Review of pH and preparation for the pH Lab

CH2O3 What would the chemical formula be for this molecule? Carbonic Acid What would the chemical formula be for this molecule? CH2O3

CO2 + H2O  H2CO3 H2CO3  HCO3- + H+ When you mix Carbon Dioxide and Water you make Carbonic Acid CO2 + H2O  H2CO3 However, since Carbonic Acid does not hold tightly to the Hydrogen atoms you get a lot of free H roaming around (an acid). H2CO3  HCO3- + H+

This is in carbonated drinks.

C2H4O2 What would the chemical formula be for this molecule? Acetic Acid What would the chemical formula be for this molecule? C2H4O2

C2H4O2  (in water becomes) C2H3O2- + H+ Acid in vinegar

pH = the number of H+ per liter of water. So if pH = the amount of H+, then a large pH should be more H+ But it does NOT! How can a bigger number mean less?

1/2 1/3 1/10 Let us consider fractions. Which is the most pie? 1/2 1/3 1/10 Which is the most pie? Notice: as the bottom of the fraction gets bigger the amount gets smaller.

1 pH The pH value goes on the bottom of a fraction. So as the pH value goes up the amount of H+ goes down.

However: the pH number is not alone on the bottom of the fraction. The pH value is actually a power of 10 on the bottom of the fraction. 1 pH

However: the pH number is not alone on the bottom of the fraction. The pH value is actually a power of 10 on the bottom of the fraction. 1 10pH

1 101 1 10 pH 1 = = 1 103 1 1,000 = pH 3 = 1 1010 1 10,000,000,000 pH 10 = =

But this does not make any sense! pH 1 = 1/10 H+ per liter of water. How do you have 1 tenth of a H+ per liter of water?

= 6 x 1023 There is one thing forgot to tell you! It is not 1/10 of a H+ It is 1/10 of a “gram” of H+ “gram” = 600,000,000,000,000,000,000,000 = 6 x 1023

1 10pH 1 100 A 0 pH solution would have Gram of H+ per liter.

A pH 0 solution Gram of H+ per liter. 1 100 Gram of H+ per liter. 1

A pH 0 solution Gram of H+ per liter. 1 Gram of H+ per liter. 1

1 1 x gram = 6 x 1023 A pH 0 solution Gram of H+ per liter. 6 x 1023 H+ per liter. 1 x

1 x A pH 0 solution 6 x 1023 H+ per liter. So, a pH 0 solution has 6 x 1023 H+ in each liter.

Or 1 100 A pH 0 solution would have Gram of H+ per liter. 6 x 1023 H+ per liter.

x 6 x 1023 1 101 Any math people out there? pH of 1 = 1/101 grams of H+ per liter x 6 x 1023 1 101 Any math people out there?

1 x 6 x 1023 101 6 1023 x x 101 1 1 6 1022 1 1 1 x

x 6 x 1023 6 1023 101 1 1 x 1 101 6 1022 1 1 1 x

6 1022 1 1 1 x 6 x 1022 H+ per liter 60,000,000,000,000,000,000,000

Even a liter of pH 14 has a lot of H+ in it. (a strong base) has a lot of H+ in it.

pH 14 x 6 x 1023 1014 1 pH 6 x 1023 1014 6 x 109 1 6,000,000,000 H+ per liter of water.

6 x 1016 H+ per liter A pH 7 (neutral) would have. So how can something with so many H+ ions NOT be highly reactive, how can it be neutral? It is balanced out by an equal amount of OH- (hydroxide ions).

Measuring pH: But not today

We are going to use Indicators: chemicals that change color based on the pH of the solution they are in.

Actually we are going to use papers that have be soaked in indicators = pH paper

measuring½ ml using the pipets.

1. Using a pipit, put ½ ml of a solution in wells 1. Using a pipit, put ½ ml of a solution in wells #1,2,and 3 of your chem-plate. (Be sure to put the same chemical in all three wells)

You should never have more than one chemical at your table. All the same chemical.

If you have more than 1 ph paper at your table then I will subtract 10 from your score.

2. Dip a small piece (about ½ cm) of pH paper into well # 1 (using tweezers) and then remove. Using the pH color card, determine the pH value before the strip has time to dry, and record the pH value in your chart above. pH = 10

Do NOT use this big color chart with for determining pH.

pH = 10

10

10 Base

10 Base Medium

Phenolphthalein Phen

D4

10 Base Medium D4

Bromthymol Blue B B

A5

10 Base Medium D4 A4

Universal Indicator U I

B7

10 Base Medium D4 A4 B7

1 pH 3 = 103 grams of H+ per liter Sample had a measured pH of 3 Gram of Hydrogen = 1 mole 1 103 pH 3 = grams of H+ per liter

Sample had a measured pH of 3 1 103 X 6 x 1023 moles H+ per liter

Sample had a measured pH of 3 1 103 6 x 1023 X H+ per liter 1

Sample had a measured pH of 3 6 x 1023 103 H+ per liter

Sample had a measured pH of 3 H+ per liter 6 x 1020