Ch.9 J.C. Rowe

1. Windsor University School of Medicine ACIDS, BASES & SALTSNothing in the world is more dangerous than sincere ignorance and conscientious stupidity. Martin Luther King Jr. Ch.9 J.C. Rowe

2. What are Acids ? • An Acid is a substance which gives hydrogen ions when dissolved in water. • STRONG ACID is any acid that dissociates completely when it dissolves in water. • WEAK ACID is any acid that doesn’t dissociate completely when it dissolves in water. • Any compound that has a definite Ka (acidity constant) is a weak acid.

3. Strong Acids • The key point is that strong means 100% ionized. For some generic strong acid (with the generic formula HA) dissolved in water, we would write this equation: HA(s) ---> H+(aq) + A¯ • 100% of the HA molecules dissociate in solution. • The [H+] of a strong acid is equal to the concentration of the acid

4. Strong Acids vs. Weak Acids Strong Acids Weak Acids • HCl Hydrochloric acid • H2SO4 Sulphuric acid • HNO3 Nitric acid • HBr Hydrobromic acid • HI Hydroiodic acid • HF Hydrofluoric acid • H2SO3 Sulphurous acid • H2O water • HNO2 Nitrous acid • H2CO3 Carbonic acid • CH3COOH Acetic acid

5. What are Bases ? • A base is a substance which reacts with an acid to give a salt & water only. • A base is a substance which accepts protons. • STRONG BASE is any metal hydroxide that dissociates completely when it dissolves in water. • In fact all ALKALI METAL HYDROXIDES are strong bases. • WEAK BASE is a base that is partially dissociated when dissolved in water.

6. Strong Bases • the key point is that strong means 100% ionized. For some generic strong base (with the generic formula BOH) dissolved in water, we would write this equation: BOH(s) ---> B+(aq) + OH¯ • 100% of the BOH molecules dissociate in solution. • The [OH¯] of a strong acid is equal to the concentration of the base.

7. Strong Bases vs. Weak Bases Strong Bases Weak Bases • NaOH Sodium hydro-xide • KOH Potassium hydro-xide • LiOH Lithium hydroxide • NH3 Ammonia • CH3NH2 methylamine • (CH3) 2NH dimethyl-amine • H2O water • NH4OH Ammonium hydroxide

8. Kw: The Water Ionization Constant • Kw = [H3O+] [OH¯] • It can be determined by experiment and has the value 1.011 x 10¯14 at 25 °C. • Generally, a value of 1.00 x 10¯14 is used. • Hence, both [H3O+] and [OH¯] = 1.00 x 10¯7 M in pure water. This leads to several important results in the acid base world.

9. Result #1 • The pH of pure water is 7 • By definition, pH = -log [H3O+] • The pH of pure water then equals -log10-7 , which is 7.

10. Result #2 • If the pH or the pOH is known, the other can be found. • Take the negative logarithm of each side of the Kw equation as follows: • - log Kw = -log [H3O+] + -log [OH¯] • -log 1.00 x 10¯14 = -log [H3O+] + -log [OH¯] • Note the use of the add sign on the right side of the equation. The result is usually written as: pKw = pH + pOH = 14 • This is an extremely important equation. Learn it well

11. Result #3 • If the [H3O+] or the [OH¯] is known, the other can be found. • Simply divide Kw by the known value to get the other. • Suppose [H3O+] is known, then: • [OH¯] = Kw / [H3O+] • Suppose [OH¯] is known, then: • [H3O+] = Kw / [OH¯]

12. Result #4 • If one variable ( [H3O+] or [OH¯] ) changes value (either up or down), the other variable will change in the opposite direction. • The change in values will still preserve this fundamental equality: Kw = [H3O+] [OH¯] • Suppose [H3O+] became larger, therefore the [OH¯] becomes smaller. • Suppose [OH¯] became larger, therefore the [H3O+] becomes smaller. • This happens automatically and cannot be stopped.

13. Acidity & pH • The pH of a solution is defined as the negative log(base 10) of the hydrogen ion (H +) molarity. • The pOH of a solution is defined as the negative log of the hydroxide ion (OH-) molarity. • At or around room temperature, the sum of the pH + the pOH is always equal to 14.

14. Acidity & pH Cont’d. • pH = -log (H+) ; pOH = -log (OH-) • pH + pOH = 14 • Molarity (M) is the # mole of solute in 1 liter of solution. • Solution is an homogeneous mixture • Solute is the part of a solution that gets dissolved into the solvent. • Solvent is the part of a solution into which the solute is dissolved.

15. pH of solutions Cont’d. • Pure water has a pH of 7. It is neutral. • If you add an acid to water, the pH goes down. The solution becomes acidic. • If you add a base to pure water, the pH goes up. The solution becomes basic. • In a solution of a strong acid the hydrogen (H+) ion concentration equals the concentration of the acid bcz the dissociation of the acid is complete. • In a solution of a strong base, the hydroxide (OH- ) ion concentration equals the concentration of the base.

16. pH of solutions : acidic, basic & neutral

17. pH scale

18. The Observable Properties of Acids and Bases 1. Acid Property #1 Base Property #1:  • The word acid means "sour." All acids taste sour. • Well known from ancient times were vinegar, sour milk and lemon juice. • Aspirin (scientific name: acetylsalicylic acid) tastes sour if you don't swallow it fast enough. • All bases taste bitter. For example, mustard is a base. It tastes bitter. • Many medicines, because they are bases, taste bitter. • This is the reason cough syrups are advertised as having a "great grape taste." The taste is added in order to cover the bitterness of the active ingredient in cough syrup.

19. The Observable Properties of Acids and Bases 2. Acid Property #2 Base Property #2 • Acids make a blue vegetable dye called litmus turn red • Bases are substances which will restore the original blue color of litmus after having been reddened by an acid.

20. The Observable Properties of Acids and Bases 3. Acid Property #3:  Base Property #3 • Acids destroy the chemical properties of bases • Bases destroy the chemical properties of acids • Neutralization is the name for this type of reaction

21. The Observable Properties of Acids and Bases 4. Acid Property #4: Base Property #4:  • Acids conduct an electric current • Bases conduct an electric current. • This is a common property shared with salts. Acids, bases and salts are grouped together into a category called electrolytes, meaning that a water solution of the given substance will conduct an electric current. • Non-electrolyte solutions cannot conduct a current. The most common example of this is sugar dissolved in water.

22. The Observable Properties of Acids #5. • Upon chemically reacting with an active metal, acids will evolve hydrogen gas (H2). The key word, of course, is active. • Some metals, like gold, silver or platinium, are rather unreactive and it takes rather extreme conditions to get these "unreactive" metals to react. • Not so with the metals in this property. This include the alkali metals (Group I, Li to Rb), the alkaline earth metals (Group II, Be to Ra), as well as zinc and aluminum. Just bring the acid and the metal together at anything close to room temperature and you get a reaction. • Here's a sample reaction: Zn + 2 HCl(aq) ---> ZnCl2 + H2 • Another common acid reaction some sources mention is that acids react with carbonates (and bicarbonates) to give carbon dioxide gas: HCl + NaCO3 ---> CO2 + H2O + NaCl

23. The Observable Properties of Bases #5. • Bases feel slippery, sometimes people say soapy. This is because they dissolve the fatty acids and oils from your skin and this cuts down on the friction between your fingers as you rub them together. • In essence, the base is making soap out of you. Yes, bases are involved in the production of soap! • In the early years of soap making, the soaps were very harsh on the skin and clothes due to the high base content.

24. Salts & classifications of oxides Salts Monoatomic Ions Polyatomic Ions Classifications of Oxides

25. What are Salts? • Salts are the non-water product of an acid base neutralization. • There are four possible acid base reactions that produce salts. They are the reaction of a: 1) strong acid with a strong base.2) weak acid with a strong base.3) weak base with a strong acid.4) weak acid with a weak base.

26. Example reactions 1. • 1) strong acid with a strong base HCl + NaOH --> Na+ + Cl¯ + H2O A salt of a strong acid and a strong base will produce a solution with pH = 7.

27. Example reactions 2. • 2) weak acid with a strong base HC2H3O2 + NaOH --> Na+ + C2H3O2¯ + H2O A salt of a weak acid and a strong base will produce a solution with pH greater than 7. In other words, a salt of a weak acid produces a basic solution. notice that the salts produced an opposite pH to its "parent.“ salt of a weak acid ---> greater than 7 (basic) Leads to

28. Example reactions 3. • 3) weak base with a strong acid. NH3 + HCl --> NH4+ + Cl¯ A salt of a weak base and a strong acid will produce a solution with pH less than 7. In other words, a salt of a weak base produces an acidic solution notice that the salts produced an opposite pH to its "parent.“ • salt of a weak base ---> less than 7 (acidic) Leads to

29. Example reactions 4. • 4) weak acid with a weak base HC2H3O2 + NH3  --> NH4+ + C2H3O2¯ A salt of a weak acid and a weak base produces a solution whose pH depends on the strengths of the acid and base which made the salt.

30. SALTS • When the hydrogen atom of an acid is replaced by a metal, the result is a salt. • Normal salt is the result of replacement of more than one hydrogen by a metal atom. • Acid salt is the result of replacement of only one of two hydrogen ions.

31. How to name a salt ? • The name of a salt has 2 parts: • The 1rst is the name of the metal in the salt • The 2nd comes from the name of the acid used. • RULES: • The name ends in –IDE- if the salt does not have any oxygen in it. • The name ends in –ATE- if the salt does have oxygen in it. • EXCEPTION: “sulphite” is an old-fashioned name

32. Examples of naming

33. Properties of salts • Salts are ionic. They consist of cation & anion • Some salts are soluble in water; others are not. • If the salt can be dissolve in water, the solution will conduct electricity. It is an electrolyte. • Salts have no color unless they contain a transition metal in either or both of its ions. • Precipitate is a solid deposit that forms when a substance comes out of a solution.

34. Solubility of some salts in water

35. Monoatomic ions

36. Polyatomic ions with a-2charge/Derivative • SO42- sulfate ion • SO32- sulfite ion • CO32- carbonate ion • CrO42- chromate ion • Cr2O72- dichromate ion • HSO4- hydrogen sulfate ion • HSO3- hydrogen sulfite ion • HCO3- hydrogen carbo-nate ion

37. Polyatomic ions with a -3 charge/derivative • PO43- phosphate ion/ HPO42- hydrogen phosphate ion • PO33- phosphite ion/ H2PO4- dihydrogen phosphate ion • There is only one polyatomic cation, NH4+ = ammonium ion

38. How to classify oxides? • The oxides of non-metallic elements form acids with water. • Metal oxides are basic; they react with acids to give a salt & water only. • An acidic oxide reacts with water to produce an acidic solution. • A basic oxide reacts with water to produce an alkaline solution. • An amphoteric oxide(aluminium oxide) will react with both acids & bases • A neutral oxide(water, carbon monoxide) has no reaction with water.

39. Albert Schweitzer Example is not the main thing in influencing others. It is the only thing.