1 Substances are identified as acids based on their properties. Acids taste sour. Acids give the sour taste to many common foods. Acids will change the color of acid-base indicators. Indicators are substances that change their color at different pH levels. Some acids react with metals in a single displacement reaction to produce H 2 gas. Acids react with bases to produce salts and water. Acids are electrolytes even though they are covalent substances.

2 Binary Acids Binary Acids are acids that only contain 2 elements (hydrogen and one other). When dissolved in water, HF HCl HBr HI H 2 S are the most common binary acids Binary acids are named by adding the prefix “hydro-” to the root name of the second element and adding the suffix “-ic acid”. For Example: HF contains the fluoride ion, so the root name is “fluor” Therefore the entire name of HF is: hydrofluoric acid Practice: write the names of the other four common binary acids.

3 Oxy Acids Oxy Acids are acids that contain hydrogen, oxygen and usually just one other element. Oxy acids are named based on the name of the oxyanion (negatively charged polyatomic ion from earlier in the year). If the oxyanion name ends in –ite, then the acid name will end in –ous acid. If the oxyanion name ends in –ate, then the acid name will end in –ic acid (note no prefix is added). The rest of the acid name is the root name of the oxyanion. For Example: ClO  is the hypochlorite ion, so HClO is hypochlorous acid ClO 2  is the chlorite ion, so HClO 2 is chlorous acid ClO 3  is the chlorate ion, so HClO 3 is chloric acid ClO 4  is the perchlorate ion, so HClO 4 is perchloric acid Practice try naming any acid that contains a polyatomic oxyanion (See Figure 1.5 on page 443 for some examples)

4 Substances are identified as bases because of their properties. Bases taste bitter Bases will change the color of acid-base indicators. Indicators are substances that change their color at different pH levels. Bases feel slippery to the touch. Bases react with acids to produce salts and water. Bases are electrolytes. The most common bases in this classes are ionic compounds containing the hydroxide ion (OH  ) or the carbonate ion (CO 3 -2 ). Bases containing these ions are just named like the ionic compounds they are: NaOH is sodium hydroxide and Li 2 CO 3 is lithium carbonate.

5 Arrhenius Definition of acids and bases: An acid is any substance that increases the concentration of hydrogen ions in aqueous solution. A base is any substance that increases the concentration of hydroxide ions in aqueous solution. HCl (g) + H 2 O (l) → H 3 O  (aq) + Cl  (aq) KOH (s) + H 2 O (l) → K  (aq) + OH  (aq) H  + H 2 O (l) → H 3 O  A hydrogen ion in water will react with a water molecule to make the hydronium ion (H 3 O + ).

6 For example: what is the molarity of a solution that contains 0.53 moles of HCl dissolved in mL of aqueous solution? Concentration of acids and bases is usually described in Molarity For example: How many moles of H  ion are present in 36.7 mL of M aqueous HNO 3 ?

7 Acid Strength The strength of an acid is based on the percent ionization (or dissociation) that the acid undergoes when it is dissolved in water. Acid strength is not based on concentration of the acid or how harmful the acid may be (or not) A Strong acid is one that ionizes virtually 100% when it is dissolved in water. This means that there are no molecules of the original acid present in the solution- all of the molecules have been converted into ions. HCl (g) + H 2 O (l) ↔ H 3 O  (aq) + Cl  (aq) 100% on this side! Note that the double headed arrow shown here represents the two arrows pointing in opposite directions (as seen in the book). The two arrows (or the double headed arrow) means that a reaction is reversible-it can work in either direction. In the case of strong acids, none of the reverse reaction takes place! B7 End

8 Of all the acids we may use, memorize the fact that these seven acids are STRONG ACIDS: HCl, HBr, HI, HClO 4, HClO 3, HNO 3, H 2 SO 4 All other acids we use are considered to be weak acids in this class. A weak acid is any acid that partially ionizes (is partly dissociated) when it is dissolved in water. HF (g) + H 2 O (l) ↔ H 3 O  (aq) + F  (aq) Typically only a few % on this side! In the case of weak acids, much more of the reverse reaction takes place than the forward reaction! As a result, very little H 3 O  is created when the weak acid is dissolved in water. Therefore, the concentration of H 3 O  in the solution will be much less than the concentration of the acid that was put into the solution.

9 Brønsted-Lowry definition of acids and bases: An acid is any substance that donates hydrogen ions. A base is any substance that accepts hydrogen ions. HF (g) + H 2 O (l) → H 3 O  (aq) + F  (aq) The HF gives a H + ion to the water, so HF is an acid. The water accepts a H + ion, so the water is a base. H 3 O  (aq) + F  (aq) → HF (g) + H 2 O (l) What happens if the reaction is written in the opposite direction? What substance is an acid in this reaction? What substance is a base in this reaction?

10 A conjugate base is the substance remaining when an acid has given away a proton (H + ion) A conjugate acid is the substance that forms when a base accepts a proton (H + ion) HCl, HBr, HI, HClO 4, HClO 3, HNO 3, H 2 SO 4 Identify the conjugate bases that would be created by each of the acids below: H 3 PO 3 + Base ↔ HBase + + H 2 PO 3  Since the H 2 PO 3  ion was created by losing a H  ion, it is a conjugate base NH 3 + HAcid ↔ Acid  + NH 4  Since the NH 4  ion was created by gaining a H  ion, it is a conjugate acid HSO 3 , SO 3 , OH , CH 3 NH 2, HCO 3 , H 2 O Identify the conjugate acids that would be created by each of the bases below:

11 A conjugate acid is a substance that will behave like an acid in the “reverse” reaction of an acid-base reaction. A conjugate base is a substance that will behave like a base in the “reverse” reaction of an acid-base reaction. NH 3 (aq) + H 2 O (l) ↔ NH 4  (aq) + OH  (aq) Identify the acid, base, conjugate acid, and conjugate base in the reaction above. BACACB Note: Conjugates always appear on the right side of an acid-base equation. Note: Technically, all acid-base reactions can be written as equilibrium reactions. CH 3 CO 2 H (aq) + NaHCO 3 (aq) ↔ NaCH 3 CO 2 (aq) + H 2 CO 3 (aq) Identify the acid, base, conjugate acid, and conjugate base in the reaction above. Conjugate Acids and Bases can be recognized by how they behave in a reaction.

12 Polyprotic Acids: Acids that have more than one acidic hydrogen atom. These acids undergo successive ionization steps when they are dissolved in water. H 2 SO 4 (aq) + H 2 O (l) ↔ H 3 O  (aq) + HSO 4  (aq) HSO 4  (aq) + H 2 O (l) ↔ H 3 O  (aq) + SO 4  (aq) First Ionization: Second Ionization: Overall Reaction (steps 1 and 2 added together) H 2 SO 4 (aq) + 2 H 2 O (l) ↔ 2 H 3 O  (aq) + SO 4  (aq) What is the meaning of: monoprotic, diprotic and triprotic?

13 Notice that the HSO 4  ion can act either as an acid or as a base. It acts like an acid when mixed with water, but will act like a base when mixed with a strong acid. Amphoteric: substances that can act like an acid or like a base. Water is an example of a common substance that is amphoteric. H 2 SO 4 (aq) + H 2 O (l) ↔ H 3 O  (aq) + HSO 4  (aq) NH 3  (aq) + H 2 O (l) ↔ HO  (aq) + NH 4  (aq) Water acting as an acid: Water acting as a base: Notice that when water acts as an acid, it makes the conjugate base hydroxide ion. When water acts as a base, it makes the conjugate acid hydronium ion. Water will act the way it does based on what is put into it!

14 Lewis definition of acids and bases: An acid is any substance that accepts an electron pair to form a covalent bond. A base is any substance that donates a pair of electrons to form a covalent bond. BF 3 (aq) + F  (aq) ↔ BF 4  (aq) BF 3 (aq) + H 2 O (l) ↔ BF   OH 2 Draw Lewis structures of the reactants and products of these reactions to clearly see the definition of Lewis Acid and Lewis Base. B2 Start HCl (aq) + NaOH (aq) ↔ H 2 O (l) + NaCl (aq) Explain how the reaction above also fits with the Lewis definition of Acid-Base.

15 The strength of a conjugate is related to the strength of the substance that created it. A strong acid will create a conjugate base that is essentially not basic (extremely weak base). A weak acid will create a conjugate base that is a weak base (moderate). An extremely weak acid will create a conjugate base that is a strong base. A strong base will create a conjugate acid that is essentially not acidic (extremely weak acid). A weak base will create a conjugate acid that is a weak acid (moderate). An extremely weak base will create a conjugate acid that is a strong acid.

16 NH 3  (aq) + H 2 SO 4 (aq) ↔ HSO 4  (aq) + NH 4  (aq) The strength of acids and bases can be used to predict which direction a reaction will run. For example, in the reaction below will there be more products or more reactants present at equilibrium? To answer the question, never compare the strength of an acid to the strength of a base! Instead, compare the strength of an acid to the strength of the conjugate acid (or compare the strength of a base to the strength of the conjugate base. The reaction will always produce the weaker substances. In the reaction above, H 2 SO 4 is the acid and NH 4 + is the conjugate acid. Looking at figure 3.1 on page 459, we can see that H 2 SO 4 is a stronger acid than NH 4 +, therefore the reaction will have more products present (reaction equilibrium lies to the right or product side). We could have compared the base strength of NH 3 to HSO 4 . Looking at figure 3.1 on page 459, we can see that NH 3 is a stronger base than to HSO 4 , therefore the reaction will have more products present (reaction equilibrium lies to the right or product side). The stronger acid will always be on the same side of the equation as the stronger base, so we can use either one to determine the outcome.

17 We can use the ideas about relative acid and base strength to make some predictions about whether a solution will be acidic, basic or neutral when an acid is mixed with a base. If a strong acid is mixed with an equal amount of a strong base, the resulting solution will be neutral (pH of 7) because there will really be no acids or bases remaining in the solution after the reaction finishes. For example: HNO 3  (aq) + KOH (aq) ↔ KNO 3  (aq) + H 2 O (l) Since HNO 3 is a strong acid, the NO 3  ion is essentially not a base, so it will not effect pH. Since KOH is a strong base, the K + ion is essentially not an acid, so it will not effect pH. As a result, the only species in the solution that could have any impact on pH is the water, and pure water is neutral (pH = 7). Since the pH of the final solution is neutral (pH = 7), the reaction can be called a neutralization reaction.

18 If a strong acid is mixed with an equal amount of a weak base, the resulting solution will be acidic (pH less than 7) because the conjugate acid of the weak base really is an acid. HNO 3  (aq) + NH 3 (aq) ↔ NO 3  (aq) + NH 4 +1 (aq) Since HNO 3 is a strong acid, the NO 3  ion is essentially not a base, so it will not effect pH. Since NH 3 is a weak base, the NH 4 + ion is a weak acid, so it will make the solution acidic as seen in the equation below. Any solution containing H 3 O +1 is going to be acidic. NH 4 +1 (aq) + H 2 O  (l) ↔ NH 3 (aq) + H 3 O +1  (aq)

19 If a weak acid is mixed with an equal amount of a strong base, the resulting solution will be basic (pH greater than 7) because the conjugate base of the weak acid really is a base. HF  (aq) + KOH (aq) ↔ H 2 O (l) + F  (aq) + K +1 (aq) Since HF is a weak acid, the F  ion is a weak base, so it will effect pH. Since KOH is a strong base, the K + ion is not an acid, so it will not effect the pH. The equation below show why the resulting solution is basic. Any solution containing OH  1 is going to be basic. F  1 (aq) + H 2 O  (l) ↔ HF (aq) + OH   (aq)

20 If a weak acid is mixed with an equal amount of a weak base, we will need to know more details about the relative strength of each component before we can make a prediction about the resulting solution. HF  (aq) + NH 3 (aq) ↔ F  (aq) + NH 4 +1 (aq) We would need to compare the relative strengths of F  and NH 4  to determine which one of the two would dominate the situation. If the F  is stronger, then the solution would be basic. If the NH 4  is stronger, then the solution would be acidic. The two possible equations are shown below. Whichever of the two substances is stronger, that reaction will produce more of the ion that effects pH. F  1 (aq) + H 2 O  (l) ↔ HF (aq) + OH   (aq) NH 4 +1 (aq) + H 2 O  (l) ↔ NH 3 (aq) + H 3 O +1  (aq)