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Chem Exam Main Topics Flashcards

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1
Q

What is Polymerisation?

A

When alkenes join together

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2
Q

When alkenes join together, what happens to their double bond?

A

Their double bond opens up

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3
Q

How do you find the monomer used to make an addition polymer?

A

You find the repeat unit, add a double bond between the carbon atoms and remove the single bonds from each end

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4
Q

What do all alkenes have?

A

At least one C=C double bond

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5
Q

What are single covalent bonds in organic molecules?

A

Sigma bonds

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6
Q

When are sigma bonds formed?

A

When two orbitals overlap in a straight line, in the space between 2 atoms, giving the highest possible electron density between the 2 atoms

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7
Q

Why are sigma bonds the strongest type of covalent bond?

A

There is a high electron density between the nuclei so there is strong electrostatic attraction between the nuclei and shared pair of electrons, so there is high bond enthalpy

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8
Q

What is a double bond made up of?

A

A sigma bond and a pi bond

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9
Q

How is a pi-bond formed?

A

When 2 lobes of p-orbitals overlap sideways

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10
Q

In a pi-bond, how is the electron density spread out?

A

Above and below the nuclei

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11
Q

Why do pi-bonds have lower bond enthalpy than sigma bonds?

A

The electron density in a pi-bond is spread out above and below the nuclei, causing the electrostatic attraction between the nuclei and shared pair of electrons to be weaker in pi-bonds

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12
Q

In alkenes, what does the C=C bond contain?

A

A pi bond and a sigma bond

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13
Q

What causes alkenes to form sterioisomers?

A

The restricted motion around the C=C double bond

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14
Q

Ethene is said to be ‘completely planar’, what does this mean?

A

All the H-C-H bond angles are all the same. The atoms all lie in the same plane

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15
Q

What are sterioisomers?

A

Molecules which have the same structural formula, but different arrangement in space

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16
Q

When do stereoisomers occur?

A

When two double bonded carbon atoms each have 2 different groups or atoms attatched to them

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17
Q

What is the ‘E-isomer’?

A

The isomer which has the same groups positioned across the double bond

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18
Q

What is the ‘Z-isomer’?

A

The isomer which has the same groups positioned either both above or both below the double bond

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19
Q

What happens to the E/Z system when all the groups are different around the C=C double bond?

A

You assign each group/atom a number of priority. The 2 atoms/ groups with the highest mass number are labelled 1, whilst the 2 atoms or groups with the lowest mass number are labelled 2.

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20
Q

When do you use the cis-trans naming system?

A

If the carbon atoms have at least one group in common

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21
Q

When do you use the ‘cis’ naming system?

A

The the groups are on the same side of the double bond

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22
Q

When do you use the ‘trans’ naming system?

A

When the same groups are on opposite sides of the double bond

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23
Q

When does the cis-trans naming system not work?

A

When the carbon atoms have totally different groups attached to them

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24
Q

What happens in an alkene electrophilic reaction?

A

The alkene double bond opens up and atoms are added to the carbon atoms

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25
Q

Why do electrophilic addition reactions happen to alkenes?

A

Because the carbon double bond has plenty of electrons

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26
Q

What are electrophiles?

A

Electron pair acceptors-attracted to areas where there are lots of electrons

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27
Q

What are the 2 types of electrophiles?

A

Positively charged ions and polar molecules (as the delta+ is attracted to electrons)

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28
Q

What is required for the reaction between ethene and hydrogen?

A

A nickel catalyst, 150 degrees

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29
Q

What happens when halogens react with alkenes?

A

They form dihalogenoalkanes

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30
Q

What happens when you shake an alkene with bromine water?

A

The brown bromine water is decolourised as bromine is added across the double bond to form dibromoalkane

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31
Q

How do you form ethanol from ethene?

A

React ethene with steam with a solid phosphoric acid catalyst, 300 degrees and a pressure of 60-70 atm.

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32
Q

What colour is acidified potassium manganate?

A

Purple

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33
Q

What happens when you shake an alkene with acidified potassium managnate?

A

The purple solution is decolourised, and the alkene is oxidised to form a diol.

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34
Q

What is formed when alkenes react with hydrogen halides?

A

A halogenoalkane

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35
Q

What happens when hydrogen halides are added to an unsymmetrical alkene?

A

There are two possible products

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36
Q

What makes a carbocation more stable?

A

Having more alkyl groups attached to it

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37
Q

Why do alkyl groups attached to a carbocation make it more stable?

A

Because the alkyl groups feed electrons towards the positive charge

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38
Q

What is more likely to form, the stable carbocation or the unstable carbocation?

A

The stable carbocation

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39
Q

What is Markownikoff’s law?

A

The major product from an addition reaction of a hydrogen halide(HX) to an unsymmetrical alkene is the one where the hydrogen adds to the carbon with the most hydrogens already attached

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40
Q

What is the first way of determining whether an organic substance is an alkene?

A

Add bromine water to the substance and it will turn from brown to colourless

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41
Q

What is the second way of determining whether an organic substance is an alkene?

A

Add acidified potassium manganate (purple) and shake which will decolourise the manganate as a diol is formed

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42
Q

How do you test for a carbonyl group?

A

Add small amount of 2,4-dinitrophenylhydrazine and a yellow/orange precipitate will slowly form

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43
Q

What is Brady’s reagent?

A

2,4-dinitrophenylhydrazine dissolved in methanol and conc sulfuric acid

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44
Q

What is the main difference between aldehydes and ketones?

A

Aldehydes are easily oxidised, whilst ketones aren’t

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45
Q

How do you make Tollens’ reagent?

A

Dissolve silver nitrate in aqueous ammonia

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46
Q

What happens when an aldehyde is heated in a test tube with Tollens’ reagent?

A

A silver mirror is formed

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47
Q

What is the ionic equation of the formation of a silver mirror?

A

Ag(NH3)2 + +e- —-> Ag +2NH3

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48
Q

What is Fehling’s solution?

A

A blue solution of complexed copper (2) ions dissolved in NaOH

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49
Q

What happens when Fehling’s solution is heated with an aldehyde?

A

The blue copper(2) ions are reduced to a brick-red precipitate of copper(1) oxide. Cu2+ +e- –> Cu+

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50
Q

What is Benedict’s solution?

A

The same as Fehling’s solution, however the copper (2) ions are dissolved in sodium carbonate instead of sodium hydroxide

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51
Q

What happens when Benedict’s solution is heated with an aldehyde?

A

The blue copper (2) ions are reduced to a brick-red precipitate of copper(1) oxide

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52
Q

What happens when you heat an aldehyde with acidified dichromate ions?

A

A carboxylic acid is formed

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53
Q

When an aldehyde is oxidised by acidified dichromate ions, what is the colour change of the dichromate ions?

A

Orange to green

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54
Q

If something contains a methyl carbonyl group, what must it be?

A

Either ethanal or a ketone with at least one methyl group

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55
Q

What happens when carbonyls which contain a methyl carbonyl group are heated with iodine in the presence of an alkali?

A

If there is a methyl carbonyl group a yellow precipitate of triidomethane will form and an antiseptic smell

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56
Q

How do you test for primary or secondary alcohols?

A

Warm with potassium dichromate and add dilute sulfuric acid and the substance will change from orange to green

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57
Q

How do you test for a carboxylic acid?

A

Add some sodium carbonate solution and carbon dioxide will be formed

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58
Q

How do you test for an acyl chloride?

A

Add substance to water and hydrogen chloride will be formed

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59
Q

What happens when phenol is added to sodium carbonate solution?

A

It dissolves without the evolution of carbon dioxide

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60
Q

What happens when you add phenol to water, shake and then add a few drops of iron chloride solution?

A

A purple colour is seen

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61
Q

What happens when you add phenol/phenylamine to brown bromine water and shake?

A

Bromine colour goes and white precipitate is formed

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62
Q

What is the empirical formula?

A

The simplest whole number ratio of atoms in a compound

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63
Q

When an organic compound containing carbon and hydrogen (and oxygen) is completely burned, what are the products?

A

Carbon dioxide and water

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64
Q

When a completely combusted and carbon dioxide is formed, where has all the carbon in the carbon dioxide come from?

A

The organic compound

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65
Q

What is produced in an SN1 mechanism?

A

A racemic mixture of 2 optical isomers which won’t rotate plane-polarised light

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66
Q

How many steps are there in an SN1 mechanism?

A

2 steps

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67
Q

What happens in the first step of an SN1 mechanism?

A

A group breaks off, leaving a planar (flat ion)

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68
Q

What happens in the second step of an SN1 mechanism?

A

The planar ion can be attacked by either side, resulting in 2 optical isomers

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69
Q

What is the rate determining step of an SN1 mechanism, hence what is the rate equation of an SN1 mechanism?

A

The rate determining step is the first step, so the rate equation is r = k X (concentration of halogenoalkane)

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70
Q

Do Primary halogenoalkanes react by SN1 or SN2?

A

Only by SN2

71
Q

Do Secondary halogenoalkanes react by SN1 or SN2?

A

Both

72
Q

Do Tertiary halogenoalkanes react by SN1 or SN2?

A

Only SN1

73
Q

What is produced in an SN2 mechanism?

A

A single enantiomer product, which rotates plane-polarised light differently to the reactant

74
Q

How many steps are there in an SN2 mechanism?

A

1 single step where the nucleophile always attacks the opposite side to the leaving group, so only 1 product is produced

75
Q

What is the rate equation of an SN2 mechanism?

A

r = k X (conc of halogenoalkane) X (conc of OH-)

76
Q

What equation relates concentration of hydrogen ions and the pH value?

A

pH = -log(conc of H+)

77
Q

For strong, monoprotic acids, what does the concentration of H+ equal?

A

The acid concentration

78
Q

To find the pH of a weaker acid, what do you use?

A

Ka, the acid dissociation constant

79
Q

What is Ka?

A

An equilibrium constant, which applies to a particular acid at a specific temperature regardless of the concentration

80
Q

What is Kw?

A

The ionic product of water, Kw = (H+)(OH-)

81
Q

For pure water, what is the ratio of OH- ions to H+ ions?

A

1 to 1

82
Q

At room temperature, what is the value of Kw?

A

10^-14

83
Q

How do you calculate pKa?

A

pKa = -log (Ka)

84
Q

List in acidic order, sodium hydoroxide, hydrochloric acid, ammonia, sodium chloride, propanoic acid:

A

1-Hydrochloric acid, 2- Propanoic acid, 3-Sodium chloride, 4 -Ammonia, 5-Sodium hydroxide

85
Q

When you dilute a strong acid, what does the pH increase by?

A

A factor of 1

86
Q

When you dilute a weak acid by 10, what does the pH increase by?

A

0.5

87
Q

At the half equivalence point, what does pH equal?

A

pKa

88
Q

What does the pH of a buffer solution equal?

A

pH = pKa + log(A- / HA)

89
Q

Why does water have an abnormally high melting and boiling point?

A

Because of the hydrogen bonds between the water molecules

90
Q

Why is the density of ice far less than the density of water?

A

In ice a lattice is formed which wastes a lot of space. When ice melts some of the hydrogen bonds are broken and the lattice breaks down, allowing molecules to fill their spaces

91
Q

In order for a substance to dissolve in another, what 3 things must happen?

A
  • Bonds in substance must break
  • Bonds in solvent must break
  • New bonds have to form between substance and solvent
92
Q

What is the case when a substance dissolves?

A

The strength of the new bonds formed are about the same as, or greater than the strength of the bonds broken

93
Q

What are the two main types of solvent?

A

Polar and non-polar solvents

94
Q

What are polar solvents?

A

Solvents made up of polar molecules, such as water

95
Q

Why do many polar molecules have limited solubility in water?

A

Because they either do not form hydrogen bonds with the water, or the hydrogen bonds they form are weak compared with the hydrogen bonds in water

96
Q

What is the ‘rule of thumb’ for what dissolves in what?

A

Like dissolved in like, e.g. crude oil is made up of alkanes dissolved in one another

97
Q

Why can alcohols dissolve in water?

A

Hydrogen bonds can form

98
Q

Why does the solubility of alcohols decrease as the length of the carbon chain increases?

A

The carbon chain part of the alcohol isn’t attracted to the water, so the more carbons there are, the less soluble it is

99
Q

What type of solvent is water?

A

A polar solvent

100
Q

When an ionic substance is mixed with water, what happens?

A

The ions in the ionic substance are attracted to the oppositely charged ends of the water molecules. The ions are pulled away from the ionic lattice by the water molecules, which surround the ions.

101
Q

What is hydration?

A

The process in which water molecules pull apart ions from an ionic lattice and surround it

102
Q

Why do some ionic substances not dissolve?

A

Because the bonding between their ions is too strong

103
Q

Why can’t halogenoalkanes dissolve?

A

They contain polar bonds but their dipoles aren’t strong enough to form hydrogen bonds with water

104
Q

As halogenoalkanes can dissolve can form permanent dipole-permanent dipole bonds, what does this mean they can dissolve in?

A

Polar solvents that form permanent dipole-permanent dipole bonds

105
Q

What happens to the solubility of group 2 hydroxides as you go down the group?

A

The solubility increases

106
Q

What happens to the solubility of group 2 sulfates as you go down the group?

A

The solubility decreases

107
Q

Is barium sulfate soluble or insoluble?

A

Insoluble

108
Q

What are compounds that have very low solubilities said to be?

A

Sparingly soluble

109
Q

What is thermal decomposition?

A

When a substance breaks down when heated

110
Q

What does it mean if a substance is very thermally stable?

A

More heat is required to break it down

111
Q

What are carbonate and nitrate ions examples of?

A

Large negative ions (cations)

112
Q

How are large negative ions made unstable?

A

By the presence of a positively charged ion ( a cation)

113
Q

What happens when a cation polarises an anion?

A

It is distorted, the greater the distortion, the less stable the compound

114
Q

Why do large cations cause less distortion than small cations?

A

They have a lower charge density, so as you go down the group the cations distort the anion less, so the more stable the carbonate/nitrate compound is

115
Q

Why does thermal stability increase down a group?

A

Larger cations cause less distortion, so the more thermally stable the nitrate/carbonate compound is

116
Q

Why are group 2 compounds less thermally stable than group 1 compounds?

A

The greater the charge on the cation, the more distortion and less stable the carbonate/nitrate compound is

117
Q

Do group 1 carbonates thermally decompose?

A

No, they are thermally stable other than lithium carbonate which decomposes to lithium oxide + carbon dioxide

118
Q

Do group 2 carbonates thermally decompose?

A

Yes, and they form the oxide + carbon dioxide

119
Q

Do group 1 nitrates thermally decompose?

A

Yes to form the nitrite (NO2) and oxygen

120
Q

Do group 2 nitrates thermally decompose?

A

Yes, to form the oxide, nitrogen dioxide and oxygen

121
Q

How do you test how easily nitrates decompose?

A
  • Measure how long it takes to produce a certain amount of oxygen (e.g. relight a glowing splint)
  • How long it takes form a certain amount of brown gas (NO2) to be produced, which needs to be done in a fume cupboard as NO2 is toxic
122
Q

How do you test how easily carbonates decompose?

A

How long it takes for a certain amount of carbon dioxide to be produced

123
Q

How do you test for carbon dioxide?

A

Use lime water, which will turn cloudy with carbon dioxide

124
Q

What is the enthalpy change?

A

The heat energy change in a reaction at a constant pressure, units kJ/mol

125
Q

What is an exothermic reaction?

A

A reaction which gives out energy, so delta H is negative, so the tempreature often goes up

126
Q

What is an endothermic rection?

A

A reaction which absorbs heat energy, so delta H is positive, and the temperature often falls

127
Q

What is the relationship between stability and enthalpy?

A

The less enthalpy a substance has, the more stable it is

128
Q

What is the activation energy?

A

The minimum amount of energy needed to begin breaking reactant bonds and start a chemical reaction

129
Q

Why do we use standard conditions (100kPa and 298K) when measuring enthalpy change?

A

Because changes in enthalpy are affected by temperature and pressure, so standard conditions means everyone knows exactly what the enthalpy change is describing

130
Q

What is the standard enthalpy change of reaction?

A

The enthalpy change when the reaction occurs in molar quantities shown in the chemical equation, under standard conditions

131
Q

What is the standard enthalpy change of formation?

A

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions

132
Q

What is the standard enthalpy change of formation?

A

The enthalpy change when and acid and alkali react together, under standard conditions to form 1 mole of water

133
Q

What is the standard enthalpy change of combustion?

A

The enthalpy change when 1 mole of a substance is completely burned in oxygen, under standard conditions

134
Q

How do you find the standard enthalpy changes of combustion?

A

Use a calorimeter to find out how much heat is given out by a reaction by measuring the temperature change of water
-As the fuel burns it heats the water, and ideally all all the heat given out by the fuel is absorbed by the water

135
Q

What equation do you use to calculate energy changes?

A

q = mcT

136
Q

Why is the actual combustion enthalpy often higher than observed?

A
  • Heat can be lost through the calorimeter

- The fuel may not have burned completely

137
Q

What is Hess’s law?

A

The total enthalpy change of a reaction is exactly the same, no matter which route is taken

138
Q

When reactions happen, what happens with bonds?

A

Bonds are broken and product bonds are formed. The overall enthalpy change of a reaction is the overall effect of these 2 changes

139
Q

Is bond breaking endothermic or exothermic?

A

Bond breaking is endothermic

140
Q

Is bond forming endothermic or exothermic?

A

Bond breaking is exothermic

141
Q

What is bond enthalpy?

A

The amount of energy required to break 1 mole of a type of bond in a molecules in the gas phase

142
Q

What is the mean bond enthalpy?

A

The energy needed to break one mole of bonds in the gas phase, averaged over many different compounds

143
Q

What is the enthalpy change of reaction in terms of bond enthalpies?

A

Sum of bond enthalpies of reactants - Sum of bond enthalpies of products

144
Q

What is the lattice energy?

A

The energy change when 1 mole of an ionic solid is formed from its gaseous ions under standard conditions

145
Q

What is the enthalpy change of hydration?

A

The enthalpy change when 1 mole of gaseous ions dissolves in water

146
Q

What is the enthalpy change of solution?

A

The enthalpy change when 1 mole of a solute dissolves in water

147
Q

What does the enthalpy change of solution equal?(Hess’s cycle)

A

-lattice energy + enthalpy change of hydration

148
Q

What is entropy?

A

The measure of disorder of particles (the number of ways they can arrange themselves)

149
Q

What happens to the value of entropy as you go from solid, to liquid to gas?

A

The entropy increases

150
Q

What is the relationship between energy and entropy?

A

The more energy particles have, the more entropy they have

151
Q

What is the relationship between number of particles and entropy?

A

The more particles a substance has, the more entropy it has

152
Q

What happens to entropy as the temperature increases?

A

The entropy increases

153
Q

Why is the big changes in entropy at the melting and boiling point?

A

Because the particles change state instead of just vibrating more

154
Q

Why is the increase in entropy at the boiling point far greater than the increase in entropy at the melting point?

A

There are far more ways a gas can arrange itself than a liquid compared to the amount of ways a liquid can arrange itself compared to a gas

155
Q

What are the units we use for entropy?

A

Joules / K / mol

156
Q

What does the entropy change of a system equal?

A

Entropy of products - Entropy of reactants

157
Q

Why do particles move to increase their entropy?

A

So that they are more energetically stable

158
Q

Why are some endothermic reactions feasible(can happen without the addition of energy) when their energy change is endothermic?

A

Due to favourable entropy values

159
Q

What does the total entropy change equal?

A

Entropy of system + Entropy of surroundings

160
Q

What does the entropy of surrounding equal?

A
  • delta H / Temperature
161
Q

What sign will the entropy change of surroundings be for an endothermic reaction?

A

Negative

162
Q

What does it mean when the total change in entropy is positive?

A

The reaction is kinetically feasible, meaning that it can react spontaneously at standard conditions

163
Q

What does it mean when the total change in entropy is negative?

A

The reaction is not kinetically feasible, so therefore is not spontaneous at standard room temperature

164
Q

What is the equilibrium constant Kc?

A

The ratio of products to reactants at equilibrium

165
Q

For homogenous equilibria, what is included in the expression for Kc?

A

All the products and reactants

166
Q

For heterogenous equilibria, what do you include in the expression for Kc?

A

Solids or pure liquids

167
Q

Why don’t you include solids or pure liquids in the expression for Kc when dealing with heterogenous equilibria?

A

Because their concentrations stay constant throughout

168
Q

Why don’t you include catalysts in the expression for the equilibrium constant?

A

Because they do not affect equilibrium concentrations, they only speed up the rate at which dynamic equilibrium is reached

169
Q

What does the total pressure in a gas mixture equal?

A

The sum of the partial pressures of the individual gases

170
Q

What is the equilibrium constant, Kp?

A

The constant you use when dealing with equilibria involving gases

171
Q

To calculate Kp, what do you do?

A

You put in the individual partial pressures

172
Q

What is the unit of partial pressure?

A

Atm

173
Q

Why does changes in concentration and pressure not affect the value of Kc and Kp?

A

They affect the amount of products and reactants present at equilibrium, but the ratio stays the same

174
Q

What does change in tempreature do to the value of Kc and Kp?

A

It alters the amounts of products and reactants present at equilibrium, and changes the value of Kc and Kp

Chemistry (25 decks)

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