09P4

Tue 5 May

§4.2-§4.3

Week 3 · Lesson 6 of 17

Recap — synthesis, decomposition, and displacement reactions

Friday's net-ionic ladder closed §4.3 — but four reaction families is a lot to carry into §4.4. Today we walk back through synthesis, decomposition, single displacement, and double displacement. By the end you should be able to look at any equation and name the family, predict the products, and write a balanced net ionic when ions are involved.

Learning Intentions + Success Criteria

LITo consolidate §4.2 synthesis/decomposition and §4.3 displacement before §4.4 acid chemistry begins.

SC: I can:

01I can classify any reaction as synthesis, decomposition, single displacement, or double displacement from its equation.
02I can predict the products of a single-displacement reaction using the activity series (Figure 4.9, 16 metals).
03I can use Table 4.2 solubility rules to predict whether a double displacement produces a precipitate.
04I can write a balanced net ionic equation in four steps and identify the spectator ions.

Engage

6 min

Quick recap · from last class

L8 · §4.3 Displacement reactions — virtual prac (Metals in Aqueous Solutions)

Try these 2questions before today's new content. Click an answer for instant feedback — your teacher will walk through them with you.

This is a consolidation lesson — no new chemistry. We'll walk back through §4.2 and §4.3 in the first 32 minutes, then spend the remaining time on retrieval questions that pull from across the chapter so far.

Have these two open in the Toolbox (bottom-left icon) for the whole period:

Figure 4.9 — the activity series (16 metals, Li at top → Au at bottom).
Table 4.2 — the solubility rules (8 ion groups).

Predict · your turn

Write before you watch

Of the four reaction families we've met (synthesis, decomposition, single displacement, double displacement), which one do you feel LEAST confident about? Write the family name AND one specific question you'd want answered by the end of today.

Explicit

32 min

Family map — every reaction we've met fits one of four shapes

Look at the equation. Match the shape.

You see an equation. Don't panic — first look at the SHAPE of the reactants and products.

↓ A + B → AB

SYNTHESIS · §4.2
two or more substances → one product
e.g. 2Mg + O₂ → 2MgO

↓ AB → A + B

DECOMPOSITION · §4.2
one compound → two or more products
e.g. CaCO₃ → CaO + CO₂

↓ A + BC → AC + B

SINGLE DISPLACEMENT · §4.3
one element kicks another out
e.g. Zn + CuSO₄ → ZnSO₄ + Cu

↓ AB + CD → AD + CB

DOUBLE DISPLACEMENT · §4.3
two compounds swap partners
e.g. AgNO₃ + NaCl → AgCl + NaNO₃

Pause · write in your notes§3 — Double displacement (§4.3)

Pattern: two ionic compounds in solution swap partners — AB + CD → AD + CB.
Three signals that a reaction actually occurred (otherwise: no reaction):
1. A precipitate (insoluble solid, denoted (s)) forms.
2. Water (l) forms — this is the case for neutralisation, which we'll meet in §4.4.
3. A gas (g) bubbles out.
Predicting precipitates uses Table 4.2 (Toolbox · Solubility rules). The shortcut map:
- Nitrates (NO₃⁻) — always soluble.
- Group 1 cations (Na⁺, K⁺) and ammonium (NH₄⁺) — always soluble.
- Chlorides (Cl⁻) — soluble except AgCl, PbCl₂, Hg₂Cl₂.
- Sulfates (SO₄²⁻) — soluble except BaSO₄, PbSO₄, SrSO₄, CaSO₄.
- Carbonates (CO₃²⁻), hydroxides (OH⁻), sulfides (S²⁻) — mostly insoluble (the few exceptions are Group 1 + ammonium). Worked example — predict the outcome of AgNO₃(aq) + NaCl(aq).

Apply

18 min

Three retrieval questions — first one is rapid classify, then one prediction, then a stretch net-ionic. Climb in order.

Question 1Q1 — classify the reaction

For each equation, name the family. (Hint: look at the SHAPE first, before the chemicals.)

Question 2Q2 — predict the products (single displacement)

Use Figure 4.9 (Toolbox · Activity series). Magnesium ribbon is dropped into a solution of silver nitrate.

Mg sits above Ag on Figure 4.9, so the displacement happens. Mg goes into solution as Mg²⁺; the silver drops out as solid metal (often as a sparkly grey deposit on the magnesium ribbon).

Question 3Q3 — soluble or insoluble (Table 4.2)

For each ionic compound, decide what Table 4.2 says about its behaviour in water. Match each compound to the correct verdict.

Question 4Q4 — net ionic in 4 steps (stretch)

Mix Pb(NO₃)₂(aq) with 2KI(aq). Write the net ionic equation. Try the 4 steps yourself first, then reveal the worked answer below.

Catch

3 min

A single integration question — uses everything from today.

Reflect

1 min

Your turnReflect · One thing you learned

Of the four reaction families (synthesis, decomposition, single displacement, double displacement), which one do you now feel most confident with — and which one do you still want more practice on before §4.4 starts on Wednesday?

I've finished this lesson

Next class (Wed 6 May, P5): §4.4 begins — pH, indicators, and the chemistry of acids and bases.