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A-LEVEL CHEM > PHYSICAL CHEM - AMOUNT OF SUBSTANCE > Flashcards

PHYSICAL CHEM - AMOUNT OF SUBSTANCE Flashcards

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1
Q

What is the equation to calculate moles?

A

moles (mols) = mass (g) / RFM (n = m/Mr)

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2
Q

What is Avagadro’s constant?

A

6.02 x 10^23

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3
Q

What is relative atomic mass?

A

the avg mass of 1 atom of an element compared to 1/12th the mass of an atom of carbon-12

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4
Q

What is relative molecular mass?

A

the avg mass of 1 molecule of a substance compared to 1/12th the mass of an atom of carbon-12

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5
Q

What is theoretical yield?

A

what you could make in theory

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6
Q

What is actual yield?

A

what you actually make

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7
Q

How do you calculate % yield?

A

(actual/theoretical) x 100

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8
Q

What are 3 reasons why the actual yield can never be 100%?

A
  • reaction is reversible
  • other side reactions
  • some product lost
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9
Q

What is the equation for density?

A

density (kg/m^3) = mass (kg) / volume (m^3) (ρ = m/V)

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10
Q

What is the equation for atom economy?

A

(RFM of wanted product/RFM of total reactants) x 100

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11
Q

What is the empirical formula of a substance?

A

the simplest ratio of atoms of each element in a substance

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12
Q

What is the ideal gas equation?

A

pressure (Pa) x volume (m^3) = moles (mol) x temp (K) x gas constant (J mol^-1 K^-1) (pV = nRT)

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13
Q

How do you convert from °C to K?

A

+ 273

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14
Q

How do you convert from mols to g?

A

x Mr

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15
Q

How do you convert from mol dm^-3 to g dm^-3?

A

x Mr

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16
Q

How do you convert from g to mols?

A

÷ Mr

17
Q

How do you convert from g dm^-3 to mol dm^-3?

A

÷ Mr

18
Q

RP - Titrations: method

A
  • using pipette and pipette filler measure 25 cm^3 of alkali into the conical flask
  • add a few (5-10) drops of indicator (could be methyl orange/phenolphthalein) to the flask
  • place a white tile under the conical flask
  • use a funnel to fill burette with acid of known conc. remove funnel and record initial volume
  • add acid from the burette slowly and swirl the flask constantly
  • add acid drop wise towards the end
  • as soon as there is a colour change stop adding acid
  • calculate volume of acid added
  • repeat titration and calculate mean
19
Q

Why is it important to remove the funnel before doing the titration?

A

so no additional drops fall into the burette whilst you’re doing the titration as this would affect the volume

20
Q

What should you rinse the burette and pipette with? Why?

A
  • pipette and burette should be rinsed with the solution you will be using in each one
  • this is because rinsing them with water would affect the conc. of the solutions
21
Q

Why should you only add a few drops of indicator?

A

so it doesn’t react with the solution in the flask which would affect the end point

22
Q

What are concordant results?

A

results within 0.1 of each other

23
Q

When calculating mean titre which results should you use?

A

only use concordant results

24
Q

What is the equation used to calculate % error?

A

% error = (uncertainty in measurement / measurement) x 100

25
Q

How can % error be reduced?

A
  • taking a larger measurement
  • use equipment with a smaller resolution
26
Q

How do you form an ionic equation?

A

remove any ions that don’t react
eg: original: HCl (aq) + NaOH (aq) → NaCl (aq) + H2O(l)
ionic equation: H^+ (aq) + OH^- (aq) → H2O (l)

27
Q

What is a standard solution?

A

a solution containing a precisely known conc of an element in a substance

28
Q

How do you make a standard solution (of Na2CO3)?

A
  • measure mass of Na2CO3 in a weighing boat using a mass balance
  • pour Na2CO3 into beaker
  • re-weigh empty weighing boat and subtract its mass from the mass of the weighing boat with NaCO3 and record this value
  • dissolve Na2CO3 in ~100cm^3 of distilled water and pour into volumetric flask
  • rinse beaker with distilled water and pour rinses into volumetric flask (repeat at least 3 times)
  • use pipette to add distilled water until meniscus reaches 250cm^3
  • invert flask many times

A-LEVEL CHEM (6 decks)

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