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Preparation of Salts

Preparation of Salts. What are salts?. When hydrogen in an acid is replaced by a metal H Cl ( aq ) + Na OH ( aq ) NaCl ( aq ) + H 2 O(l) the compound formed is called a salt. NaCl , ZnSO 4 , Ba (NO 3 ) 2 , KCl ….. are examples of salts.

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Preparation of Salts

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  1. Preparationof Salts

  2. What are salts? When hydrogenin an acid is replaced by a metal HCl(aq) + NaOH (aq) NaCl (aq) + H2O(l) the compound formed is called a salt. NaCl , ZnSO4, Ba(NO3)2, KCl….. are examples of salts.

  3. How can I know which salts are soluble?Solubility Patterns Soluble Salts Insoluble Salts Carbonates except sodium, potassium and ammonium carbonates Metal hydroxides except sodium, potassium and ammonium hydroxides • All sodium, potassium and ammonium compounds • All nitrates • Most chlorides except lead (II) chloride and AgCl • Most sulfates except lead (II) sulfate, barium sulfate and calcium sulfate.

  4. TO MAKE A SALT ASK YOURSELF:What is the solubility of the salt in water? Soluble Is it a sodium, potassium or ammonium salt? No Yes i) Acid Reaction ii) Titration Insoluble iii)Precipitation method

  5. i)Making soluble salts (except Na, K and NH4 salts) React an acid with: • Metals (above hydrogen in reactivity series) e.g. Zn, Al, Mg… • Metal Oxides or Hydroxide e.g. Cu(II)Oxide, MgO, Ca(OH)2… 3. Metal Carbonates e.g. CuCO3, CaCO3…

  6. 1. Acid + Metals Excess Mg + H2SO4 Fizzing observed • The gas pops with a lighted splint (H2 gas). • The solution in the test tube contains a salt (MgSO4) Mg(s) + H2SO4 (aq) MgSO4(aq)+ H2(g) Displacement Reaction

  7. To produce MgSO4 Crystals • Filter excess Mg using a funnel and filter paper. 2. Boil gently to concentrate solution 3. Cool to obtain crystals. When some salts form crystals, water from the solution chemically bounds to the salt “Water of Crystalization” MgSO4(aq) + 7H2O(l) MgSO4.7H2O(s)

  8. 2. Acid + Metal Oxide/ Metal Hydroxide Filter CuO(s) + H2SO4(aq) CuSO4 (aq) + H2O (l) Boil to concentrate and cool CuSO4 (aq) + 5H2O (l) CuSO4.5H2O (s) Neutralization Reaction

  9. 3. Metal Carbonates CuCO3(s) + H2SO4 (aq) CuSO4(aq) + CO2 (g) + H2O (l) CuCO3(s)+2HNO3(aq) Cu(NO3)2(aq) +CO2(g) + H2O(l) • The salts produced are also obtained by crystallization. • CO2 gas produced turns lime water milky. Neutralization Reaction

  10. ii)Making soluble salts (Na, K and NH4 salts) NaOH(aq) + HCl (aq) NaCl (aq) + H2O (l) • Na, K and NH4 salts are soluble, so excess dissolves in water, can’t be filtered. • But we need pure NaCl salt (no excess NaOH or HCl) • So NaOH and HCl must exactly react with each other. • We do titration to know the volume of HCl needed to react with NaOH.

  11. Acid only Acid>Base Salt only Base>Acid

  12. 1. Acid solution is clear. 2. Pink spot indicates you are close to the endpoint 3. When solution turns pale pink, you have reached endpoint (NEUTRAL: only NaCl present). 4. If solution turns dark pink ,you have gone too far (basic solution) 5. Repeat using the same amounts, without indicator. 6. Obtain salt by crystallization. Neutralization Reaction

  13. iii)Making insoluble salts

  14. Example 1: preparing pure Lead (II) Iodide (PbI2): Pb(NO3)2(aq) + 2KI (aq) PbI2(s) + 2KNO3 (aq) Pb2+ (aq) + 2I- (aq) PbI2(s)

  15. Example 2: preparing pure silver chloride (AgCl): AgNO3(aq) + NaCl (aq) AgCl (s) + NaNO3(aq) Ag+ (aq) + Cl- (aq) AgCl (s) Filter Wash with pure water

  16. Example 3: preparing pure Barium Sulfate (BaSO4): Mix solutions of soluble barium and sulfate compounds (e.g. barium nitrate and sulfuric acid). A white precipitate is formed. Ba2+ (aq) + SO42- (aq) BaSO4(s)

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