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Chemistry A Level > Chemistry Topic 5 > Flashcards

Chemistry Topic 5 Flashcards

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1
Q

What is the definition of a mole?

A

The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

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2
Q

What is relative atomic mass?

A

Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.

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3
Q

What is molar mass?

A

Molar mass is the mass in grams of 1 mole of a substance and is given the unit of g mol⁻¹.

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4
Q

What is the equation for calculating amount for pure solids, liquids, and gases?

A

amount = mass / Molar Mass

Unit of Mass: grams, Unit of amount: mol

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5
Q

What is the conversion between milligrams and grams?

A

1000 mg = 1 g

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6
Q

What is the conversion between grams and kilograms?

A

1000 g = 1 kg

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7
Q

What is the conversion between kilograms and tonnes?

A

1000 kg = 1 tonne

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8
Q

What is the equation for calculating gas volume?

A

Gas Volume (dm³) = amount x 24

This equation gives the volume of a gas at room pressure (1 atm) and room temperature (25°C).

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9
Q

How is molar mass for a compound calculated?

A

Molar mass for a compound can be calculated by adding up the mass numbers (from the periodic table) of each element in the compound.

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10
Q

What is the equation for calculating concentration in solutions?

A

Concentration = amount / volume

Unit of concentration: mol dm⁻³ or M, Unit of Volume: dm³

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11
Q

What is the equation for calculating amount in solutions?

A

amount = mass / Mr

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12
Q

What is the conversion from cm² to dm²?

A

cm² → dm² + 1000

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13
Q

What is the conversion from cm³ to m³?

A

cm³ → m³ + 1000000

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14
Q

What is the conversion from dm³ to m²?

A

dm³ → m² + 1000

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15
Q

How should answers be given in terms of significant figures?

A

Give your answers to the same number of significant figures as the number of significant figures for the data given in a question.

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16
Q

What is a hydrated salt?

A

A hydrated salt contains water of crystallisation.

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17
Q

What is the formula for hydrated copper (II) nitrate (V)?

A

Cu(NO3)2 .6H2O

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18
Q

What is the formula for anhydrous copper (II) nitrate (V)?

A

Cu(NO3)2

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19
Q

What happens when calcium sulfate xH2O is heated?

A

CaSO4.xH2O(s) → CaSO4(s) + xH2O(g)

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20
Q

What is the first step in the heating method for hydrated salts?

A

Weigh an empty clean dry crucible and lid.

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21
Q

What should be done after heating the crucible strongly?

A

Allow to cool and weigh the crucible and contents again.

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22
Q

How much hydrated calcium sulfate should be used in the experiment?

A

Add 2g of hydrated calcium sulfate to the crucible.

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23
Q

Why should large amounts of hydrated calcium sulfate not be used?

A

Decomposition is likely to be incomplete.

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24
Q

What effect does a wet crucible have on the experiment?

A

It would cause mass loss to be too large as water would be lost when heating.

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25
Q

What should be done to ensure the reaction is complete?

A

Heat the crucible again and reweigh until you reach a constant mass.

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26
Q

How is the mass of H2O calculated in the example?

A

Calculate the mass of H2O = 3.51 - 1.97 = 1.54g.

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27
Q

What is the molar mass of ZnSO4?

A

The molar mass of ZnSO4 is 161.5.

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28
Q

What is the ratio of moles of ZnSO4 to H2O in the example?

A

The ratio is 0.0122.

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29
Q

What is the molar mass of Na2SO4.xH2O?

A

The molar mass is 322.1.

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30
Q

How is the value of x calculated for Na2SO4.xH2O?

A

Molar mass xH2O = 322.1 - (23x2 + 32.1 + 16x4) = 180.

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31
Q

What is the calculated value of x for Na2SO4.xH2O?

A

X = 180/18 = 10.

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32
Q

What is the importance of the lid during the experiment?

A

The lid improves the accuracy of the experiment as it prevents loss of solid from the crucible.

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33
Q

What should be avoided in terms of sample size for accuracy?

A

Small amounts of the solid, such as 0.100 g, should not be used as errors in weighing are too high.

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34
Q

What is Avogadro’s Constant?

A

Avogadro’s Constant is the number of particles in one mole of a substance, which is 6.02 x 10^23.

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35
Q

What is a mole?

A

A mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

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36
Q

How do you calculate the number of particles?

A

Number of particles = amount of substance (in mol) x Avogadro’s constant.

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37
Q

How do you calculate the number of atoms in a sample?

A

Number of atoms = amount x 6.02 x 10^23

Example: For a 6.00 g sample of tin, amount = 6 / 118.7 = 0.05055 mol.

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38
Q

What is the formula for density?

A

Density = mass / volume.

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39
Q

How do you calculate mass from density and volume?

A

Mass = density x volume.

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40
Q

What is the density of ethanol?

A

The density of ethanol is 0.789 g/cm³.

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41
Q

How do you calculate the number of molecules of ethanol?

A

Number of molecules = amount x 6.022 x 10^23

Example: For 8.576 mol of ethanol, number of molecules = 8.576 x 6.022 x 10^23.

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42
Q

How do you calculate the amount of chloride ions in a solution?

A

Amount of chloride ions = amount x 2

Example: For 0.0100 mol of MgCl₂, amount of chloride ions = 0.0100 x 2 = 0.0200 mol.

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43
Q

How do you calculate the number of ions?

A

Number of ions = amount x 6.02 x 10^23.

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44
Q

How do you calculate the density of gold?

A

Density = mass / volume

Example: For 980 mol of gold, mass = 980 x 197 = 193060 g, volume = 10,000 cm³, density = 193060 g / 10000 cm³ = 19.3 kg/dm³.

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45
Q

What is an empirical formula?

A

An empirical formula is the simplest ratio of atoms of each element in the compound.

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46
Q

What is the first step in calculating an empirical formula?

A

Divide each mass (or % mass) by the atomic mass of the element.

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47
Q

What is the second step in calculating an empirical formula?

A

For each of the answers from step 1, divide by the smallest one of those numbers.

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48
Q

What is the third step in calculating an empirical formula?

A

Sometimes the numbers calculated in step 2 will need to be multiplied up to give whole numbers.

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49
Q

What do the whole numbers obtained represent?

A

These whole numbers will be the empirical formula.

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50
Q

How do you calculate the empirical formula for a compound containing 1.82g of K, 5.93g of I, and 2.24g of O?

A

Step 1: K=1.82/39.1=0.0465 mol, I=5.93/126.9=0.0467 mol, O=2.24/16=0.14 mol.

Step 2: Divide by the smallest number: K=0.0465/0.0465=1, I=0.0467/0.0465=1, O=0.14/0.0465=3. Empirical formula = KIO.

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51
Q

What is a molecular formula?

A

A molecular formula is the actual number of atoms of each element in the compound.

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52
Q

How can you deduce the molecular formula from the empirical formula?

A

From the relative molecular mass (Mr), work out how many times the mass of the empirical formula fits into the Mr.

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53
Q

What types of data can be used to determine an empirical formula?

A
  1. Masses of each element in the compound. 2. Percentage mass of each element in the compound.
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54
Q

Does the Mr need to be exact to determine the molecular formula?

A

No, the Mr does not need to be exact because the molecular formula will be a whole number multiple of the empirical formula.

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55
Q

What is a solution?

A

A solution is a mixture formed when a solute dissolves in a solvent.

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56
Q

What is the most common solvent used in chemistry?

A

Water is the most commonly used solvent to form aqueous solutions.

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57
Q

What can a solute be?

A

A solute can be a solid, liquid, or gas.

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58
Q

How is molar concentration calculated?

A

Molar concentration is calculated by dividing the amount in moles of the solute by the volume of the solution.

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59
Q

What is the unit of molar concentration?

A

The unit of molar concentration is mol dm³, also called molar with the symbol M.

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60
Q

What is the formula for concentration?

A

Concentration = amount / volume

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61
Q

What is the volume measurement in dm?

A

The volume is measured in dm³.

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62
Q

How many cm³ are in 1 m³?

A

1 m³ is equivalent to 1,000,000 cm³.

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63
Q

How do you convert m³ into dm³?

A

To convert m³ into dm³, multiply by 1000.

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64
Q

What is the relationship between dm and m²?

A

1 dm = 1000 cm².

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65
Q

What is the relationship between cm³ and dm³?

A

To convert cm³ into dm³, divide by 1000.

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66
Q

How do you calculate the concentration of a solution?

A

Concentration = amount / volume

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67
Q

What is the formula to find amount from mass?

A

Amount = mass / Mr

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68
Q

How do you calculate the concentration of a solution made by dissolving 5.00 g of Na₂CO₃ in 250 cm³ of water?

A

Concentration = 0.0472 / 0.25 = 0.189 mol dm⁻³

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69
Q

How do you calculate the concentration of a solution made by dissolving 10 kg of Na₂CO₃ in 0.50 m³ of water?

A

Concentration = 94.2 / 500 = 0.19 mol dm⁻³

70
Q

What is mass concentration?

A

The concentration of a solution measured in terms of mass of solute per volume of solution.

Mass concentration = mass/volume

71
Q

What are the units of mass concentration?

A

Unit of mass concentration: g/dm³

Unit of mass: g, Unit of volume: dm³

72
Q

What happens when soluble ionic solids dissolve in water?

A

They dissociate into separate ions, leading to differing concentrations of ions and solute.

Example: NaCl → Na⁺ + Cl⁻

73
Q

What is the concentration of sodium chloride when 5.86 g is dissolved in 1 dm³ of water?

A

The concentration of sodium chloride solution would be 0.1 mol/dm³.

The concentration of sodium ions is 0.1 mol/dm³ and chloride ions is also 0.1 mol/dm³.

74
Q

What is the concentration of magnesium chloride when 9.53 g is dissolved in 1 dm³ of water?

A

The concentration of magnesium chloride solution would be 0.1 mol/dm³.

The concentration of magnesium ions is 0.1 mol/dm³ and chloride ions is 0.2 mol/dm³.

75
Q

What is the formula to convert concentration from mol/dm³ to g/dm³?

A

conc in g/dm³ = conc in mol/dm³ x Mr of the substance.

76
Q

What is the process to prepare a solution?

A

Weigh the sample, transfer to a beaker, add distilled water, stir, and make up to the mark in a volumetric flask.

Ensure uniform solution by inverting the flask several times.

77
Q

What is the chemical equation for the dissociation of sodium chloride?

A

NaCl(s) → Na⁺(aq) + Cl⁻(aq)

Concentrations: 0.1 mol Na⁺ and 0.1 mol Cl⁻.

78
Q

What is the chemical equation for the dissociation of magnesium chloride?

A

MgCl₂(s) → Mg²⁺(aq) + 2Cl⁻(aq)

Concentrations: 0.1 mol Mg²⁺ and 0.2 mol Cl⁻.

79
Q

How should the meniscus be positioned when filling a volumetric flask?

A

Fill so the bottom of the meniscus sits on the line on the neck of the flask.

80
Q

What is the volume of water added to dilute 5.00 cm of 1.00 mol dm-3 hydrochloric acid?

A

Volume of water added = 100 - 5 = 95 cm³ = 0.1 dm³ = 100 cm³

81
Q

How is the new volume calculated?

A

New volume = amount lconc = 0.005 = 1.00 x 0.005

82
Q

How do you calculate the amount in mol of the original solution?

A

Amount in mol original solution = conc x vol

83
Q

What is the new diluted concentration if 50 cm of water are added to 150 cm of a 0.20 mol dm-3 NaOH solution?

A

New diluted concentration = 0.20 x 0.150

84
Q

What is the formula for calculating the new diluted volume?

A

New diluted volume = original volume of solution added + volume of water added

85
Q

What is the relationship between original and diluted concentrations and volumes?

A

Original volume x original concentration = new diluted volume x new diluted concentration

86
Q

What happens to the amount of moles when diluting a solution?

A

Diluting a solution will not change the amount of moles of solute present but increase the volume of solution.

87
Q

What should you do to ensure a uniform solution when diluting?

A

Invert flask several times to ensure uniform solution.

88
Q

What tool should be used to make up to the mark in a volumetric flask?

A

Use a teat pipette to make up to the mark.

89
Q

Why is using a volumetric pipette more accurate than a measuring cylinder?

A

Using a volumetric pipette is more accurate than a measuring cylinder because it has a smaller uncertainty.

90
Q

What is the first step in diluting a solution?

A

Pipette 25 cm³ of original solution into a 250 cm³ volumetric flask.

91
Q

What is the ideal gas equation?

A

The ideal gas equation applies to all gases and mixtures of gases.

92
Q

What does ‘n’ represent in the ideal gas equation for a mixture of gases?

A

‘n’ represents the total moles of all gases in the mixture.

93
Q

What is a common problem students face with the ideal gas equation?

A

Choosing and converting to the correct units.

94
Q

What is the formula for calculating moles using the ideal gas equation?

A

moles = PV/RT

95
Q

How do you calculate the mass of a gas?

A

Mass = amount x Mr

96
Q

What is the value of R in the ideal gas equation?

A

R = 8.31 J K⁻¹ mol⁻¹

97
Q

How do you convert pressure from kPa to Pa?

A

100 kPa = 100,000 Pa

98
Q

How do you convert Celsius to Kelvin?

A

To convert °C to K, add 273.

99
Q

What is the volume of gas measured in for the ideal gas equation?

A

Volume is measured in m³.

100
Q

What are potential errors in using a gas syringe?

A

Gas escapes before bung inserted, syringe sticks.

101
Q

What should be noted when recording the volume of a gas?

A

The temperature and pressure of the room.

102
Q

What is the unit of temperature in the ideal gas equation?

A

The unit of temperature (T) is Kelvin (K).

103
Q

What is the calculated molar mass (Mr) of a volatile liquid in Example 18?

A

Mr = 53.4 g mol⁻¹

104
Q

What is the volume of gas in Example 17?

A

Volume = 500 cm³ = 0.0005 m³

105
Q

What is the volume of gas in Example 18?

A

Volume = 80 cm³ = 0.00008 m³

106
Q

What is necessary in quality control for testing samples?

A

It is necessary to do titrations/testing on several samples.

107
Q

What should be considered when titrating a mixture?

A

The amount/concentration of the chemical being tested may vary between samples.

108
Q

What should be recorded during titrations?

A

Record titre volumes to 2dp (0.05 cm) and both initial and final readings.

109
Q

How should results be recorded?

A

Results should be clearly recorded in a table.

110
Q

What indicates that titration results are accurate?

A

If 2 or 3 values are within 0.10 cm3, then the results are considered accurate.

111
Q

What should be done with concordant titre results?

A

Only make an average of the concordant titre results.

112
Q

What can lead to errors during titration?

A

If the jet space in the burette is not filled properly prior to commencing the titration.

113
Q

What should be used to wash out conical flasks?

A

Only distilled water should be used.

114
Q

What happens to the pipette after use?

A

There will be a small amount of the liquid left in the pipette when emptied.

115
Q

What is the preferred type of flask for titration?

A

A conical flask is used in preference to a beaker.

116
Q

What is the purpose of using a white tile during titration?

A

To help observe the colour change.

117
Q

What indicators are used for acid-base titrations?

A

Methyl orange (yellow to red) and phenolphthalein (pink to colourless).

118
Q

What safety precautions should be taken during titration?

A

Wear eye protection and gloves, and treat unknown substances as potentially toxic.

119
Q

What should be done immediately if a spillage occurs?

A

Immediately wash affected parts.

120
Q

What should be done with the burette before adding acid?

A

Make sure the jet space in the burette is filled with acid.

121
Q

What should be done with the pipette before use?

A

Rinse the pipette with alkali.

122
Q

What are acids and alkalis considered at low concentrations?

A

Acids and alkalis are irritants and potentially corrosive.

123
Q

What is the formula to calculate percentage difference?

A

% = (difference / actual value) x 100

124
Q

How do you calculate the difference in values?

A

difference = actual value - calculated value

125
Q

What is the percentage difference if the calculated Mr is 203 and the real value is 214?

A

5.41%

126
Q

What does a discrepancy in results indicate?

A

It can be explained by the sensitivity of the equipment.

127
Q

What happens if % uncertainty due to apparatus is greater than the actual value?

A

There is a percentage difference between the actual value and the calculated value.

128
Q

What happens if % uncertainty due to apparatus is less than the actual value?

A

There is no percentage difference between the actual value and the calculated value.

129
Q

How can you reduce % uncertainty in weighing a solid?

A

By weighing a larger mass.

130
Q

What is one method to reduce uncertainty in a burette reading?

A

Make the titre a larger volume by increasing the volume and concentration of the substance.

131
Q

What is a way to reduce uncertainties in titration?

A

Replace measuring cylinders with pipettes or burettes.

132
Q

How do you calculate maximum percentage apparatus uncertainty?

A

% uncertainty = (uncertainty / measurement) x 100

133
Q

What is the uncertainty for a 25 cm pipette?

A

±0.1 cm

134
Q

What is the uncertainty for a burette reading?

A

±0.05 cm

135
Q

What is the uncertainty of a measurement using a balance?

A

±0.001 g

136
Q

What is the uncertainty of a reading based on one judgement?

A

At least ±0.5 of the smallest scale reading.

137
Q

What is the uncertainty of a reading based on two judgements?

A

At least ±1 of the smallest scale reading.

138
Q

What is a hazard?

A

A hazard is a substance or procedure that has the potential to do harm.

139
Q

What are typical hazards in the laboratory?

A

Typical hazards are toxic, flammable, harmful, irritant, corrosive, oxidizing, and carcinogenic.

140
Q

How can we minimize the risk of irritants?

A

For irritants like dilute acids and alkalis, wear goggles.

141
Q

What precautions should be taken with corrosive substances?

A

For corrosive substances like stronger acids and alkalis, wear goggles.

142
Q

What should be done to prevent flammable hazards?

A

Keep flammable substances away from naked flames.

143
Q

What is risk in the context of hazardous substances?

A

Risk is the probability or chance that harm will result from the use of a hazardous substance or procedure.

144
Q

What precautions should be taken with toxic substances?

A

Wear gloves, avoid skin contact, and wash hands after use.

145
Q

What should be done with oxidizing materials?

A

Keep oxidizing materials away from flammable or easily oxidized materials.

146
Q

How do hazardous substances in low concentrations compare to pure substances?

A

Hazardous substances in low concentrations or amounts will not pose the same risks as the pure substance.

147
Q

What substances can neutralize excess acid safely?

A

Sodium hydrogen carbonate (NaHCO₃) and calcium carbonate (CaCO₃) are good for neutralizing excess acid because they are not corrosive and will not cause a hazard if used in excess.

148
Q

What is a suitable substance for dealing with excess stomach acid?

A

Magnesium hydroxide is suitable for dealing with excess stomach acid as it has low solubility in water and is only weakly alkaline.

149
Q

What is a key difference between magnesium hydroxide and sodium hydroxide?

A

Magnesium hydroxide is not corrosive or dangerous to drink, unlike the strong alkali sodium hydroxide.

150
Q

What are metal displacement reactions?

A

More reactive metals will displace less reactive metals from their compounds.

151
Q

Provide an example of a metal displacement reaction.

A

Mg + CuSO₄ → Cu + MgSO₄

Ionic: Mg + Cu²⁺ → Cu + Mg²⁺

152
Q

What are halogen displacement reactions?

A

A halogen that is a strong oxidizing agent will displace a halogen that has a lower oxidizing power from one of its compounds.

153
Q

Provide an example of a halogen displacement reaction.

A

Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq)

154
Q

What are precipitation reactions?

A

Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed.

155
Q

Provide an example of a precipitation reaction.

A

Lead nitrate (aq) + sodium chloride (aq) → lead chloride (s) + sodium nitrate (aq)

156
Q

What is a precipitate?

A

A precipitate is a solid formed in a precipitation reaction.

157
Q

How are insoluble salts typically removed?

A

The salt would be removed by filtration, washed with distilled water to remove soluble impurities, and then dried on filter paper.

158
Q

What is the purpose of writing ionic equations for precipitation reactions?

A

Ionic equations only show the ions that are reacting and leave out spectator ions.

159
Q

What are spectator ions?

A

Spectator ions are ions that are not changing state or oxidation number.

160
Q

Provide an example of writing an ionic equation for a precipitation reaction.

A

Pb(NO₃)₂(aq) + 2NaCl(aq) → PbCl₂(s) + 2NaNO₃(aq)

Ionic: Pb²⁺(aq) + 2Cl⁻(aq) → PbCl₂(s)

161
Q

What are metal displacement reactions?

A

More reactive metals will displace less reactive metals from their compounds.

162
Q

Provide an example of a metal displacement reaction.

A

Mg + CuSO₄ → Cu + MgSO₄

Ionic: Mg + Cu²⁺ → Cu + Mg²⁺

163
Q

What are halogen displacement reactions?

A

A halogen that is a strong oxidizing agent will displace a halogen that has a lower oxidizing power from one of its compounds.

164
Q

Provide an example of a halogen displacement reaction.

A

Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq)

165
Q

What are precipitation reactions?

A

Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed.

166
Q

Provide an example of a precipitation reaction.

A

Lead nitrate (aq) + sodium chloride (aq) → lead chloride (s) + sodium nitrate (aq)

167
Q

What is a precipitate?

A

A precipitate is a solid formed in a precipitation reaction.

168
Q

How are insoluble salts typically removed?

A

The salt would be removed by filtration, washed with distilled water to remove soluble impurities, and then dried on filter paper.

169
Q

What is the purpose of writing ionic equations for precipitation reactions?

A

Ionic equations only show the ions that are reacting and leave out spectator ions.

170
Q

What are spectator ions?

A

Spectator ions are ions that are not changing state or oxidation number.

171
Q

Provide an example of writing an ionic equation for a precipitation reaction.

A

Pb(NO₃)₂(aq) + 2NaCl(aq) → PbCl₂(s) + 2NaNO₃(aq)

Ionic: Pb²⁺(aq) + 2Cl⁻(aq) → PbCl₂(s)

Chemistry A Level (3 decks)

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