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AS Chemistry > 1.3 - Chemical Calculations > Flashcards

1.3 - Chemical Calculations Flashcards

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1
Q

What is the definition of relative atomic mass?

A

The average mass of one atom of the element relative to one twelth the mass of one atom of carbon-12

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2
Q

What is the definition of relative isotopic mass?

A

The mass of an atom of an isotope relative to one twelth the mass of one atom of carbon-12.

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3
Q

What is the definition of relative formula mass?

A

The sum of all atomic masses of all atoms present in its formula.

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4
Q

How do you find the relative formula mass?

A

Mass of an atom x number of atoms

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5
Q

What does a mass spectrometer do?

A

Used to measure relative atomic mass of an element.

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6
Q

What are the 4 stages within a mass spectrometer?

A

Ionisation
Acceleration
Deflection
Detection

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7
Q

What does ionisation do in a mass spectrometer?

A
  • vaporised sample passes through ionisation chamber
  • sample is bombarded with a stream of electrons to knock electrons out of sample and create positive ions
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8
Q

What does acceleration do in a mass spectrometer?

A

An electric filed accelerates the positive ions to high speed.

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9
Q

What does deflection do in a mass spectrometer?

A

Depends on -
Mass of the ion (lighter ions are deflected more than heavier ones)
The charge of the ion (more than 2+ are deflected more)

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10
Q

What does detection do in a mass spectrometer?

A
  • Beam of ions passing through the machine is detected electrically
  • Only ions with the correct mass/charge ratio make it through the machine to the ion detector
  • the signal is then amplified and recorded
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11
Q

How do you find the relative atomic mass from a mass spectrometer?

A

Ar = (abundance x ar isotope 1)+(abundance x Ar isotope 2) / 100

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12
Q

What are 3 uses of mass spectrometry?

A
  • identifying unknown compounds
  • identifying trace compounds in forensic science
  • analysing molecules in space
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13
Q

What is fragmentation in mass spectrometry?

A

Molecular ions are unstable, therefore can break into fragments, causing a wide range of lines in the mass spectrum.

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14
Q

What is the definition of one mole?

A

The amount of any substance that contains the same number of particles as there are atoms in exactly 12g of carbon-12.

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15
Q

What is the definition of avogadros constant?

A

The number of atoms per mole.

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16
Q

What is the definition of molar mass?

A

Mass of one mole of a substance.

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17
Q

What is the equation for the number of atoms per mole?

A

mass per mole of 12C/mass of one atom of 12C

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18
Q

What is the equation for moles?

A

Moles = mass/molar mass
Moles = conc x vol/1000

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19
Q

How do you work out the amount of a substance from an equation?

A

1) Work out moles of known substance
2) Go back to the equation to work out ratio
3) Work out moles of missing number from ratio
4) Work out mass or mr of target using moles = mass/mr
5) Find percentage yield using real mass/ theoretical mass x 100

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20
Q

What is the empirical formula?

A

The simplest formula showing the simplest whole number ratio of the number of atoms of each element present.

21
Q

What is the molecular formula?

A

Shows the actual number of atoms of each element present in the molecule. It is the simple multiple of the empirical formula.

22
Q

How do you work out the empirical formula?

A

1) Find the amount of moles in each element present (%/molar mass)
2) Find the ratio of elements (moles/smallest moles)
3) Round these into whole numbers.

23
Q

For gasses, what do you need to consider instead of masses?

A

Reactants and products

24
Q

What is standard temperature and pressure?

A

0* and 1atm

25
Q

What is the gas molar volume?

A

22.4dm^3

26
Q

How do you find out the vol of gas in a question?

A

1) Change mass into moles (m=mass/mr)
2) Work out ratio between 2 gasses
3) Change moles in volume (m=cxv)

27
Q

What is Boyle’s law?

A

At a constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.

28
Q

What is Charles’ law?

A

The volume of a fixed mass of a given gas, at constant temperature, is directly proportional to its temperature in kalvins.
V/T = constant

29
Q

What is avogadros principle?

A

Equal volumes of different gases, measured at the same temperature and pressure, contain the same number of molecules.
The volume of gas is dependant on number of moles.

30
Q

What is the ideal gas equation?

A

PV/T = nR (n = number of moles)(R= gas constant)

31
Q

What are the Si units of PV/T?

A

Pressure - Pa (pascels)
Volume - m3
Temperature - K (kalvins)

32
Q

How do you change from cm3 to m3?

A

Divide by 1,000,000

33
Q

What is 1atm in KPa?

A

100kPa

34
Q

What is 0* in K?

A

273K

35
Q

How do you work out V2 of a reaction?

A

P1V1/T1 = P2V2/T2
1) substitute in
2) cross multiply to find x

36
Q

What is the definition of ‘concentrated’?

A

A solution with a large quantity of solute in a small quantity of solvent is described as concentrated.

37
Q

What is the definition of ‘dilute’?

A

A solution with a small quantity of solute in a large quantity of solvent is described as dilute.

38
Q

What is the equation for concentration?

A

Concentration = amount of moles in solute/volume of solution

39
Q

How do you find concentration in a question?

A

1) Find molar mass of a substance (pt)
2) Change mass into moles (m=mass/mr)
3) Change cm into dm^3 (divide by 1000)
4) Divide moles by volume to find concentration

40
Q

What is an acid base titration?

A

Finding the unknown concentration of a solution.

41
Q

How do you do an acid base titration calculation?

A

1) Find the moles of the solution with the known concentration
2) Use a balanced chemical equation to give the stoichiometric ratio between the acid and the base
3) Calculate the concentration of the second solution from the known volume and amount in moles.

42
Q

What is the equation for atom economy?

A

mass of requirement product/total mass of reactants x 100%

43
Q

What is the equation for percentage yield?

A

Mass of product obtained/ maximum theoretic mass x 100%

44
Q

How do we know the process of a reaction is efficient?

A

The higher the atom economy or percentage yield, the more efficient the process.

45
Q

What is the percentage error on a burette?

A

0.05cm3

46
Q

What is the percentage error on a thermometer?

A

0.1*

47
Q

What is the percentage error on a 3 plate balance?

A

0.5mg

48
Q

What do you have to do with percentage errors if there are before and after values?

A

Multiply uncertainties by 2

AS Chemistry (15 decks)

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