that is converted into USEFUL products

Question 2

what is the equation for % atom economy

Answer 2

mass of desired product/ total mass of reactants * 100

Question 3

what is a mole or 6.02 * 10 to the 23 also known as

Answer 3

Avagadros number

Question 4

Relative atomic mass is the Ar in ? that contains 1 ? of atoms of that element, eg 23g of sodium will contain ? Mole of ? atoms

Answer 4

GRAMS, mole, 1, Na

Question 5

difference between RAM and RFM

Answer 5

RAM is the relative atomic mass - the average atomic mass of the element/atom compared to for example a 1/12 of the mass of 12C isotope, whereas RFm is the relative formula mass of the whole compoun

Question 6

Equation for mass of one atom of a substance?

Answer 6

m = Ar/ 6.02 *10 to the 23

Question 7

equation for number of moles of a substance given the mass and RFM

Answer 7

moles = mass/ RFM or n =m/Mr

Question 8

equation for mass given RFM and no of moles

Answer 8

mass = moles * RFM or m = n * Mr

Question 9

what is the empirical formula of a compound?

Answer 9

the simplest whole number ratio of atoms present in a compound

Question 10

what is meant by molecular formula?

Answer 10

number of atoms of each element in a molecule

Question 11

equation for molecular formula?

Answer 11

Mr(molecule)/ Mr(empirical formula)

Question 12

magnesium oxide experiment- why was the lid needed in the experiment?

Answer 12

to prevent any powdered MgO - which looks like smoke being lost during heating

Question 13

why was the kid lifted off and replaced on the crucible in the MgO experiment

Answer 13

to allow a small amount of O2 to enter the crucible in order to keep burning off the Mg ribbon

Question 14

why are the results in the MgO experiment not very reliable?

Answer 14

• very small change of mass so % error can be very large
• MgO can cost the ribbon so some Mg will never react with air
• it’s easy to lose MgO

Question 15

3 steps of reacting mass calculations :
1. use mass to find the number of ? of the substance using the equation ?
2. use the balancing numbers in ? equation to find the ? of moles of the substance ? about
3. find the mass of this using the equation ?

Answer 15

moles, n= m/Mr, symbol, no. , asked, m = n *Mr

Question 16

calculating percentage yield : 3 reasons why you may not get as much product as you would expect

Answer 16

1. some product is lost in purification
2. reaction may be incomplete
3. there may be side reactions

Question 17

equation for % yield?

Answer 17

actual yield (how much is made)/ theoretical yield ( max amount possible) * 100

Question 18

how to work out concentration from mass and volume - equation

Answer 18

conc. = mass (in g)/ vol (in dm cubed)

Question 19

what is the conversion from vol in cm3 to vol in dm3

Answer 19

divide cm3 by 1000

Question 20

equation for conc using no of moles and volume

Answer 20

Conc. = number of moles/ volume

Question 21

equation for conc in g/dm3

Answer 21

conc (g/dm3) = conc (mol/dm3) * Mr

Question 22

how to work out no of moles in a gas?

Answer 22

n = v(in dm3)/ 24dm3

Question 23

volume equation in gases

Answer 23

V(gas) = n * 24dm3

Question 24

3 step solution to most mole questions!!!
1. find the no of ? of one of the subjects using the equations : n= m/Mr - if given a ? , n= ? if given a conc and volume, or n(gas) = ?
2. use the balancing numbers in the symbol ? to find the ? of moles asked about
3. find the asked about thing/ ? using any of about 5 equations : m= nMr, Mr = ?, V(gas) = n ?dm3, C= n/V or V(for a solution) = ?

Answer 24

1. moles, mass, cV, v/24dm3
2. equation, number
3. m/n, 24, n/c