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Bases

Acids. and. Bases. Properties of acids and bases. Get a spot plate. Rinse well with water. Add acid to 6 wells, base to the other four. Add litmus papers to 2 base wells and pH paper to another (for pH paper use a colour key to find a number). Record results. Repeat for acid.

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Bases

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  1. Acids and Bases

  2. Properties of acids and bases • Get a spot plate. Rinse well with water. Add acid to 6 wells, base to the other four. • Add litmus papers to 2 base wells and pH paper to another (for pH paper use a colour key to find a number). Record results. Repeat for acid. • Into the four base tubes add: a) two drops (or one strip) of phenolphthalein b) 2 drops of bromothymol c) a piece of Mg d) a small scoop of baking soda. Record results. Repeat for acid. • Cleanup(wash tubes,pH/litmus paper in trash).

  3. Observations *Usually, but not always NaOH(aq) HCl(aq) Taste Bitter Sour Feel (choose slippery or not slippery) Slippery Not slippery pH (# from the key) 14 1 Litmus (blue or red) Blue Red Phenolphthalein *Pink *Cloudy/ white Bromothymol *Blue *Yellow Magnesium NR Bubbles Baking soda NR Bubbles

  4. Historical views on acids and bases

  5. Ionization + H H O H O Cl Cl H H H Arrhenius’ theory • Acid  gives out H+ when in water (H3O+) • Base  gives out OH- in water + + Ionization?

  6. More theories • Bronsted-Lowry concept Acid  donates protons Base  accepts protons • Lewis theory Acid  accepts electron pair Base  donates electron pair

  7. Strong vs. weak • Strong: completely ionized (~99%) • Weak: not completely ionized (<50%) • Strong acids: Produce many H+ ions Know: HCl, H2SO4, HNO3, HBr, HI, HClO4 • Weak acids: Produce few H+ ions (ex: HC2H3O2) • Strong bases: Produce many OH- ions Know: Strong bases are all Group I and II oxides and hydroxides (ex: LiOH, Ba(OH)2, MgO) • Weak bases: Produce few OH- ions (ex: NH3)

  8. + + + H H O H O Cl Cl H H H Conjugate acids/bases • Bronsted  Acids and bases are identified based on whether they donate or accept H+. conjugate acid conjugate base acid base conjugate acid-base pairs • “Conjugate” acids and bases are found on the products side of the equation.

  9. The Brønsted definition means NH3 is a BASE in water — and water is itself an ACID

  10. Conjugate Pairs

  11. Learning Check! Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH-   Cl- + H2O H2O + H2SO4   HSO4- + H3O+

  12. Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: Practice problems HC2H3O2(aq) + H2O(l)  C2H3O2–(aq) + H3O+(aq) conjugate base conjugate acid acid base conjugate acid-base pairs OH–(aq) + HCO3–(aq)  CO32–(aq) + H2O(l) base acid conjugate base conjugate acid conjugate acid-base pairs • Reference: pg. 386 – 387 • Try Q18 (p389), Q 8 & 11 (p392): do as above

  13. Answers: question 18 HF(aq) + SO32–(aq)  F–(aq) + HSO3–(aq) (a) conjugate base conjugate acid acid base conjugate acid-base pairs (b) CO32–(aq)+HC2H3O2(aq)C2H3O2–(aq)+HCO3–(aq) base acid conjugate base conjugate acid conjugate acid-base pairs (c) H3PO4(aq) + OCl–(aq)  H2PO4–(aq) + HOCl(aq) conjugate base conjugate acid acid base conjugate acid-base pairs

  14. 8a) HCO3–(aq) + S2–(aq)  HS–(aq) + CO32–(aq) conjugate acid conjugate base acid base conjugate acid-base pairs 8b) H2CO3(aq) + OH–(aq)  HCO3–(aq) + H2O(l) acid base conjugate base conjugate acid conjugate acid-base pairs 11a) H3O+(aq) + HSO3–(aq)  H2O(l) + H2SO3(aq) conjugate base conjugate acid acid base conjugate acid-base pairs 11b) OH–(aq) + HSO3–(aq)  H2O(l) + SO32–(aq) conjugate acid conjugate base base acid conjugate acid-base pairs

  15. The pH scale is a way of expressing the strength of acids and bases. (pH = power of Hydrogen pH = -log[H+]Under 7 = acid 7 = neutralOver 7 = base

  16. pH of Common Substances

  17. Calculating the pH pH = - log [H+] Example: If [H+] = 1 X 10-10pH = - log 1 X 10-10 pH = - (- 10) pH = 10 Example: If [H+] = 1.8 X 10-5pH = - log 1.8 X 10-5 pH = - (- 4.74) pH = 4.74

  18. Try These! Find the pH of these: A 0.15 M solution of Hydrochloric acid pH = 0.82 2) A 3.00 X 10-7 M solution of Nitric acid pH = 6.52

  19. pH calculations – Solving for H+ If the pH of Coke is 3.12, [H+] = ??? Because pH = - log [H+] then - pH = log [H+] Take antilog (10x) of both sides and get 10-pH =[H+] [H+] = 10-3.12 = 7.6 x 10-4 M *** to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button

  20. Try this • A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution? 3.16 X 10-9 = [H+] • The pH of rainwater collected in a certain region of Toronto on a particular day was 4.82. What is the H+ ion concentration of the rainwater? [H+] = 1.51 x 10-5

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