Two clear solutions, one yellow solid
Lead nitrate and potassium iodide are both colourless solutions. Mixed, they produce lead iodide: a brilliant yellow solid that will not dissolve, and that neither liquid gave any warning of. It is the clearest demonstration in the Class 10 syllabus that a reaction can produce something with none of the properties of what went into it, and the standard example of a double displacement — the two salts swap partners, and one of the pairings has nowhere to stay in solution.
3 steps · Chemical Reactions
What you will use
Apparatus
- Beaker
Chemicals
- Lead Nitrate Solution
- Potassium Iodide Solution
The steps
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Pour lead nitrate solution into the beaker.
Colourless. Nothing about it suggests what is coming.
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Add potassium iodide solution.
A bright yellow solid forms at once and settles through the liquid.
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Watch the solid settle.
It sinks rather than dissolving — that is what makes it a precipitate rather than a colour.
What it shows
The two salts exchanged partners: lead iodide and potassium nitrate. Potassium nitrate stays dissolved and invisible; lead iodide cannot dissolve, so it falls out of solution as the yellow solid you can see. A double displacement is named for the swap, but what drives it is that one of the new pairings has nowhere to stay.