Salts : Video Playlist

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8.2.2 - Laboratory Activity : Qualitative analysis of salts

Laboratory Activity 8.2.2: Qualitative analysis of salts

Aim: To confirm the presence of Mg²⁺ and NO^- ions in a salt sample, X

Material: » Magnesium nitrate powder » FeSO4 solution » Dilute sulphuric acid » Concentrate sulphuric acid » Sodium hydroxide solution » Ammonia solution

Apparatus: » Test tube » Test tube holder » Bunsen burner

Procedure:

	►	(A) Heat test 1. A spatula of compound is heated in a test tube, slowly at first and then strongly. 2. The observation and inferences made are recorded. Experiment Observation Inference (a) the colour of gases released (b) the effect on damp litmus (c) the effect on glowing splint
	►	(B) Brown ring test 1. Add water to compound X to make solution. 2. Add 2cm3 of dilute sulphuric acid and iron(II) sulphate, FeSO4 solution to the solution. 3. Concentrated sulphuric acid is then added slowly along the wall of the tilted test tube to the mixture without shaking.
	►	(C) Compound X is dissolved in distilled water. The solution is divided into 2 portion. 1. Sodium hydroxide solution is added to the first portion of solution X until in excess. 2. Aqueous ammonia is added to the second portion of solution until in excess.

Results:

	►	(A) Heat test ○ A spatula of compound is heated in a test tube, slowly at first and then strongly. The observation and inferences made are recorded. Experiment Observation Inference (a) the colour of gases released Brown gas. NO2 released. (b) the effect on damp litmus Blue litmus turned red. Acidic gas released. (c) the effect on glowing splint Rekindles glowing splint O2 released. ○ Probably NO3- present.
	►	(B) Brown ring test. ○ Brown ring formed at the middle section of the solution mixture in the test tube, nitrate ion present.
	►	(C) Compound X is dissolved in distilled water. ○ Experiment Observation Inference (a) Add with NaOH White precipitate, insoluble in excess NaOH May be Ca2+ or Mg2+ (b) Add with aqueous ammonia White precipitate, insoluble in excess NaOH May be Pb2+, Al3+ or Mg2+ ○ Probably NO3- present.

Conclusion:

►

The ions present in salt X are confirmed as Mg2+ and NO3- ions

↶ 8.2 Qualitative analysis of salts

⇲ For exercise(objective and subjective), download for free on Android OS.

8.2.1 - Laboratory Activity : Test for anions

Laboratory Activity 8.2.1: Test for anion

Aim: To test for carbonates, nitrates, chlorides and sulphates

Material: » Sodium carbonate » Sodium nitrate » Sodium chloride » Sodium sulphate » Zinc carbonate » Zinc nitrate » Zinc chloride » Zinc sulphate » Copper carbonate » Copper nitrate » Copper chloride » Copper sulphate

Apparatus: » Test tubes » Test tube rack » Test tube holder » Wooden splint » Litmus paper » Bunsen holder

Procedure:

	►	(A) Colour and solubility in water 1. The colour of each salt is observed 2. 10cm3 water is added in test tube. The mixture is shakes and its solubility is observed
	►	(B) Effect of heat 1. The salts are heated separately and the gas/gases which evolved are tested.
	►	(C) Effect of dilute acid 1. Dilute hydrochloric acid is added to the salts. 2. The gas is passed into limewater.
	►	(D) Confirmatory test for anions in solution i. Confirmatory test for nitrates ion. 1. Dilute H2SO4 and FeSO4 is added to NaNO3 and mixed. 2. Then, a few drops of concentrated H2SO4 is added slowly along the test tube side. 3. These steps are repeated with Zn(NO3)2 and Cu(CO3)2. ii. Confirmatory test for chloride ion. 1. Dilute HNO3 is added to NaCl solution, followed by silver nitrate solution. 2. Some Pb(NO3)2 solution is added to NaCl solution. 3. These steps are repeated with ZnCl2 and CuCl2. iii. Confirmatory test for sulphate ion. 1. Dilute HCl is added to Na2SO4 solution followed by PbCl2 solution. 2. Pb(NO3)2 solution is added to Na2SO4 solution. 3. These steps are repeated with ZnSO4 and CuSO4 solutions.

Result:

	►	(A) Colour and solubility in water Salt In water Colour of salt Na2CO3, ZnCO3, CuCO3 All salts are soluble except ZnCO3 and CuCO3. All salts are white except CuCO3 (green). NaNO3, Zn(NO3)2, Cu(NO3)2 All salts are soluble All salts are white except Cu(NO3)2 (blue) . NaCl, ZnCl2, CuCl2 All salts are soluble All salts are white except CuCl2 (blue). Na2SO4, ZnSO4, CuSO4 All salts are soluble All salts are white except CuSO4 (blue).
	►	(B) Effect of heat Salt Observation Inference Na2CO3 Does not decompose − ZnCO3 Gas released turns limewater chalky. Residue is yellow when hot, white when cooled. Blue litmus turns red. Carbon dioxide released. CO32- and Zn2+ ions present CuCO3 Gas released turns limewater chalky. Residue is black. Blue litmus turns red. Carbon dioxide released. CO32- and Cu2+ ions present NaNO3 Gas released rekindles glowing splint. Oxygen released Zn(NO3)2 Brown gas released, Glowing splint rekindled. Residue is yellow when hot, white when cold. Blue litmus turns red. NO2 and O2 released. NO3- and Zn2+ ions present CU(NO3)2 Brown gas released, Glowing splint rekindled. Brown residue. Blue litmus turns red. NO2 and O2 released. NO3- and Cu2+ ions present
	►	(C) Effect of dilute acid Salt Observation Inference Na2CO3, ZnCO3, CuCO3 Effervescence seen. Colourless gas produced turns limewater chalky. CO2 gas released. CO32- ion is confirmed to be present.
	►	(D) Confirmatory test for anions in solution Salt Observation Inference (i) Confirmatory test for nitrates ion. A brown ring is formed. NO3- ion is confirmed to be present. (ii) Confirmatory test for chloride ion. A white precipitate is formed. White precipitate which dissolves when heated, then forms back when cooled is formed. Cl- ion is confirmed to be present. PbCl2 which is insoluble in cold water is formed. (iii) Confirmatory test for sulphate ion. A white precipitate is formed. White precipitate insoluble in nitric acid. SO4- ion is confirmed to be present.

Discussion:

	►	○ All Na+, K+, NH4+ nitrates salts are soluble in water. ○ All chlorides are soluble except for AgCl, HgCl and PbCl2. ○ All sulphates are soluble except for PbSO4, BaSO4 and CaSO4. ○ All carbonates are insoluble except for Na2CO3 and K2CO3.
	►	The blue or green salts and solutions indicate the presence of Cu2+ ions. ○ All carbonates except Na2CO3 and K2CO3 release CO2 when heated. ○ All carbonates release CO2 when a dilute acid is added, confirming the presence of carbonate ions.
	►	○ All nitrates except NaNO3 and KNO3 release NO2 and O2 when heated. NaNO3 and KNO3 release only O2 when heated ○ All nitrates from a brown ring when concentrated H2SO4 is added to a mixture of nitrate, dilute H2SO4 and FeSO4 solution.
	►	All chlorides form a white precipitate with dilute HNO3 and AgNO3 solution. With Pb(NO3)2, a white precipitate soluble in hot water is formed.
	►	All sulphates form a white precipitate with dilute HCl and BaCl2 solution. They also form a white precipitate with Pb(NO3)2 solution.

Conclusion:

►

Anions can be tested by ○ observing the colour and solubility of salts ○ observing the effect of heat on salts ○ performing confirmatory tests for specific anions

↶ 8.2 Qualitative analysis of salts

⇲ For exercise(objective and subjective), download for free on Android OS.

8.2 Qualitative analysis of salts

Qualitative analysis of salts
■ Qualitative analysis

	►	A series of tests conducted on a chemical substance to identify the unknown component or components in it.
	►	Can determine the cation and anion present.

■ This video contains information on the qualitative analysis of salt .

■ Technique of qualitative analysis.

	►	Colour of salt
	►	Solubility of salt in water
	►	The effect of heat on the salt
	►	Flame test and gas test
	►	Identifying the precipitate formed with a specific chemical reagent
	►	Confirmatory tests for ions

Colour of salt
■ Colour of salt

	►	All cations are not coloured except copper(II) ions, [blue], iron (II) ion [green], iron (III) ion [yellow or brown].
	►	None of the anions are coloured.
	►	Colour Solid state Aqueous state Colourless None Salts for Ca2+, Mg2+, Al3+, Pb2+, NH+4 White Salts for Ca2+, Mg2+, Al3+, Pb2+, NH+4 None Black CuO, CuS, PbS, FeS None Brown Fe3+, PbO Salt for Fe3+ Green Fe2+, CuCO3, CuCl2 Fe2+, Cu2+ Blue Salt for Cu2+ Salt for Cu2+ Yellow PbO, PbI2, PbCrO4, BaCrO4 Fe3+, CrO2-4

Solubility of salt in water
■ Solubility of salt in water

	►	Solubility in water enable inferences to be formed on the type of cation and anion that may be present in the salt.
	►	Salt Solubility in water Na+, K+, NH+4 All are soluble Nitrates All are soluble Chlorides All are soluble except AgCl, HgCl and PbCl2 (soluble in hot water) Sulphates All are soluble except BaSO4, PbSO4 and CaSO4 Carbonates All are soluble except Na2CO3, K2CO3 and (NH4)2CO3 Oxides All are soluble except Na2O, K2O and CaO Hydroxides All are soluble except NaOH, KOH, Ca(OH2) and Ba(OH2)

Effect of heat on salts
■ Effect of heat on salts

	►	A salt may dissociate to release certain gases. (Give information regarding the identity of the anion)
	►	A salt may change in colour. (Give information regarding the identity of the cation)

■ This video contains information on the effects of heat on salts.

■ Gas tests (to identify the type of gas) :

	►	Observation of the colour
	►	Tested with damp blue litmus paper and damp red litmus paper
	►	Tested with limewater
	►	Tested with glowing wooden splinter
	►	Tested with acidic potassium manganate(VII) solution

■ Characteristics and confirmatory tests for several gases.

►

Gas Colour Smell Confirmatory Test Hydrogen Colourless Odourless Give 'pop' sound with lighted wooden splinter Oxygen Colourless Odourless Lights up a glowing wooden splinter Water vapour Colourless Odourless White anhydrous copper (II) sulphate turns blue Carbon dioxide Colourless Odourless Turns limewater chalky Ammonia Colourless Pungent Turns damp red litmus blue. Produces thick white fumes with hydrogen chloride gas Chlorine Greenish yellow Pungent Bleaches damp red litmus paper. Turns damp blue litmus paper to red and the bleaches it. Nitrogen dioxide Brown Pungent Turns damp blue litmus paper red Sulphur dioxide Colourless Pungent Bleaches the purple colour of acidic potassium manganate (VII) solution Hydrogen chloride Colourless Pungent Fumes with glass rod dipped in concentrated ammonia solution

■ Effects of heat on salts:

	►	Carbonate ions ○ All carbonate salts (except Na2CO3 and K2CO3) will decomposes when heated to release carbon dioxide gas, CO2. ○ Example: ${\mathit{MgCO}}_3(s)\begin{array}{c}\to \\ \Delta \end{array}\mathit{MgO}(s)+{\mathit{CO}}_2(g)$ ${\mathit{CuCO}}_3(s)\begin{array}{c}\to \\ \Delta \end{array}\mathit{CuO}(s)+{\mathit{CO}}_2(g)$
	►	Nitrate salts ○ Sodium nitrate and potassium nitrate decomposes when heated to produce oxygen gas, and nitrites ○ Other metal nitrates produces oxygen gas, nitrogen dioxide gas and metal oxides when heated. ○ Example: ${\text{2NaNO}}_3(s)\begin{array}{c}\to \\ \Delta \end{array}{\text{2NaNO}}_2(s)+{\mathit{O}}_2(g)$ $\mathit{Zn}{({\mathit{NO}}_3)}_2(s)\begin{array}{c}\to \\ \Delta \end{array}\mathrm{2ZnO}(s)+{\mathrm{4NO}}_2(g)+O_2(g)$
	►	Sulphate salts ○ Most sulphate salts are not decomposed by heat. ○ Only a few sulphates such as iron(II) sulphate, zinc sulphate and copper sulphate decompose to sulphur dioxide or sulphur trioxide when heated. ○ Example: ${\mathrm{2FeSO}}_4(s)\begin{array}{c}\to \\ \Delta \end{array}\mathit{Fe2}{O}_3(s)+{\mathit{SO}}_2(g)+{\mathit{SO}}_3(g)$ ${\mathit{ZnSO}}_4(s)\begin{array}{c}\to \\ \Delta \end{array}\mathit{ZnO}(s)+{\mathit{SO}}_3(g)$ ${\mathit{CuSO}}_4(s)\begin{array}{c}\to \\ \Delta \end{array}\mathit{CuO}(s)+{\mathit{SO}}_3(g)$
	►	Chloride salts ○ All chlorides salts are stable when heated except ammonium chloride. ○ Example: ${\text{NH}}_4\text{Cl}(s)\begin{array}{c}\to \\ \Delta \end{array}{\text{NH}}_3(s)+\text{HCl}(g)$

■ Gas produced in heat test enable inferences to be made on the types of salts.

►

Type of gas produced Types of ion present CO2 CO2-3 ion present (except Na2CO3 and K2CO3) O2 NO-3 ion present NO2 NO-3 ion present (except NaNO3 and KNO3) SO2 sO2-4 ion present NH3 NH-4 ion present

■ Residues in heat test enable inferences to be made on the types of salts.

►

Colour of original salts Colour of residue Inference White Yellow when hot, white when cooled ZnO, presence of ion Zn2+ White Brown when hot, yellow when cooled PbO, presence of ion Pb2+ Blue/Green Black CuO, presence of ion Cu2+ Green/Yellow Brown Fe2O3, presence of ion Fe3+ or Fe2+

Test for anions
■ Anions that are normally tested in qualitative analysis:

	►	Test for carbonate ions, CO2-3 ○ All carbonates except K2CO3 and Na2CO3 release carbon dioxide when heated. ${\mathit{MgCO}}_3(s)\begin{array}{c}\to \\ \Delta \end{array}\mathit{MgO}(s)+{\mathit{CO}}_2(g)$ All carbonates produce carbon dioxide when reacts with dilute acid. MgCO3(s) + 2HCl(aq) → MgCl2 + H2O(l) + CO2(g) Na2CO3(aq) + 2HCl(aq) → 2NaCl2 + H2O(l) + CO2(g) This video shows the test for carbonate ions.
	►	Test for nitrate ions, NO-3 ○ All nitrates except NaNO3 and KNO3 give out brown gas, nitrogen dioxide and oxygen when heated. NaNO3 and KNO3 release oxygen when heated. 2NaNO3(aq) → 2NaNO2(aq) + O2(g) 2Mg(NO3)2(aq) → 2MgO(aq) + 4NO2(g) + O2(g) This video shows the effects of heat on nitrate ions. ○ Brown Ring Test About 2cm3 nitrate solution is mixed with dilute sulphuric acid and iron(II) sulphate solution in test tube. Then a few drops of concentrated sulphuric acid are added slowly and carefully down the side of the test tube. A brown ring is formed between the layers of concentrated acid and the nitrate mixture. The brown ring, composed of a complex ion, confirm the presence of nitrate. This video shows the Brown Ring test for nitrate ions.
	►	Test for sulphate ions, SO2−4 ○ About 2cm3 sulphate solution is mixed with dilute hydrochloric acid followed by barium chloride solution. A white precipitate, barium sulphate forms, confirming the presence of a sulphate. Ba2+(aq) + SO2−4(aq) → BaSO4(s) This video shows the test for sulphate ions.
	►	Test for chloride ions ○ About 2cm3 of a chloride solution is mixed with dilute nitric acid followed by the silver nitrate solution. A white precipitate, silver chloride forms, confirming the presence of a chloride. Ag+(aq) + Cl−(aq) → AgCl(s) This video shows the test for chloride ions.

Laboratory Activity 8.2.1 :Test for anions

Test for cations
■ The following tests are conducted to identify cations in solutions:

	►	Test with aqueous sodium hydroxide, NaOh (aq)
	►	Test with aqueous ammonia, NH3 (aq)
	►	Confirmatory tests with specific reagents.

■ This video contains information on the test for cations

■ Test with aqueous sodium hydroxide, NaOH (aq)

	►	Colourless cation aqueous Observation Inferences Ammonia gas NH3 is released when heated up. NH4+ ions may be present. White precipitate not soluble in excess NaOH solution Mg2+ or Ca2+ ions may be present. White precipitate soluble in excess NaOH solution Zn2+ or Al3+ or Pb2+ ions may be present.
	►	Coloured cation aqueous Observation Inferences Blue precipitate not soluble in excess NaOH solution Cu2+ ions may be present. Green precipitate not soluble in excess NaOH solution Fe2+ ions may be present. Brown precipitate not soluble in excess NaOH solution Fe3+ ions may be present.
	►	This video contains information on the test for cations with NaOH

■ Test with aqueous ammonia, NH₃(aq)

	►	Observation Inferences No reaction Na4+ or Ca2+ ions may be present. White precipitate not soluble in excess NH3 solution Mg2+ or Al2+ or Pb2+ ions may be present. White precipitate soluble in excess NH3 solution Zn2+ ions may be present.
	►	Coloured cation aqueous Observation Inferences Blue precipitate soluble in excess NH3 solution forming dark blue solution Cu2+ ions may be present. Green precipitate not soluble in excess NH3 solution Fe2+ ions may be present. Brown precipitate not soluble in excess NH3 solution Fe3+ ions may be present.
	►	This video contains information on the test for cations with ammonia solution

■ Confirmatory test for :

	►	iron(II) ion, Fe2+ and iron(III) ion, Fe3+ Cation Potassium hexacyanoferrate(II), K4Fe(CN)6 Potassium hexacyanoferrate(III), K3Fe(CN)6 Potassium thiocyanate, KSCN Fe2+ Light blue precipitate Dark blue precipitate No red solution Fe3+ Dark blue precipitate Greenish brown precipitate Blood red solution
	►	lead (II) ion, Pb2+ Cation Potassium iodide, KI Potassium chloride, KCl Potassium sulphate, K2SO4 Pb2+ Yellow precipitate Pb2+ + 2I− → PbI2 Dissolves in hot water when heated White precipitate Pb2+ + 2Cl− → PbCI2 Dissolves in hot water when heated White precipitate Pb2+ + SO2−4 → PbSO4
	►	This video contains information on the confirmatory test for cations
	►	ammonium ion, NH4+ ○ Brown precipitate formed with Nessler reagent.

■ Analysis qualitative summary of cations:

►

Cation NaOH(aq) NH3(aq) Na2CO3(aq) H2SO4 or Na2SO4(aq) HCl or NaCl (aq) Confirmatory test Na+ − − − − − Flame test - yellow flame Al3+ White precipitate soluble in excess NaOH White precipitate soluble in excess NH3 White precipitate soluble in excess HNO3 − − − Pb2+ White precipitate soluble in excess NaOH White precipitate soluble in excess NH3 White precipitate soluble in excess HNO3 White precipitate White precipitate soluble in hot water KI - yellow precipitate KCL - white precipitate Both soluble in hot water Zn2+ White precipitate soluble in excess NaOH White precipitate soluble in excess NH3 White precipitate soluble in excess HNO3 − − White precipitate with potassium hyxacyanoferrate(II), K4Fe(CN)6 Mg2+ White precipitate soluble in excess NaOH White precipitate soluble in excess NH3 White precipitate soluble in excess HNO3 − − − Ca2+ White precipitate soluble in excess NaOH No precipitate White precipitate soluble in excess HNO3 White precipitate − − Cu2+ Blue precipitate soluble in excess NaOH Blue precipitate soluble in excess NH3 Blue precipitate Blue solution Blue solution Blue precipitate with potassium hyxacyanoferrate(III), K3Fe(CN)6 Fe2+ Dirty green precipitate insoluble in excess NaOH Dirty green precipitate soluble in excess NH3 Green precipitate Green solution Green solution Dark blue precipitate with potassium hyxacyanoferrate(III),K3Fe(CN)6 Fe3+ Brown precipitate soluble in excess NaOH Brown precipitate soluble in excess NH3 Brown precipitate Brown solution Brown solution Blood red solution with potassium thiocyanate, KSCN NH4+ NH3 released upon heating − − − − Brown precipitate with Nessler's reagent

Laboratory Activity 8.2.2 : Qualitative analysis of salts

Flow chart for qualitative analysis of anion and cation
■ Qualitative analysis of a salt

	►	To confirm the presence of the cation and anion of a named salt.
	►	To identify the cation and anion of one or more unknown salts.
	►	The animation below summarized the analysis of anions in salts.
	►	The animation below summarized the analysis of cations in salts.

← 8.1 Salts

Video Playlist →

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8.1.4 - Laboratory Activity : Constructing an ionic equation through the continuous variation method

Laboratory Activity 8.1.4: Constructing an ionic equation through the continuous variation method

Aim: To form a balanced ionic equation to represent the precipitation of barium chromate(VI) through the continuous variation method.
Problem statement: How can the ionic equation to represent the reaction between barium chloride and potassium chromate(VI) be determined?
Hypothesis: The height of the precipitate increases when the volume of BaCl2 solution is increased until it reaches a maximum height.
Variable:

	»	Fixed variable : Size of test tubes, concentration and volume of BaCrO4 solution, concentration of BaCl2 solution.
	»	Manipulated variable : Volume of BaCl2 solution
	»	Responding variable : Height of precipitate

Material: » Potassium chromate (VI) solution (0.5M) » Barium chloride solution (0.5M)

Apparatus: » 8 test tube » Test tube rack » Burette » Ruler » Retort stand

Procedure:

	►	The animation below shows the arrangement and the results of the experiment.
	►	1. 8 test tubes of the same size and height are prepared. 2. 5cm3 of potassium chromate(VI), K2CrO4 0.5M is poured into each test tube by using a burette. 3. Using another burette filled with barium chloride, BaCl2 solution. 1cm3 of BaCl2 solution, 0.5M is added into the first test tube, 2cm3 into the second test tube, and so on until 8cm3 into the eighth test tube. 4. Each test tube is shaken and left to stand on the rack until the precipitate settles. 5. The height of the precipitate in each test tube is measured with a ruler.

Observation:

	►	A yellow precipitate of barium chromate(VI) is formed when BaCl2 is added to K2CrO4 solution.
	►	The colour of the solution becomes lighter from test tubes 1 to 4 until it becomes colourless in test tube 5 to 8.

Results:

►

Test tube number 1 2 3 4 5 6 7 8 Volume of potassium chromate(VI) solution, K2CrO4 (cm3) 5 5 5 5 5 5 5 5 Volume of barium chloride solution, BaCl2 (cm3) 1 2 3 4 5 6 7 8 Height of precipitate (cm) 0.9 1.8 2.7 3.6 4.5 4.5 4.5 4.5

Discussion:

►

A graph of precipitation height is plotted against the volume of BaCl2 solution.

Calculation:

	►	The maximum height is obtained in test tube 5, showing that the reaction is complete in test tube 5. Thus 5cm3 of K2CrO4(0.5 M) reacts completely with 5cm3 of BaCl2(0.5M). The number of moles of K2CrO4 and BaCl2 is calculated as follows: Number of moles of K2CrO4 = $\frac{\mathrm{MV}}{1000}$ = $\frac{0.5\mathrm{\times }5}{1000}$ = 0.0025 moles Number of moles of BaCl2 = $\frac{\mathrm{MV}}{1000}$ = $\frac{0.5\mathrm{\times }5}{1000}$ = 0.0025 moles That is, if 0.0025 mole K2CrO4 reacts with 0.0025 moles BaCl2, then 1 mole K2CrO4 will react with 1 mole BaCl2.
	►	The chemical equation is written as: K2CrO4(aq) + BaCl2(aq) → BaCrO4(s) + 2KCl(aq) or the ionic equation involving Ba2+ and CrO2-4 ions only is: Ba2+(aq) + CrO2-4(aq) → BaCrO4(s)

Discussion:

	►	The yellow colour of the aqueous solution indicates excess CrO2-4 ions which have not reacted.
	►	The colourless solution(test tube 5 -8) shows that all the CrO2-4 ions have reacted with BaCl2 solution.

Conclusion:

	►	The height of the precipitate increases until all the CrO2-4 ions have reacted with the Ba2+ ions. ○ The ionic equation is: Ba2+(aq) + CrO2-4(aq) → BaCrO4(s)
	►	The hypothesis is accepted.

↶ 8.1 Salts

⇲ For exercise(objective and subjective), download for free on Android OS.

8.1.3 - Laboratory Activity : Preparation of insoluble salts

Laboratory Activity 8.1.3: Preparation of insoluble salts

Aim: To prepare insoluble lead(II) iodide through precipitation reaction.

Material: » Lead (II) nitrate solution (0.5M) » Sodium iodide

Apparatus: » Filter funnel » Glass rod » Beaker » Conical flask » Filter paper

Procedure:

►

1. 25cm3 of 0.5M of lead solution is added to 25cm3 of 0.5 M sodium iodide solution in a beaker. 2. The mixture is stirred thoroughly with a glass rod. A yellow precipitate is formed immediately. 3. The mixture is filtered to obtain the yellow solids of lead(II) iodide as the residue. 4. The residue is rinsed with distilled water to remove any traces of other ions in it. 5. The yellow solid is dried by pressing between two pieces of filter paper.

Discussion:

►

The chemical equation for the reaction in the preparation of lead(II) iodide is: ○ PbNO3(aq) + 2NaCl(aq) → PbCl2(s) + 2NaNO3(aq) ○ Ionic equation : Pb2+(aq) + 2Cl- → PbCl2(s)

Conclusion:

►

Insoluble salts of lead(II) iodide can be prepared by double decomposition through precipitation reaction.

↶ 8.1 Salts

⇲ For exercise(objective and subjective), download for free on Android OS.

8.1.2 - Laboratory Activity : Preparation of non-potassium and non-sodium soluble salts.

Laboratory Activity 8.1.2: Preparation of non-potassium and non-sodium soluble salts.

Aim: To prepare zinc sulphate through the reaction between an acid and a metal oxide

Material: » Sulphuric acid (1M) » Zinc oxide

Apparatus: » Conical flask » White tile » Beaker » Glass rod » Bunsen burner » Filter funnel » Filter paper » Measuring cylinder (100cm3)

Procedure:

►

1. 25cm3 of 1M sulphuric acid is put in a beaker and is heated. 2. Using a spatula, zinc oxide powder is added a little at a time, into the hot sulphuric acid while stirring continuously with a glass rod. The addition of zinc oxide is stopped when some white solids remain undissolved. 3. The mixture is filtered to remove the excess zinc oxide. 4. The filtrate is evaporated until a saturated solution (⅓ of original volume) of zinc sulphate is obtained. 5. The saturated solution is allowed to cool down until white crystal are formed. 6. The salt crystals are filtered, washed with a little distilled water and dried with filter paper.

Discussion:

	►	Zinc oxide is a white powder. It dissolves in sulphuric acid to for a zinc sulphate solution The equation for the reaction is as follows: ○ ZnO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)
	►	Excess zinc oxide is used to ensure that all the sulphuric acid is reacted, so as not to be present as an impurity in the zinc sulphate solution formed. The insoluble excess zinc oxide is then removed from the zinc sulphate solution by filtration.
	►	Zinc sulphate can also be prepared by the reaction between sulphuric acid and zinc carbonate or metal zinc.

Conclusion:

►

Zinc sulphate can be prepared by the reaction between zinc oxide and sulphuric acid.

↶ 8.1 Salts

⇲ For exercise(objective and subjective), download for free on Android OS.