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chem > topic 5: formulae, equations and amounts of substance > Flashcards

topic 5: formulae, equations and amounts of substance Flashcards

1
Q

mole is

A

unit for amount of a substance
same no. of particles as there are atoms in 12g of 12C

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2
Q

avogadros constant

A

6.02 x 10^23 mol-1

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3
Q

molar mass

A

mass of 1 mole of substance in g/mol

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4
Q

ideal gas equation

A

pV = nRT
pressure = pa
V = m3
n= mol
R= gas constant (data book)
T = kelvin

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5
Q

conc =

A

mol/vol

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6
Q

(dm3)vol (gas)=

A

mol/24
ROOP TEMP AND PRESSURE

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7
Q

molecular formula

A

shows number and type of each atom in a. molecule

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8
Q

empirical formula

A

simplest whole number ratio of the elements present in one molecule of a compound

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9
Q

celcius to kelvin

A

add 273

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10
Q

relative atomic mass

A

average mass of one atom compared to the mass of 1/12 of c-12 atom

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11
Q

relative isotopic mass

A

mass of an isotope compared to the mass of 1/12 of c-12 atom

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12
Q

mol, mass , mr

A

mol = mass/mr

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13
Q

1 tonne

A

1000kg

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14
Q

water of crystallisation experiment is done by …

A

heating in a crucible

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15
Q

heating in a crucible experiment method

A
  • weigh an empty can dry crucible + lid
  • add 2g of hydrated and reweigh
  • heat strongly
  • cool
  • reweigh
  • heat and reweigh until a constant mass
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16
Q

what happens if the crucible is wet

A
  • mass loss too large as water lost when heating
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17
Q

purpose of lid in crucible

A
  • prevents loss of solid but still lets gas out
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18
Q

why not use tiny masses of solid in crucible experiment

A

errors in weighing too high

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19
Q

calculation from the crucible experiment

A
  • moles anhydrous salt
  • moles water
  • divide by smallest and find ratio
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20
Q

no. particles, mol, AC

A

particles = mol*AC

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21
Q

density equation

A

mass/ vol
g/cm3

22
Q

M unit of conc

A

mol/dm3

23
Q

how to go from moldm-3 to gdm-3

A

multiply by the Mr

24
Q

making a standard solution

A
  • weigh mass by difference
  • transfer mass to beaker
  • add distilled water, use a glass rod to store
  • pour through funnel into volumetric flask
  • washings
  • make up to the mark and invert so its UNIFORM
  • bottom of meniscus
25
Q

what does diluting change

A

NOT moles of solute but increases the vol so conc is lower

26
Q

how to calc diluted conc

A

CONSTANT MOLES SO
og conc * og vol = new conc * new vol

27
Q

what to remember with volumes in concentrations

A

add / subtract the ORIGINAL when they’re asking how much new

28
Q

mixture of gases moles with ideal gas equation

A

n is the total moles of all gases in the mixture

29
Q

errors in gas syringe (3)

A
  • friction - use a lubricant
  • gas escapes before bung inserted - use the vial
  • some gases are soluble in water so true amount isn’t measured
30
Q

reacting volumes of gases

A
  • same at room temp
31
Q

reading

A

SINGLE judgement- one reading

32
Q

measurement

A

DIFFERENCE between 2 readings

33
Q

uncertainty is

A

at least +- 0.5 of the smallest scale reading

34
Q

how to decrease uncertainty

A
  • use apparatus with a greater resolution
  • increase the size of the measurement made
35
Q

balance uncertainty

A

0.001

36
Q

volumetric flask uncertainty

A

0.1

37
Q

25cm3 pipette unceratinty

A

0.1

38
Q

burette uncertainty

A

0.05

39
Q

% uncertainty

A

uncertainty/measurement * 100

40
Q

% uncertainty vs percentage diff in the measured and real value

A
  • if % of equipment is less than the measured and real, there are other errors
  • if % of equipment is greater than measured and real, no other errors
41
Q

% yield

A

actual yield/theoretical yield * 100

42
Q

factors lowering percentage yield

A
  • incompleet reactions
  • side reactions
  • losses during transfer
43
Q

atom economy

A

mr of useful products / mr of all reactants * 100
USE REACTING RATIO

44
Q

why might economy be lower

A

reaction not gone to completion

45
Q

reactions with one product has …

A

100% atom economy

46
Q

observations with acid + carbonate

A
  • effervescent (CO2)
  • carboante dissolves
  • TEMP INCREASE
47
Q

spectator ions

A
  • same state
  • same oxidation number
48
Q

why must gas be dry

A
  • water vapour affects molar mass
49
Q

reason for vol of gas lower

A
  • gas lost when replacing bung (put mg in a vial so reacts after bung replaced)
  • magnesium coated in oxide, so water produced instead of H2 (clean it before)
  • co2 soluble in water
  • temp lower than room temp (if u used 24)
50
Q

how to know if gas syringe leaky

A
  • plunger doesnt return to 0 when released
  • mr decreases because air has a lower mr
51
Q

why deos phenolphthalein turn pink in alkali

A

forms a pink anion by loss of H+ ions

chem (12 decks)

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