Acids, Bases & pH

What are Acids? Acids taste SOUR –Lemons, vinegar Compounds that have Hydrogen (H + ) as their cation. Examples: –HCl – Hydrochloric Acid –H 2 SO 4 – Sulfuric Acid

Acids Form Hydronium Ions When acids dissolve in water, their ions separate. The Hydrogen ion (H + ) combines with H 2 O to form a Hydronium ion (H 3 O + ) Acids are PROTON DONORS (they give their hydrogen ion away) HCl+H2H2 O  +H 3 O + Cl -

More Info About Acids Anything with high concentration of Hydronium ion is considered to be an acid. Acids turn blue litmus paper RED

What are Bases? Bases are bitter and slippery. Bases either have Hydroxide (OH - ) as their anion OR they will form Hydroxide in solution Examples: –NaOH – Sodium Hydroxide –NH 3 - Ammonia

Bases Form Hydroxide Ions If the Hydroxide Ion is not already present in the Base, the base will make the Hydroxide ion by taking a Hydrogen ion from water. Bases are PROTON ACCEPTORS (they take a hydrogen ion) NH 3 +HOH  (Water) NH 4 + OH - +

More Info About Bases Anything with a high concentration of hydroxide ion is considered to be a base. Bases turn Red litmus paper BLUE

Can you tell the difference between an acid and a base? Let’s do a Lab to find out!

What is pH? The pH of a solution indicates its concentration of Hydronium Ions (H 3 O + ) or its concentration of Hydroxide Ions (OH - ) pH is short for the “power of Hydrogen” Something with more (OH - ) will be a base Something with more (H 3 O + ) will be an acid The pH scale ranges from 0-14

The Scale In a neutral solution, the pH is 7 –The amount of H 3 O + = OH - Acids have a pH of less than 7 –The amount of H 3 O + > OH - Bases have a pH of greater than 7 –The amount of OH - > H 3 O + Lots of OH - Lots of H 3 O + Neutral

Calculating pH Concentration is written as Molarity, or the number of moles per liter of solution Example: the Hydronium concentration of pure water is mol/L or M This means that in one liter of water, we have mol of Hydronium ions

Calculating pH pH is the negative of the power of 10 used to describe the concentration of Hydronium ions Example: hydronium concentration of pure water = (-7) = pH of 7

Small Differences in pH Mean LARGE Differences in Acidity Each number on the pH scale is a difference of a factor of 10 pH of 2 is 10 times stronger than a pH of 3 pH of 1 is 100 times stronger than a pH of 3 Example problem: the pH of apple juice is 3. the pH of coffee is 5. What is the acidity difference? There are 2 spaces between 3 and = Apple juice is 100 times more acidic than coffee

Review Questions Which ions do acids form in solution? –H3O+–H3O+ Which ions do bases form in solution? –OH - Classify the following as acidic, basic, or neutral. –Soap (pH = 9) basic –Sour liquid (pH = 5) acidic –Solution with 4x as many hydronium as hydroxide ions acidic –Pure water neutral Arrange the following substances in order of increasing acidity: vinegar (pH = 2.8), gastric juices from your stomach (pH = 2.0), soft drink (pH = 3.4) –Soft drink, vinegar, gastric juice

Determine the pH of a M solution of HCl = (-4) = pH of 4 What is the pH of 0.01 M solution of HClO 4, perchloric acid? 0.01 = (-2) = pH of 2 The concentration of hydronium ions in a certain acid is times the concentration of hydronium ions in a second acid solution. If the second solution has a pH of 6, what is the pH of the first solution? = steps down pH scale6-4 = pH of 2 Hand soap has a pH of 10. Drain cleaner has a pH of 14. How much more acidic is the hand soap than the drain cleaner? 4 steps = 10 4 = 10,000 times more acidic

Can you find the pH of the solutions you just tested? Let’s do a lab to find out!