quantitative chem 3

Question 1

percentage mass of an element in a compound =

Answer 1

Ar * number of atoms of that element/

Mr of the compound * 100

Question 2

moles =

Answer 2

mass / Mr

Question 3

volume of gas =

Answer 3

mass of gas /

Mr of gas *24

Question 4

concentration (g/dm cubed) =

Answer 4

mass(g) /

volume (dm cubed)

Question 5

concentration(mol/dm cubed) =

Answer 5

number of moles(mol) /

volume (dm cubed)

Question 6

atom economy =

Answer 6

relative formula mass of desired products /

relative formula mass of all reactants *100

Question 7

percentage yield =

Answer 7

mass of product actually made /

maximum theoretical mass of product *100

Question 8

Why do you never get 100% yield

Answer 8

Not all reactants react to make a product(reversible)
There might be side reactions
You lose some product when you separate it from the reaction mixture

Question 9

(yield) what happens if you want to keep the liquid

Answer 9

you lose a bit that remains with the solid and filter paper

Question 10

(yield) what happens if you want to keep the solid

Answer 10

some of it will get left behind when you scrape it off the paper

Question 11

what is the atom economy

Answer 11

tells you how much of the mass of the reactant is wasted when manufacturing a chemical and how much ends up as useful product

Question 12

disadvantages of low atom economy

Answer 12

use up resources quickely
make lots of waste product
unsustainable
aren't profitable
raw materials are expensive
waste is expensive to remove

Question 13

the best way of getting rid of waste product

Answer 13

find a use for it

Question 14

what is concentration

Answer 14

The amount of a substance in a certain volume of a solution

The more solute the more concentrated

Question 15

why is the a amount of product formed directly proportional to the amount of limiting reactant

Answer 15

if you add more reactant there will be more reactant particles to take part in the reaction.

Question 16

step to find the limiting reactant

Answer 16

1) Write out balanced equation
2) work out Mr
3) find out the moles there are of the known substance
4) use the balanced equation to work out the moles needed of the other
5) calculate mass

Question 17

steps to balance equations using reactant masses

Answer 17

1) divide the mass of each substance by it’s Mr to find the moles
2) Divide the moles by the smallest number of moles in the reaction
3) make sure they are all whole numbers
4) re write the balanced equation

Question 18

what is one mole of a substance

Answer 18

is just an amount of that substance that contains an Avogadro number of particles- 6.02 * 10 to 23 particles`

Question 19

What happens to the number of atoms during a reaction

Answer 19

no atoms are destroyed and no atoms created this means that the same number of atoms are on each side so are conserved

Question 20

How to find out if the mass is conserved

Answer 20

1)add up the the relative formula masses of the substance on each side

Question 21

explanation 1 of why mass seems to change(reactant is gas)

Answer 21

one of the reactants is a gas and all the products are solids, liquids.

Before the reaction the gas is floating in the air

when the gas reacts to form a product it becomes contained so the total mass of the stuff in the reaction increases.

Question 22

explanation 2 of why mass seems to change(product is gas)

Answer 22

product is gas and all reactants are solids

Before the reaction all the reactants are contained

If the vessel isn’t enclosed then the gas can escape from the reaction