YOU SHOULD ALREADY KNOW..methods of purification and analysis:• describe methods of separations and purification for the components of a solid-liquid mixture• the use of filtration and crystallisation or evaporation
OBJECTIVES• (a) describe the techniques used in the preparation, separation and purification of salts as examples of some of the techniques specified in Section 1.2(a) – methods for preparation should include precipitation and titration together with reactions of acids with metals, insoluble bases and insoluble carbonates• (b) describe the general rules of solubility for common salts to include – nitrates, chlorides (including silver and lead), – sulfates (including barium, calcium and lead), – carbonates, hydroxides, – Group I cations and ammonium salts• (c) suggest a method of preparing a given salt from suitable starting materials, given appropriate information
RECAP• What is an acid? What is an alkali? – What are the ions produced in water? – What’s the pH range? – Typical reactions of acids with bases, carbonates and bases?• What is neutralization? – H+ + OH- → H2O
SALTS FOUND AT HOME
These are salts, too!
SO WHAT ARE SALTS…• H+ + OH- → H2O• HX + MOH H2O + MX
SO WHAT ARE SALTS…• Product of neutralization / acid-base reaction – But is neutralization the only way to produce a salt?• Metallic cation or ammonium + non-metallic anion ionic compounds• May be soluble (e.g. NaCl) or insoluble (e.g. CuCO3) in water.• Definition: a salt is a compound formed when the hydrogen ions in an acid is completely or partially replaced by metal ions from a base, or ammonium ions from ammonia.
Important SOLUBILITY OF SALTSSalts containing… Solubility in waterPotassium, Sodium, All solubleAmmonium (“PSA”), and otherGroup I metal ionsLead(II) ion All insoluble except lead(II) nitrateNitrates All solubleHalides (Chlorides, Bromides, All soluble except Ag+ andIodides) Pb2+Sulfates All soluble except Ba2+, Pb2+ and Ca2+Carbonates All insoluble except “PSA”
Enrichment WHY PREPARE SALTS？ NAME FORMUL USES A ammonium in soldering, as electrolyte in dry chloride NH4Cl cells sodium in baking powder, in manufacture of bicarbonate NaHCO3 glass sodium for seasoning and preserving food, chloride NaCl essential in life processes calcium as a drying agent to absorb chloride CaCl2 moisture, in freezing mixturessilver bromide AgBr in making photographic film potassium in manufacture of explosives; nitrate KNO3 fertilizer
Is the N salt o Precipitation soluble? method Ye s Are the reagents soluble? N Ye s o Acid and Titration “excess” method method Evaporation or crystallizationImportant
INSOLUBLE SALT PREPARATION(PRECIPITATION)• For preparing insoluble salts• Starting materials: – 1 solution contains the cation of the salt – 1 solution contains the anion of the salt• Starting materials must be soluble, e.g.: – Barium chloride – Barium nitrate – Hydrochloric acid
PRECIPITATION• Insoluble salt preparation• Preparation of + - Insoluble salt + - + - + - + -Soluble reagents Soluble product
SOLUBLE SALT PREPARATION• Titration• For preparing soluble salts• Reactants are both soluble – Acids (soluble) + Alkali (soluble) – Acids (soluble) + Carbonate (soluble)
TITRATION• Reactants are both soluble• Products are also soluble• Reactions:- Acid + Alkali (soluble) salt + water- Acid + carbonate (soluble) salt + water + carbon dioxide
TITRATION• Why must the amount of reactants be in exact stoichiometric ratio? – This is to make sure that both reactants are used up at the end of the reaction, leaving only the salt in the solution.• Why must the reactants only be acid with alkali or acid with soluble carbonate? - As water formed becomes part of the solvent, and carbon dioxide formed bubbles out and escapes the solution, - the reaction effectively leave only a salt at the end.
TITRATION• Suitable for preparing salts formed from STRONG ACID and alkali: – All “PSA” and other Group I salts – Reason: • Group I metals are highly reactive, which reacts with water. • Group I carbonates and hydroxides are all soluble cannot use acid + excess solid method
ACID + “EXCESS” METHOD• Why must the insoluble reactant be added in excess? – This is to make sure that ALL the acid has been used up in the reaction, and ONLY the salt produced is left in the solution. – Also: unreacted insoluble solid is easily removed at the end by filtration.
HOW ARE SALTS FORMED? – SUMMARY VIEW Acid + Acid Metal Acid + + Metal oxide Alkali (insoluble) Acid Salt (soluble) + Carbonate (insoluble) Salt + Salt (soluble)Important
HOW ARE THEY SEPARATED? Acid + Acid Metal Acid + + Metal oxide Alkali (insoluble) Acid Salt (soluble) +Carbonate(insoluble) Salt + Salt (soluble)
THINGS TO CONSIDER • Soluble or insoluble Property of salt • ions reactive or not • Soluble & insolubleSolubility of reagents • Workable combinations • FiltrationSeparation & purification • Evaporation / crystallization
NOW YOU TRY IT! (GROUPWORK)• Present a workable plan to prepare a given salt in the lab• Be creative! Feel free to use diagrams, pictures, flowcharts, etc• You may consider including some of the following: – Solubility of the salt – Names or chemical formulae of the reagents used, and their solubility – Method and techniques to be used, from putting reagents together all the way to getting a dry, pure salt sample at the end – Probable observations, precautions, etc
INSOLUBLE SALTS…• Barium sulfate, BaSOAcid 4 + Acid Metal Acid + + Metal oxide Alkali (insoluble) Acid Salt (soluble) + Carbonate (insoluble) Salt + Salt (soluble)
INSOLUBLE SALTS… Acid + Acid Metal Acid + + Metal oxide Alkali (insoluble) Acid Salt (soluble) + Carbonate (insoluble) Salt + Salt (soluble)
SOLUBLE SALTS• NaCl Acid + Acid Metal Acid + + Metal oxide Alkali (insoluble) Acid Salt (soluble) + Carbonate (insoluble) Salt + Salt (soluble)
SOLUBLE SALTS• CuSO4 Acid + Acid Metal Acid + + Metal oxide Alkali (insoluble) Acid Salt (soluble) + Carbonate (insoluble) Salt + Salt (soluble)
SALT PREPARATIONFLOWCHART Solubility of Solubility of What salt? reagents & Reactions Separation salt combination Evaporation soluble + HX + MOH soluble Salt + Salt Crystallization soluble Filtration, followed by HX + M evaporation or Soluble + Salt insoluble HX + MO crystallizatio n HX + MCO3 Soluble + Same as insoluble HX + MOH soluble above
TRY THESE ON YOUR OWN..• For the following salts, choose the appropriate method of preparation and describe the preparation with balanced equations and state symbols.• a) ammonium sulfate• b) zinc sulfate• c) calcium carbonate• d) lead(II) chloride• e) copper(II) chloride