Introduction to Acid/Base Chemistry

Name:  Marilyn Alswede

Date of lesson: Unit Project Week 2 Monday

Description of the class:  Chemistry High School

Length of lesson: 45 – 50 minutes

Source of the lesson:

TEKS addressed:

Chemistry (1) Scientific processes. The student, for at least 40% of instructional time, conducts field and laboratory investigations using safe, environmentally appropriate, and ethical practices. The student is expected to:

(A) demonstrate safe practices during field and laboratory investigations

Chemistry (3) Scientific processes. The student uses critical thinking and scientific problem solving to make informed decisions. The student is expected to:

                        (D) describe the connection between chemistry and future careers

Chemistry (11) Science concepts. The student knows that balanced chemical equations are used to interpret and describe the interactions of matter. The student is expected to:

(A) identify common elements and compounds using scientific nomenclature;

(B)demonstrate the use of symbols, formulas, and equations in describing interactions of matter such as chemical and nuclear reactions

I. Overview

This lesson is an introduction to acid base chemistry.  The properties of acids will be compared to the properties of bases.  Also the nomenclature rules of binary acids and oxyacids are taught.

II. Performance objectives (learner outcomes)

            Students should be able to:

  1. Identify properties and differences between acids and bases.
  2. Demonstrate the transfer of protons from hydronium ions to water molecules.
  3. Write the nomenclature of binary acids and oxyacids.
  4. Recognize the difference between binary acids and oxyacids.

III. Resources, materials and supplies (per box/teaching pair)

                     Engagement:

Explore:

Explain:

Evaluate:

Copy of partner review quiz on an overhead

IV. Advanced Preparation:

Prepare Lemon Cheese for engagement.  (See instructions below 5E's).

VI. Vocabulary & Definitions: 

Oxyacid- an acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal

Binary acid- an acid that contains only two different elements: hydrogen and one of the more electronegative elements

VII. Safety Considerations:

            Be sure students do not spill water from buckets on the floor.  Warn students to be careful not slip in any puddles that may occur from spillage of the buckets.

Five-E Organization

Teacher Does                          Probing Questions                       Student Does         

Engage:

"Today we are going to begin learning more about acids and bases."

In front of the classroom have two cups, one filled with milk and the other with lemon juice.

"I have a cup of milk and a cup of lemon juice.

"Well to determine if your guesses are correct let's test the milk and lemon juice with some pH paper."

Using two pieces of pH paper test the milk and lemon juice.  "The pH paper turned yellow signifying that the milk is slightly acidic and the lemon juice turned the pH paper orange also signifying that it is acidic.  Now let's mix the two liquids together."  Again test with pH paper, the pH will vary, but still be acidic and lower than the pH of just the milk.

"I've previously heated the milk and lemon juice together and let it drain in a cheesecloth."  Offer lemon cheese to students who would like to try it.

"You can try this at home if you'd like I have copies of the directions."

Time: 5 minutes

Is milk considered an acid or a base?

Is lemon juice an acid or a base?

Do you think the mixture is an acid or a base?

What does this look like now that I've heated the mixture and drained it?

 

Acid (students may believe that the milk is a base)

Acid

Acid

Cheese

Explore:

On a blank overhead, write down the student's responses to the following questions.

If the students do not list all the expected responses be sure to add them to the list.

"As you know, reactions are a part of chemistry.  To demonstrate the reaction that is taking place when an acid and base are mixed we are going to do an activity called the bucket brigade."

Divide the class in half to form two groups.  Take students outside or open area of school where water spillage will not damage anything. 

Pass out hanging signs.  "Please place the signs around your necks.  Half of the group have the sign saying H3O+ facing out and the other half H2O facing out.  Line up next to each other so that you are an arm's length apart."  The students whose sign says H3O+ will be handed a bucket of water.  They will then pass the bucket to the next student on the teacher's signal, and the students will switch their signs.  "As you pass the bucket of water (H+), you are passing the proton to your neighboring water molecule and now you've given up your proton so you should change your sign to say H2O.  As a group you are a solution." 

Time: 20 minutes

What are some properties of acids?

What are some properties of bases?

What happens when you give up your proton?

What happens when you gain a proton?

While answering these questions as class students should be taking notes.

Acids have a sour taste, change the color of acid-base indicators, react with metals to release hydrogen gas H2, react with bases to produce salts and water, and some conduct current.

Bases have a bitter taste, change the color of acid-base indicators, feel slippery, react with acids to produce salts and water, and bases conduct electric current.

I become H2O.

I become H3O+.

Explain:

Write on blank overhead the reaction the students did in their activity. 

H3O+         H+ + H2O

 


Also draw a molecular model of the atoms.  If available use a plastic ball and stick molecular model.

"As you noticed in the activity, as you passed the proton (hydrogen cation) or bucket of water along you either were water deprotonated form or the protonated form hydronium ion. Label water and hydronium ion on the written reaction.  In a solution such as water, successive transfers of protons from H3O+ to H2O make the hydronium ion appear to move through a solution much faster than an ion can actually move."

"Just as we learned a little about nomenclature last semester, acids have special nomenclature.  There are two major categories binary acids and oxyacids."

Write these two words and definitions on the overhead.  "Binary acid is an acid that contains only two different elements: hydrogen and one of the more electronegative elements." Give example HF hydrofluoric acid. 

"The three rules for naming binary acids are 1.  The name of the binary acid begins with the prefix hydro-. 2. The root of the name of the second element follows this prefix.  3. The name then ends with the suffix –ic."

"An oxyacid is an acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal."  Give example CH3COOH acetic acid.  "Unfortunately oxyacids do not have well defined rules as do binary acids."  Show table of prefixes and suffixes.  "The names are based on the oxyacids anion.  So acetic acid's anion is acetate CH3COO-. 

Time: 15 minutes

What are the more electronegative elements on the periodic table?

How do we name the binary acid HI?

What is an anion?

Back earlier the semester we studied polyatomic ions, how do we name HNO2?

Students should continue writing their notes.

The halogens.

Students write down the definition and naming rules for naming binary acids.

Hydroiodic acid

Students write down the definition and table of prefixes and suffixes for naming oxyacids.

A negative ion.

Nitrous acid

Extend / Elaborate:

"In our world today, acids are used daily.  For instance sulfuric acid is used in our car batteries, nitric acid is used to make explosives, phosphoric acid is used for manufacturing fertilizers, hydrochloric acid is used for maintaining the acidity in swimming pools, and acetic acid is used in the manufacture of plastics."

Write down each chemical name down while mentioning the facts. 

Time: 5 minutes

What are the chemical formulas for each of the chemicals I've listed?

Students should write down the example chemicals.

H2SO4, HNO3, H3PO4, HCl, CH3COOH

Evaluate:

"As a wrap to today's class let's do a partner quiz.  You may use your notes as guidance. Answer the following questions on sheet of paper."

On overhead have the questions.

Time: 5 minutes
  1. Name at least 2 properties of an acid.
  2. Name at least 2 properties of a base.
  3. In a sentence describe the movement of the hydronium ion through an aqueous solution.
  4. Name the binary acid HBr.
  5. Name the oxyacid HClO.
  

Directions for Lemon Cheese:

  1. Pour 2L whole milk into a saucepan. Heat the milk until its temperature is about 40-45¡C. Stir the milk frequently while heating.
  2. Turn off the heat, and remove the saucepan from the stove.
  3. Pour 6.0mL of lemon juice into the milk while stirring. 
  4. Let the milk mixture stand for 15 minutes.
  5. Line a colander with cheesecloth.  The edges of the cloth should hang over the sides of the colander.
  6. Pour the contents of the saucepan into the colander.
  7. Pull the corners of the cheesecloth to form a sack, and allow the contents to drain for about 1 hour.
  8. Open the sack, and scrape the cheese from the cloth into a bowl.  Add salt and herbs to taste.

Naming Oxyacids

Name of Oxyacid

Name of Oxyanion

Prefix

Suffix

Prefix

Suffix

Hypo-

-ous

Hypo-

-ite

None

-ous

None

-ite

None

-ic

None

-ate

Per-

-ic

Per-

-ate

Partner Review Quiz

1.    Name at least 2 properties of an acid.

2.    Name at least 2 properties of a base.

3.    In a sentence describe the movement of the hydronium ion through an aqueous solution.

4.    Name the binary acid HBr.

5.    Name the oxyacid HClO.