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Physical Science Notes 416-436
pH Math
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The pHunest math you will ever do

Know this

 

When dealing with pH math always remember that the equation will be 1x10-?  (?= to the negative something). The negative has to range from -1 to -14 because that is the numbers on the pH scale. To do the math you have to remember that your final product with your exponents HAS to be equal to -14.

 

e.g.: (1x10-) X (1x10-)

            - +- = -14

 

pH

 

dH2O  = distilled water

            = no conduction of electricity

            = no salt = no ions!

Distilled water is pure, which means there is nothing in it. Normal tap water contains other chemicals that cause it to conduct.

Sometimes water molecules break down in water causing ions charges in water. The picture below demonstrates its different components.

phbreakdown.jpg

pure H2O 1 H+    + 1 OH -

         conc.       conc.

         [H+]        [OH -]

1x107mol/L  1x107mol/L

 

.0000001 mol/L

 

Ionization Constant

 

Ionization Constant of water = Kw

Kw= 1x1014 = [H+] x [OH -]

                        (1x10-7)(1x10-7)

 

Adding  an Acid

 

In an Acid the [H+] > [OH- ]

                                   

ionization.jpg

By adding an Acid to water you have added H+. Therefore [H+]

 

HCl = 1x10- mol/L ==> [H+] = 1x10- mol/L

Acid = [H+] > [OH- ]

         (1x10-)(1x10-)

 

 

Adding a Base

 

Adding a base to water increases the [OH- ].

            1x10-4 = [H+] [OH- ]

                      (1x10-)(1x10-)

                      (1x10-)(1x10-)

                      (1x10-)(1x10-)

 

e.g.: you add .001 mol/L NaOH to water.

 

                        (1x10-) mol/L = [OH- ]

 

 

What will happen if

 

Adding an A ==> [H+]  [OH-]

Adding a B ===> [H+]  [OH-]

 

pH

 

pH = powerful H+ ion

      = how much H+ is in the water

 

pH chart

 

This chart might help you understand how the pH works on different amounts. See if you can find the pattern.

 

A= Acid

B= Base

 

Solution (aq)

[H+] mol/L

[OH-] mol/L

pH

0.1 mol/L HCl

(A)

1x10- mol/L

1x10- mol/L

pH 1

0.1 mol/L NaOH (B)

1x10- mol/L

1x10- mol/L

pH 13

1 x 10 mol/L HCl (A)

1x10- mol/L

1x10- mol/L

pH 2

1 x 10 mol/L KOH (B)

1x10- mol/L

1x10- mol/L

pH 12

1 x 10 mol/L HCl (A)

1 x 10 - mol/L

1 x 10- mol/L

pH 3

1 x 10 mol/L NaOH (B)

1 x 10- mol/L

1 x 10- mol/L

pH 11

1 x 104 mol/L HCl (A)

1 x 10-4 mol/L

1 x 10-10 mol/L

pH 4

1 x 104 mol/L NaOH (B)

1 x 10-10 mol/L

1 x 10-4 mol/L

pH 10

1 x 105 mol/L HCl (A)

1 x 10-5 mol/L

1 x 10-9 mol/L

pH 5

1 x 105 mol/L NaOH (B)

1 x 10-9 mol/L

1 x 10-5 mol/L

pH 9

1 x 106 mol/L HCl (A) 

1 x 10-6 mol/L

1 x 10-8 mol/L

pH 6

1 x 106 mol/L NaOH (B)

1 x 10-8 mol/L

1 x 10-6 mol/L

pH 8

 

Things to notice:

            -The pH is determined by the negative from the H+

            -If you add the negative from the H+ and the OH- it equals 14

 

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