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Chemistry > Amount of Substance > Flashcards

Amount of Substance Flashcards

1
Q

Relative atomic mass

A

Average mass of one atom compared to 1/12th of the mass of one atom of carbon 12

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2
Q

Relative molecular mass

A

the average mass of a molecule to 1/12th the mass of one atom of carbon 12

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3
Q

What is the definition of Avogadro’s constant

A

Number of particles in a mole

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4
Q

equation relating mass, moles and Mr

A

moles = mass / Mr

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5
Q

Ideal gas equation

A

PV = nRT

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6
Q

equation for number of moles in an aqeuous solution

A

moles = concentration x volume

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7
Q

Unit for pressure

A

Pa

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8
Q

Unit for volume

A

m^3

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9
Q

cm^3 to m^3

A

n/1000000

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10
Q

cm^3 to dm^3

A

n/1000

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11
Q

dm^3 to m^3

A

n/1000

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12
Q

unit of temperature

A

K

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13
Q

degrees celsius to kelvin

A

+ 273

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14
Q

1 tonne =

A

1000kg

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15
Q

Number of atoms in 1 mole of copper atoms

A

6.022 x 10^23

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16
Q

number of molecules in 1 mole of carbon dioxide molecules

A

6.022 x 10^23

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17
Q

Number if ions in 1 mole of sodium ions

A

6.022 x 10^23

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18
Q

Number of particles =

A

moles x Avogadro’s constant

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19
Q

density =

A

mass / volume

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20
Q

Unit of density

A

g cm^-3

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21
Q
A
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22
Q

Empirical formula

A

Empirical formula is the simplest whole number ratio of atoms of each element in a compound.

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23
Q

How do you find the empirical formula

A
  1. mass/Mr
  2. moles / smallest amount
  3. convert to whole numbers
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24
Q

Molecular formula

A

Molecular formula is the actual number of atoms of each element in a compound.

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25
Q

Relationship between empirical formula and molecular formula

A

From the Mr work out how many times the mass of the empirical formula fits into the Mr

n x Mr = relative formula mass
n = relative formula mass / Mr

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26
Q

How to find the Mr from a mass spectrometer

A

The molecular ion (peak with highest m/z) = Mr

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27
Q

Percentage atom economy =

A

Mr of all desired products / sum of Mr of all reactants x 100

28
Q

Equation linking mass, concentration and volume

A

mass = concentration x volume

29
Q

Why is the actual yield less than the theoretical yield

A

Reaction does not go to completion

There were unwanted side reactions competing with the main reaction

30
Q

Percentage yield =

A

Actual yield / theoretical yield x 100

31
Q

What is the actual yield and theoretical yield

A

The actual yield is the number of moles or mass of product obtained experimentally
The predicted yield is the number of moles or mass obtained by calculation

32
Q

How to determine which reactant is the limiting reagent

A

Calculate the numbers of moles, with the ratios taken into account
The reactant left over is in excess so the other is the limiting reactant

33
Q

Why is atom economy in addition reactions always 100%

A

Only one product is formed

34
Q

What is water of crystallisation

A

when some compounds can form crystals which have water as part of their structure

35
Q

concentration in g dm^-3 =

A

concentration in mol dm^-3 x Mr

36
Q

new diluted concentration =

A

original concentration x (original volume / new diluted volume)

37
Q

safety precautions for irritants

A

wear goggles

38
Q

safety precautions for corrosive

A

wear goggles

39
Q

safety precautions for flammable

A

avoid naked flames by using water baths or electric heaters

40
Q

safety precautions for toxic

A

wear gloves, avoid skin contact and wash hands after use

41
Q

safety precautions for oxidising

A

keep away from flammable and easily oxidising materials

42
Q

How do you find the average titre results

A

By averaging only the concordant results

43
Q

Why is a conical flask used in titrations instead of beakers

A

It is easier to swirl a conical flask without spilling the contents

44
Q

Why is only a few drops of indicator used

A

They are generally weak acids and if too much is added it will affect the titration result

45
Q

Concordant

A

within 0.10cm^3

46
Q

Method for making a volumetric solution

A
  1. Use a balance to measure out a precise mass of the solid
  2. Measure out a small volume of water and add to a beaker and pre-dissolve the solid using a glass rod
    3.Transfer to a volumetric flask through a funnel
  3. Rinse the beaker with distilled water and add to the flask
  4. Add more water until the bottom of the meniscus
  5. Add the stopper/bung and mix the contents
47
Q

What equipment is used when making a volumetric solution to reduce impact of measurement uncertainties

A

3 decimal place balances and volumetric flasks

48
Q

What is volumetric analysis

A

a process that uses the volume and concentration of one chemical reactant (volumetric solution) to determine the concentration of another unknown solution

49
Q

What precise equipment is used to measure volume

A

Volumetric or graduate pipette and a burette

50
Q

What is the uncertainty of a burette measured to

A

half the smallest marking, usually 0.05

51
Q

Why are white tiles used in titrations

A

To make it easier to see colour change

52
Q

What are the steps in a titration

A

*rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water)

*pipette 25 cm3 of alkali into conical flask

*touch surface of alkali with pipette

*adds acid solution from burette

*make sure the jet space in the burette is filled with acid

*add a few drops of indicator and refer to colour change at end point

*use a white tile underneath the flask to help observe the colour change

*add acid to alkali whilst swirling the mixture and add acid dropwise at end point

*note burette reading before and after addition of acid

*repeats titration until at least 2 concordant results are obtained

53
Q

What is the colour change when using phenolphthalein

A

pink in alkali to colourless in acid.

End point is colourless

54
Q

What is the colour change when using methyl orange

A

yellow in alkali and red in acids
The end point is orange

55
Q

What uncertainty is the tire calculated and recorded to

A

double the uncertainty because 2 burette reading are made to obtain titre, initial and final

56
Q

A student rinses a burette with deionised water before filling with sodium hydroxide solution. State and explain the effect, if any, that this rising will have on the value of the titre.

A

Titre value would increase
Because the sodium hydroxide solution would be more dilute

57
Q

A student notices some of the liquid injected into the gas syringe did not vaporise. What effect would this have on the Mr calculated by the student.

A

Calculated Mr would be greater than the actual value
A lower volume would have been recorded / mass recorded would be too high / mass evaporated less than mass of liquid

58
Q

Importance of percentage yield

A

Idea of getting as much products as possible in the reaction / efficient conversion of reactants to products

59
Q

Importance of percentage atom economy

A

Idea of maximising the mass of reactants / atoms that ends up in desired product and minimising amount of by products

60
Q

State why the student should use NaOH to rinse a burette which is about to be filled with NaOH rather than water for the final rinse of the burette

A

Use of water would dilute the NaOH or would change the conc.

61
Q

Why did using deionised water when approaching end point to rinse the inside of the conical flask improve the accuracy of the titration

A

It ensured all the alkali / reactants are in the mixture

62
Q

Give the meaning of concordant titres

A

Titres that are within 0.1 cm^3 of each other

63
Q

Suggest why other than apparatus inaccuracy why the Mr value determined from the experimental results differs from the actual Mr

A

Volume in gas syringe is greater than true volume.
Use pv=nrt equation to prove

64
Q

Suggest the safety precaution and reason a student using toxic chloroalkane should use

A

Carry out experiment in a fume cupboard to avoid toxic vapour.

65
Q
A

Chemistry (20 decks)

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