1. Stoichiometry (SL+HL)

Question 1

mole

Answer 1

the SI unit of amount of substance. One mole contains exactly the number of elementary entities given by the Avogadro constant: 6.02 x 10^23

*international standard of measurement

Question 2

elementary enities

Answer 2

any chemical particle such as atoms, molecules, ions or electrons

Question 3

the unit for Avogadro constant

Answer 3

mol^-1

Question 4

relative atomic mass

Answer 4

the weighted average mass of an atom compared to 1/12 the mass of an atom of carbon-12

Question 5

relative formula mass, Mr

Answer 5

the mass of a compound relative to 1/12 the mass of an atom of carbon-12

includes both ionic and molecular compounds

Question 6

molar mass, M

Answer 6

the mass of one mole of a substance

Question 7

the unit for molar mass M

Answer 7

g mol^-1

Question 8

formula for moles

Answer 8

n = m / M
moles = mass / Mr

Question 9

relative isotopic mass

Answer 9

mass of an isotope of an atom relative to 1/12 of a carbon-12 atom

Question 10

mass spectrometer

Answer 10

a tool to measure the abundance of different isotopes in an atom

Question 11

Law of Definite Proportions

Answer 11

the fixed ratio of constituent elements of a given compound eg. H20

Question 12

emperical formula

Answer 12

gives the simplest ratio of atoms of each element present in a compound

Question 13

molecular formula

Answer 13

gives the actual number of atoms of each element present in a molecule

Question 14

what is Avogadro’s law?

Answer 14

it states that equal volumes of all gases measured under the same conditions of temperature and pressure contain equal numbers of molecules

Question 15

formula for molar concentration

Answer 15

c = n / V
c = concentration (molarity), g/dm
n = moles
V = volume, dm^3

Question 16

factors affecting gases

the number of gas particles that can fit inside a closed container

Answer 16

• volume of the container
• temperature of the gas
• pressure of the gas -> caused by a difference in the number of particles

Question 17

calculating percentage composition

Answer 17

1. calculate the molar mass of the compound
2. calculate the mass that each element contributes individually to the molar mass of the compound
3. divide the mass of each element by the molar mass of the compound and multiply by 100 to get the percentage

make sure to use the appropriate units and the number of significant numbers

Question 18

formula for molecular formula

Answer 18

Mr / EF
Relative formula mass / emperical formula

Question 19

formula for Atom Economy

Answer 19

= (Mr of desired/useful product / Mr of all products) x 100

Question 20

formula for Percentage Yield

Answer 20

(actual yield / theoretical yield) x 100

yield = amount of product made

actual yield - what is made
theoretical yield - assumes a complete reaction

Question 21

reasons why actual yield is not the same as theoretical yield

Answer 21

• incomplete reaction
• reactants were inpure
• reactants/products were left behind on equipment (transfer losses)

Question 22

Ideal Gas equation

Answer 22

PV = nrt
P = pressure, Pascals Pa
V = volume, metres cubed m^3
n = moles
R = the gas constant, 8.13 J mol^-1 K^1
T = temperature, Kelvin K

C° -> K = +273
KPa -> Pa = / 1000
cm^3 -> m^3 = / 1000

Question 23

number of dm^3 in 1 mole of any gas

Answer 23

24 dm^3 (at room temperature)

Question 24

temperature, T

Answer 24

a measure of the average kinetic energy (Ek) of particles. In Kelvin (K)

Question 25

ideal gas model

Answer 25

An ideal gas consists of moving particles with negligible volume and no intermolecular forces. All collisions between particles are considered elastic (no energy is lost).

Question 26

what happens to gases at low temperature and high pressure?

Answer 26

at high pressure - gas particles are closer together and are influenced by forces of attraction. at low temperature - particles move less rapidly meaning there is a greater opportunity for intermolecular forces to have an effect. For both conditions the gas *no longer behaves as an ideal gas* and behaves as a real gas | *deviates from the ideal gas model

Question 27

under which conditions do real gases deviate from the ideal gas model?

Answer 27

at high pressure and low temperature

Question 28

which gases show the most ideal behaviour?

Answer 28

those with a low molar mass and weakest intermolecular forces

Question 29

when is the *molar volume* of an ideal gas constant | *volume of 1 mole

Answer 29

under standard conditions of temperature and pressure

Question 30

formula for combined gas law

Answer 30

P1V1 / T1 = P2V2 / T2 P = pressure, KPa V = volume, dm^3 T = Temperature, K

Question 31

limitations of the ideal gas model

Answer 31

gas laws only apply to ideal gases. With real gases, some of the assumptions made about ideal gases no longer apply under certain conditions.

Question 32

Titration

Answer 32

a practical technique that is used to calculate unknown things about a solution, usually its concentration in mol dm^-3

Question 33

# Standard Solution practical carrying out a titration

Answer 33

To carry out tirtration we use a standard solution. This is an acid or base that we know the precise concentration of. We then measure the V of that solution used and calculate the number of moles. The end result should be very pale pink

Question 34

# Standard Solution practical Explain why the solution must be allowed to cool before making it up to the final volume

Answer 34

The solution got hot whilst dissolving. The water will expand and the volume will be increased. The water will cool and contract and ∴ the volume will decrease until the final conc. will be higher than it should be.

Question 35

formula for percentage uncertainty

Answer 35

(ununcertainty x number of measurements) x 100 final measurement value ## Footnote Total uncertainty = sum of all uncertainties used in the investigation

Question 36

nuetralisation reaction

Answer 36

acid + base -> soluble salt + water

Question 37

nuetralisation reaction of water

Answer 37

H+ (aq) + OH- (aq) -> H2O

Question 38

# Acid-Base Titration practical improving the titration method

Answer 38

regularly pausing the titration to rinse the inside of the conical flask with small amounts of water. This helps to return any unreacted substances to the reaction mixture improving the accuracy of the results.

Question 39

# Acid-Base Titration practical state the sources of error in the investigation

Answer 39

- paradox error - not filling the space under the top of the burette (volume lower than measured)

Question 40

characteristics of a Primary Standard

Answer 40

must be: - a pure compound - must not lose or gain mass when exposed to air - must be soluble in water

Question 41

formula for molecular formula using *molar mass* | *=Mr

Answer 41

1. calculate the emperical formula's molar mass 2. divide the compounds molar mass by the emperical formula's molar mass to find the ratio 3. multiply the emperical formula by the ratio

Question 42

calculating back Titration

Answer 42

1. calculate the moles of acid that reacted 2. calculate the number of moles of pure substance the impure sample contains 3. convert moles to grams and work out percentage purity