ACIDS, BASES SALTS.ppt

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1、ACIDS, BASES & SALTS,Topic 10: ACIDS, BASES & SALTS,2,T E R M S,ACIDS are substances that form hydrogen ions (H+(aq) when dissolved in water egHydrochloric acid HCl gives H+(aq) and Cl-(aq) ions,Sulphuric acid H2SO4 gives 2H+(aq) and SO42- ions Nitric acid HNO3 gives H+(aq) and NO3-(aq) ions. BASES

2、are oxides and hydroxides of metals that react and neutralise acids to form salts and water only. Bases which are soluble in water are called alkalis. Not all bases fit into these categories e.g. ammonia. Alkalis are substances that form hydroxide ions OH-(aq) in water eg Sodium Hydroxide NaOH gives

3、 Na+(aq) and OH-(aq) ions, Calcium Hydroxide Ca(OH)2 gives Ca2+(aq) and 2OH-(aq) ions., 29 1440,Topic 10: ACIDS, BASES & SALTS,3,In acid solutions there are more H+ ions than OH- ions. In alkaline solution there are more OH- ions than H+ ions. Acids that dissociate (ionize) to a large extent are str

4、ong electrolytes and Strong Acids. Acids that dissociate only to a small extent are Weak Acids and weak electrolytes Bases can be strong or weak depending on the extent to which they dissociate and produce OH ions in solution. Most metal hydroxides are strong electrolytes and Strong Bases. Ammonia,

5、NH3, is a weak electrolyte and Weak Base., 29 1440,Topic 10: ACIDS, BASES & SALTS,4,Basicity of Acid,It is the number of ionizable H+ ions present in an acid e.g. HCl is mono basic, it ionizes to produce one H+ ion HCl = H+ + Cl- H2SO4 is Dibasic, It ionizes to produce two H+ ions. H2SO4 = 2H+ + SO4

6、2- H3PO4 is Tribasic, it ionizes to produce three H+ ions. H3PO4 = 3H+ + PO43-, 29 1440,Topic 10: ACIDS, BASES & SALTS,5,Acidity of a Base,It is the ionizable OH- ions present in an alkali. e.g. NaOH is monoacidic NaOH = Na+ + OH- Ca(OH)2 is diacidic Ca(OH)2 = Ca2+ + 2OH-, 29 1440,Topic 10: ACIDS, B

7、ASES & SALTS,6,Common Strong Acids & their Anions, 29 1440,Topic 10: ACIDS, BASES & SALTS,7,Common Weak Acids & their Anions, 29 1440,Naming of Acids,Binary Acids (H+ and a nonmetal) hydro (nonmetal) -ide + ic acid HCl (aq) = hydrochloric acid Ternary Acids (H+ and a polyatomic ion) (polyatomic ion)

8、 -ate +ic acid HNO3 (aq) = nitric acid (polyatomic ion) -ide +ic acid HCN (aq) = cyanic acid (polyatomic ion) -ite +ous acid HNO2 (aq) = nitrous acid, 29 1440,Topic 10: ACIDS, BASES & SALTS,8,Formula Writing of Acids,Acids formulas get written like any other. Write the H+1 first, then figure out wha

9、t the negative ion is based on the name. Cancel out the charges to write the formula. Dont forget the (aq) after itits only an acid if its in water! Carbonic acid: H+1 and CO3-2 = H2CO3 (aq) Chlorous acid: H+1 and ClO2-1 = HClO2 (aq) Hydrobromic acid: H+1 and Br-1 = HBr (aq) Hydronitric acid:, 29 14

10、40,Topic 10: ACIDS, BASES & SALTS,9,Properties of Bases,Bases react with fats to form soap and glycerol. This process is called saponification. Bases have a pH of more than 7. Dilute solutions of bases taste bitter. Bases turn phenolphthalein PINK, litmus BLUE and bromthymol blue BLUE. Bases neutral

11、ize acids. Bases are formed when alkali metals or alkaline earth metals react with water. The words “alkali” and “alkaline” mean “basic”, as opposed to “acidic”., 29 1440,Topic 10: ACIDS, BASES & SALTS,10,Topic 10: ACIDS, BASES & SALTS,Naming of Bases,Bases are named like any ionic compound, the nam

12、e of the metal ion first (with a Roman numeral if necessary) followed by “hydroxide”.,Fe(OH)2 (aq) = iron (II) hydroxide Fe(OH)3 (aq) = iron (III) hydroxide Al(OH)3 (aq) = aluminum hydroxide NH3 (aq) is the same thing as NH4OH:NH3 + H2O NH4OH Also called ammonium hydroxide., 29 1440,11,Topic 10: ACI

13、DS, BASES & SALTS,Formula Writing of Bases,Formula writing of bases is the same as for any ionic formula writing. The charges of the ions have to cancel out. Calcium hydroxide = Ca+2 and OH-1 = Ca(OH)2 (aq) Potassium hydroxide = K+1 and OH-1 = KOH (aq) Lead (II) hydroxide = Pb+2 and OH-1 = Pb(OH)2 (

14、aq) Lead (IV) hydroxide = Pb+4 and OH-1 = Pb(OH)4 (aq) Lithium hydroxide = Copper (II) hydroxide = Magnesium hydroxide =, 29 1440,12,Topic 10: ACIDS, BASES & SALTS,13,Physical Properties of Acids & Bases,ACIDS Acids taste sour (e.g. vinegar, lemon juice). Acids are harmful to living cells. Aqueous s

15、olutions of all acids contain hydrogen ions. Acid turns blue litmus red. Strong acids are corrosive.BASES Alkalis are taste bitter Strong alkalis are corrosive. Aqueous solutions of all alkalis contain hydroxide ion. Alkalis turns red litmus blue. Soapy touch., 29 1440,Topic 10: ACIDS, BASES & SALTS

16、,14,Chemical Properties of Acids,With metals Metals above copper in the reactivity series will react with acids, giving off hydrogen gas, forming a salt. Mg(s) + H2SO4(aq) MgSO4(aq) + H2(g) With bases (metal oxides and hydroxides) The base dissolves in the acid and neutralises it. A salt is formed.H

17、2SO4(aq) + CuO(s) CuSO4(aq) + H2O(l) With metal carbonates With metal carbonates, effervescence occurs, salt, water and carbon dioxide gas is produced.2HCl(aq) + CaCO3(s) CaCl2(s) + H2O(l) + CO2(g), 29 1440,Neutralization,H+1 + OH-1 HOH Acid + Base Water + Salt (double replacement) HCl (aq) + NaOH (

18、aq) HOH (l) + NaCl (aq) H2SO4 (aq) + KOH (aq) 2 HOH (l) + K2SO4 (aq) HBr (aq) + LiOH (aq) H2CrO4 (aq) + NaOH (aq) HNO3 (aq) + Ca(OH)2 (aq) H3PO4 (aq) + Mg(OH)2 (aq) , 29 1440,Topic 10: ACIDS, BASES & SALTS,15,Topic 10: ACIDS, BASES & SALTS,16,Formation of Hydronium ion( H30+).,The hydrogen ion H+(aq

19、) does not exist as such in aqueous solutions. Hydrogen ions combine with water molecules to give a more stable species, the hydronium ion H3O+. HCl(aq) + H2O(l) = H3O+(aq) + Cl-(aq) Acids can contain different numbers of acidic hydrogens, and can yield different numbers of H3O+ ions in solution., 2

20、9 1440,Topic 10: ACIDS, BASES & SALTS,17,USES OF ACIDS,HCl in stomachH2SO4 in car batteries, as drying agentHNO3 in manufacturing of fertilizersEthanoic acid in food industryFatty acids in soap makingAscorbic acid in medicine, 29 1440,Topic 10: ACIDS, BASES & SALTS,18,Chemical Properties of Bases,Ne

21、utralisation. Ammonium salts are decomposed when mixed with a base eg sodium hydroxide. The ammonia is readily detected by its pungent odour (strong smell) and by turning damp red litmus blue. NaOH + NH4Cl = NaCl + H2O + NH3 Ionically: NH4+ + OH- = H2O + NH3 This reaction can be used to prepare ammo

22、nia gas and as a test for an ammonium salt., 29 1440,Topic 10: ACIDS, BASES & SALTS,19,Chemical Properties of Bases,Alkalis are used to produce the insoluble hydroxide precipitates of many metal ions from their soluble salt solutions. 2NaOH(aq) + CuSO4(aq) = Na2SO4(aq) + Cu(OH)2(s)ionically: Cu2+(aq

23、) + 2OH-(aq) = Cu(OH)2(s) This reaction can be used as a simple test to help identify certain metal ions., 29 1440,Topic 10: ACIDS, BASES & SALTS,20,TYPES OF OXIDES,: BASIC OXIDESOn the left and middle of the Periodic Table are the basic metal oxides eg Na2O, MgO, CuO etc They react with acids to fo

24、rm salts. e.g 2HCl + MgO - MgCl2 + H2OCuO + H2SO4 - CuSO4 + H2OThese metal oxides tend to be ionic in bonding character with high melting points. As you move left to right the oxides become less basic and more acidic., 29 1440,Topic 10: ACIDS, BASES & SALTS,21,TYPES OF OXIDES,ACIDIC OXIDES: On the r

25、ight of the Periodic Table the acidic oxides of the non-metals are present e.g. CO2, P2O5, SO2, SO3 etc.These tend to be covalent in bonding character with low melting/boiling points.Those of sulphur and phosphorus are very soluble in water to give acidic solutions which can be neutralised by alkali

26、s to form salts. SO2 + H2O - H2SO3 SO3 + H2O - H2SO4, 29 1440,Topic 10: ACIDS, BASES & SALTS,22,TYPES OF OXIDES,AMPHOTERIC OXIDES: They are metallic oxides.They react with both acids and alkalis. They are usually relatively insoluble and have little effect on indicators.An example is aluminium oxide

27、 dissolves in acids to form normal aluminium salts like the chloride, sulphate and nitrate. However, it also dissolves in strong alkalis like sodium hydroxide solution to form aluminate salts., 29 1440,Topic 10: ACIDS, BASES & SALTS,23,TYPES OF OXIDES,NEUTRAL OXIDES: They are non- metallic oxides. T

28、hey tend to be of low solubility in water and have no effect on litmus. do not react with acids or alkalis. eg CO carbon monoxide and NO nitrogen monoxide, H2O. There is no way of simply predicting this kind of behavior from periodic table patterns!, 29 1440,Topic 10: ACIDS, BASES & SALTS,24,PERIODI

29、C TRENDS IN OXIDES, 29 1440,Topic 10: ACIDS, BASES & SALTS,25,SALTS,When H+ ion of an acid is replaced by a metal ion, a salt is produced e.g. H2SO4(aq) + 2NaOH(aq) = Na2SO4(aq) + 2H2O(l) Here sodium sulphate (Na2SO4) is the salt formed. Salts are ionic compounds. Note: Ammonia (NH3) is an unusual b

30、ase - it does not contain a metal. It forms ammonium salts, containing the ammonium ion, NH4+. e.g. NH3(aq) + HNO3(aq) NH4NO3(aq) (ammonium nitrate), 29 1440,Topic 10: ACIDS, BASES & SALTS,26,Methods of making Soluble Salts,ACID + METAL SALT + HYDROGEN2) ACID + BASE SALT + WATER3) ACID + CARBONATE S

31、ALT + WATER + CARBON DIOXIDEACID + ALKALI SALT + WATERDIRECT COMBINATION, 29 1440,Topic 10: ACIDS, BASES & SALTS,27,Method 1 (Acid + Metal) Not suitable for making salts of metals above magnesium, or below iron/tin in reactivity. e.g. Zn + 2HCl - ZnCl2 + H2 Fe + H2SO4 - FeSO4 + H2Method 2 (Acid + Ba

32、se) Useful for making salts of less reactive metals, e.g. lead, copper. e.g. CuO + H2SO4 - CuSO4 + H2O MgO + 2HCl - MgCl2 + H2O Add excess base to acid., 29 1440,Topic 10: ACIDS, BASES & SALTS,28,Method 3 (Acid + Carbonate) Useful particularly for making salts of more reactive metals, e.g. calcium,

33、sodium. e.g. CaCO3 + 2HCl - CaCl2 + H2O + CO2. Na2CO3 + H2SO4 - Na2SO4 + H2O + CO2. Method 4 (Acid + Alkali) This is useful for making salts of reactive metals, and ammonium salts. It is different from methods 1-3, as both reactants are in solution. This means neutralisation must be achieved, by add

34、ing exactly the right amount of acid to neutralise the alkali. This can be worked out by titration e.g. NaOH + HCl - NaCl + H2O 2NH4OH + H2SO4 - (NH4)2SO4 + 2H2O, 29 1440,Topic 10: ACIDS, BASES & SALTS,29, 29 1440,Topic 10: ACIDS, BASES & SALTS,30,Making Insoluble Salts,This involves mixing solution

35、s of two soluble salts that between them contain the ions that make up the insoluble salt. It is made by two methods. PRECIPITATION BaCl2(aq) + MgSO4(aq) BaSO4(s) + MgCl2(aq)DIRECT COMBINATION Fe + S -heat- FeS, 29 1440,Topic 10: ACIDS, BASES & SALTS,31,PRECIPITATION REACTION, 29 1440,Topic 10: ACID

36、S, BASES & SALTS,32,Types of Salts,Normal Salts: Normal salts are formed when all the replaceable hydrogen ions in the acid have been completely replaced by metallic ions. HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) H2SO4(aq) + ZnO(aq) ZnSO4(aq) + H2O(l) Normal salts are neutral to litmus paper., 29 1440,T

37、opic 10: ACIDS, BASES & SALTS,33,Acid salts: Acid salts are formed when replaceable hydrogen ions in acids are only partially replaced by a metal. Acid salts are produced only by acids containing more then one replaceable hydrogen ion. Therefore an acid with two replaceable ions e.g. H2SO4 will form

38、 only one acid salt, while acid with three replaceable hydrogen ions e.g. H3PO4 will form two different acid salts. H2SO4(aq) + KOH(aq) KHSO4(aq) + H2O(l) H3PO4(aq) + NaOH NaH2PO4(aq) + H2O(l) H3PO4(aq) + 2NaOH(aq) Na2HPO4(aq) + 2H2O(l) An acid salt will turn blue litmus red. In the presence of exce

39、ss metallic ions an acid salt will be converted into a normal salt as its replaceable hydrogen ions become replaced. KHSO4(aq) + KOH = K2SO4(aq) + H+O(l), 29 1440,Topic 10: ACIDS, BASES & SALTS,34,Basic Salts: Basic salts contain the hydroxide ion, OH-. They are formed when there is insufficient sup

40、ply of acid for the complete neutralization of the base. A basic salt will turn red litmus blue and will react with excess acid to form normal salt. Zn(OH)2(s) + HCl(aq) Zn(OH)Cl(aq) + H2O(l) Zn(OH)Cl(aq) + HCl(aq) ZnCl2(aq) + H2O(l)Mg(OH)2(s) + HNO3(aq) Mg(OH)NO3(aq) + H2O(l) Mg(OH)NO3(aq) + HNO3(a

41、q) Mg(NO3)2(aq) + H2O(l), 29 1440,Topic 10: ACIDS, BASES & SALTS,35,HYDRATED & ANHYDROUS SALTS,Hydrated Salt: Salt that contains Water of Crystallization is called Hydrated Salt e.g. CuSO4.5H2O, Na2CO3.10H2O. Anhydrous Salt: Salt with out Water of Crystallization is called Anhydrous Salt. e.g. CuSO4

42、, Na2CO3, 29 1440,Topic 10: ACIDS, BASES & SALTS,36, 29 1440,Topic 10: ACIDS, BASES & SALTS,37,USES OF SALTS, 29 1440,Topic 10: ACIDS, BASES & SALTS,38,Self Ionization of Water,Pure water is often used as an example of non- conducting liquid. In fact water will conduct electricity if there is suffic

43、ient electrical energy present. The fact that pure water conduct electricity suggest that it contains ions. The ions present are due to water undergoing self ionization.2H2O(l) = H3O+(aq) + OH- (aq) The concentration of H3O+ ions in pure water at 25oC is 10-7 moles/dm3. The concentration of OH- ion

44、should also be 10-7 moles/dm3., 29 1440,Topic 10: ACIDS, BASES & SALTS,39,The pH Scale, 29 1440,Topic 10: ACIDS, BASES & SALTS,40,The pH scale is a measure of the relative acidity or alkalinity of a solution. It is defined as negative log of H+ ion concentration. pH = -log H+ Water is a neutral liqu

45、id with a pH of 7 (green). When a substance dissolves in water it forms an aqueous solution that may be acidic, neutral or alkaline. Acidic solutions have a pH of less than 7, and the lower the number, the stronger the acid is Neutral solutions have a pH of 7. These are quite often solutions of salt

46、s, which are themselves formed from neutralizing acids and bases. Alkaline solutions have a pH of over 7 and the higher the pH the stronger is the alkali. Weak alkalis like ammonia give a pH of 10-11 but strong alkalis like sodium hydroxide give a pH of 13-14., 29 1440,pH,A change of 1 in pH is a tenfold increase in acid or base strength. A pH of 4 is 10 times more acidic than a pH of 5. A pH of 12 is 100 times more basic than a pH of 10., 29 1440,Topic 10: ACIDS, BASES & SALTS,41,Topic 10: ACIDS, BASES & SALTS,