C4 Quantative Chemistry

Question 1

What is a mole?

Answer 1

The relative atomic mass of a substance in grams.

Question 2

What is the formula for working out mass?

Answer 2

mass, m = no. of moles x Mr

Question 3

What is Avogadro’s constant?

Answer 3

The number of atoms/molecules in 1 mole of a substance.

6.02 x 10^23

Question 4

What is a limiting reactant?

Answer 4

The reactant that gets used up first. It is NOT in excess.

Question 5

What is yield?

Answer 5

The mass of the desired product that is made in a chemical reaction.

Question 6

What is percentage yield?

Answer 6

How much product is made compared to the maximum theoretical yield.

Question 7

What is the formula for percentage yield?

Answer 7

percentage yield = (actual mass/theoretical mass) x 100

Question 8

What affects percentage yield?

Answer 8

• Reversible reactions
• Unwanted products from alternative reactions
• Lost in apparatus
• Not pure reactants
• Lost in separation

Question 9

What is atom economy?

Answer 9

Measure of the amount of starting material ends up as useful products

Question 10

What is the formula for percentage atom economy?

Answer 10

percentage atom economy =
formula mass of desired product/sum of masses of reactants x 100
including big numbers

Question 11

Why is atom economy important?

Answer 11

• Conserves resources

- Minimises pollution

Question 12

What is concentration?

Answer 12

The amount of a substance dissolved in 1 dm^3 of solution
or
the mass of a solute in a given volume

Question 13

What is the concentration formula?

Answer 13

c (g/dm^3) = solute, m (g)/volume, v(dm^3)
or
c (mol/dm^3) = no. of moles / volume

Question 14

How can the concentration of an aqueous solution be increased?

Answer 14

• Add more solute in v of solution

- Evaporate water to have same m of solute and less solution

Question 15

What is a titration?

Answer 15

A method to measure the volumes of two solutions that react together

Question 16

What is the end point?

Answer 16

When the acid and alkali have completely reacted with each other.

Question 17

What does a certain volume of gas always contain?

Answer 17

The same number of gas molecules under the same conditions

Question 18

What is the molar gas volume?

Answer 18

the v of 1 mole of any gas is 24dm^3 at r.t.p

Question 19

what is the formula for molar gas volume?

Answer 19

n = v (dm^3)/24dm^3

Question 20

How many cm^3 are in 1dm^3?

Answer 20

1000 cm^3 = 1 dm^3

Question 21

what is the equipment needed for a titration?

Answer 21

pipette
pipette filler
beaker
conical flask
burette
funnel
indicator

Question 22

why use a conical flask in titrations?

Answer 22

it reduces risk of splashing

Question 23

why is the conical flask placed on a white tile in titrations?

Answer 23

to see a colour change more easily

Question 24

how do you read the reading on the burette?

Answer 24

make sure the eye is level with the BOTTOM of the meniscus

Question 25

how many times to you repeat the titration?

Answer 25

until you get concordant results within 0.1 cm^3

Question 26

how do you convert a concentration in mol/dm^3 into g/dm^3?

Answer 26

multiply by the relative formula mass of the substance

Question 27

which non-metal ions are positive?

Answer 27

H+ (hydrogen ion)

NH4+ (ammonium ion)

Question 28

why is the overall charge of an ion zero?

Answer 28

the charges of the ions have to be cancelled out

Question 29

why can the little numbers of a chemical formula not be altered?

Answer 29

it will produce a different molecule

Question 30

what makes a balanced equation?

Answer 30

the same number of atoms on the left and right hand side

Question 31

what is relative formula mass (Mr)?

Answer 31

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

Question 32

what are two key facts about relative formula mass?

Answer 32

it has no units
it never involves big numbers (the numbers in front of formulas e.g. 2CH4, you would not use the 2 when working out the Mr)

Question 33

what is the percentage by mass?

Answer 33

the percentage of the relative formula mass that is due to one of the elements in a compound

Question 34

what is the formula for percentage by mass of an element?

Answer 34

% by mass = (total Ar of the atoms in element / Mr) x 100

Question 35

what is the method for balancing an equation using masses and moles?

Answer 35

using the masses given, work out the number of moles using n=m/Mr
put these numbers in front of the chemical formulas
divide all the big numbers by the smallest number in front of a chemical formula
boom - you done

Question 36

what is the method to calculate the mass of a chemical in a reaction when you are given the mass of one of the other chemicals?

Answer 36

calculate the number of moles of the chemical with the known mass
see the ratio of the amount of moles of the two chemicals (look at the big numbers)
work out mass (use m = n x Mr(or Ar))

Question 37

what is a solute?

Answer 37

a chemical dissolved in a solvent

Question 38

what does 100% yield mean?

Answer 38

that every single atom of the reactants reacts to produce the maximum amount of product possible

Question 39

why can you not have a greater yield/atom economy that 100%?

Answer 39

it would mean you created atoms

Question 40

what do chemists try to do with unwanted side products of reactions?

Answer 40

find a use for them so it does not waste money

Question 41

what does concentration mean? (in terms of moles)

Answer 41

the number of moles of a solute in a given volume of solution

Question 42

what are the values of room temperature and pressure?

Answer 42

temp - 20 degrees c

pressure - 1 atmosphere