EDEXCEL C2 Lesson 5 – Solubility Mrs Barnes CCYD

Learning Objectives By the end of this lesson you should be able to: recall the general ruled which describe solubility of common types of substances in water. Demonstrate an understanding that insoluble salts can be formed as precipitates.

Success Criteria All of you will make a revision card of the solubility rules Most of you will be able to show precipitation reactions with symbol equations. Some of you will use the revision card to make a rap/or song and record it

A substance is soluble if it dissolves in water. Substances that do not dissolve are insoluble in water.

Prac You are going to investigate the solubility of three different lead compounds – lead chloride, lead bromide and lead iodide. These are insoluble in cold water but small amounts will dissolve in hot water. Prediction What will happen to the lead compounds when they are heated in water, and then cooled down again?

Apparatus 3 × test tubes250 cm3 beakerBunsen burner heat resistant mat teat pipettetest tube holdertest tube rack eye protection solutions of lead nitrate, potassium chloride, potassium bromide and potassium iodide Health and safety ●Eye protection should be used. When heating, take care not to point the mouth of the boiling tube towards people or to overheat its contents. ●Lead compounds are toxic.

Method APour potassium chloride solution into a boiling tube to a depth of around 3 cm. Do this also for potassium bromide solution and then potassium iodide solution – making sure you know what each boiling tube contains. BAdd five drops of lead nitrate solution to each boiling tube. CShake the boiling tubes gently to mix their contents. Record your observations.

Method DHold one of the boiling tubes using the test tube holder. Use a low flame (but not an orange one) to heat the mixture – the aim is to warm it until it just begins to boil. Return the boiling tube to the test tube rack and record the appearance of its contents. ERepeat step D for the other two mixtures. FSupport the three boiling tubes in a beaker of cold water. Observe and record any changes over the next few minutes.

Considering your results/conclusions 1How could you tell that precipitates were formed when lead nitrate solution was added in step B? 2aWhat happened to the precipitates when the reaction mixtures were heated? bExplain why this happened. 3The least soluble precipitate should form crystals first as it cools down. Put the three precipitates (lead chloride, lead bromide and lead iodide) in order of solubility from the most soluble to the least.

There is a general set of rules about the solubility of ionic substances: – all sodium, potassium and ammonium salts are soluble in water – all nitrates are soluble in water – common chlorides are soluble, but not silver chloride or lead chloride – common sulfates are soluble, but not lead sulfate, barium sulfate or calcium sulfate – most carbonates and hydroxides are insoluble, but those of sodium and potassium are soluble (see the first rule).

Solubility rules Make a revision card, Bullet points Spider diagram Table Learn it!!!

A song Choose a song and add your words to it Make a rap to learn it Get ready to be recorded!

If a substance is insoluble in water, it can be made in a precipitation reaction – this is when two solutions are mixed and a solid (precipitate) is formed. For example, when a solution of sodium chloride is mixed with a solution of silver nitrate a white precipitate of insoluble silver chloride is formed: NaCl(aq) + AgNO 3 (aq)  AgCl(s) + NaNO 3 (aq)

Silver nitrate and Lime water (ca(oh) and co2 Lead nitrate potassium iodide Sulphric acid lead nitrate

1What is the difference between a substance that is soluble in water and one that is insoluble? A:A soluble substance will dissolve in water but an insoluble one will not.

2Which substances in this list are soluble in water and which are insoluble in water? Sodium chloride, lead nitrate, calcium sulfate, potassium hydroxide, silver chloride, calcium carbonate, ammonium carbonate. A: Soluble: sodium chloride, lead nitrate, potassium hydroxide, ammonium carbonate. Insoluble: calcium sulfate, silver chloride, calcium carbonate.

3What is a precipitate? A:The insoluble solid formed in a precipitation reaction.

4How can you tell from the equation that lead iodide forms a precipitate? A:The letter (s) following the formula.

5Explain why lead chloride could form a precipitate but potassium chloride could not. A:Lead chloride is insoluble in water but potassium chloride is soluble.

6Potassium sulfate K 2 SO 4 and barium nitrate Ba(NO 3 ) 2 are soluble in water. They react to form potassium nitrate KNO 3 solution and insoluble barium sulfate BaSO 4. a Write a word equation for the reaction. A: potassium sulfate + barium nitrate → potassium nitrate + barium sulfate

6b Write a balanced equation for the reaction and include the state symbols. A:K 2 SO 4 (aq) + Ba(NO 3 ) 2 (aq) → 2KNO 3 (aq) + BaSO 4 (s)

7A school laboratory technician has been asked to make solutions containing a chloride, a nitrate, a carbonate, a sulfate, a hydroxide and a silver salt. Suggest, with reasons, suitable substances that the technician could use.

A:Any suitable soluble substances (use Table C to check) with the explanation that these substances have been chosen because they are soluble in water.

Write a method to prepare a dry insoluble salt sample using a precipitation reaction.