c3 quantitative chemistry

Question 1

what does the conservation of mass state?

Answer 1

no atoms are destroyed or made during a reaction, therefore the mass of the product equals the mass of reactants.

Question 2

what is the relative formula mass of a compound?

Answer 2

the sum of relative atomic masses of the atoms in the numbers shown in the formula

Question 3

what should the RFM be in a balanced equation?

Answer 3

balanced on both sides

Question 4

how can you calculate percentage mass of an element in a compound?

Answer 4

(Ar x number of atoms in the element // Mr of compound) x 100

Question 5

what is the mass of one mole in a substance numerically equal to?

Answer 5

the substance’s relative formula mass

Question 6

what is avogrado’s constant?

Answer 6

6.02x10^23

Question 7

why is avogrado’s constant used?

Answer 7

the mass of that number of atoms or molecules of any substance is exactly the same number as the relative atomic mass or relative formula mass of the element/ compound

Question 8

what can the measurement of amounts in moles apply to?

Answer 8

atoms, molecules, ions, electrons, formulae and equations

Question 9

how to calculate the number of moles in a substance?

Answer 9

mass of element or compound (g) // Mr of element or compound

Question 10

why might the mass increase in a reaction?

Answer 10

one of the reactants is a gas and all the products are solid, liquid or aqueous
— before the reaction, the gas is floating in the air , so its not contained in the reaction vessel, therefore it is not counted for its mass
— then in the products, it becomes contained inside the reaction vessel

Question 11

why might the mass decrease in a reaction?

Answer 11

one of its products is a gas and all the reactants are solid, liquids or aqueous
— the reactants where contained in the reaction vessel
— if the vessel isnt enclosed, the gas product can escape, decreasing the mass

Question 12

how can masses of products or reactants be calculated?

Answer 12

using a balanced equation

Question 13

how to determine the amount of moles in a reaction?

Answer 13

look at the BIG number at the front of the compounds or elements. only in a balanced equation

Question 14

what is a limiting reactant?

Answer 14

the reactant which is completely used up in a chemical reaction

Question 15

what is an excess reactant?

Answer 15

the reactant which is still left over after the chemical reaction

Question 16

why would a scientist use excess of one reactant in a chemical reaction?

Answer 16

to ensure that the other reactant is completely used up

Question 17

what is the relationship between the limiting factor and product formed?

Answer 17

they are directly proportional

Question 18

how to calculate the mass of a product formed?

Answer 18

1) write out a balanced equation
2) work out the relative formula masses of the reactant and product wanted
3) find out the number of moles in the substances you know the mass of
4) use the balanced equation to work out how many moles there’ll be of the other substance. thats how many moles of product will be made of this many moles of reactant
5) use the number of moles to calculate the mass

Question 19

what can the concentration of a solution be measured in?

Answer 19

mass per given volume of solution

Question 20

what is concentration?

Answer 20

the amount of substance in a certain volume of a solution

Question 21

what is the relationship between the solute added and the concentration?

Answer 21

the more solute added, the higher the concentration. they are proportional

Question 22

how to calculate the concentration of a solution in g/dm^3 ?

Answer 22

mass of solute (g) // volume of solvent (dm^3)

Question 23

how to calculate the concentration of a solution in mol/dm^3 ?

Answer 23

moles of solute // volume of solvent (dm^3)

Question 24

why is it not possible to obtain the calculated amount of a product?

Answer 24

1) the reaction may not go through completion as it is reversible
2) some of the product may be lost when separated from the reaction mixture
3) some reactants may react in different ways different to the expected reaction

Question 25

what is the yield of a product called?

Answer 25

the amount of product made

Question 26

how to calculate percentage yield?

Answer 26

(mass of product actually made // maximum theoretical mass of product) x100

Question 27

what is atom economy?

Answer 27

the measure of the amount of reactants that end up as useful products

Question 28

why is atom economy important?

Answer 28

for sustainable development and for economic, reasons such as:
- by minimising unwanted products, we save money
- increase sustainability by not wasting any resources

Question 29

what is the equation of atom economy?

Answer 29

(RFM of desired product // RFM of all the reactants) x100

Question 30

how is the concentration of a solution related to the mass of solute and volume of solution?

Answer 30

1) increase in the mass of the solute = increase concentration
2 increase in the volume of solution = decrease concentration

Question 31

how many moles of any gas occupies 24dm^3 at 20 degrees celsius?

Answer 31

one mole

Question 32

equation of the volume of gas?

Answer 32

(mass of gas (g) // Mr of gas ) x24