GCSE · Chemistry · Edexcel · Spec 1CH0
Solubility rules for common salts
Pour one clear solution into another and a white solid suddenly appears. Could you have predicted it before you poured?
Sort the salts
Soluble or insoluble?
Pick a salt, then pick the column you think it belongs in. Commit first, then read the rule that decides it.
Still to sort
Soluble: (aq) (0)
Dissolves in water, so it's in solution: aqueous, written (aq).
Where the line is: Any sodium, potassium or ammonium salt, and any nitrate, lands here. Most chlorides and sulfates do too, unless they're one of the named exceptions.
Insoluble: (s) (0)
Doesn't easily dissolve in water, so it stays a solid, written (s).
Where the line is: Most carbonates and hydroxides land here, unless the partner is sodium, potassium or ammonium. A chloride or sulfate only lands here if it's a named exception.
Here's the trick: check the quick wins first. Is there sodium, potassium or ammonium in it, or is it a nitrate? Then it dissolves, every time. Only if the answer is no do you need the chloride, sulfate, carbonate and hydroxide rules, and their exceptions.
Predict, then check
Now use the rules on a mixture. Both starting solutions are clear, so every salt in them is dissolved.
Iron(II) chloride solution is poured into sodium hydroxide solution. What happens?
Read the rules onto the equation
Remember the white solid from the start? This is that reaction: silver nitrate solution poured into sodium chloride solution. Tap each substance to see which rule gives its state symbol.
Tap a molecule to see what it does in the reaction.
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
Pour one clear solution into another and a solid can appear out of nowhere. A handful of rules, plus a few exceptions, tells you when it will happen and which solid it is.
What you need to know
- Soluble means it dissolves in water, written (aq). Insoluble means it doesn't easily dissolve, written (s).
- Always soluble: every sodium, potassium and ammonium salt, and every nitrate.
- Most chlorides are soluble. Exceptions: silver chloride and lead chloride.
- Most sulfates are soluble. Exceptions: lead sulfate, barium sulfate and calcium sulfate.
- Most carbonates and hydroxides are insoluble. Exceptions: sodium, potassium and ammonium carbonates and hydroxides.
- A precipitation reaction makes an insoluble product; the solid formed is the precipitate.
The big picture
Soluble salts dissolve in water and are written (aq); insoluble ones don't easily dissolve and are written (s). All sodium, potassium and ammonium salts dissolve, and so do all nitrates. Most chlorides and sulfates dissolve, apart from a few named exceptions; most carbonates and hydroxides don't, unless the partner is sodium, potassium or ammonium. When two solutions are mixed, the ions swap partners, and any insoluble new pairing appears as a solid precipitate. Run that backwards to choose two solutions that make an insoluble salt.
Key points
Worked example
Problem
Barium nitrate solution is mixed with sodium carbonate solution. Does a precipitate form? If so, name it, and give the state symbol for each product.
⚠ Watch out
Deciding there's no precipitate because both starting solutions are soluble. Of course they are: they're solutions! The question is whether one of the NEW pairings, made when the ions swap partners, is insoluble.
Memory hook
SNAP always dissolves: Sodium, Nitrate, Ammonium, Potassium. Carbonates and hydroxides only dissolve with a SNAP partner. Chlorides lose silver and lead; sulfates lose lead, barium and calcium.
Check yourself
From memory, write out the rules and their exceptions. Then: silver nitrate solution meets potassium chloride solution. Name the precipitate and give both products' state symbols.
Flashcards
(13)What does it mean for a substance to be soluble?
Does 'insoluble' mean none of the salt dissolves?
Sodium, potassium, ammonium, nitrate: what do salts containing these have in common?
Chlorides: the rule and its exceptions?
Sulfates: the rule and its exceptions?
Carbonates and hydroxides: the rule and its exceptions?
State symbol for a soluble salt in water?
State symbol for an insoluble salt formed in water?
What is a precipitation reaction?
Silver nitrate solution + sodium chloride solution gives…?
Barium chloride solution + sodium sulfate solution gives…?
Iron(II) chloride solution + sodium hydroxide solution gives…?
How do you choose two solutions to make an insoluble salt?
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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