2. - the basic idea that scientists went with for acids and bases was that acidic properties were related to the presence of hydrogen ions and basic properties related to the presence of hydroxide ions It was hard to believe that such a tiny hydrogen ion could exist on its own

3. It was later discovered that hydrogen bonded to water molecules, forming the hydronium ion H 3 O + (aq) Now we state that it is the presence of H 3 O + (aq) that contributes to acidic properties

4. Testing acids and bases A convenient and quick test is the litmus test However testing for the concentration of hydronium ions is a more effective way to determine the strength of acidity. Soren Sorensen introduced the term pH ( the power of hydrogen) which is the negative exponent to the base 10 of hydronium ion concentration.

5. [ H 3 O + ] = 10 -pH Neutral point = pH=7 pH<7 is acidic pH>7 is basic The lower the pH the stronger the acid The higher the pH the stronger the base

6. Calculating pH/concentration The pH of vinegar is 2, what is the concentration of hydronium ions? [ H 3 O + ] = 10 -pH = 10 -2 = 0.01 mol/L

7. If the concentration of hydronium is 10 -4 mol/L. What is the pH? pH = -log [ H 3 O + ] = -log(10 -4 ) = 4

8. pOH Even thought pH is the more commonly used, we can also measure the power of hydroxide ions, pOH This works similar to pH, instead measuring hydroxide ion concentrations [ OH - (aq) ] = 10 -pOH pOH=-log [ OH - (aq) ]

9. assignment Read page 236-244 Do page 239#1,2 Do page 242 #5,6,9,10 Do page 244 #3-9