Shapes and Polarity
Structure & Properties of Solids
Thermochemistry & Energy
Organic Structure & Naming
Organic Reactions & Identification
100
Name the molecular shape of a molecule that has 3 bonding electron regions and 0 non-bonding lone pairs around the central atom (such as BF3)
Trigonal planar
100
Which type of solid consists of positive metal cations held in a 3D lattice surrounded by a "sea" of delocalised valence electrons?
Metallic Solid
100
Is bond breaking an endothermic or exothermic process?
What is the sign of its enthalpy (ΔrH) change?
Endothermic
Its enthalpy is positive
100
What is the functional group present in carboxylic acids, and what colour does damp blue litmus paper turn when exposed to a carboxylic acid?
Carboxyl group (-COOH); damp blue litmus turns red.
100
What type of reaction occurs when propene reacts with hydrogen gas (H2) in the presence of a nickel catalyst to form propane?
Addition reaction
200
What is the electron arrangement (geometry) AND the actual molecular geometry/shape of a water molecule (H2O)
Electron Geometry: Tetrahedral
Molecule Geometry: Bent
200
Explain why molecular solids like iodine (I2) have low melting points, whereas ionic solids like sodium chloride (NaCl) have very high melting points.
Molecular solids are held together by weak intermolecular forces that require little thermal energy to break.
Ionic solids are held by strong 3D ionic bonds (electrostatic attractions between cations and anions) that require large amounts of heat energy to break.
200
What are the standard units for enthalpy of reaction (ΔrH)
And - does an exothermic reaction release or absorb heat from the surroundings?
Units: kJ mol -1.
An exothermic reaction releases heat energy to the surroundings (causing the temperature to rise).
200
Give the IUPAC name for the following alcohol:
CH3CH2CH(OH)CH3
Butan-2-ol
200
Describe the observations when bromine water (Br2) is added to hex-1-ene and hexane in the dark.
Hex-1-ene (alkene): Rapidly decolourises bromine water from orange/brown to colourless.
Hexane (alkane): No immediate reaction; remains orange (requires UV light for slow substitution).
300
Define electronegativity, and explain why a C-Cl bond is polar.
Electronegativity is the relative ability of an atom to attract bonding electrons in a covalent bond.
Chlorine is more electronegative than carbon, pulling shared electrons towards itself to create a bond dipole
300
Both diamond and graphite are covalent network solids made purely of carbon. Why does graphite conduct electricity while diamond does not?
In diamond, every carbon atom is covalently bonded to 4 other carbons with no free electrons. In graphite, each carbon atom is bonded to 3 others in 2D layers, leaving one delocalised electron per carbon atom free to move and carry an electrical charge.
300
Define an exothermic reaction in terms of the energy involved in bond breaking versus bond making.
An exothermic reaction occurs when the energy released during bond formation in the products is greater than the energy absorbed to break bonds in the reactants.
300
What are structural isomers?
Draw or name the two structural isomers of butane (C4H10)
Structural isomers are molecules with the same molecular formula but different structural arrangements/connectivity of atoms.
Isomers:
Butane CH3CH2CH2CH3
2-methylpropane CH3CH(CH3)CH3
300
State Markovnikov's rule used to predict major and minor products in addition reactions.
When an asymmetrical reagent (HX or H2O) adds across an asymmetrical double bond, the hydrogen atom attaches to the carbon of the double bond that already has more hydrogen atoms attached ("the rich get richer").
400
Carbon dioxide (CO2) contains two polar C=O bonds, yet the molecule is non-polar overall. Explain why.
CO2 has a linear shape, which is symmetrical.
The two equal bond dipoles point in opposite directions and cancel each other out, resulting in no net molecular dipole.
400
Explain why solid NaCl does NOT conduct electricity, but molten NaCl (l) or aqueous NaCl (aq) does
In solid NaCl, the Na+ and Cl- ions are fixed in position within the rigid 3D lattice and cannot move.
When melted or dissolved in water, the lattice breaks apart and the ions become free to move and carry an electrical current.
400
Calculate enthalpy (ΔrH) for the reaction:
H2 (g) + Cl2 (g) --> 2HCl (g)
H-H = 436 kJ mol-1
Cl-Cl = 242 kJ mol-1
H-Cl = 431 kJ mol-1
Answer:
Bonds broken = 436 + 242 = +678 kJ
Bonds formed = 2 x 431 = 862 kJ
ΔrH= Sum (Bonds Broken) - Sum (Bonds Formed) = 678 - 862 = -184kJ mol-1
400
State the TWO conditions required for an organic compound to show geometric (cis-trans) isomerism.
A carbon-carbon double bond (C=C) that restricts rotation.
Two different atoms or groups of atoms attached to each carbon atom of the double bond.
400
Identify the reagents and conditions needed to oxidize ethanol (CH3CH2OH) into ethanoic acid (CH3COOH), and state the expected colour change.
Reagent: Acidified potassium dichromate (Cr2O72-) or acidified potassium permanganate (MnO4-/H+) with heat.
Colour change: Dichromate turns from orange to green (or Permanganate turns from purple to colourless)
500
Ammonia (NH3) has 4 electron density regions (3 bonding pairs, 1 lone pair) around the central nitrogen atom.
Justify its molecular shape, bond angle, and polarity
The 4 negative electron density regions repel for maximum separation / minimum repulsion into a tetrahedral electron geometry (bond angle approx 109.50).
Because there are 3 bonding pairs and 1 non-bonding lone pair, the molecular shape is trigonal pyramidal. The N-H bonds are polar due to electronegativity differences, creating bond dipoles.
Because the trigonal pyramidal shape is asymmetrical, the bond dipoles do not cancel out, making NH3 a polar molecule.
500
Explain in terms of structure and bonding why metals (e.g., copper) are malleable and ductile, while ionic crystals (e.g., NaCl) are brittle when struck with a hammer.
Metals: Contain non-directional metallic bonds. When force is applied, layers of cations can slide over one another without breaking the continuous metallic bonding with delocalised electrons.
Ionic solids: When struck, layers of ions shift, causing like charges to align (Na+ next to Na+, Cl- next to Cl-). The strong electrostatic repulsion causes the crystal to shatter (brittle).
500
When ice melts into liquid water (H2O(s) --> H2O(l)), is the process endothermic or exothermic?
Explain what is happening at a molecular level regarding chemical bonds/forces.
Answer:
The melting of ice is endothermic (ΔH > 0).
Energy is absorbed to overcome/break the weak intermolecular forces between water molecules holding them in the solid lattice.
Crucially, covalent bonds within the H2O molecules are NOT broken during a phase change.
500
Explain why but-2-ene exists as cis and trans isomers, whereas propene does not.
Both molecules have a double bond (C=C) preventing rotation.
But-2-ene: Carbon 2 and Carbon 3 each have two different groups attached (H and CH3), fulfilling the criteria for geometric isomerism.
Propene: Carbon 1 ($\text{C}_1$) has two identical atoms ($-\text{H}$ and $-\text{H}$) attached to it, so switching their positions creates the exact same molecule.
500
You are given 3 unlabelled bottles containing hex-1-ene, hexan-1-ol, and hexanoic acid. Outline a 2-step chemical test procedure using observations to positively identify all three liquids
Step 1: Add sodium hydrogen carbonate (NaHCO3)(aq) or damp blue litmus paper to all three bottles.
Observation: Hexanoic acid produces effervescence/bubbles of CO2 gas (or turns blue litmus red). The other two show no reaction.
Step 2: Add bromine water (Br2) to the remaining two bottles.
Observation: Hex-1-ene rapidly decolourises bromine water from orange to colourless. Hexan-1-ol shows no reaction (remains orange).