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Chapter 16: Acids and Bases. Students will learn… 3 definitions of Acids and Bases Acid Strength – pH scale Water as acid and base Calculating pH of strong.

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Presentation on theme: "Chapter 16: Acids and Bases. Students will learn… 3 definitions of Acids and Bases Acid Strength – pH scale Water as acid and base Calculating pH of strong."— Presentation transcript:

1 Chapter 16: Acids and Bases

2 Students will learn… 3 definitions of Acids and Bases Acid Strength – pH scale Water as acid and base Calculating pH of strong acids and bases Buffered solutions *Review naming acids, Pg 132 & 133

3 Three Definitions of Acids-Bases Arrhenius Br Ø nsted-Lowry Lewis

4 3 Definitions of Acids and Bases *H + ion always combines with water molecule, forming hydronium ion, H 3 O + AcidsBases ArrheniusProduce H + ion * (= proton) Produce OH – ion BrØnsted-LowryDonate H + ionsAccept H + ions LewisAccept an electron-pair Donate an electron-pair

5 Arrhenius Acids: HCl, HC 2 H 3 O 2, HCN Arrhenius Bases: NaOH, Ca(OH) 2 BrØnsted-Lowry Acids and Bases: can only be determined from chemical equations H 2 O + HCl → H 3 O + + Cl - base acid conjugate conjugate acid base conjugate pair

6 Conjugate Acid-Base Pair An acid and a base that only differ by one H + ion Always made of one reactant and one product Often in reversable reactions (Ex) HSO H 2 O ↔ SO H 3 O + acid base base acid HSO H 2 O ↔ H 2 SO 4 + OH - base acid acid base

7 Examples 1. Which of the following represent conjugate acid– base pairs? a)HCl, HNO 3 b)H 3 O +, OH – c)H 2 SO 4, SO 4 2– d)HCN, CN –

8 2. Write the conjugate base for each of the following. (a) HClO 4 (b) H 3 PO 4 (c) CH 3 NH 3 +

9 Strong vs. Weak Strong: 100% dissociation of H + or OH – – Strong electrolytes (conduct electricity very well) Weak: Less than 100% dissociation of H + or OH – – Weak electrolytes (conduct electricity somewhat)

10 Common Strong and Weak Acids/Bases Strong acids: H+7A, H 2 SO 4, HClO 4, HNO 3 Weak acids: HCN, HC 2 H 3 O 2 Strong bases: 1A+OH, Sr(OH) 2, Ba(OH) 2 Weak bases: NH 3 (ammonia) in water = NH 4 OH (ammonium hydroxide)

11 Relative Strength of Acids and Bases

12 Example Acetic acid (HC 2 H 3 O 2 ) and HCN are both weak acids. Acetic acid is a stronger acid than HCN. Arrange these bases from weakest to strongest : Cl – CN – C 2 H 3 O 2 –

13 Terms related Acids Amphoteric: Ions or molecules that can become an acid and a base (Ex) HSO H 2 O → SO H 3 O + acid base HSO H 2 O → H 2 SO 4 + OH - base acid (Ex) H 2 O + H 2 O → H 3 O + + OH - Oxyacids: acids containing oxygen (Ex) HNO 3, H 2 SO 4, HClO

14 Monoprotic Acids – Have one proton (H + ) to donate (Ex) HCl, HNO 3, HI, HClO 3 Diprotic Acids – Have more than two protons to donate (Ex) H 2 SO 4 Triprotic Acids – Have three protons to donate (Ex) H 3 PO 4

15 Self-ionization of Water In neutral water, (1)H 2 O + H 2 O ↔ H 3 O + + OH – (2) [H 3 O + ] = [OH – ] = 1×10 -7 mol/L (3) [H 3 O + ] · [OH – ] = (1×10 -7 )·(1×10 -7 )=1×10 25 °= K w K w = ion-product constant for water *The constant changes to the temperature

16 Acidic or Basic Solutions K w =1× always maintained [H 3 O + ][OH - ] pure water [H 3 O + ]=1×10 -7 mol/L[OH - ]= 1×10 -7 mol/L acidic solution [H 3 O + ]>1×10 -7 mol/L[OH - ]< 1×10 -7 mol/L basic solution [H 3 O + ]<1×10 -7 mol/L[OH - ]> 1×10 -7 mol/L

17 Common Misunderstanding An acidic solution has only H + ions A basic solution has only OH ‒ ions

18 Example (1) In an acidic aqueous solution, which statement below is correct? a)[H + ] < 1.0 × 10 –7 M b)[H + ] > 1.0 × 10 –7 M c)[OH – ] > 1.0 × 10 –7 M d)[H + ] < [OH – ]

19 (2) In an aqueous solution in which [OH – ] = 2.0 x 10 –10 M, the [H + ] = ________ M, and the solution is ________. a)2.0 × 10 –10 M ; basic b)1.0 × 10 –14 M ; acidic c)5.0 × 10 –5 M ; acidic d)5.0 × 10 –5 M ; basic

20 pH and pOH Scale pH = –log[H + ] – A compact way to represent solution acidity – pH decreases as [H + ] increases – [H + ] = 10 -pH pOH = ‒ log [OH ‒ ] – pOH decreases as [OH ‒ ] increases – [OH ‒ ] = 10 -pOH pH + pOH = 14

21 pH = 7; neutral pH > 7; basic  Higher the pH, more basic. pH < 7; acidic  Lower the pH, more acidic.

22 Acidity and pH Scale high pH = weak acid high pOH = weak base

23 Examples (1) Calculate the pH for each of the following solutions. a) 1.0 × 10 –4 M H + b) M OH –

24 (2) The pH of a solution is What is the [H + ] for this solution?

25 (3) Consider an aqueous solution of 2.0 × 10 –3 M HCl. What is the pH? *If the solution was 2.0 × 10 –3 M HNO 2, a weak acid, you can’t take the same approach. Why?

26 Buffered Solutions resists a change in its pH when either an acid or a base has been added.  Presence of a weak acid and its conjugate base buffers the solution.

27 Characteristics of Buffered Solutions 1.The solution contains a weak acid HA and its conjugate base A –. 2.The buffer resists changes in pH by reacting with any added H + or OH – so that these ions do not accumulate. 3.Any added H + reacts with the base A –. H + (aq) + A – (aq) → HA(aq) 4.Any added OH – reacts with the weak acid HA. OH – (aq) + HA(aq) → H 2 O(l) + A – (aq)

28 Example If a solution is buffered with NH 3 to which has been added NH 4 Cl, what reaction will occur if a strong base such as NaOH is added? a)NaOH + NH 3 → NaNH 4 O b)NaOH + NH 4 + → Na + + NH 3 + H 2 O c)NaOH + Cl – → NaCl + OH – d)NaOH + H 2 O → NaH 3 O 2


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