Snow in a Test Tube

Why it matters

Two crystal-clear solutions. Pour one into the other and — instantly — white 'snow' appears and sinks. Nothing was hiding in either liquid. So where did the solid come from?

The idea in plain words

Balance check — a clean one-to-one partner swap.

Predict first

Mixing silver nitrate and sodium chloride solutions makes a white solid. What is it?

the ions swap partners: Ag⁺ meets Cl⁻ and the new pair, AgCl, cannot stay dissolved — it falls out as a precipitate.

• Salt crystallising out
• Silver chloride — a brand-new, insoluble compound — correct
• Frozen water
• Powdered silver metal

What you do

Pour and watch the swap: AB + CD → AD + CB. The particle view shows the partner exchange in real time.

Check yourself

A precipitate is…

Key word: formed. Sand stirred in water is just undissolved solid; AgCl born from two clear solutions is a precipitate — marked ↓ in equations.

In AgNO₃ + NaCl → AgCl↓ + NaNO₃, what swapped?

Double displacement = two compounds exchange their ions. The ↓ tells you why it goes: one new pair escapes the solution as a solid.

Which observation below also signals a double-displacement (precipitation) reaction?

FeSO₄ + 2NaOH → Fe(OH)₂↓ + Na₂SO₄ — same swap-and-drop pattern. (a) is displacement, (c) combination, (d) physical change.

• any solid in a liquid
• an insoluble solid formed BY a reaction in solution — correct
• undissolved leftover powder
• frozen solvent
• Electrons between silver and sodium
• The partners: Ag took Cl, Na took NO₃ — correct
• Nothing — the substances only mixed
• Protons between the two salts
• Gas bubbles from zinc in acid
• A dirty-green solid forming when FeSO₄ meets NaOH solutions — correct
• Magnesium flaring white in air
• Ice melting in a warm room