Acids n Bases_2

7/30/2019 Acids n Bases_2

1/33

1


2/33

2Acids

Have a sour taste. Vinegar is a solution of acetic acid. Citrus

fruits contain citric acid.

React with certain metals to produce hydrogen gas.

React with carbonates and bicarbonates to produce carbon

dioxide gas

Have a bitter taste.

Feel slippery. Many soaps contain bases.

Bases


3/33

3

Acid and Bases


4/33

4

Acid and Bases


5/33

5

Acid and Bases


6/33

6

Some Properties of Acids

Produce H+ (as H3O+) ions in water (the hydronium ion is a

hydrogen ion attached to a water molecule)

Taste sour

Corrode metals

Electrolytes

React with bases to form a salt and water

pH is less than 7

Turns blue litmus paper to red Blue to Red A-CID


7/33

7

Some Properties of Bases

Produce OH- ions in water

Taste bitter, chalky

Are electrolytes

Feel soapy, slippery

React with acids to form salts and water

pH greater than 7

Turns red litmus paper to blue Basic Blue


8/33

8

Acid/Base definitions

Definition #1: Arrhenius (traditional)

Acids produce H+ ions (or hydronium ionsH3O

+)

Bases produce OH- ions

(problem: some bases dont have hydroxideions!)


9/33

9Arrhenius acid is a substance that produces H+ (H3O

+) in water

Arrhenius base is a substance that produces OH- in water


10/33

10

Acid/Base Definitions

Definition #2: Brnsted Lowry

Acids proton donor

Bases proton acceptor

A proton is really just a hydrogenatom that has lost its electron!


11/33

11

A Brnsted-Lowryacidis a proton donor

A Brnsted-Lowrybaseis a proton acceptor

acid conjugatebase

base conjugateacid


12/33

12

ACID-BASE THEORIES

The Brnsted definition means NH3 isaBASEin water and water isitself anACID

BaseAcidAcidBase

NH4+ + OH-NH3 + H2O


13/33

13

Conjugate Pairs


14/33

14

Learning Check!

Label the acid, base, conjugate acid, andconjugate base in each reaction:

HCl + OH- Cl- + H2O

H2O + H

2SO

4 HSO

4- + H

3O+


15/33

15Acids & Base Definitions

Lewis acid - asubstance that

accepts an electronpair

Lewis base - asubstance thatdonates an electronpair

Definition #3 Lewis


16/33

16

Formation ofhydronium ion is also anexcellent example.

Lewis Acids & Bases

Electron pair of the new O-H bondoriginates on the Lewis base.

HH

H

BASE

OHOH

H+

CID


17/33

17

Lewis Acid/Base Reaction


18/33

18

The pH scale is a way ofexpressing the strength ofacids and bases. Instead ofusing very small numbers, wejust use the NEGATIVE powerof 10 on the Molarity of the H+(or OH-) ion.

Under 7 = acid7 = neutral

Over 7 = base


19/33

19

pH of Common

Substances


20/33

20

More About Water

H2O can function as both an ACID and a BASE.

In pure water there can beAUTOIONIZATION

Equilibrium constant for water = Kw

Kw = [H3O+

] [OH-

] = 1.00 x 10-14

at 25o

C


21/33

21

pH [H

+

] [OH

-

] pOH


22/33

22pH testing

There are several ways to test pH

Blue litmus paper (red = acid)

Red litmus paper (blue = basic)

pH paper (multi-colored)

pH meter (7 is neutral, 7base)

Universal indicator (multi-colored)

Indicators like phenolphthaleinNatural indicators like red cabbage,

radishes


23/33

23Paper testing

Paper tests like litmus paper and pH

paper Put a stirring rod into the solution

and stir.

Take the stirring rod out, and

place a drop of the solution fromthe end of the stirring rod onto apiece of the paper

Read and record the colorchange. Note what the colorindicates.

You should only use a smallportion of the paper. You can useone piece of paper for several

tests.


24/33

24

pH meter

Tests the voltage of theelectrolyte

Converts the voltage topH

Very cheap, accurate

Must be calibrated witha buffer solution


25/33

25

pH indicators Indicators are dyes that can be

added that will change color inthe presence of an acid or base.

Some indicators only work in aspecific range of pH

Once the drops are added, the

sample is ruined

Some dyes are natural, like radishskin or red cabbage


26/33

26Setup for titrating an acid with a base


27/33

27

Titration

1. Add solution from the buret.

2. Reagent (base) reacts withcompound (acid) in solution

in the flask.3. Indicator shows when exact

stoichiometric reaction hasoccurred. (Acid = Base)

This is calledNEUTRALIZATION.


28/33

28

PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH.

What do you do?

Add water to the 3.0 M solution to lowerits concentration to 0.50 M

Dilute the solution!


29/33

29

PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH. What doyou do?

But how much water

do we add?


30/33

30

PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH. What do

you do?

How much water is added?

The important point is that --->

moles of NaOH in ORIGINAL solution =

moles of NaOH in FINAL solution


31/33

31

PROBLEM: You have 50.0 mL of 3.0 M NaOH andyou want 0.50 M NaOH. What do you do?

Amount of NaOH in original solution =

M V =

(3.0 mol/L)(0.050 L) = 0.15 mol NaOH

Amount of NaOH in final solution must also =

0.15 mol NaOH

Volume of final solution =

(0.15 mol NaOH) / (0.50 M) = 0.30 L

or 300 mL


32/33

32

PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH. What doyou do?

Conclusion:

add 250 mL

of waterto50.0 mL of

3.0 M NaOH

to make 300mL of 0.50 M

NaOH.


33/33

33

A shortcut

M1 V1 = M2 V2

Preparing Solutions by

Dilution

Acids n Bases_2

Documents

Transcript of Acids n Bases_2