THEME : INTERACTION BETWEEN CHEMICALS

Learning Area: 8. Salts

Learning Objectives:8.1 Synthesising salts

Learning Outcomes:A student is able to: State examples of salts used in daily life Explain the meaning of salt Identify soluble and insoluble salts

Interesting way to start a lessonTeacher Students’ expected correct answer Notes

Teacher shows a labelled packet of sodium chloride.

Q: What is this?

Q: Is sodium chloride the only salt?

Teacher then shows samples of a few salts (e.g. crystal salts of different colours such as potassium chloride, copper (II) sulphate, lead (II) iodide, iron (II) sulphate and iron (III) chloride) in labelled beakers.

Q: Do you know these are salts too?

Table salt

Yes/No (accept any answer with no comments)

Ooooh!!!Why do you call them ‘salts’?

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Q: (i)In which chapter have you learned about salts ?

(ii) Name the type of reaction that can produce salts.

T: In this chapter, we are going to learn more about salts.

Chapter 7, Acid and base

Neutralisation

(short pause)

T: These are salts found in the lab.(Pointing at the coloured salts)T: Sodium chloride is the salt that we

use in cooking everyday.(Pointing at table salt)

Q: Can you name any salts that we normally use at home?

Teacher shows a packet of ‘Ajinomoto’ and asks, “Can you name the chemical compound used in ‘Ajinomoto’?

Teacher asks a student to read the content stated on the packet label.

Q: Any other examples of salts used in daily life?

No answer from students.

Monosodium glutamate

Baking powder (sodium bicarbonate)Fertiliser (ammonium phosphate)Disinfectant (Potassium manganate (VII))

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(To develop the meaning of salt)

Teacher helps students to recall the previous lesson on neutralisation by showing the CD 5 (Lesson 78*) from PPK.

Q: Can you still remember the two products of neutralisation?

Teacher writes the following equations on the board and then asks students to come out and complete the equations:

a) NaOH + HCl →

b) KOH + HCl →

c) NH4OH + HNO3 →

Teacher then asks students to write the name of the salts (below the formula) in the equations stated above.

Teacher highlights all the ‘H’s in the acids in the equations on the board with red colour and also the metal and ammonium ions in the salts with the same colour.

Salt and water.

a) NaCl + H2O

b) KCl + H2O

c) NH4NO3 + H2O

a) sodium chlorideb) potassium chloridec) ammonium nitrate

* Take note of the error on the word equation for the neutralisation reaction.

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Q: Let’s compare the formulae of the acids and the salts formed. What do you notice?

Q: So what are salts?(This question may need to be broken down as follows if no answer is given.)

Q: What are salts formed from?

Q: What happened to the acids after forming the salts?

(Reinforcement activity)

Teacher asks students to write down the name of some salts formed from:

a) hydrochloric acid

b) sulphuric acid

c) nitric acid

The ‘H’s in the formulae of the acids have been replaced by the metal or ammonium ions from the alkalis.

Salts are compounds formed from acids when the hydrogen ions in the acids are replaced by the metal or ammonium ions.

Acids

The hydrogen ions in the acids are replaced by the metal or ammonium ions.

[chloride salts]

[sulphate salts]

[nitrate salts]

Teacher may have to repeat this activity until the students can see the replacement of ‘H’s by the metal ions or ammonium ions from the alkalis.

If answer given by students is ‘acid and base’, then teacher asks this question:Q: What about this reaction? Zn + 2HCl → ZnCl2 + H2

Teacher should emphasize that the metal ions in the salt need not come from the alkalis/bases but the H+ ions in the acids are always replaced to form a salt.

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Teacher asks students to complete the following equations:

a) ________ + ________ → NaNO3 + H2O

b) ________ + ________ → CuCl2 + H2O

c) ________ + ________ → (NH4)2SO4 + ___H2O

(Extension)

Q: Is magnesium oxide a salt?

Q: Why? Can you explain your answer?

Q: If magnesium oxide is not a salt, then what type of compound is

HNO3, NaOH

HCl, Cu(OH)2/CuO

H2SO4, NH4OH

Yes/No.

Magnesium oxide is not a salt because there is no such acid formed when magnesium is replaced back by ‘H’ in the formula of MgO.

This extension is a counter example to emphasize on the meaning that salts are derivatives of acids i.e. if there is no such acid, then there is no such salt.

Accept both answers until reasons are given.

There is no such acid as ‘HO’ or H2O is not an acid when Mg in MgO is replaced back by H.

If no answer, then teacher asks the following question:

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magnesium oxide? Base/ionic compound Q: Is it a base or an acid?

(Take home task)Refer to the worksheet given.Q1: What is meant by salt?

Q2: Give two examples of salts formed from

a) hydrochloric acidb) sulphuric acidc) nitric acid

d) carbonic acid e) ethanoic acid

Q3: (i) Name the acid used to produce the following salts:

a) lead (II) nitrate b) iron (II) chloride c) potassium sulphate

(ii) Write the equation for the formation of the salts mentioned in Q3 (i) using the acids that you have named.

Salts are compounds formed from acids when the hydrogen ions in the acids are replaced by the metal or ammonium ions.

a) [any two chlorides]b) [any two sulphates]c) [any two nitrates]d) [any two carbonates]e) [any two ethanoates]

a) nitric acidb) hydrochloric acidc) sulphuric acid

[Answers depend on the alkali/base/metal used]

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Teacher Students’ expected correct answer NotesTeacher asks a few question such as :

(i) What substance do you add in to make your food more salty ?

(ii) Can you name the salt ?

(iii) Do you think it is soluble in water ?

Teacher gives a few samples of salt and ask the student to identify soluble or insoluble salts. The salts given are :* Lead (II) nitrate* Iron (II) chloride* Potassium sulphate* Copper(II) carbonate* Copper(II) sulphate* Silver chloride* Lead(II) sulphate* Ammonium chloride* Calcium sulphate

Teacher help student to differentiate soluble or insoluble salt by using acronym.

Salt

Sodium chloride

Yes

Soluble salt – lead(II) nitrate, iron(II) chloride,potassium sulphate, copper(II) sulphate, ammonium chloride

Insoluble salt – copper(II) carbonate, silver chloride, lead(II) sulphate, calcium sulphate

Note : Students must do the experiment to determine solubility of salt and the salts must include PbCl2, AgCl, BaSO4,PbSO4, CaSO4.

Refer to the CD courseware for further reinforcement.

Refer to the sheet of acronym given

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WORKSHEET

TAKE HOME TASK

Q1: What is meant by salt?

………………………………………………………………………………………………………………………………………

………………………………………………………………………………………………………………………………………

Q2: Give two examples of salts formed from :

(a)(b)(c)(d)(e)

Acid Example of saltsHydrochloric acidSulphuric acidNitric acidCarbonic acidEthanoic acid

Q3: Complete the table below to produce the following salts and write its chemical equation.

Salt Chemicals used Chemical equationLead(II) nitrate

Iron(II) nitrate

Potassium sulphate

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TASK SHEET

Complete the table below by ( ) for soluble salt and ( X ) for insoluble saltSalt Soluble Insoluble

Lead(II) nitrateIron(II) chloridePotassium sulphateCopper(II) carbonateCopper(II) sulphateSilver chlorideLead(II) sulphateAmmonium chlorideCalcium sulphate

SHEET OF ACRONYM

Salt Solubility in waterSodium, potassium and ammonium salts (Na+, K+, NH4

+)

All are soluble

Nitrate salt (NO3-)

All are soluble

Chloride salt (Cl -) All chloride salts are soluble in water except

PbCl2, AgCl and HgCl2

Sulphate salt (SO42-)

All sulphate salts are soluble in water except PbSO4, BaSO4 and CaSO4

Carbonate salt (CO32-)

All carbonate salts are insoluble except Na2CO3,

K2CO3 and (NH4)2CO3

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