Hydrogen Ions and Activity

1. Chapter 19 Hydrogen Ions and Activity ***CHANGE notes packet….update!!! May 2011

3. Hydrogen Ions from Water Self ionization of water- the reaction in which 2 water molecules react to give ions Proton Hydronium ion (extra H+) H3O+ H2O loses a H+

4. What do the new symbols mean? • [ ] means concentration of the compound or ion inside the brackets • So…..[H+] = 4.3 x 105M means that the concentration of hydrogen ion in the solution that you are examining is 4.3 x 105M (moles per liter)

5. Neutral solution: • [H+] and [OH-] are equal • [H+] = 1 x 10-7 M • [OH-] = 1 x 10-7 M • Ion-product constant for water (Kw) is the product of the [H+] and [OH-] • Kw = [H+] [OH-] = 1 x 10-14

6. Acidic solution [H+] > [OH-] Basic solution [OH-] > [H+] If the [H+] in a solution is 1 x 10-5 M What is the [OH-] of the solution? Is the solution basic or neutral?

7. pH Concept Power of hydrogen * pH = -log [H+] (Neutral solution [H+] = 1 x 10-7 M) pH = -log (1 x 10-7 ) pH = 7

8. Acidic solution pH < 7 [H+] > 1 x 10-7 M Neutral solution pH = 7 [H+] = 1 x 10-7 M Basic solution pH > 7 [H+] < 1 x 10-7 M Ex. [H+] = 1 x 10-2 pH = [H+] = 1 x 10-10 pH = 2 10

9. pOH The Power of Hydroxide * pOH = -log [OH-] * pH + pOH = 14 In an acidic solution with a pH of 3.25, are there any OH- ions? Yes 3.25 + pOH = 14 pOH = 14 – 3.25 = 10.75

10. What is the pH of a solution if the [H+] is  6.0 x 10-10 mol/L ?is it an acid or base? • pH = -log [H+] • pH = -log [6.0 x 10-10 ] • pH = 9.22 • Base NEW Calculator - (negative sign) LOG 6.0 EE -10 = OLDER Calculator Conc Log -

11. What is the [H+] if pH = 3.7? • pH = -log [H+] • -pH = log [H+] • -3.7 = 10H+ • [H+] = 10-3.7 • [H+] = 0.000199526 • [H+] = 2.0 x 10-4 M 3.7 - 2nd button Log (which is 10x)

12. What is the pH of a solution if [OH-] is 4.0 x 10-11 mol/L? Is it an acid or a base? 1. calculate pOH 2. calculate pH (pH = 14 – pOH) Step 1: Step 2: pOH = -log [OH-] pOH = -log 4.0 x 10-11 pOH = 10.39 pH = 14 – 10.39 pH = 3.6 SO……IT’s an ACID 4 - (negative sign) 2nd button 10x button X (times) 2.5 = log button

13. [OH-] 1.0 x 10-14 [OH-] 10-pOH 1.0 x 10-14 [H+] -Log[OH-] [H+] pOH 10-pH 14 - pOH -Log[H+] 14 - pH pH

14. Acid: hydrogen-ion donor : an acid is defined as a hydrogen ion donor (gives) Base: hydrogen-ion acceptor: a base is defined as a hydrogen ion acceptor (takes) Conjugate Acid “Base” Accepts a H “Acid” Gives a H+ Conjugate Base

15. Conjugate acid- a particle formed when a base gains a hydrogen ion Conjugate base- a particle that remains when an acid has donated a hydrogen ion Conjugate acid-base pair- 2 substances that are related by the loss or gain of a single hydrogen ion

16. Conjugate Base Acid gives a H+ HCl(g) + H2O(l) → H3O(aq) + Cl-(aq) Conjugate Acid Base Accepts a H

17. Amphoteric- a substance that can act as both an acid and a base H2SO4 + H2O → H3O+ + HSO4- Acid gives H+ Conjugate Base Conjugate Acid Base Accepts H+

19. Strengths of Acids & Bases **** • Strength: depends on how much they ionize in water • Strong acids completely ionize in water • Weak Acids: ionize only slightly in water

20. Concentration vs Strength • Concentration ***** • Strength ***** • number of moles of acid/base in a given volume • How many of the molecules break into ions A concentrated but weak acid can be very corrosive. A dilute strong acid can also be very damaging

21. Bases • Strong ***** • Weak ***** • Completely dissociate into metal ions, hydroxide ions in water • Partially dissociate into conjugate acid and hydroxide ions

22. Acid-Base Reactions ******** • Neutralization Reaction: an acid and a base react to produce a salt and water • Double replacement reaction HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) acid base salt water H2SO4(aq) +2KOH(aq) → K2SO4(aq) + 2H2O(l) acid base salt water

23. Titration • 1. Add solution from the buret. • 2. Reagent (base) reacts with compound (acid) in solution in the flask. • 3. Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) • This is called NEUTRALIZATION.

24. PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do? But how much water do we add?

25. M1 • V1 = M2 • V2 M1 = 3.0 M ; V1 = 50.0 ml ; M2 = 0.50M Solve for V2 = = M1 • V1 M2 (3.0M) (50.0ml) 0.50M V2 = 300 ml You need a total volume of 300 ml so if you start with 50 ml you will need to add 250 ml of water

26. ***Rainwater • Rainwater is acidic (about 5.6 pH) • due to the reaction of carbon dioxide with water to form carbonic acid CO2 (g) + H2O(l) → H2CO3 (aq) • Both natural and artificial events can add to the acid rain

27. Acid Rain *** • Acid rain: a fog, • sleet, • snow • or rain • With a pH lower than about 5.6

28. What contributes to acid rain? • Natural events • Artificial sources (man-made)

29. Natural events such as: Volcanic Eruptions Forest Fires Lightning Bolts

30. Natural events such as: produce sulfur dioxide, sulfur trioxide, and nitrogen dioxide

31. Artificial sources (man made events) • Cars • power plants • factories • add pollutants to atmosphere

32. What are the major chemicals that create acid rain? Sulfur dioxide (SO2) and nitrogen oxides (NOx) So what happens? SO2 (g) + H2O(l) → H2SO3 (aq) SO3 (g) + H2O(l) → H2SO4 (aq) 2NO2 (g) + H2O(l) → HNO3 (aq) + HNO2 (aq)

33. Why do we care? • Acid rain can lower the pH of lakes and streams killing aquatic life • Acid rain can leach into soil killing plants • Acid rain can damage buildings (damages metal limestone and concrete.)

34. **What region of US is most affected?** Northeast (NY / PA / NJ) **Why?** Weather patterns carry the acid rain to the east. Soil in Northeast can not neutralize the acid rain

36. Acid Rain in China

37. What has the US done to reduce pollution? • Clean Air Act Amendments of 1990 address acid rain. • It imposes emission limits of sulfur dioxide. National sulfur dioxide emissions has decreased 12% from 1988 to 1997

38. How do they do it? Lower sulfur containing coal and install scrubbers in factory smokestacks

39. END