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Chemistry HL > 1. Stoichiometry (SL+HL) > Flashcards

1. Stoichiometry (SL+HL) Flashcards

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1
Q

mole

A

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

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2
Q

elementary enities

A

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

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3
Q

the unit for Avogadro constant

A

mol^-1

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4
Q

relative atomic mass

A

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

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5
Q

relative formula mass, Mr

A

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

includes both ionic and molecular compounds

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6
Q

molar mass, M

A

the mass of one mole of a substance

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7
Q

the unit for molar mass M

A

g mol^-1

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8
Q

formula for moles

A

n = m / M
moles = mass / Mr

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9
Q

relative isotopic mass

A

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

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10
Q

mass spectrometer

A

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

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11
Q

Law of Definite Proportions

A

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

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12
Q

emperical formula

A

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

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13
Q

molecular formula

A

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

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14
Q

what is Avogadro’s law?

A

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

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15
Q

formula for molar concentration

A

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

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16
Q

factors affecting gases

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

A
  • volume of the container
  • temperature of the gas
  • pressure of the gas -> caused by a difference in the number of particles
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17
Q

calculating percentage composition

A
  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

18
Q

formula for molecular formula

A

Mr / EF
Relative formula mass / emperical formula

19
Q

formula for Atom Economy

A

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

20
Q

formula for Percentage Yield

A

(actual yield / theoretical yield) x 100

yield = amount of product made

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

21
Q

reasons why actual yield is not the same as theoretical yield

A
  • incomplete reaction
  • reactants were inpure
  • reactants/products were left behind on equipment (transfer losses)
22
Q

Ideal Gas equation

A

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

23
Q

number of dm^3 in 1 mole of any gas

A

24 dm^3 (at room temperature)

24
Q

temperature, T

A

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

25
Q

ideal gas model

A

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).

26
Q

what happens to gases at low temperature and high pressure?

A

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

27
Q

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

A

at high pressure and low temperature

28
Q

which gases show the most ideal behaviour?

A

those with a low molar mass and weakest intermolecular forces

29
Q

when is the molar volume of an ideal gas constant

*volume of 1 mole

A

under standard conditions of temperature and pressure

30
Q

formula for combined gas law

A

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

31
Q

limitations of the ideal gas model

A

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

32
Q

Titration

A

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

33
Q

Standard Solution practical

carrying out a titration

A

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

34
Q

Standard Solution practical

Explain why the solution must be allowed to cool before making it up to the final volume

A

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.

35
Q

formula for percentage uncertainty

A

(ununcertainty x number of measurements) x 100 final measurement value

Total uncertainty = sum of all uncertainties used in the investigation

36
Q

nuetralisation reaction

A

acid + base -> soluble salt + water

37
Q

nuetralisation reaction of water

A

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

38
Q

Acid-Base Titration practical

improving the titration method

A

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.

39
Q

Acid-Base Titration practical

state the sources of error in the investigation

A
  • paradox error
  • not filling the space under the top of the burette (volume lower than measured)
40
Q

characteristics of a Primary Standard

A

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

41
Q

formula for molecular formula
using molar mass

*=Mr

A
  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
42
Q

calculating back Titration

A
  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

Chemistry HL (2 decks)

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