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A-level Chemistry > Topic 5 - Amount of Substance > Flashcards

Topic 5 - Amount of Substance Flashcards

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1
Q

Avogadro’s constant

A

6.02 × 10^23 mol^-1

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2
Q

Molar mass

A

The mass per mole of the substance in g mol^-1

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3
Q

Empirical formula

A

the simplest whole number ratio of the elements present in one molecule or formula unit of the compound

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4
Q

Molecular formula

A

the actual number of atoms of each element in a molecule of the compound

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5
Q

Accuracy

A

How close a measured quantity is to the true value.

The true value is often unknown in chemical analysis, so estimations of the measurement uncertainty is needed.

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6
Q

Acid-base indicator

A

substances used to show changes in pH of solutions and detect end-points in titrations (e.g. phenolphthalein, methyl orange, bromothymol blue)

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7
Q

Atom economy

A

a measure of how efficiently a chemical reaction converts the atoms in its reactants to atoms in the product

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8
Q

Atom economy equation

A

(Mr of atoms in product/sum of Mr of all products) × 100%

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9
Q

Bias

A

the systematic deviation of laboratory test results from the actual value

arises from systematic errors, which affect all measurements in the same way and do not average out

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10
Q

Concentration

A

how much solute is dissolved in a certain volume of solution (g/dm^3 or mol/dm^3)

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11
Q

Concentration/g dm^-3 equation

A

mass of solute (g)/volume of solution (dm^3)

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12
Q

Concentration/mol dm^-3 equation

A

amount of solute (mol)/volume of solution (dm^3)

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13
Q

Dilution

A

the process of adding more solvent to a solution to lower the concentration

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14
Q

End point

A

the point at which a colour change shows that enough of the solution in the burette has been added to react with amount of chemical in the flask

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15
Q

Equivalence point

A

reached when the amount of reactant added from a burette is just enough to react exactly with all the measured amount of chemical in the flask as shown by the balanced equation

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16
Q

Measurement uncertainty

A

unavoidable differences between measured values and true values arising from random and systematic errors of measurement

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17
Q

Ideal gas equation

A

pV = nRT

p = N/m^2 or Pa
V = m^3
T = K
n = moles
R = gas constant (J K^-1 mol^-1)

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18
Q

Limiting reactant

A

a substance which is present in an amount which limits the theoretical yield

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19
Q

Molar volume

A

the volume of one mole of the gas molecules under specified conditions

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20
Q

Percentage composition

A

the percentage by mass of each of the elements in a pure sample of a compound

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21
Q

Precise

A

when repeat measurements have values which are close to each other. Precise measurements have a small random error

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22
Q

Pressure

A

force per unit area in Pa
1 Pa = 1 N/m^2

23
Q

Primary standard

A

a chemical which can be weighed out accurately to make up a standard solution

24
Q

Relative atomic mass (Ar)

A

the mean mass of the atoms of an element relative to 1/12 of the mass of an atom of the isotope carbon-12

25
Q

Relative formula mass (Mr)

A

the sum of the relative atomic masses of all the atoms in a substance’s formula

26
Q

Relative molecular mass

A

the sum of the relative atomic masses of all the atoms in a substance’s molecular formula (formula mass but for molecules)

27
Q

Standard solution

A

a solution with an accurately known concentration

28
Q

Strong acids

A

acids that are fully ionised when they dissolve in water

29
Q

Titration

A

a volumetric analysis technique for finding the concentrations of solutions and to investigate the amounts of chemicals involved in reactions

30
Q

Volume

A

the amount of space taken up by a sample (m^3)

31
Q

Weak acid

A

acids that are only slightly ionised when they dissolve in water

organic acids e.g. ethanoic acid, citric acid
inorganic acids nitrous acid, chloric (I) acid

32
Q

% yield equation

A

actual yield/theoretical yield × 100

33
Q

Writing ionic equations

A
  • write out the full equation for the reaction
  • replace the formulae of ionic compounds by their separate ions
  • remove spectator ions
34
Q

Writing ionic half equations

A
  • make the electrons balance
  • combine the equations
  • cancel electrons on each side out
35
Q

Acid + metal

A

-> salt + hydrogen

36
Q

Acid + base

A

-> salt + water

37
Q

Acid + alkali

A

-> salt + water

38
Q

Acid + metal oxide

A

-> salt + water

39
Q

Acid + metal hydroxide

A

-> salt + water

40
Q

Acid + metal carbonate

A

-> salt + water + carbon dioxide

41
Q

Acid + metal hydrogencarbonate

A

-> salt + water + carbon dioxide

42
Q

Amount of substance

A

the means of counting atoms

symbol: n
unit: mol

43
Q

Mole

A

the amount of substance that contains the same number of particles as there are atoms in 12.0 g of carbon-12

44
Q

Ideal gases

A

gases which obey the gas laws perfectly

45
Q

Avogadro’s law

A

equal volumes of gases at the same temperature and pressure contain equal numbers of molecules

46
Q

mol, vol, 24 equation

A

mol = vol (dm^3)/24
or
mol = vol (cm^3)/24,000

47
Q

Concentration equations

A

mol. = conc. × vol. (dm^3)

mol. = (conc. × vol. (cm^3))/1000

conc. (mol/dm^3) = amount of solute (mol)/vol. of solution (dm^3)

conc. (g/dm^3) = mass of solute (g)/vol. of solution (dm^3)

48
Q

Preparing a standard solution

A
  • dissolve a weighted sample of a primary standard in water
  • mark the solution up to a definite volume in a graduated flask
49
Q

reasons for carrying out dilutions

A
  • to make a solution with the concentration needed for a particular experiment from a standard solution
  • to dilute an unknown sample for analysis
  • to give a concentration suitable for titration
50
Q

diluting a solution (method)

A
  • take a measured volume of the more concentrated solution with a pipette and run it into a graduated flask
  • fill the flask to the mark with purified water
51
Q

concentration volume equation

A

CaVa = CbVb

52
Q

Phenolphthalein colour change

A
  • bright pink in alkaline solutions
  • colourless in acidic/near-neutral solutions
53
Q

Methyl orange colour change

A
  • yellow in alkaline solutions
  • orange in neutral solutions
  • red in acidic solutions

A-level Chemistry (4 decks)

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