Notes: ACIDS AND BASES (use 19.1, 19.2 and 19.3 for space)

Transcription

1 Notes: ACIDS AND BASES (use 19.1, 19.2 and 19.3 for space) OBJECTIVES: Students will be able to (SWBAT) 1. Identifythe physical and chemical properties of acids and bases 2. Describe the strength of acids and bases 3. Identifyacids and bases by ph and poh

2 Notes: ACIDS AND BASES (use 19.1, 19.2 and 19.3 for space) QUESTIONS TO PONDER: 1. How are acids and bases different? How are they the same? 2. How do you know a solution is a strong electrolyte? What is happening to the ions in a strong electrolyte? 3. What does water ionize itself into? 4. What makes something an acid? Something a base? 5. What makes something a strong acid or base? A weak acid or base? 6. What is the difference between ph and poh? 7. What is the relationship between ph and acidity? Between ph and basicity? 8. How do you find ph from poh? 9. How can you find out if something is an acid or a base? Strong or weak? 10. What is happening during neutralization? What type of reacton is it?

3 19.1: Acids and Bases

4 Characteristics of Acids and Bases Acids 1. Tastes sour, tart 2. ph is less than 7 3. Turns bluelitmus paper red 4. Are electrolytes 5. Increases H + ion concentration in solution Reacts with alkali/alkaline earth metals and carbonates to produce gas Bases 1. Tastes bitter 2. ph is more than 7 3. Turns redlitmus paper blue 4. Are electrolytes 5. Increases OH - ion concentration in solution Feels slippery

5 Dissociation: Separation of Ions Ionic compounds separate, or dissociate, into component ions when put in solution

6 Electrolytes: solutions with ionic cpdsthat conduct electricity Types of Electrolytes Strong(electrolyte): ionic cpd dissociates completely Weak: ionic cpd dissociates partially (or very little) Non(electrolyte): covalent cpdsthat doesn t dissociate at all (but does dissolve in solution)

7 Na+ Na+ Cl- Cl-

8 Many salts (ionic cpd s) are strong electrolytes like sodium chloride. Strong Electrolytes

9 Weak Electrolytes Some salts do not dissociate easily, like silver chloride.

10 Covalent cpd slike sugar (sucrose) do not dissociate at all in water but do dissolve. Nonelectrolyte

11 Ions in solution conduct electricity

12 Water self ionizes itself H 2 O (H-OH) can slightly dissociate itself H 2 O H + + OH - H + : called hydrogen ionor proton OH - : called hydroxide ion [ ] symbol means concentration of Ex: [H + ] read as concentration of hydrogen ions/protons

13 H O - H H +

14 Actually, water molecules ionize with each other One H 2 O donates an H + to another water molecule H 2 O + H 2 O H 3 O + + OH - H 3 O + is called a hydroniumion Basically, acts like a holder of H + in water so, H + = H 3 O +

15 H O H HYDRONIUM ION, carrier of a H + HYDROXIDE ION H O - H + H

16 Water is neutral (ph of 7) In pure water, [H + ] = [OH - ] or [H 3 O + ] = [OH - ]

17 Acids and Bases Acidic solutions: higher [H + ] or [H 3 O + ] than [OH - ] Basic solutions: higher [OH - ] than [H + ] or [H 3 O + ] Acids: H + donors (gives up H + in solution) Bases: OH - donors (gives up OH - in solution)

18 Acid H + H + H + H + H + H + Cl - Cl - H + H + H + H + H +

19 H + donated to water molecules! H + H O H + Cl - Cl - H + H

20 Base OH - OH - Na + OH - Na + OH - OH - OH - OH -

21 Ammonia is a base But there are no OH - ions to give up!

22 Another Definition of Acids and Bases Acids: H + donors Bases: H + acceptors(takes H + in solution)

23 Ammonia is a H + ACCEPTOR! H H N + H + ions acceptedfrom a WATER MOLECULE! A BASE!!! H O - H H H

24 H + O H - Na + Na + O H - O H H -

25 19.2: Strengths of Acids and Bases Strongvs. Weak Strong Acids: very high [H + ] or [H 3 O + ] Strong Bases: very high [OH - ] Weak Acids: low [H + ] or [H 3 O + ] Weak Bases: low [OH - ] weak because ions do not completely dissociate low concentration in solution

26 Neutral Solutions [H + ] = [OH - ] Since water self-ionizes, amount of H + released = amount of OH - formed Pure Water is neutral (ph of 7)

27 STRONG ACID WEAK ACID H+ H+ H + H H H + H H+ H + H H + + H H + H + H + H + + H H H + + +

28 STRONG BASE WEAK BASE OH - OH - OH- OH OH - - OH - OH - OH - OH- OH - OH - OH - OH - OH- OH- OH - OH - OH - OH -

29 19.3: What is ph? ph: related to [H + ] measure of the acidity (or basicity) of a solution ph value < (less than) 7 is an acid ph value > (greater than) 7 is a base ph value = 7 is neutral

30 poh poh: related to [OH - ] measure of the basicityof a solution pohvalue < 7 is a base pohvalue > 7 is an acid pohvalue = 7 is neutral

31 Calculate ph or poh Of any solution, ph + poh= 14 Stomach acid: ph = 1.5 poh= = 12.5 Try this: pohof blood = 6.6 What is the ph? ph = 7.4

32 ph Scale = from 0 to 14

33 ph and pohscales are reversed 0

34 Strong Acids/Bases are at the ends of the scale Weak acids/bases are toward 7 (the middle)

35 Indicators: Indicators change colors when they detect the presence of an acid or a base Each type of indicator only detects at a certain range Common indicators: Red/blue litmus paper Phenolphthalein Universal indicator Cabbage juice

36

37 Acid or Base? Sodium Chloride solution is NEUTRAL. Na + Na + Cl - Cl -

38 Acid and Base Together H + Na H + + Cl Cl - - Cl - H + OH - Na + Na + OH - OH -

39 NEUTRALIZATION REACTIONS Acid + base salt (ionic cpd) + water Ex: Products of Neutralization rxn s: SALTand H 2 O DOUBLE REPLACEMENT REACTIONS HCl + NaOH NaCl + H-OH acid base salt water H + from acids and OH - from basescombine and form H-OH or H 2 O H 2O is NEUTRAL