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Chemistry A-Level > 3.1.2 Amount of substance > Flashcards

3.1.2 Amount of substance Flashcards

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1
Q

What does chemical formulae show?

A
  • The atoms/ions present in a compound or molecule as well as number of each atom/ion.
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2
Q

What is the chemical formula of water and what does it show?

A
  • H2O.
  • Water molecule contains 2 hydrogen molecules and 1 oxygen molecule.
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3
Q

What can the formula of familiar and unfamiliar ionic compounds be determined from?

A
  • Charges on ions.
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4
Q

What is the charge and formula of sulfate?

A
  • SO4.
  • 2-.
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5
Q

What is the charge and formula of nitrate?

A
  • NO3.
  • 1-.
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6
Q

What is the charge and formula of carbonate?

A
  • CO3.
  • 2-.
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7
Q

What is the charge and formula of hydroxide?

A
  • OH.
  • 1-.
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8
Q

What is the charge and formula of ammonium?

A
  • NH4.
  • 1+.
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9
Q

What is the formula for methane?

A
  • CH4.
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10
Q

What is the formula of ammonia?

A
  • NH3.
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11
Q

What is the formula of hydrogen peroxide?

A
  • H2O2.
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12
Q

What is the empirical formula?

A
  • Shows the simplest whole number ratio of atoms of each element in a compound.
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13
Q

What is the empirical formula used for?

A
  • Ionic compounds.
  • Macromolecules (Giant covalent molecules).
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14
Q

What is an example of three chemicals that have the same empirical formula but are different chemicals

A
  • Glucose, found in sweet tasting foods.
  • Ethanoic acid, found in vinegar.
  • Formaldehyde, pungent substance used as a preservative in medical labs.
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15
Q

What is a molecular formula?

A
  • Actual number of atoms in each element in one molecule of the substance.
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16
Q

What is the molecular formula used for?

A
  • All molecular (simple) covalent substances.
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17
Q

What are some examples of diatomic molecules?

A
  • Hydrogen.
  • Nitrogen.
  • Oxygen.
  • Flourine.
  • Chlorine.
  • Bromine.
  • Iodine.
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18
Q

What molecules do sulfur and phosphorous exist as?

A
  • S8.
  • P4.
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19
Q

Is the molecular formula of a covalent substance the same as the empirical formula?

A
  • May be the same or may be different.
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20
Q

What does a balanced equation show?

A
  • Rearrangement of atoms in a chemical reaction.
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21
Q

What is an ionic equation?

A
  • Balanced equation written leaving out ions which do not take part in the reaction.
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22
Q

What are ions called that don’t take part in the ionic equation?

A
  • Spectator ions.
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23
Q

How to work out which ions should be included in the ionic equation?

A
  • Write ions present in each ionic substance in equation.
  • If ion appears on both sides of equation (in same state) then shouldn’t be included.
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24
Q

What to do with covalent substances in an ionic equation?

A
  • Should be left as they are.
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25
Q

What is the charge of a cation?

A
  • Positive.
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26
Q

What is the charge of an anion?

A
  • Negative.
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27
Q

What is avagadro’s constant number?

A
  • 6.022 X 10^23.
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28
Q

What letter usually represents avagadro’s constant?

A
  • Capital letter L.
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29
Q

How is avagadro’s constant defined?

A
  • Number of atoms in 12g of Carbon-12.
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29
Q

What is avagadro’s constant used for?

A
  • To get a measurable mass.
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30
Q

What is a mole of substance?

A
  • The amount of substance that contains the number of particles (atoms, ions, molecules, e-) equal to avagadro’s constant.
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31
Q

What does the term “amount” mean?

A
  • Quantity measured in moles.
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32
Q

For any substance, what is the mass of one mole?

A
  • Total of the relative atomic masses (Ar) of all the atoms that make up the substance.
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33
Q

What is the total of the relative atomic masses in any substance referred to as?

A
  • Relative molecular mass (Mr).
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34
Q

What can Relative Formula Mass (RFM) be used for?

A
  • Used for ionic compounds.
  • But Mr is accepted for all compounds.
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35
Q

What does molar mass mean and what are the units for this?

A
  • Mass of one mole.
  • g/mol or g mol-1.
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36
Q

What is the equation for calculating Moles from Mass?

A
  • n = m / Mr.
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36
Q

How can moles be calculated from mass?

A
  • Moles = mass / Mr.
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37
Q

What is the meaning of avagadro’s constant?

A
  • Number of particles in one mole.
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38
Q

What is the equation of moles in terms of avagadro’s constant?

A
  • Moles = number of particles / Avagadro’s constant.
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39
Q

What is the equation for the number of particles?

A
  • Number of particles = n X L.
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40
Q

What does quantitatively mean?

A
  • Measuring and calculating quantities.
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41
Q

What is theoretical yield?

A
  • Calculated amount in moles of product formed or calculated mass of product formed.
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42
Q

What is the actual yield and how is this obtained?

A
  • Moles or mass obtained from reaction.
  • Obtained experimentally.
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43
Q

What is the percentage yield?

A
  • Percentage of theoretical yield achieved in reaction.
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44
Q

What is the equation for percentage yield?

A
  • Percentage yield = (actual yield / theoretical yield) X 100.
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45
Q

What are actual yield and theoretical yield usually measured in?

A
  • Moles or mass but usually in grams.
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46
Q

What are the reasons that percentage yield is not 100%?

A
  • Loss by mechanical transfer.
  • Loss by separating technique.
  • Side reactions occurring.
  • Reaction not complete.
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47
Q

Do drugs produced in industry ever have a percentage yield of 100%?

A
  • No.
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48
Q

What is the overall percentage yield for production of the drug?

A
  • Sum of % yields of individual steps.
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49
Q

How does % yield relate to drug price?

A
  • Many step mean very low % yield.
  • Can contribute to huge cost of some drugs.
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50
Q

What is a solution made up of?

A
  • Solute dissolved in a solvent.
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51
Q

What can the number of moles of solvent in a solution be dissolved from?

A
  • Solution volume used and conc of solution.
52
Q

What is the equation for finding the amount of moles of solute dissolved in a solution?

A
  • Amount (in moles) = (solution volume (cm^3) X concentration (mol dm^-3)) / 1000.
53
Q

What is the symbol equation for finding the amount of moles of solute dissolved in a solution?

A
  • n = (v X c) / 1000.
54
Q

What are the units for solution volume in solution calculations?

A
  • cm^3.
55
Q

What are the units for concentration in solution calculations?

A
  • mol dm^-3.
56
Q

How can the concentration of a solution formed be calculated?

A
  • Mass of substance which reacts, ratios of balanced equation + final volume of solution.
57
Q

How can you calculate the volume of solution required to react w a solid or another solution?

A
  • c = (nX1000) / v.
58
Q

What information will you be given in a question where you have to calculate the mass or identity of a solid reacting with a solution?

A
  • Information in solution + asked to calculate the amount, in moles, of solute present in the solution.
  • Moles = mass x mr from mass and moles.
  • Can then be identified from Mr.
59
Q

What solutions are used in neutralisation reactions?

A
  • Acid neutralises alkali.
60
Q

What are properties of acids and alkalis?

A
  • Most often colourless solutions + indicator can be used to determine end point / neutralisation.
61
Q

What type of method is a titration?

A
  • Volumetric analysis.
62
Q

How to carry out a titration?

A
  • One solution is placed in a burette the other in a conical flask.
  • Indicator added to conical flask.
  • Solution in burette is added to conical flask.
  • Indicator shows end point when reaction is complete.
63
Q

What are the pieces of apparatus used in titrations?

A
  • Burette.
  • Pipette w safety filler.
  • Volumetric flask.
  • Conical flask.
64
Q

What steps are there in preparing a burette?

A
  • Rinse burette w deionised / distilled water.
  • Ensure water flows through jet.
  • Discard the water.
  • Rise burette w solution it will be filled w.
  • Ensure solution flows through the jet.
  • Discard the solution.
  • Charge (fill) solution that it will be filled w.
65
Q

How should a burette be read?

A
  • At eye level using the lower meniscus.
66
Q

What hand should be used for what in titrations?

A
  • Right handed then use tap w left hand to allow right hand to swirl mixture.
67
Q

How to prepare a pipette for use in a titration?

A
  • Use pipette filler to rinse pipette w deionised water.
  • Discard the water.
  • Rise pipette w solution.
  • Discard this solution.
68
Q

How to use a pipette?

A
  • Pipette filler attached to top of pipette.
  • Pipette placed in solution + suction applied to draw solution up.
  • Solution drawn up above line on pipette.
  • Solution released until meniscus sits on line.
69
Q

What are the volumes measured using a pipette?

A
  • 10 or 25 cm^3.
70
Q

Why is it vital to know the exact volume of solution in volumetric work?

A
  • Exact vol of conc of solution means we know how many moles of dissolved substance are present in conical flask.
71
Q

Why are conical flasks used in titrations?

A
  • Swirled easily to mix reactants.
  • Sloped sides prevent any solution spitting out when added.
72
Q

How should the conical flask be prepped for titrations?

A
  • Rinsed out w deionised water before use.
  • Should be completely dry before use as exact volume of solution added contains exact number of moles of solute.
  • Extra deionised water does not add to the number of moles of solute.
73
Q

What are volumetric flasks used for?

A
  • Diluting a solution before titration.
  • Used when preparing a solution of a solid.
74
Q

What is the dilution factor?

A
  • Amount original solution is diluted by.
75
Q

How is the dilution factor calculated?

A
  • Dividing new total vol by vol of original solution put into the mixture.
76
Q

How to carry out the dilution of a solution?

A
  • Pipette 25cm^3 of original solution into volumetric flask.
  • Add deionised water just below line.
  • Use dropping pipette so lower meniscus is on line.
  • Stopper the flask + invert to mix thoroughly.
77
Q

How to prepare a solution from a mass of solid?

A
  • Weigh accurate mass of solid in weighing boat the dilute w deionised water.
  • Stir w glass rod and rise weighing boat into beaker.
  • Place funnel on top of volumetric flask + pour prepared solution down glass rod into funnel.
  • Rinse glass rod into funnel.
  • Rinse funnel w deionised water.
  • Remove funnel + add water until just below line.
  • Use dropping pipette to add until lower meniscus touches line.
  • Stopper the flask + invert to mix thoroughly.
78
Q

What are the major points in carrying out a titration?

A
  • Use a retort stand and a burette clamp to hold burette firmly in place.
  • Left hand to operate tap.
  • Use funnel to transfer solution into burette - remember to remove when making initial reading.
  • Place white tile under conical flask.
79
Q

What is the 1st titration and what should it show?

A
  • 1st rough titration.
  • Should have a higher value than the more accurate subsequent titrations.
80
Q

How should the solution be added near the end-point of the titration?

A
  • Drop-wise.
81
Q

What do values need to be in order to calculate the average titre?

A
  • Concordant.
  • Within 0.10cm^3 of each other.
82
Q

What is a standard solution and what are they used in?

A
  • A solution of a known conc.
  • Used in volumetric analysis.
83
Q

What value is the graduated volume of a burette?

A
  • 50cm^3.
84
Q

What resolution should the titration readings of a burette be?

A
  • 0.05cm^3.
85
Q

How many titrations should be carried out?

A
  • Until two results are obtained that are within 0.10cm^3 of each other.
86
Q

How must the average titre be stated?

A
  • To 2 dp.
  • With units.
87
Q

What are the units of volume in?

A
  • cm^3.
88
Q

What are the units of concentration?

A
  • mol dm^-3.
89
Q

What is 1 dm^3 the same as?

A
  • A litre.
90
Q

What is a 1M solution the same as?

A
  • A solution of 1 mol dm^-3.
91
Q

How can g dm^-3 be calculated?

A
  • Multiplying conc of solution by Mr.
92
Q

What is the percentage error caluclated from?

A
  • Measurements obtained from different pieces of apparatus - resolution.
93
Q

How is % error calculated?

A
  • (error/volume) X 100.
94
Q

What are the factors affecting the choice of what indicator to use in a titration?

A
  • The type of acid and base used.
95
Q

What type of acids and bases are phenolphthalein used for?

A
  • Strong acid, strong base.
  • Weak acid, strong base.
96
Q

What types of acids and bases are Methyl orange used for?

A
  • String acid, strong base.
  • Strong acid, weak base.
97
Q

What colour is phenolphthalein in acidic, neutral and alkaline solutions?

A
  • Acid –> colourless.
  • Neutral –> colourless.
  • Alkaline –> pink.
98
Q

What colour is methyl orange in acidic, neutral and alkaline solutions?

A
  • Acid - red.
    -Neutral –> orange.
  • Alkaline –> yellow.
99
Q

What are monoprotic acids?

A
  • Acid which can release 1 mole of H+ ions per mole of acid.
100
Q

What are the three main monoprotic acids?

A
  • Hydrochloric acid (HCl).
  • Nitric acid (HNO3).
  • Ethanoic acid (CH3COOH).
101
Q

Which acids are strong acids?

A
  • Hydrochloric acid.
  • Nitric acid.
102
Q

Which acid is a weak acid?

A
  • Ethanoic acid.
103
Q

What are two examples of strong bases?

A
  • Sodium hydroxide (NaOH).
  • Potassium hydroxide (KOH).
104
Q

What is an example of a weak base?

A
  • Ammonia (NH3).
105
Q

What is an example of a diprotic acid?

A
  • Sulfuric acid (H2SO4).
106
Q

What is a back titration?

A
  • Reacting an insoluble solid w a known excess of HCl.
  • Excess acid then titrated using standard solution of an alkali.
107
Q

What are the steps in a back titration?

A
  • Known mass of insoluble solid.
  • Add excess known vol + conc of HCl.
  • Place solution in volumetric flask + add deionised water to make 250.0 cm^3.
  • Take 25.0 cm^3 from diluted solution + add a few drops of indicator.
  • Add 0.1M NaOH from burette until indicator just changes colour.
108
Q

What is the molar volume (Vm) of gas at room temp + pressure?

A
  • 1 mole of gas occupies 24 dm^3.
109
Q

What is the equation for working out the number moles of gas related to the volume of gas?

A
  • n = gas volume / Vm.
  • Vm = 240000 where vol is in cm^3.
    Vm = 24 when vol is in dm^3.
110
Q

How can gas vol be calculated?

A
  • Gas volume (V) = n X Vm.
111
Q

What does the ideal gas equation show?

A
  • As pressure increases at constant temp, vol of gas decreases.
  • As temp increases at constant pressure, vol increases.
  • Amount of moles in gas is directly proportional to its volume.
112
Q

what is the ideal gas equation?

A
  • pV = nRT.
113
Q

What are the different parts of the ideal gas equation and what are their units?

A
  • p = pressure (pascals).
  • V = gas vol (m^3).
  • n = number of moles of gas.
  • R = gas constant (8.31 J K^-1 mol^-1).
  • T = temp (kelvin).
114
Q

What is the absolute zero for temp?

A
  • When temp reaches 0K.
  • All movement of particles stops.
115
Q

How to convert from °C to K?

A
  • Add 273.
116
Q

What is the unit of pascals equivilent to?

A
  • 1 Pa = 1 Nm^-2
117
Q

How to convert to m^3 for use of the ideal gas equation?

A
  • 1 m^3 = 1000 dm^3 = 1 000 000 cm^3.
118
Q

hat does the ideal gas equation allow for conversion of?

A
  • Allows for conversion between moles of gas and volume at a particular pressure + temp.
119
Q

What is the empirical formula?

A
  • Simplest whole number ratio of atoms of each element in a compound.
120
Q

What is the molecular formula?

A
  • Actual number of atoms of each element in a compound.
121
Q

How does the molecular formula relate to the empirical formula?

A
  • Molecular formula is a simple multiple of the empirical formula.
122
Q

What are simple compounds formed from?

A
  • 2 elements.
123
Q

How can you determine the empirical formula?

A
  • By using the percentage information by mass.
124
Q

What are the steps taken to determine the empirical formula?

A
  • Amount of moles converted to a simple ratio.
  • Divide the moles by the lowest number if moles!!!
125
Q

How can you determine the degree of hydration by heating to a constant mass?

A
  • Use mass of anhydrous compound to determine amount of water lost.
  • Then use moles calculation to work out empirical formula.
  • Divide moles through by smallest amount of moles!!!
126
Q

What is atom economy?

A
  • Measure of how efficiently atoms in reactants are used in a chemical reaction.
127
Q

How can percentage atom economy be calculated?

A
  • % atom economy = (Mr of desired product/sum of Mr of all reactants) X 100.
128
Q

What do chemists use percentage yield for?

A
  • To determine efficiency of chemical synthesis process.
129
Q

What does it mean if a reaction has a high % yield but low atom economy?

A
  • Other products in reaction would be waste.
  • With high % yield there are more of them.

Chemistry A-Level (5 decks)

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