1 / 40

Salts

Salts. Salts. All salts are ionic compounds. A salt is formed when a metallic ion or an ammonium ion (NH 4 + ) replaces one or more hydrogen ions of an acid. replaced by. H Cl. Na Cl. replaced by. H NO 3. NH 4 NO 3. Find out what is an acid salt!. Salts.

calvin
Download Presentation

Salts

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Salts

  2. Salts • All salts are ionic compounds. • A salt is formed when a metallic ion or an ammonium ion (NH4+) replaces one or more hydrogen ions of an acid. replaced by HCl NaCl replaced by HNO3 NH4NO3 Find out what is an acid salt!

  3. Salts • Where have you heard of salts? • Salts are essential to animal life in small quantities, but in large excess will be very harmful. • Are all salts salty? • Group I ions similar in size to sodium tend to give salty taste. Which ions do you think give a salty taste?

  4. Example • How do you form CaSO4? • Acid + Base  Salt + water CaSO4 Comes from base Comes from acid • One base that can be used is Calcium hydroxide. • One acid that can be used is Sulfuric acid. • Ca(OH)2 + H2SO4 CaSO4 + 2H2O • Can you use calcium carbonate or calcium?

  5. Example • How do you form NaNO3? • Acid + Base  Salt + Water NaNO3 Comes from base Comes from acid • One base that can be used is Sodium hydroxide. • One acid that can be used is Nitric acid. • NaOH + HNO3 NaNO3 + H2O

  6. Negative ion (anion) Sulfuric acid (H2SO4) Nitric acid (HNO3) Hydrochloric acid (HCl)

  7. Quickcheck • What acids do you use to get the following salts? • Sodium nitrate • Potassium phosphate • Ammonium ethanoate • Copper(II) iodide • Sodium citrate • Aluminium sulfate

  8. Water of crystallization • Many salts combine with water molecules to form crystals. • These water molecules are called water of crystallization. • Salts that contain water of crystallization are called hydrated salts. • Salts that do not contain water of crystallization are called anhydrous salts.

  9. Water of crystallization What does the ‘dot’ mean?

  10. Removing water of crystallization • Heating a hydrated salt removes water of crystallization. Heat hydrated copper(II) sulfate anhydrous copper(II) sulfate + water Heat CuSO4.5H2O CuSO4 + 5H2O

  11. Removing water of crystallization • Cobalt(II) chloride Heat hydrated cobalt(II) chloride anhydrous cobalt(II) chloride + water Heat CoCl2.6H2O CoCl2 + 6H2O Find out the use of cobalt(II) chloride paper in the lab.

  12. Soluble and insoluble salts Chlorides/ bromides/ iodides Carbonates Sulfates Nitrates • All are soluble except: • barium sulfate • calcium sulfate • lead(II) sulfate • All are NOTsolubleexcept: • Sodium carbonate • Potassium carbonate • Ammonium carbonate All are soluble. • All aresolubleexcept: • lead(II) chloride/bromide/iodide • silver chloride/bromide/iodide Sodium salts Potassium salts Ammonium salts All are soluble.

  13. Salt Preparation • There are 3 ways of preparing salts. But to choose which way depends on: • 1. Whether the salt is soluble in water? • 2. Whether the starting materials are soluble in water?

  14. Methods of preparing salts Is the salt soluble? Yes No • Reaction with acids • Acid + metal • Acid + base • Acid + carbonate Method 3: Precipitation Are the starting materials soluble? No Yes • Method 1: Reaction of acids with insoluble substances • Acid + metal • Acid + base • Acid + carbonate • Method 2: Titration • Acid + alkali • Acid + carbonate solution • Filter the mixture • Collect filtrate Salt solution • Concentrate • Crystallize • Filter Salt crystals (dry with filter paper)

  15. Method 1 • Recap: • Acid + Metal oxide/hydroxide Salt + Water • Acid + Carbonate  Salt + Water + Carbon dioxide • Acid + Metal  Salt + Hydrogen gas • In Method 1, all the substances in red are insoluble.

  16. Method 1 • The acid is reacted with an excess of the substances (metal, carbonate or base). • Why? Acid Insoluble base

  17. Method 1a • Acid + Metal  Salt + Hydrogen gas ZnSO4 Comes from metal Comes from acid • Zinc is insoluble in water and reacts with sulfuric acid. We can use zinc here.

  18. Method 1a: Using metal Keep adding zinc until no more effervescence is observed. zinc sulfate solution + unreacted zinc sulfuric acid • Filter the mixture • Collect filtrate zinc sulfate crystals zinc sulfate solution • Concentrate • Crystallize • Filter

  19. Metals that can be used • Only moderately reactive metals like zinc, aluminum, magnesium and iron can be used. • Not suitable for • Very reactive metals such as sodium, potassium and calcium. Why? • Unreactive metals like copper and silver. Why?

  20. Method 1b • Acid + Metal oxide/ hydroxide  Salt + Water CuSO4 Comes from metal oxide Comes from acid • Copper(II) oxide is insoluble in water and reacts with sulfuric acid. We can use Copper(II) oxide here. Why can’t we use copper metal?

  21. Method 1b: Using insoluble base Keep adding copper(II) oxide until no more effervescence is observed. Copper(II) sulfate solution + unreacted Copper(II) oxide sulfuric acid • Filter the mixture • Collect filtrate Copper(II) sulfate crystals Copper(II) sulfate solution • Concentrate • Crystallize • Filter

  22. Method 1c • Acid + Carbonate  Salt + Carbon dioxide + Water MgCl2 Comes from carbonate Comes from acid • Magnesium carbonate is insoluble in water and reacts with hydrochloric acid. • NOTE: ALL carbonates are insoluble except potassium, sodium and ammonium carbonate!

  23. Method 1c: Using carbonate Keep adding magnesium carbonate until no more effervescence is observed. Magnesium chloride solution + unreacted magnesium carbonate hydrochloric acid • Filter the mixture • Collect filtrate Magnesium chloride crystals Magnesium chloride solution • Concentrate • Crystallize • Filter

  24. Summary of method 1

  25. Method 2: Titration • Notice that all sodium, potassium and ammonium salts are SOLUBLE in water. • So you cannot use Method 1 for any of such salts! Why?

  26. Method 2: Titration • To tell when all the acid has been completely used up, we have to use titration, by using an indicator. • What is an indicator?

  27. Steps to titration (Sodium nitrate) Fill up a burette with dilute nitric acid and note down the initial burette reading (V1 cm3). V1 cm3 Record the final burette reading (V2 cm3). Hence, the volume of acid required for complete neutralization = (V2 – V1) cm3. Add one or two drops of methyl orange to the NaOH solution. The solution turns yellow. V2 cm3 Pipette 25.0 cm3 of dilute sodium hydroxide into a conical flask. Add dilute HNO3 from the burette slowly until the solution turns orange permanently. This is the end-point. The acid is all used up.

  28. Getting Sodium nitrate • Pipette 25.0cm3 of NaOH into a beaker. Then add (V2 – V1) cm3 of dilute nitric acid from the burette. This time do not add indicator. Why? • Heat to evaporate the water till it is saturated. • Cool the saturated solution so that the salt crystallizes. • Filter to collect the crystals. • Dry the crystals between a few sheets of filter paper.

  29. Titration • Simulation

  30. Summary of method 2

  31. Summary of method 2

  32. Insoluble salts • Easiest to prepare • Just need to use precipitation • Mix a solution containing the positive ions of the salt with another solution containing the negative ions of the salt to be prepared. • What salts are insoluble?

  33. Example: Lead(II) sulfate • Using lead(II) nitrate and dilute sulfuric acid • First, pour 50 cm3 of lead(II) nitrate solution into a small beaker. Add sulfuric acid (in excess) and stir until no more precipitate forms. • Filter and collect precipitate. • Wash the precipitate with a small amount of distilled water to remove impurities. • Allow the precipitate to dry on filter paper.

  34. Summary of method 3

  35. Test yourself • How do you get the following salts: • Magnesium sulfate • Lead(II) chloride • Potassium nitrate • Sodium sulfate • Zinc nitrate

  36. Questions • Are these salts soluble? • iron(III) nitrate • potassium carbonate • sodium ethanoate • silver chloride • lead(II) nitrate • copper(II) carbonate • ammonium iodide • titanium(IV) chloride • barium sulfate Yes Yes Yes No Yes No Yes Yes No

  37. Test yourself • Which method will you use to get the following salts: • Magnesium sulfate • Lead(II) chloride • Potassium nitrate • Sodium sulfate • Copper(II) chloride • Lead(II) carbonate • Silver chloride • Zinc chloride

  38. Test Yourself • When an acid Z is added to a solution of lead(II) nitrate, an insoluble precipitate is formed. • When Z is added to a solution of silver nitrate, an insoluble precipitate is formed too. • What acid could Z be? A) hydrochloric acid B) sulfuric acid C) nitric acid

  39. Test Yourself • A metal oxide A dissolves in sulfuric acid, hydrochloric acid and nitric acid and does NOT give any precipitate with any of the acids. Which of the following could be A? A) Barium oxide B) Calcium oxide C) Silver oxide D) Sodium oxide

More Related