Acids Bases p H What are Acids Acids
Acids, Bases & p. H
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 + H 2 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: – Na. OH – 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) (Water) NH 3 + HOH 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 p. H? • The p. H of a solution indicates its concentration of Hydronium Ions (H 3 O+) or its concentration of Hydroxide Ions (OH-) • p. H 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 p. H scale ranges from 0 -14
The Scale Neutral Lots of H 3 O+ Lots of OH- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 • In a neutral solution, the p. H is 7 – The amount of H 3 O+ = OH • Acids have a p. H of less than 7 – The amount of H 3 O+ > OH • Bases have a p. H of greater than 7 – The amount of OH- > H 3 O+
Calculating p. H • Concentration is written as Molarity, or the number of moles per liter of solution • Example: the Hydronium concentration of pure water is 0. 0000001 mol/L or 10 -7 M • This means that in one liter of water, we have 0. 0000001 mol of Hydronium ions
Calculating p. H • p. H is the negative of the power of 10 used to describe the concentration of Hydronium ions • Example: hydronium concentration of pure water = 10 -7 -(-7) = p. H of 7
Small Differences in p. H Mean LARGE Differences in Acidity • Each number on the p. H scale is a difference of a factor of 10 • p. H of 2 is 10 times stronger than a p. H of 3 • p. H of 1 is 100 times stronger than a p. H of 3 • Example problem: the p. H of apple juice is 3. the p. H of coffee is 5. What is the acidity difference? • There are 2 spaces between 3 and 5. • 102 = 100 - Apple juice is 100 times more acidic than coffee
Review Questions • Which ions do acids form in solution? – H 3 O + • Which ions do bases form in solution? – OH • Classify the following as acidic, basic, or neutral. – Soap (p. H = 9) • basic – Sour liquid (p. H = 5) • acidic – Solution with 4 x as many hydronium as hydroxide ions • acidic – Pure water • neutral • Arrange the following substances in order of increasing acidity: vinegar (p. H = 2. 8), gastric juices from your stomach (p. H = 2. 0), soft drink (p. H = 3. 4) – Soft drink, vinegar, gastric juice
• Determine the p. H of a 0. 0001 M solution of HCl 0. 0001 = 10 -4 -(-4) = p. H of 4 • What is the p. H of 0. 01 M solution of HCl. O 4, perchloric acid? 0. 01 = 10 -2 -(-2) = p. H of 2 • The concentration of hydronium ions in a certain acid is 10000 times the concentration of hydronium ions in a second acid solution. If the second solution has a p. H of 6, what is the p. H of the first solution? 10000 = 104 4 steps down p. H scale 6 -4 = p. H of 2 • Hand soap has a p. H of 10. Drain cleaner has a p. H of 14. How much more acidic is the hand soap than the drain cleaner? 4 steps = 104 = 10, 000 times more acidic
Can you find the p. H of the solutions you just tested? • Let’s do a lab to find out!
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