Acids and Bases 1

Boon Chemistry January 14 and 15, 2013

Catalyst Use your flashcards to

answer the following questions.

1. When sodium hydroxide (a strong base) is dissolved in water, it conducts electricity. Sodium hydroxide is an example of an _______.

2. According to the Bronsted-Lowry definition of acid and base, acids _____ a proton and bases _______ a proton.

3. What is pH?

ObjectivesI can describe and compare the properties of strong acids, weak acids, strong bases and weak bases.I can write acid/base chemical reaction equation and identify the conjugate acids and bases.

Agenda Catalyst Demonstration pH Notes and white board practice:

Properties of Acids and bases Group work: conjugate acid and

base pairs.

Ouchi Chemistry Scores 4th out of 12 Alliance High Schools on Benchmark 2! We are moving up!!!

Think, Pair Share: Lets set a goal as a class for the next benchmark. What can we do to reach that goal?

Demonstration: What is pH? Introduction:

Read the introduction silently. Highlight the answers to following questions as you read: What does pH measure? The pH scale goes from _____ to _____. A neutral solution has a pH of ______. An _____ has a pH

below 7, and a _____ has a pH above 7. Water has a pH of ______ and is therefore considered

_____. A solution with a pH of 2 has ten times more hydrogen

ions in it than a solution with a pH of _______.

Demonstration: What is pH? Procedure: Watch as we measure the pH of

several household acids and bases using an indicator. Based on the results, add the different household acids and bases to the pH scale below.

Notes: Properties of acids and basesProperties of acids Properties of basespH < 7 Dissociate to form hydronium ions (H3O+) in solution

pH > 7 Dissociate to form hydroxide ions (OH-) in solution

Notes: Properties of acids and basesProperties of acids Properties of basesSour, tart, or sharp taste Examples: citrus fruits, coffee, soda, vinegar, rain water, stomach acid

Tastes bitter, feels slippery Examples: soap, baking soda, ammonia based cleaning products, drain cleaner, bleach

Notes: Properties of acids and basesProperties of acids Properties of basesReact with Some Metals Conducts electricityReacts with bases to form water and salt

Conducts electricityReacts with acids to form water and salt

Acids and bases at the molecular level Simulation!

As we go through the simulation fill in the questions and pictures on your worksheet.

Icons for Acid Base Solutions

Strong Acid 

Acids are substances that readily donate a proton (a hydrogen ion H+) to another substance. Strong acids dissociate completely when dissolved in a solvent. In other words, every acid molecule donates a proton (H+).

Example: hydrochloric acid (stomach acid – pH = 2.0)

HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq)

Weak Acid

Weak acids do not dissociate completely when dissolved in a solvent. In other words, only some of the acid molecules donate a proton (H+) to the solvent. Example: acetic acid (vinegar – pH = 3.0)

CH3COOH(aq) + H2O(l) ↔ H3O+(aq) + CH3COO-

(aq)

Draw a picture and graph depicting a weak acid solution.

Strong Base

Bases are substances that accept a proton (a hydrogen ion H+) from another substance. Strong bases dissociate completely when dissolved in a solvent. In other words, every base molecule accepts a proton (H+).

Example: potassium hydroxide (caustic potash pH = 13)   KOH(aq) → K+(aq) + OH-(aq)

In the presence of an acid, the hydroxide ion (OH-) accepts a proton (H+) to form water.

Draw a picture and graph depicting a strong base solution.

Weak Base

 Weak bases do not dissociate completely when dissolved in a solvent. In other words, only some of the base molecules accept a proton (H+) from the solvent.  Example: ammonia (cleaning product pH=10)

NH3(aq) + H2O(l) ↔ NH4+(aq) + OH-(aq)

Draw a picture and graph depicting a weak base solution.

1.Order the solutions from lowest to highest pH.

A. X<Y<Z B. Y<X<Z C. Z<Y<X D. Z<X<Y E. Y<Z<X

X Y Z

4. Which image is from a weak base?

A. X B. Y C. Z D. more than one E. none

X Y Z

3. Which image is from a strong acid?

A. X B. Y C. Z D. more than one E. none

X Y Z

2.Order the solutions from lowest to highest pH.

A. X<Y<Z B. Y<X<Z C. Z<Y<X D. Z<X<Y E. Y<Z<X

X Y Z

5. Acids have pH from ___ to _____. Bases have a pH from ______ to _______.

6. What ALWAYS distinguishes a weak acid from a strong acid?

A. A weak acid doesn’t react much in water; strong acids completely react.

B. A weak acid is more dilute than a strong acid.

C. A weak acid has a higher pH than a strong acid.

D. Statements a and c are both characteristics that distinguish weak acids from strong acids.

E. Statements a, b, and c are all characteristics that distinguish weak acids from strong acids.

7. What ALWAYS distinguishes a weak base from a strong base?

A. A weak base doesn’t react much in water; strong bases completely react.

B. A weak base is more dilute than a strong base.

C. A weak base has higher pH than a strong base.

D. Statements a and c are both characteristics that distinguish weak bases from strong bases.

E. Statements a, b, and c are all characteristics that distinguish weak bases from strong bases.

Bronsted-Lowry Acids and Bases According to the Bronsted-Lowry theory, an

acid is a proton (H+) donor, and a base is a proton acceptor.

Example: HCl + OH- Cl- + H2O

The HCl acts as an acid, the OH- as a base.

Bronsted-Lowry Quick Check Thumbs up for true and thumbs down for

false.

In the following equation, H2O acts as an acid by donating a proton.

PH3(aq) + H2O(l) ↔ PH4+(aq) + OH-

(aq)

On your white board, label the acid, base, conjugate acid, and conjugate base.

Group Work Work with the person next to you to complete

the acid and base worksheet. Label the acid, base, conjugate acid, and

conjugate base for each equation. Draw arrows indicating how protons are donated.

Exit Slip Show your work on a half sheet of paper. Use your notes

and include proper units.1. How many liters is 770 mL?

2. A chemist dissolves 0.75 mol NaCl in 500 mL of water. What is the molarity of the solution?

3. A solution contains 46 g of ethanol (C2H5OH) dissolved in 4 L of water. What is the molarity of the solution?

4. A 200 g water sample contains 0.5 mg chromium. What is the concentration of chromium in parts per million?

5. On a scale of 1-4 (with 4 the highest) rate your level of comfort with the new acids/bases material.

Homework Read pp. 530 – 538 pp. 538 # 1, 3, 5, 6, 7, 9,

13

Exit Slip: Answers1. How many liters is 770 mL?

770 mL = 0.770 L

2. A chemist dissolves 0.75 mol NaCl in 500 mL of water. What is the molarity of the solution?

500 mL = 0.500 L 0.75 mol = x mol1.5 M

0.500 L 1 L

3. A solution contains 46 g of ethanol (C2H5OH) dissolved in 4 L of water. What is the molarity of the solution?

convert from grams to moles. Molar mass of C2H5OH = 46 g/mol. 46 g ethanol = 1 mol ethanol

1 mol = x mol x = 0.25 M 4 L 1 L

Exit Slip answers continued4. A 200 g water sample contains 0.5 mg

chromium. What is the concentration of chromium in parts per million?

0.5 mg = 0.0005 g 0.0005 g x 1,000,000 = 2.5 ppm

200 g

5. On a scale of 1-4 (with 4 the highest) rate your level of comfort with the new acids/bases material.