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Chem Mr D > Moles > Flashcards

Moles Flashcards

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1
Q

Moles equation

A 
Moles = volume/ concentration 
Moles = mass/ mr
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2
Q

What is moles equation used for?

A

Solids

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3
Q

Gas equation

A

Pressure x volume = no. Moles x gas constant x temp

PV=nRT

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4
Q

Mass equation

A

Mass= Mr x moles

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5
Q

What unit is mass in?

A

Grams

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6
Q

What is Avogadro’s constant?

A

6.02 x 10 to the power of 23

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7
Q

How to find mass (steps)

A

1) find moles (mass/mr)
2) ratio
3) find mass (mr x moles)

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8
Q

What to do is there is 2 masses given?

A

1) Work out moles of each
2) work out ratio and which one is in excess
3) mr x moles to work out mass

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9
Q

What do you need to make a solution?

A

Solid - the solute

Liquid - the solvent

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10
Q

Known concentration practical the solid

What do you need to know ?

A
  • mass
  • use a balance
  • Mr
  • calculate the moles
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11
Q

Known concentration practical - how to weigh by difference?

A
  • put balance to zero
  • put weighing boat onto balance and record mass (m1)
  • add rough amount of solid to boat and record mass (m2)
  • add solid mass to beaker and record mass of boat again (m3)
  • m2-m3=exact mass of solid added
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12
Q

Known concentration practical -dissolving the solid

A
  • use small beaker
  • add solid to the beaker
  • add approx 50cm3 of distilled water
  • stir until full dissolved
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13
Q

Why do we use distilled water when dissolving the solid?

A

So the water doesn’t have any other chemicals and results aren’t inaccurate

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14
Q

Known concentration practical

-what do we know about the liquid?

A
  • the volume

- use a 250cm3 volumetric flask (always state size)

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15
Q

Know concentration - how to work out liquid?

A
  • transfer the 50cm3 from beaker into flask using funnel
  • rinse beaker with distilled water and add the washings
  • slowly add water until near the meniscus
  • use as dropper to add water until meniscus is level with the line (250cm3)
  • place stopper on top and invert 10 times to mix the solution thoroughly
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16
Q

Things to include in known concentration results table

A
  • mass of empty boat
  • mass of boat + solid
  • mass of boat after solid
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17
Q

What is volume measured in?

A

Dm3

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18
Q

Concentration calculation

A

Concentration=moles/volume

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19
Q

What is uncertainty measured in?

A

%

20
Q

Uncertainty calculation

A

(Error value of equipment/value measured) x 100

21
Q

Testing known concentration (acid to alkali method)

A
  • use pipettes and pipette filler to add 25cm3 of sodium hydroxide solution to clean conical flask
  • add drops of indicator and put the conical flask on a white tile
  • fill the burette with hydrochloric acid and note starting volume
  • add acid from burette to alkali in conical flask,swirl to mix
  • stop adding acid when indicator first permanently changed colour and note final volume
  • calculate volume of acid added to neutralise alkali (titre value)
  • repeat steps 1-5 until concordant titres are obtained (more accurate results are obtained of acid is added drop by drop near end point)
22
Q

How many times do you test the known concentration?

A

A rough time, then 1,2 and 3 as u need 2 results that are within 0.1 of eachother

23
Q

Titration practical method

A
  • weigh it accurately about 1.3 g of anhydrous sodium carbonate and make it up to 250cm3 of solution in volumetric flask. Record masses in table
  • titration 25.0 cm3 portions of this dilution against hydro caloric acid until concordat result are achieved. Use methyl orange as indicator. Record results in table.
24
Q

Uncertainty for balance

A

2 x 0.000.5g/amount of sodium carbonate x 100

25
Q

Uncertainty for volumetric flask

A

0.1cm3/250 x 100

26
Q

Uncertainty for 25cm3 pipette

A

0.1cm3/ 25 x 100

27
Q

Uncertainty of burette

A

0.15cm3/mean titre x 100

28
Q

Concordant definition

A

Within 0.10cm3 of each number

29
Q

How to work out total apparatus uncertainty?

A

Burette + volumetric flask + pipette + balance

30
Q

How to convert kPa to Pa (pressure)

A

x 1000

31
Q

How to convert MPa to Pa (pressure)

A

x 1000000

32
Q

How to convert degrees C to K (temperature)

A

+ 273

33
Q

What is gas constant?

A

8.31 J mol-1 K-1

34
Q

How to convert dm3 to m3 (volume)

A

/ 1000

35
Q

How to convert cm3 to m3 (volume)

A

/ 1000000

36
Q

How to convert dm3 to cm3

A

/ 1000

37
Q

What is 1 atm pressure in Pa

A

101000 Pa

38
Q

Atom economy equation

A

Total Mr of the desired product / Total Mr of all reactants or products x 100

39
Q

Does atom economy have anything to do with the amount you used?

A

No

40
Q

% yields equation

A

Mass of product actually made / maximum theoretical mass of product x 100

41
Q

What is % yields about?

A

Mistakes experimenter makes

42
Q

Reasons to lose some of reactants

A
  • human error
  • some left on filter paper
  • could have dropped some
43
Q

Reason to gain some reactants

A

If it is wet it may have soaked in water

44
Q

How to calculate theoretical moles?

A

Mass / Mr

45
Q

How to calculate empirical formula?

A

1) Write out each element
2) write out mass or % of each element
3) divide by atomic mass
4) divide by smallest to get a whole number ratio

46
Q

How to find water of crystallisation in ?

A

1) find mass of an empty boiling tube and record in table
2) place about 2cm depth of hydrated (element given in question) and record mass in table
3) heat tube for 2 minute
4) record mass of tube in table
5) repeat steps 3 and 4 until mass remains constant
( if steam is still being given off then there is still water to be lost )

Chem Mr D (8 decks)

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