Acids and Bases Let’s start with a review of some things you may already know about Acids and Bases!

Characteristics of Acids Tastes Sour Conduct Electricity Some acids react strongly with metals Turns blue litmus paper red Corrosive, which means they break down certain substances.

Examples of Acids Acetic Acid = Vinegar Citric Acid = lemons, limes, & oranges. It is in many sour candies. Ascorbic acid = Vitamin C which your body needs to function. Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics, car batteries

Back to Basics! Bases have a bitter taste. Conduct Electricity Turns Red litmus paper Blue Bases are usually slippery and give give soaps, ammonia, other cleaning products some of their properties. Your blood is a basic solution.

Examples of Bases Magnesium Hydroxide = Milk of Magnesia – Help for upset stomach Drain Cleaner = Unclogs pipes Sodium Bicarbonate – Baking Soda = Useful for cooking and cleaning

pH Scale and all it’s glory!

pH Scale pH is a measure of how acidic or basic a solution is. The pH scale ranges from 0 to 14. Acidic solutions have pH values below 7, Basic solutions have pH values above 7. A solution with a pH of 7 is neutral, such as pure water.

What is it really measuring… pH is a measurement of the H+ ion concentration. The number of H+ ions in the solution. The greater the number of H+ ions in a solution, the more acidic, and lower the number on the pH scale.

What is it really measuring… The actual concentrations are very small so a logarithmic scale is used, which is based on a power of ten! If a solution has a pH of 1 and a second solution has a pH of 2, the first solution is not twice as acidic as the second—it is ten times more acidic.

Calculating the pH of Strong Acids To determine the pH of a strong acid, you first need the Hydrogen ion concentration. Remember that in a strong acid, all the molecules dissociate into the hydrogen ions. This is expressed in Molarity and abbreviated in brackets. Ex [H+] = 2.05 M To determine the pH: pH = - log [H+]

Significant Digits * One Sig Fig so One Decimal pH = −log [1 x 10−4 ] Significant digits in pH calculations are tricky because of the logarithmic scale. The number of decimal places in the pH is determined by the number of significant figures in the coefficient. Example: For a solution with [H+] = 1 x 10−4 pH = −log [1 x 10−4 ] pH = - [-4.0] pH = 4.0 * One Sig Fig so One Decimal

Here’s a helpful hint to help you remember. Dolphins The number of Decimal Places in the pH San Francisco Is equal to the Significant Figures in the Concentration

Significant Digits Examples: [H+] = 2 x 10-5 [H+] = -log[2 x x 10-5] pH = 4.7 [H+] = 8.0 x 10-6 [H+] = -log[8.0 x 10-6] pH = 5.10 [H+] = 2.45 x 10-8 [H+] = -log[2.45 x 10-8] pH = 7.611

Practice: Calculate the pH Find the pH of these strong acids: pH = - log [H+] 1) A 0.15 M solution of Hydrochloric acid pH = - log[0.15] Ans: pH = 0.82 – 2 sig figs in conc. = 2 decimal places in pH 2) A 3.00 x 10-7 M solution of Nitric Acid pH = -log[3.00 x 10-7] Ans: pH = 6.523 – 3 sig figs in conc. = 3 decimal places in pH

Suppose you know the pH, but want to solve for the [H+] concentration? Calculating the [H+] Suppose you know the pH, but want to solve for the [H+] concentration? A strong acid has a pH of 3.12. Determine the [H+] concentration.

Calculating the [H+] [H+] = 10-3.12 = 7.6 x 10-4 M pH = - log [H+] How do you get [H+] by itself? First need to divide by -1…. -pH = log [H+] Take antilog (10x) of both sides and get rid of the log. 10-pH = [H+] So…. [H+] = 10-3.12 = 7.6 x 10-4 M * Remember: pH has 2 decimal places, so concentration can only have 2 significant digits:

You Try! Practice Problem A solution has a pH of 1.25. What is the concentration of hydrogen ions in the solution? pH = -log[H+] 1.25 = -log[H+] -1.25 = log[H+] *Take the antilog (10x) 10-1.25 = [H+] 2 decimal places in pH = 2 sig figs in concentration [H+] = 0.056 M

Practice Problems: 1) Determine the pH of a solution that has a hydrogen ion concentration of 5.0 x 10-2. pH = - log [5.0 x 10-2] = pH = 1.30 * 2 Sig Figs in concentration = 2 decimal places in pH 2) Human blood must maintain a pH range of 7.35 to 7.45. Determine the range of [H+] for blood. * 2 decimal places in pH = 2 sig figs in concentration 7.35 = - log [H+] = 4.5 x 10-8 M 7.45 = - log [H+] = 3.5 x 10-8 M

Practice Worksheet