ACIDS AND BASES May 28, 2015

Transcription

1 ACIDS AND BASES May 28, 2015

2 WHAT ARE ACIDS? Acids are common Some are dangerous and can burn your skin Some are safe to eat and drink Stomach acid helps digest food

3 3 ACIDS Produce H + (as H 3 O + ) ions in water Taste sour Corrode metals React with bases to form salt and water Low ph <6 Turn Litmus Paper Red Form Electrolytes

4 ACID NOMENCLATURE REVIEW No Oxygenà Anion Ending -ide Acid Name hydro-(stem)-ic acid w/oxygen -ate -ite (stem)-ic acid (stem)-ous acid An easy way to remember which goes with which In the cafeteria, you ATE something ICky

5 STRONG ACIDS Examples of Strong Acids that ionize completely Hydrochloric Acid HCl Hydrobromic Acid HBr Hydroiodic Acid HI Sulfuric Acid H 2 SO 4 Nitric Acid HNO 3

6 WEAK ACIDS Examples of Weak Acids that do NOT ionize completely Formic Acid HCOOH AcePc Acid CH 3 COOH Hydrofluoric Acid HF Hydrocyanic Acid HCN

7 STRONG VS. WEAK ACIDS A dilute acid has lots of water and a small amount of acid A concentrated acid has lots of acid and not much water so must be handled carefully A strong acid releases lots of H + A weak acid releases fewer H +

8 WHAT ARE BASES (ALKALIS)? In our home we oren use bases to clean things. Ex. Bleach and toothpaste Some things are not acids or bases, we say that they are neutral Ex. Water

9 9 BASES Produce OH - ions in water Taste biver, chalky Feel soapy, slippery React with acids to form salts and water Have a high ph >7 Turn litmus BLUE

10 BASES Examples of Strong Bases LiOH - lithium hydroxide NaOH - sodium hydroxide KOH - potassium hydroxide RbOH - rubidium hydroxide CsOH - cesium hydroxide *Ca(OH) 2 - calcium hydroxide

11 BASES Examples of Weak Bases Ammonia NH 3 Pyridine C 5 H 5 N Ammonium hydroxide NH 4 OH

12 12 ARRHENIUS ACIDS AND BASES Acids produce H + (H 3 O + ) in aqueous solupons water HCl H + (aq) + Cl - (aq) Bases produce OH - in aqueous solupons water NaOH Na + (aq) + OH - (aq)

13 13 BRONSTED-LOWRY ACID Acids are hydrogen ion (H + ) donors Bases are hydrogen ion (H + ) acceptors Base Acid Conjugate Conjugate Acid Base

14 LEWIS ACIDS AND BASES Gilbert Lewis focused on the donapon or acceptance of a pair of electrons during a reacpon Lewis Acid - electron pair acceptor Lewis Base - electron pair donor Most general of all 3 definipons; acids don t even need hydrogen

15 ACIDS AND BASES COME IN PAIRS A conjugate base is the remainder of the original acid, arer it donates it s hydrogen ion A conjugate acid is the parpcle formed when the original base gains a hydrogen ion Thus, a conjugate acid- base pair is related by the loss or gain of a single hydrogen ion

16 ACIDS AND BASES NH 3 + H 2 O NH OH 1- base acid c.a. c.b. HCl + H 2 O H 3 O 1+ + Cl 1- acid base c.a. c.b. Amphoteric a substance that can act as both an acid and base

17 PH SCALE The ph scale is a way of expressing the strength of acids and base Each step on ph is 10x bigger/smaller Instead of using very small numbers, we just use the NEGATIVE power of 10 of the Molarity of the H + (or OH - ) ion Acids will have higher [H + ] Bases will have higher [OH - ] Under 7 = acid 7 = neutral Over 7 = base

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19 CALCULATING THE PH ph = - log [H + ] (Remember that the [ ] means Molarity) Example 1: If [H + ] = 1 x ph = - log 1 x If the concentration has a base of just 1, then the ph is the same as the exponent, but positive ph = - (- 10) ph = 10

20 CALCULATING THE PH ph = - log [H + ] (Remember that the [ ] means Molarity) Example 2: If [H + ] = 1.8 x 10-5 ph = - log 1.8 x 10-5 ph = - (- 4.74) ph = 4.74

21 NOW YOU TRY! Calculate the ph of the following solupons and determine if the solupon is acidic, basic, etc. 1. [H + ] = 1 x [H + ] = 4.8 x [H + ] = 6.4 x ph = 7 neutral ph = 4.32 acidic ph = 12.2 basic

22 POH SCALE SomePmes scienpsts find it convenient to express the basicity of a solupon on a poh scale poh = - log[oh - ] [OH - ] = OH - concentrapon (M) 1.0 x = [OH - ] x [H + ] = self- ionizapon of water ph + poh = 14 If you know either the ph or the poh of a solupon, then you can subtract for the other value

23 TRY THESE POH CALCULATION! Find the poh of these: 1) [OH - ] = 1.2 x 10-7 M ph = - log [H + ] poh = - log 1.2 x 10-7 poh = - (- 6.92) poh = ) [OH - ] = 3.3 x 10-8 M ph = - log 3.3 x 10-8 ph = - (- 7.48) ph = 7.48

24 PH CALCULATIONS SOLVING FOR H+ If the ph of Coke is 3.12, [H + ] =??? Because ph = - log [H + ] then - ph = log [H + ] Take anplog (10 x ) of both sides 10 - ph = [H + ] [H + ] = = 7.6 x 10-4 M *** to find anplog on your calculator, look for ShiR or 2 nd funcpon and then the log buvon