Chem sac1 unit 2

What is the bond angle in a water molecule and why is it bent?

104.5°, bent because oxygen has two lone pairs that repel bonding pairs, compressing the H–O–H angle.

Why is water a polar molecule?

O–H bonds are polar and the bent shape means dipoles don’t cancel → net molecular dipole.

What type of intermolecular forces does water have?

Hydrogen bonding between δ+ H atoms and lone pairs on oxygen of neighbouring molecules.

Name 3 physical properties of water caused by hydrogen bonding.

High boiling/melting points, high specific heat capacity, high surface tension.

Why is ice less dense than liquid water?

In ice, hydrogen bonds create an open lattice that increases volume for the same mass.

How does water dissolve ionic compounds?

Ion–dipole interactions: water molecules hydrate ions, stabilising them in solution.

Why are non-polar substances generally insoluble in water?

No significant attractions between non-polar molecules and polar water.

What is the general equation for metal + acid?

Metal + Acid → Salt + H₂(g).

What is the general equation for carbonate + acid?

Carbonate + Acid → Salt + H₂O + CO₂(g).

What is the general equation for base + acid?

Base + Acid → Salt + H₂O.

What is the difference between strong and weak acids?

Strong acids fully ionise in water; weak acids partially ionise.

Why is the Mg + CH₃COOH reaction slower than Mg + HCl?

CH₃COOH is a weak acid → lower [H⁺] at same molarity → slower reaction.

What is the net ionic equation for metal + acid?

M(s) + 2 H⁺(aq) → M²⁺(aq) + H₂(g).

What gas is produced when a carbonate reacts with acid and how is it tested?

CO₂ gas; turns limewater milky.

What colour change occurs when NaOH + universal indicator is neutralised by acid?

Colour shifts from purple/blue (basic) to green/yellow (neutral/acidic).

Define oxidation in terms of electrons and oxidation number.

Loss of electrons; increase in oxidation number.

Define reduction in terms of electrons and oxidation number.

Gain of electrons; decrease in oxidation number.

What is an oxidising agent?

Substance that causes oxidation and is reduced itself.

What is a reducing agent?

Substance that causes reduction and is oxidised itself.

How can you predict if a redox reaction will occur?

Use the electrochemical series: more reactive metal will displace a less reactive metal ion.

In your prac, which metal was most reactive?

Magnesium — displaced Zn²⁺, Cu²⁺, Ag⁺, Fe²⁺.

Which metal was least reactive in your prac?

Silver — did not displace any metal ions.

What was the reactivity order from your prac?

Mg > Zn > Fe > Cu > Ag.

Write the oxidation half-equation for Mg in the above reaction.

Mg(s) → Mg²⁺(aq) + 2 e⁻.

Write the reduction half-equation for Cu²⁺ in the above reaction.

Cu²⁺(aq) + 2 e⁻ → Cu(s).

What is the first step when balancing redox equations in acidic medium?

Balance all atoms except hydrogen and oxygen.

How do you balance oxygen atoms in redox half-equations?

Add H₂O molecules.

How do you balance hydrogen atoms in acidic medium?

Add H⁺ ions.

How do you balance hydrogen atoms in basic medium?

Add OH⁻ to both sides to neutralise H⁺, forming H₂O.

What’s the observation → inference → chemistry chain?

Describe what you see, infer what’s happening, then explain with chemical theory.

What’s a redox reaction

a chemical process where electrons are transferred between substances.

Redox and acid–base reactions in aqueous solutions:

• Redox reactions involve electron transfer, with one substance being oxidised and another reduced. Water allows ions to move so the reaction can occur.

• Acid–base reactions involve proton (H⁺) transfer. Acids donate H⁺, bases accept it, and water enables this exchange.