Gaps

Question 1

Which statements are correct for the reaction of ethene with bromine the absence of ultraviolet light?

I. It is an addition reaction

II. The organic product is colorless

III. The organic product is saturated

Answer 1

II and III

Question 2

State the equation for the reaction between methane and bromine to form bromomethane.

Answer 2

CH₄ + Br₂ –> CH₃Br + HBr

Question 3

Bromine can be produced by electrolysis of molten sodium bromide. Deduce the half-equation for the reaction at each electrode.

Answer 3

• Positive electrode (anode): 2Br^- –> Br₂ +2e^-
• Negative electrode (cathode): Na⁺ + e^- –> Na

Question 4

State one difference in the physical properties of the isotopes between ⁶³Cu and ⁶⁵Cu and explain why their chemical properties are the same.

Answer 4

• ⁶³Cu diffuses at a greater rate than ⁶⁵Cu
• have the same number of protons and electrons

Question 5

C₅H₁₂​ exists as three isomers. Identify the structure of the isomer with the lowest boiling point and explain your choice.

Answer 5

• 2,2-dimethylpropane
• weakest London dispersion forces because has smallest surface area

Question 6

Ethanol is a primary alcohol that can be oxidised by acidified potassium dichromate (VI). Distinguish between the reaction conditions needed to produce ethanal and ethanoic acid.

Answer 6

• Ethanal: distill off product as it forms
• Ethanoic acid: use excess oxidising agent

Question 7

Deduce the half-equation for the oxidation of ethanol to ethanal.

Answer 7

CH₃CH₂OH –> CH₃CHO + 2H⁺ + 2e^-​

Question 8

If a reaction has an exothermic forward reaction, what would happen to the equilibrium constant for the reaction if the temperature were increased?

Answer 8

decrease

Question 9

coordinate (dative) bonds

Answer 9

• the electrons in the shared pair originate from the same atom
• e.g. sulfur dioxide and sulfur trioxide has dative bond between S and O

Question 10

Which forces are present between molecules of carbon dioxide in the solid state?

Answer 10

temporary dipole-induced dipole interactions

Question 11

What is the equation for the bond enthalpy of the H-I bond?

Answer 11

HI (g) –> H (g) + I (g)

Question 12

State an equation for the formation of ethanol from ethene and the necessary reaction conditions.

Answer 12

• CH₂CH₂ + H₂O –> CH₃CH₂OH
• concentrated sulfuric acid

Question 13

Bronsted-Lowry vs. Lewish acids and bases

Answer 13

• Bronsted-Lowry: acid is a proton donor, base is a proton acceptor
• Lewis: acid is an electron acceptor, base is an electron donor

Question 14

Outline how the Mg⁺ ion is formed in the mass spectrometer. Describe how Mg⁺ is accelerated in the mass spectrometer.

Answer 14

• collision of Mg atom with high energy electrons
• ion passes through oppositely charged plates

Question 15

Why in the Haber process is

1. a temperature lower than 500C not used?
2. a pressure higher than 200atm not used?

Answer 15

• slower rate, uneconomical
• high cost for maintaining plant

Question 16

Outline an experiment and its results which could be used to distinguish between a strong base and a weak base.

Answer 16

• solutions of equal concentrations of acid and base
• measure pH
• strong base has higher pH

Question 17

Identify the acid-base character of the oxides of each of the elements from sodium to chlorine in period 3.

Answer 17

Na, Mg oxides - basic

Al oxide - amphoteric

Si-Cl oxides - acidic

Question 18

Outline two reasons why the polymerisation of alkenes is of economic importance.

Answer 18

• polymers not naturally available
• wide range of uses

Question 19

allotrope

Answer 19

when an element can exist in different crystalline forms (e.g. carbon)

Question 20

Boiling points for organic molecules

Answer 20

• As the carbon chain in a homologous series increases the London dispersion forces of attraction increase so boiling point increases
• when branching occurs the molecules become more spherical in shape so the surface area decreases and the boiling point decreases

Question 21

what structural feature must a molecule possess in order that it may undergo addition polymerisation?

Answer 21

carbon-carbon double bond

Question 22

IHD equation

Answer 22

(2C + 2 + N - H - halogens) / 2

Question 23

primary, secondary, tertiary halogenoalkanes

Answer 23

• primary halogenoalkane: carbon holding halogen is attached to one other thing
• secondary halogenoalkane: carbon holding halogen is attached to two other things
• tertiary halogenoalkane: carbon holding halogen is attached to three other things

Question 25

what is the pH of acid rain?

Answer 25

less than 5.6

Question 26

why does the soil become salty in areas where soil is constantly irrigated?

Answer 26

• irrigation waters contain dissolved salts
• salts left behind when water evaporates

Question 27

describe two ways in soil organic matter contributes to preventing soil degradation

Answer 27

• provides sources of nutrients
• improves structural stability

Question 28

what is Kc for the reverse reaction?

Answer 28

Kc^-1

Question 29

How are the mass and abundance of an isotope determined in mass spectrometry?

Answer 29

• magnetic field required to deflect isotope onto detector depends on mass of isotope
• signal from detector depends on abundance of isotope

Question 30

How does the atomic radii of isotopes vary?

Answer 30

• same atomic radii
• isotopes only differ by number of neutrons whereas atomic radius is determined by electron shells and number of protons

Question 31

is dissolving endothermic or exothermic?

Answer 31

endothermic

Question 32

greater the specific heat capacity, … increase in temperature for a given energy input

Answer 32

greater

Question 33

evaporation vs. boiling

Answer 33

• evaporation occurs at all temperatures, boiling at bp only
• evaporation occurs at surface, boiling throughout

Question 34

free radical mechanism diagram

Answer 34