Warm-UpApril 25, 2013

• Write down the date and objective. • Objective: SWBAT classify and calculate the

concentration of substances by completing an Acids and Bases Lab.

• Complete the following warm-up:1. What is an Arrhenius acid?2. What is an Arrhenius base?3. What is a Bronsted-Lowry acid? 4. What is a Bronsted-Lowry base?

Objective & Agenda

• Objective: SWBAT classify and calculate the concentration of substances by completing an Acids and Bases Lab.

Agenda1.Current Event2.pH3.Acid and Base Lab4.Practice Problems5.Homework6.Exit Slip

Current Event

The The pH scalepH scale is a is a way of expressing way of expressing the strength of acids the strength of acids and bases. and bases.

pH= potential of pH= potential of hydrogenhydrogen

Under 7 =Under 7 = acid acid 7 = 7 = neutralneutral

Over 7 = Over 7 = basebase

pH of Common pH of Common SubstancesSubstances

Calculating the pH

pH = - log [H+](Remember that the [ ] mean Molarity)

Example: If [H+] = 1 X 10-10

pH = - log (1 X 10-10)

pH = - (- 10)

pH = 10

Example: If [H+] = 1.8 X 10-5

pH = - log 1.8 X 10-5

pH = - (- 4.74)

pH = 4.74

Try These!Try These!Find the pH of these:Find the pH of these:

1) A 0.15 M solution 1) A 0.15 M solution of hydrochloric acidof hydrochloric acid

2) A 3.00 X 102) A 3.00 X 10-7-7 M M solution of nitric solution of nitric acidacid

pH calculations – Solving for pH calculations – Solving for H+H+pH calculations – Solving for pH calculations – Solving for H+H+

If the pH of Coke is 3.12, [HIf the pH of Coke is 3.12, [H++] = ???] = ???

Because pH = - log [HBecause pH = - log [H++] then] then

- pH = log [H- pH = log [H++]]

Take antilog (10Take antilog (10xx) of both) of both sides and get sides and get

1010-pH -pH == [H[H++]][H[H++] = 10] = 10-3.12-3.12 = 7.6 x 10 = 7.6 x 10-4-4 M M *** to find antilog on your calculator, look for “Shift” or “2*** to find antilog on your calculator, look for “Shift” or “2nd nd function” function”

and then the log buttonand then the log button

pH calculations – Solving for H+pH calculations – Solving for H+• A solution has a pH of 8.5. What is the A solution has a pH of 8.5. What is the

Molarity of hydrogen ions in the solution?Molarity of hydrogen ions in the solution?

1010-8.5-8.5 = [H = [H++]]

3.16 X 103.16 X 10-9-9 = [H = [H++]]

1010-8.5-8.5 = [H = [H++]]

3.16 X 103.16 X 10-9-9 = [H = [H++]]

pOH• Since acids and bases are Since acids and bases are

opposites, pH and pOH are opposites, pH and pOH are opposites!opposites!

• pOH looks at the perspective of a pOH looks at the perspective of a basebase

pOH = - log [OHpOH = - log [OH--]]Since pH and pOH are on opposite Since pH and pOH are on opposite

ends,ends,pH + pOH = 14pH + pOH = 14

pHpH [H+][H+] [OH-][OH-] pOHpOH

[H[H33OO++], [OH], [OH--] and pH] and pH

What is the pH of the What is the pH of the 0.0010 M NaOH solution? 0.0010 M NaOH solution?

[OH-] = 0.0010 (or 1.0 X 10[OH-] = 0.0010 (or 1.0 X 10-3-3 M) M)

pOH = - log 0.0010pOH = - log 0.0010

pOH = 3pOH = 3

pH = 14 – 3 = 11pH = 14 – 3 = 11

Important Formulas

pH = -log[H+]

pOH = -log[OH-]

pH + pOH = 14

[H+] = 10-pH

[OH-] = 10-pOH

Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 0.9 M and (b) 0.0024 M. Calculate the [H3O+], pH, [OH-], and pOH of the two solutions at 25°C.

Problem 2: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral?

Neutralization Reaction

NaCl + H2ONaCl + H2O

Ba(NOBa(NO33))22 + 2 H + 2 H22OO

LiLi22SOSO44 + 2 H + 2 H22OO

Ca(ClOCa(ClO44))22 + 2 + 2 HH22OO

pH testing (review)

• There are several ways to test pHThere are several ways to test pH– Blue litmus paper (red = acid)Blue litmus paper (red = acid)– Red litmus paper (blue = basic)Red litmus paper (blue = basic)– pH paper (multi-colored)pH paper (multi-colored)– pH meter (7 is neutral, <7 acid, >7 pH meter (7 is neutral, <7 acid, >7

base)base)– Indicators like phenolphthaleinIndicators like phenolphthalein– Natural indicators like red cabbage, Natural indicators like red cabbage,

radishesradishes

pH indicators• Indicators are dyes that can be added that

will change color in the presence of an acid or base.

• Some indicators only work in a specific range of pH

• Once the drops are added, the sample is ruined

• Some dyes are natural, like radish skin or red cabbage

Acids and Bases Lab

• Follow all directions carefully!!• Ask if you are unsure of how to do

something. • Let me know if you run out of materials.

Homework 24

• Acid/Base Practice Problems due Friday

1. The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater?

2. The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood?