CHAPTER 8 : SALTS
Meaning and uses of Salts
A salt is an ionic compound formed when the hydrogen ion, from an acid is replaced by a metal ion or an ammonium ion
Example of salts :
(i) sodium chloride
(ii) potassium carbonate
(iii) copper(II) sulphate
Examples of salts :
Acid Formula of acid
Salt Formula Cation Anion
Hydrochloric acid
HCl Sodium chloride
NaCl Na+ Cl-
Carbonic acid
H2CO3 Potassium carbonate
K2CO3 K+ SO42-
Sulphuric acid
H2SO4 Copper(II) sulphate
CuSO4 Cu2+ SO42-
Examples of salts :
Acid Formula of acid
Salt Formula Cation Anion
Nitric acid
HNO3 Ammonium nitrate
NH4NO3 NH4+ NO3
-
Ethanoic acid
CH3COOH Sodium ethanoate
CH3COONa Na+ CH3COO-
Nitric acid
HNO3Magnesium nitrate
Mg(NO3)2 Mg2+ NO3-
Salts with their uses.
Salt Uses
Barium sulphate BaSO4 X-ray ‘meals’ in hospital
Calsium sulphate CaSO4
Plaster of Paris for broken bone
Iron sulphate FeSO4 Iron tablets for anaemia patient
Ammonium nitrate NH4NO3
Nitrogenous fertilizer
Salts with their uses.
Salt Uses
Copper(II) sulphate CuSO4
Fungicide
Sodium chloride NaCl A flavouring agent
sodium hydrogen carbonate
Baking powder
Sodium nitrite NaNO2 For preserving food/ food preservative
Salts with their uses.
Salt Uses
Sodium hypochlorite NaOCl
Bleaching agent
Tin(II) fluoride SnF2 Toothpaste
Lead(II) chromate PbCrO4
Paint for yellow line on road
Identify soluble and insoluble salt.
NaNa++
KK++ CO CO332-2-
NHNH44++
Water Water
NONO33--
PbPb2+2+
BaBa2+2+ SO SO442-2-
CaCa2+2+
PbPb2+2+
AgAg++ Cl Cl--
HgHg++
All sodium, potassium and ammonium salts are soluble in water.
All nitrate salts are soluble in water. All sulphate salts are soluble in water except lead(II)
sulphate, barium sulphate and calcium sulphate. All chloride salts are soluble in water except lead(II)
chloride, silver chloride and mercury chloride. All carbonate salts are insoluble in water except
sodium carbonate, potassium carbonate and ammonium carbonate
State whether each of the following salt is soluble or insoluble in water
Formula of salt
Solubility
( / or x)
Formula of salt
Solubility
( / or x)
PbCO3 x NaCl /
CaSO4 x AgNO3 /
K2CO3 / FeCl3 /
Na2SO4 / NH4NO3 /
CuSO4 / PbCl2 x
Chemical and ionic equations for reactions used in the preparation of soluble salts
General equation for preparing soluble salts.
a. metal + acid salt + hydrogen
b. metal oxide (or metal hydroxide) + acid salt + water
c. alkali + acid salt + water
d. metal carbonate + acid salt + water + carbon dioxide
Complete the following chemical equation.
Mg + H2SO4 MgSO4 + H2
CuO + HCl CuCl2 + H2O
Zn(OH)2 + HNO3 Zn(NO3)2 + H2O
NaOH + HCl NaCl + H2O
MgCO3 + H2SO4 MgSO4 + CO2 + H2O
Preparation of soluble salt Method of Preparation
Reactants Salt Formed
Other Product
metal + acid Magnesium + hydrogen chloride
Magnesium chloride
Hydrogen
metal oxide + acid
Copper(II) oxide + sulphuric acid
Copper(II) sulphate
water
Metal carbonate + acid
Zinc carbonate + sulphuric acid
Zinc sulphate
Water + carbon dioxide
Preparation of soluble salt Method of Preparation
Reactants Salt Formed
Other Product
metal hydroxide + acid
Potassium hydroxide + nitric acid
Potassium nitrate
water
e) alkali + acid
Sodium hydroxide + hydrochloric acid
Sodium chloride
water
The reactants which are needed to prepare the following soluble salts:
Copper(II) sulphate : Copper(II) oxide / hydroxide / carbonate + sulphuric acid
Zinc chloride : Zinc / (zinc oxide / hydroxide / carbonate) + hydrochloric acid
Potassium nitrate: potassium hydroxide + nitric acid
Ammonium sulphate : aqueous ammonia + sulphuric acid
Magnesium nitrate : Magnesium / (magnesium oxide / hydroxide / carbonate) + nitric acid
Chemical equation can be simplified into an ionic equation.
Example : Chemical equation : Zn(s) + H2SO4(aq)
ZnSO4(aq) + H2(g)
Zn(s) + 2H+(aq) + SO42-(aq) Zn2+(aq)
+ SO42-(aq) + H2(g)
Ionic equation : Zn(s) + 2H+ (aq) Zn2+ (aq) + H2(g)
Chemical equation can be simplified into an ionic equation.
Chemical equation : Mg(s) + 2HCl(aq) MgCl2(aq) + H2 (g)
Mg(s) + 2H+(aq) + 2Cl-(aq) Mg2+(aq) + 2Cl-(aq) + H2(g)
Ionic equation : Mg(s) + 2H+ (aq) Mg2+ (aq) + H2 (g)
Chemical equation can be simplified into an ionic equation.
Chemical equation :MgO(s) + 2HCl(aq) MgCl2(aq) + H2O (l)
MgO(s) + 2H+(aq) + 2Cl-(aq) Mg2+
(aq) + 2Cl-(aq) + H2O(l)
Ionic equation : MgO(s) + 2H+ (aq) Mg2+ (aq) + H2O (l)
Chemical equation can be simplified into an ionic equation.
Chemical equation :NaOH (aq) + HNO3 (aq) NaNO3 (aq) + H2O (l)
Na+(aq) + OH-(aq) + H+(aq) + NO3-(aq)
Na+(aq) + NO3-(aq) + H2O(l)
Ionic equation :OH- (aq) + H+ (aq) H2O (l)
Chemical equation can be simplified into an ionic equation.
Chemical equation :CuCO3 (s) + H2SO4 (aq) CuSO4 (aq) + CO2 (g) + H2O (l)
CuCO3(s) + 2H+(aq) + SO42-(aq)
Cu2+(aq) + SO42-(aq) + CO2(g) + H2O(l)
Ionic equation : CuCO3 (s) + 2H+ (aq) Cu2+ (aq) + CO2 (g) + H2O (l)
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Soluble salt Sodium Chloride, NaCl
Name two chemical substances to prepare the salt
sodium hydroxide
hydrochloric acid
Chemical equation NaOH + HCl NaCl + H2O
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
1. A pipette is used to transfer 25.0of sodium hydroxide solution to a conical flask. 2 to 3 drops of phenolphthalein is added.
2. A burette is filled with hydrochloric acid and record the initial burette reading.
3. Titration is carried out carefully by slowly adding the acid into the conical flask and the flask is shaken well.
4. The acid is added continuously until the indicator turns from pink to colourless. The final burette
reading is recorded.
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
5. The volume of acid used to neutralize 25.0of the alkali is determined. (let the volume be V)
6. 25.0of the same sodium hydroxide solution is pipetted into a conical flask. No indicator is addeded.
7. From the burette, exactly Vof hydrochloric acid is added to the alkali and is shaken well.
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
8. The contents of the conical flask is poured into an evaporating dish.
9. The solution is heated gently to evaporate most of the water to produce a saturated solution.
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
10. The hot saturated salt solution is cooled for crystallization to occur.
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
11.The sodium chloride crystals is filtered, and the salt is rinsed with a little distilled water.
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
12. The crystals are dried by pressing them between filter papers
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
Describe the physical characteristics of the crystals that you obtained
Salt crystal characteristic
1. Flat surfaces, straight edges and sharp angles
2. Fixed geometrical shape
3. Fixed angles between two neighbouring surfaces
4. Crystals of some substance have same hapes but maybe in different sizes
Preparation of soluble salts (not sodium, potassium or ammonium salt)
Soluble salt Copper(II) sulphate, CuSO4
Name two chemical substances to prepare the salt
copper(II) oxide and sulphuric acid
Chemical equation CuO + H2SO4 CuSO4 + H2O
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
1. 50of sulphuric acid 1 mol dm-3 is poured into a beaker. The acid is warmed.
2. By using a spatula, copper(II) oxide powder is added bit by bit into the acid. The mixture is stirred well.
3. Copper(II) oxide is added continuously until some of it no longer dissolves.
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
3. The unreacted copper(II) oxide is removed by filtration
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
4. The filtrate is filtered into an evaporating dish. The solution is heated gently to produce a saturated salt solution.
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
5. The saturated solution is cooled until crystals are formed
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
6. The copper(II) nitrate crystals are filtered, and are then rinsed with a little distilled water.
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
7. The crystals are dried by pressing them between filter papers
The procedure for the preparation of soluble salts of sodium, potassium and ammonium
Procedure: (Diagram) Description
Describe the purification process of the crystals
Purification process – Recrystallisation
1.The copper(II) sulphate crystals are placed in a beaker.
2.Enough distilled water is added to cover the crystals. The solution is gently heated and stirred with a glass rod. Water is added bit by bit until all the crystals are dissolved.
3. Impurities is removed by filtration and filtrate is poured into an evaporating dish.
4.The solution is heated gently to evaporate most of the water to produce a saturated solution.
5.The hot saturated salt solution is cooled for crystallization to occur.
6.The copper(II) nitrate crystals are filtered, and the salt is rinsed with a little distilled water.
7. The crystals are dried by pressing them between filter papers
Chemical and ionic equations for reactions used in the preparation of insoluble salts
Insoluble salts can be prepared by precipitation method through double decomposition reaction. In this reaction, two different aqueous solution mutually exchange their ions , to form precipitate.
Soluble salt solution + Soluble salt solution Insoluble salt MX
containing cation M+ containing anion X-
Chemical equation : AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3(aq)
Ionic equation : Ag+ (aq) + Cl- (aq) AgCl (s)
Preparation of insoluble salts
Example 1: Barium sulphate, Solution 1: Barium chloride/nitrate Solution 2 :sodium/potassium sulphate Chemical equation :BaCl2 + Na2SO4
BaSO4 + 2NaCl Ionic Equation : Ba2+ + SO4
2- BaSO4
Observation : White precipitate formed
Preparation of insoluble salts
Example 2 :Copper(II) carbonate, CuCO3 ,
Solution 1:copper(II) nitrate/sulphate/chloride Solution 2 :Sodium/potassium carbonate Chemical equation :Cu(NO3)2 + Na2CO3
CuCO3 + 2NaNO3
Ionic Equation : Cu2+ + CO32- CuCO3
Observation : Green precipitate formed
Preparation of insoluble salts
Example 3 : Lead(II) chromate(VI),PbCrO4 ,
Solution 1:lead(II) nitrate Solution 2 :Sodium/potassium chromate(VI) Chemical equation :Pb(NO3)2 (aq) +
K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)
Ionic Equation : Pb2+ + CrO42- PbCrO4
Observation : Yellow precipitate formed
The preparation of insoluble salts
Insoluble salt Name Lead(II) iodide, PbI2
Two chemical substances to prepare the salt
(i) Lead(II) nitrate
(ii) Sodium/potassium iodide
The preparation of insoluble salts
Chemical equation Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq)
Ionic equation Pb2+(aq) + 2I-(aq)
PbI2(s)
The preparation of insoluble salts
Procedure: (Diagram) Description
1. 50 cm3 of 0.5 mol dm-3 lead(II) nitrate solution is poured into 50 cm3 of 1.0 mol dm-3 potassium iodide in a beaker
2. The mixture is stirred with a glass rod
The preparation of insoluble salts
Procedure: (Diagram) Description
3. A yellow precipitate of lead(II) iodide is formed immediately
4. The resulting mixture is then filtered
The preparation of insoluble salts
Procedure: (Diagram) Description
5. The yellow precipitate is rinsed with distilled water to remove impurities
The preparation of insoluble salts
Procedure: (Diagram) Description
6. The yellow solid, lead(II) iodide is then pressed between a few pieces of filter papers to be dried
Solve problems involving calculation of quantities of reactants or
products in stoichiometric reactions
Example 1 : A student prepares copper (II) nitrate by reacting copper (II) oxide with 100 cm3 1.5 mol dm-3 nitric acid. Calculate the mass of copper (II) oxide needed to react completely with the acid. [Relative atomic mass: Cu, 64 ; O, 16]Solution : Chemical equation : CuO + 2HNO3 Cu(NO3)2 + H2O
Mole ratio : 1 mole 2 mole 1 mole 1 mole Number of moles of HNO3 = 1.5 x 100 = 0.15 mol 1000
Mole ratio of CuO : HNO3 = 1 : 2 Number of mole of CuO = 1 x 0.15 = 0.075 mole 2 Mass of CuO = 0.075 x (64 + 16) = 6 g
Question :
1.Excess zinc powder is added to react completely with 50 cm3 of 2.0 mol dm-3 hydrochloric acid.
(a) Write an ionic equation for the reaction between zinc and hydrochloric acid.
Zn + 2HCl ZnCl2 + H2
Question :
(b) Calculate the number of moles of hydrochloric acid used.
No of mole of HCl mol
= 2.0 x 50 = 0.1 mol
1000
Question :
(c) Calculate the volume of hydrogen gas liberated at room conditions.
[Molar volume: 24 dm3 mol-1]
Mole ratio HCl : H2 = 2 : 1
No of mole of H2 = 1/2 x 0.1 = 0.05 mol
Volume of H2 = 0.05 x 24 dm3
= 1.2 dm3
Question :
2 Excess of magnesium carbonate powder, MgCO3, is reacted with 100 cm3 of a 1 mol dm-3 sulphuric acid H2SO4 , What is the mass of magnesium sulphate formed?
[Relative atomic mass : Mg =24, O=16, S = 32 ]
Question :
No of mole of H2SO4 = 1.0 x 100 = 0.1 mol
1000
Mole ratio H2SO4 : MgSO4 = 1 : 1
No of mole of MgSO4 = 0.1 mol
Mass of MgSO4 = 0.1 x (24 + 32 + 4x16) g = 12.0 g
Question :
3. 0.12 g of magnesium reacts with excess hydrochloric acid to produce hydrogen gas. Given that the relative molecular mass of H=1, Mg = 24, CI =35.5 and 1 mol of gas occupies 24 dm3 at room temperature and pressure.
Find the
(a) mass of salt formed
Question :
No of mole of Mg = 0.12 = 0.005
24
No of mole of MgCl2 = 0.005
Mass of MgCl2
= 0.005 x (24 + 2 x 35.5)
= 0.475 g
Question :
(b) volume of gas produced
No of mole of H2 = 0.005 mole
Volume of H2 = 0.005 x 24 dm3
= 0.12 dm3 or 120 cm3
Question :
Example 2 : A sample of insoluble lead (II) sulphate is prepared by mixing 50 cm3 of 1.0 mol dm-3 lead (II) nitrate solution and y of 1.5 mol dm-3 sulphuric acid.
[Relative atomic mass: O, 16 ; S, 32 ; Pb, 207]
(a) Calculate the volume, y, of the sulphuric acid needed to react completely with the lead (II) nitrate solution.
Question :
Solution :Chemical equation :
Pb(NO3)2 + H2SO4 PbSO4 + 2 HNO3
Mole ratio : 1 mole 1 mole 1 mole 2 mole Number of moles of Pb(NO3)2 = 1.0 x 50 = 0.05 mol 1000 Mole ratio of Pb(NO3)2 : H2SO4 = 1 : 1 Number of mole of H2SO4 reacted = 0.05 mol 1.5 x y = 0.05 mole 1000 y = 0.05 x 1000 = 33.33 cm3
1.5
Question :
(b) Calculate the mass of lead (II) sulphate obtained.Solution :
Number of mole of PbSO4 = Number of moles of Pb(NO3)2 = 0.05 mol
Mass of PbSO4 = 0.05 x (207 + 32 + 4 x 16) g
= 15.15 g
Question :
4. A sample of insoluble silver chloride is prepared by mixing 50 cm3 of 1.0 mol dm-3 silver nitrate solution and z cm3 of 0.5 mol dm-3 sodium chloride solution.
[Relative atomic mass: Ag 108; Cl 35.5]
(a) Write the chemical equation for the reaction between silver nitrate and sodium chloride.
AgNO3 + NaCl AgCl + NaNO3
Question :
(b) Calculate the volume, z, of the sodium chloride needed to react completely with the silver nitrate solution
Number of moles of AgNO3 = 1.0 x 50 = 0.05 mol 1000
Mole ratio of AgNO3 : NaCl = 1 : 1 Number of mole of NaCl = 0.5 x z = 0.05 mole 1000 Z = 0.05 x 1000 = 100 cm3
0.5
Question :
(c) Calculate the mass of silver chloride obtained.
Number of mole of AgCl = Number of moles of AgNO3 = 0.05 mol
Mass of AgCl = 0.05 x (108 + 35.5) g
= 7.175 g
Qualitative Analysis
Qualtitative analysis of a salt is a chemical technique used to identify the ions that are present in a salt by analysing its physical and chemical properties.
Qualitative Analysis
Colour (solid or solution)
Substance or cation or anion
Green powder , CuCO3
Blue powder Fe2+ Cu2+
Brown powder Fe3+
Black powder CuO, MnO2
Qualitative Analysis
Colour (solid or solution)
Substance or cation or anion
Yellow powder when hot and white when cold
ZnO
Brown powder when hot and yellow when cold
PbO
Blue solution Cu 2+
Pale green solution Fe 2+
Qualitative Analysis
Colour (solid or solution)
Substance or cation or anion
Brown solution Fe3+
Solid : White
Solution : colourless
Cation : Ca2+ , Al3+ , Mg2+ , Pb2+ , Zn2+ NH4
+
Solid : White
Solution : colourless
Anion : Cl- , CO32- ,
SO42- , NO3
-
Qualitative Analysis
Salts Solubility in water Colour
Lead(II) chloride, silver chloride, barium sulphate, lead(II) sulphate and calcium sulphate
Insoluble white
Copper(II) carbonate Insoluble green
Iron(II) sulphate soluble green
Iron(III) salts except carbonate
Soluble Brown
Qualitative Analysis
Salts Solubility in water
Colour
Lead(II) sulphate
Insoluble white
Zinc chloride soluble white
Magnesium carbonate
Insoluble white
Qualitative Analysis
Salts Solubility in water
Colour
Ammonium carbonate
soluble white
Lead(II) iodide / chromate(VI)
Insoluble Yellow
Confirmatory Tests for gases
Gas Method Diagram Observation
Carbon dioxide
Bubble the gas produced into lime water
Lime water turn milky/chalky
Confirmatory Tests for gases
Gas Method Diagram Observation
Oxygen Insert a glowing splinter into the test tube
Glowing splinter will be relighted
Confirmatory Tests for gases
Gas Method Diagram Observation
Nitrogen dioxide
Observe the colour of gas produced. Bring a piece of moist blue litmus paper to the mouth of the test tube
Brown gas, blue litmus paper change to red
Confirmatory Tests for gases
Gas Method Diagram Observation
Chlorine Observe the colour of the gas.Bring a piece of moist blue litmus paper to the mouth of the test tube
Greenish yellow gas The colour of litmus paper change from blue red white
Confirmatory Tests for gases
Gas Method Diagram Observation
Ammonia Dip a glass rod into concentrated hydrochloric acid and bring a drop of acid to the mouth of the test tube/place moist red litmus paper at the mouth of the test tube
White fume formed Red litmus paper change to blue.
Confirmatory Tests for gases
Gas Method Diagram Observation
Hydrogen Bring a lighted splinter to the mouth of the test tube. Mg + HCl release hydrogen gas
‘Pop' sound is heard
Confirmatory Tests for gases
Gas Method Diagram Observation
Hydrogen chloride
Dip a glass rod into concentrated ammonia solution and bring a drop of ammonia to the mouth of test tube
White fume formed
Action of Heat On Carbonate Salts
Carbonate salts (except Na+ & K+ ) decompose on heating giving off carbon dioxide gas and residue metal oxide
Action of Heat On Carbonate Salts
Lime water turns chalky
Metal oxide colour
Copper(II) oxide
Black
Zinc oxide Hot : Yellow
Cold : White
Lead(II) oxide
Hot : Brown
Cold : Yellow
Iron(III) oxide
Brown
Action of Heat On Carbonate Salts
Carbonate salt Action of heat
Potassium carbonate K2CO3 , Sodium carbonate Na2CO3
Not decompose by heat
Action of Heat On Carbonate Salts
Carbonate salt Action of heat
Metal Carbonate metal oxide + carbon dioxide
Calcium carbonate
CaCO3 CaO + CO2 Observation : White solid formed. Gas liberated turn lime water chalky
Action of Heat On Carbonate Salts
Carbonate salt Action of heat
Magnesium carbonate
MgCO3 MgO + CO2 Observation : White solid formed. Gas liberated turn lime water chalky
Aluminium carbonate
Al2(CO3)3 Al2O3 + 3CO2 Observation : White solid formed. Gas liberated turn lime water chalky
Action of Heat On Carbonate Salts
Carbonate salt
Action of heat
Zinc carbonate
ZnCO3 ZnO + CO2 Observation : The residue is yellow when hot and white when cold. Gas liberated turn lime water chalky
Lead(II) carbonate
PbCO3 PbO + CO2 Observation : The residue is brown when hot and yellow when cold. Gas liberated turn lime water chalky
Action of Heat On Carbonate Salts
Carbonate salt Action of heat
Copper(II) carbonate
CuCO3 CuO + CO2 Observation : Black solid formed. Gas liberated turn lime water chalky
Action of Heat On Nitrate Salts
Nitrates Salts - Decompose on heating liberate nitrogen dioxide gas and oxygen gas except NaNO3 and KNO3 which liberate oxygen gas only.
Action of Heat On Nitrate Salts
Brown gas turn moist blue litmus to red(NO2)
Colourless gas relighted glowing splinter (O2 )
Heat
Heat
Action of Heat On Nitrates Salts
Nitrate salt
Action of heat
Metal Nitrate metal nitrite + oxygen
Potassium nitrate
2KNO3 2 KNO2 + O2 Observation : white solid formed, gas released relighted glowing splinter
Sodium nitrate
2NaNO3 2 NaNO2 + O2 Observation : white solid formed, gas released relighted glowing splinter
Action of Heat On Nitrates Salts
Nitrate salt
Action of heat
Metal Nitrate metal oxide + nitrogen dioxide + oxygen
Calcium nitrate
2Ca(NO3)2 2CaO + 4NO2 + O2 Observation : white solid formed, Brown gas which turns moist blue litmus red released. Another gas released relighted glowing splinter
Action of Heat On Nitrates Salts
Nitrate salt Action of heat
Magnesium nitrate
2Mg(NO3)2 2MgO + 4NO2 + O2 Observation : white solid formed, Brown gas which turns moist blue litmus red released. Another gas released relighted glowing splinter
Zinc nitrate 2Zn(NO3)2 2ZnO + 4NO2 + O2 Observation : The residue is yellow when hot and white when cold., Brown gas which turns moist blue litmus red released. Another gas released relighted glowing splinter
Action of Heat On Nitrates Salts
Nitrate salt Action of heat
Lead(II) nitrate
2Pb(NO3)2 2PbO + 4NO2 + O2 Observation : The residue is brown when hot and yellow when cold, Brown gas which turns moist blue litmus red released. Another gas released relighted glowing splinter
Copper(II) nitrate
2Cu(NO3)2 2CuO + 4NO2 + O2 Observation : black solid formed, Brown gas which turns moist blue litmus red released. Another gas released relighted glowing splinter
Confirmatory Tests for AnionsANIONS
CO32-
Cl- SO42-
No Clue So Nothing
NO3- NO3
-Cl- SO42-
Observation : White precipitate
Observation :Brown ring
Confirmatory Tests for AnionsTEST FOR ANIONS
Anion test Anion test Anion test
Clue So Nothing
Cl- SO42- NO3
-
Reagent
No
Reagent Reagent
Clue So
NO3- Cl- SO4
2-
Hati H+ NO3-
Agong Ag+ NO3-
Balik Ba 2+ Cl -
Haji H+ Cl -
Hendak H+ SO42-
Fetrah Fe 2+ SO42-
Harta H+ SO42-
Confirmatory Tests for Anions
Anions
CO3 2-
Cl-
SO4 2-
NO3 -
+ HNO3
+ AgNO3
+ Dilute acid
+ HCl+ BaCl2
+ dilute H2SO4
+ FeSO4
+ concentrated H2SO4
Effervescence – CO2
Lime water turns milky
Ionic equation : 2H+ + CO32- H2O +
CO2 White precipitate
Ionic equation : Ag+ + Cl- AgCl
White precipitate
Ionic equation : Ba2+ + SO42- BaSO4
Brown ring
Confirmatory Tests for Anions
Salt K1
Add BaCl2 solution + HCl acid
Inference : sulphate ion
White precipitateformed
Confirmatory Tests for Anions
Inference : chloride ion
Add AgNO3 solution + HNO3 acid
White precipitateformed
Salt K2
Confirmatory Tests for Anions
Inference :Nitrate ion
Brown ring formed
Add FeSO4 solution+ concentrated sulphuric acid
Salt K3
Confirmatory Tests for Anions
Effervescence,Gas bubbles,Gas turn lime water chalky
Add sulphuric acid
Inference :Carbonate ion
Salt K4
CONFIRMATORY TEST FOR CATIONS
(SODIUM HYDROXIDE AS REAGENT)
CATION
Colourless / Unchanges
Add/put in NaOH SOLUTIONWhite precipitate
Precipitate
Coloured
Green
Brown
Blue
Fe 2+
Fe 3+
Cu 2+
NH4+
White
Pb 2+ Zn 2+ Al 3+
Mg 2+ Ca 2+
PZAL
MgC
Undissolved / not solubleIn excess NaOH solution
Dissolved / solubleIn excess NaOH solution
Add / Put in EXCESS NaOH solution
Pb 2+ Zn 2+ Al 3+ Ca 2+Mg 2+
MgCPZAL
Dissolved / solublein excess NaOH solution
Undissolved / not solublein excess NaOH solution
Al 3+Pb 2+ Zn 2+ Mg 2+
MgC
Ca 2+
PZALDissolved Undissolved
White Unchanged
Ca 2+ Mg 2+
Calcium sulphate [ undissolved salt ]White Yellow Unchanged
Add KI solution
Add ion SO42- solution
Pb 2+ Zn 2+ Al 3+Lead (II) sulphate [ undissolved salt
]
Dissolved Unchanged
Zn 2+ Al 3+
Zn MAP
Add / put in NH3 solution
CONFIRMATORY TEST FOR CATIONS
(AMMONIA AS REAGENT)
CATION SOLUTION
Colourless / UnchangedPrecipitate
Add / put in NH3
NH4+ Ca 2+
Coloured White
Green
Brown
Blue
Fe 2+
Fe 3+
Cu 2+
Zn 2+
Mg 2+ Al 3+ Pb 2+
Dissolved / solublein excess NH3 solution
Undissolved / not solublein excess NH3
Add / put in EXCESS NH3
Zn 2+ Mg 2+ Al 3+ Pb 2+
Zn MAPDissolved Undissolved
Zn MAP
Mg 2+ Al 3+ Pb 2+
Dissolved Undissolved
White Soluble / colourless
Add / put in SO42- solution
Lead (II) sulphate [ undissolved salt ]
Pb 2+
Mg 2+ Al 3+
Colourless / unchangesWhite
Mg 2+ Al 3+
Add / put in EXCESS NaOH
Reaction of Cations with alkali solution
1. Positive ions are identified by their reactions with
a. sodium hydroxide NaOH solution b. Ammonia solution NH3
2. In these reactions, the cations (positive metal ions) produce different coloured precipitate which may or may not be soluble in excess alkali.
Reaction of Cations with alkali solution
See if Precipitatedissolves
5 drops of alkali(NaOH or NH3)
Solution of cations
Look for Look for precipitateprecipitate
Reaction of Cations with alkali solution
NaOH solution
A little In excess
Soluble ( , X )
Ca 2+ White precipitate X
Zn 2+ White precipitate Al 3+ White precipitate Pb 2+ White precipitate Mg 2+ White precipitate X
Cu 2+ Blue precipitate X
Fe 2+ Green precipitate X
Fe 3+ Brown precipitate X
Reaction of Cations with alkali solution
Ammonia solution , NH3
A little In excess
Soluble ( , X )
Ca 2+ No change Zn 2+ White precipitate Al 3+ White precipitate X
Pb 2+ White precipitate X
Mg 2+ White precipitate X
Cu 2+ Blue precipitate X
Fe 2+ Green precipitate X
Fe 3+ Brown precipitate X
Reaction of Cations with alkali solution
Salt K5
Add excess NaOH solution
White precipitateformed
Inference 2 : zinc, aluminium and lead(II) ionsWhite
precipitateDissolves in excess NaOH solution alkali
White precipitatedoes not dissolve in excess NaOH solution
Inference 3: magnesium or calcium ions
Inference 1 :
ammonium ion
Add 5 drops of NaOH solution
Reaction of Cations with alkali solution
Salt K6
Add 5 drops of NH3 solution Add NH3 solution in
excess
Inference 5 : zinc ion
White precipitateDissolve in excess NH3 solution
White precipitatedoes not dissolve in excess NH3 solution
White precipitateformed
Inference 6: magneisum, aluminium, lead(II) ions
No White precipitateformed
Inference 4 : calcium ion
Confirmatory Tests for Fe 2+ , Fe 3+ , Pb 2+ and NH4
+
Cation Name of Reagent Observation
Pb 2+ Add a few drops of potassium iodide
to the test tube containing 2 cm3 of lead(II) nitrate solution (Pb 2+ ions)
Add 2 cm3 of distilled water and boil the mixture. Cool the contents using running water from the tap.
Yellow precipitate is formed
Which dissolve in the hot water
and is reappear on cooling
Confirmatory Tests for Fe 2+ , Fe 3+ , Pb 2+ and NH4
+
Cation Name of Reagent Observation
Fe 2+ Add a few drops of Potassium hexacyanoferrate(III) solution to the test tube containing 2 cm3 of iron(II) sulphate solution (Fe 2+ ions)
Dark blue precipitate is formed
Confirmatory Tests for Fe 2+ , Fe 3+ , Pb 2+ and NH4
+
Cation Name of Reagent Observation
Fe 3+ Add a few drops of potassium thiocyanate solution to the test tube containing 2 cm3 of iron(III) sulphate solution (Fe 3+ ions)
Blood red solution is formed
Confirmatory Tests for Fe 2+ , Fe 3+ , Pb 2+ and NH4
+
Cation Name of Reagent Observation
NH4 + Add a few drops of Nessler reagent to the test tube containing 2 cm3 of ammonium chloride solution (NH4 + ions)
Brown precipitate is formed
Chemical test of Fe2+ ions and Fe 3+ ions.
Solution contains Fe2+ ions or Fe3+ ions.
Light blue precipitate
Dark blue precipitate
Fe2+ ions
Fe3+ ions
K4Fe(CN)6
Potassium hexacyanoferrate(II)
Test I
Chemical test of Fe2+ ions and Fe 3+ ions.
(i) Pour 2 cm3 of iron(II) sulphate solution and 2 cm3 of iron(III) chloride solution into two test tubes respectively. Then add a few drops of potassium hexacyanoferrate(II) solution to two test tubes, Fe 2+ ions solution will form light blue precipitate whereas Fe 3+ ions solution will form dark blue precipitate
Chemical test of Fe2+ ions and Fe 3+ ions.
Test II
Solution contains Fe2+ ions or Fe3+ ions.
No change
Blood red solution
Fe2+ ions
Fe3+ ions
Potassium thiocyanate
KSCN
Chemical test of Fe2+ ions and Fe 3+ ions.
(i) Pour 2 cm3 of iron(II) sulphate solution and 2 cm3 of iron(III) chloride solution into two test tube respectively. Then add a few drops of potassium thiocyanate solution to two test tubes, there is no change in Fe 2+ ions solution whereas Fe 3+ ions solution will form blood red solution.
Qualitative analysis to identify salts
Identify the salt S1
The following tests were carried out to identify salt S1. Based on the observations given for each test, state its inference. Finally, identify salt S1
Qualitative analysis to identify salts
Test Observation Inference
1. Heat S1 strongly in a test tube. Identify any gas liberated.Brown gas and a gas relights a glowing splinter are liberated.
Residue is brown when hot and yellow when cold
Nitrogen dioxide gas, oxygen gas released.
Residue is lead(II) oxide
2. Dissolve a spatulaful of S1 in distilled water. Divide into four portions and carry out the following tests:
Residue dissolve in acid to produce colourless solution
Fe 2+ , Fe 3+ or Cu 2+ ions may not be present
Qualitative analysis to identify salts
Test Observation Inference
(a) add solution until excess.
White precipitate, dissolve in excess NaOH solution
Zn 2+ , Al 3+ or
Pb 2+ ions may be present
(b) add solution until excess
White precipitate, insoluble in excess ammonia solution
Pb 2+ or Al 3+ ion may be present
Qualitative analysis to identify salts
Test Observation Inference
(c) add potassium iodide solution
Yellow precipitate formed
Confirm lead(II), Pb 2+ ions present
(d) add dilute , H2SO4 followed by FeSO4 solution. Carefully add about 1cm3 of concentrated H2SO4
Brown ring formed
Confirm nitrate , NO3
- ions present
Conclusion for salt S1 : Lead(II) nitrate
Identify the salt S2
Test Observation Inference
1. Pour about 2 cm3 of S2 into a test tube. Add NaOH solution until excess
White precipitate, dissolve in excess NaOH solution
Zn 2+ , Al 3+ or Pb 2+ ions may be present
2. Pour about 2 cm3 of S2 into a test tube. Add NH3 solution until excess
White precipitate, dissolve in excess ammonia solution
Zn 2+ ions may be present
Qualitative analysis to identify salts
Test Observation Inference
3. Pour about 2 cm3 of S2 into a test tube. Add dilute, HNO3 followed by silver nitrate, AgNO3 solution
No change Cl- ions not present
4. Pour about 2 cm3 of S2 into a test tube. Add dilute HCl solution, then add BaCl2 solution
White precipitate
SO42- ions
may be present
Conclusion for salt S2 : Zinc sulphate
SODIUM CARBONATE
AND
SODIUM NITRATE
Test 1Add dilute (any acid)
Test 2add dilute H2SO4 followed by FeSO4 solution. Carefully add 1of concentrated H2SO4
Test 3Add dilute , followed by silver nitrate, solution
Test 4Add dilute HCl, followed by barium chloride, BaCl2 solution
S O D I U M C A R B O N A T E S O D I U M N I T R A T E
Result 1Effervescence
Result 2No change
Result 3No change
Result 4No change
Result 1No change
Result 2Brown ring
Result 3No change
Result 4No change
SODIUM CHLORIDE AND
SODIUM SULPHATE
Test 1Add dilute (any acid)
Test 2add dilute H2SO4 followed by FeSO4 solution. Carefully add 1of concentrated H2SO4
Test 3Add dilute , followed by silver nitrate, solution
Test 4Add dilute HCl, followed by barium chloride, BaCl2 solution
S O D I U M C H L O R I D E S O D I U M S U L P H A T E
Result 1No change
Result 2No change
Result 3White precipitate
Result 4No change
Result 1No change
Result 2No change
Result 3No change
Result 4White precipitate
Exercise :Page 144: Quick Review APage 147: Quick Review B