Category Archives: Chemistry Unit 10: Acids and Bases

The Arrhenius model of acids and bases.

There are three theories of acids and bases. These are Arrhenius,  Bronsted – Lowry, and Lewis, each named for the person (people) who developed the theory.

You can think of representing these theories in a Venn Diagram composed of 3 concentric circles.  The innermost circle is the Arrhenius theory which was the first of the three theories and explains the behavior of a special class of acids and bases.  The next larger circle, containing the Arrhenius circle, is the Bronsted-Lowry theory which is larger because it explains the behavior of a much larger class of chemicals.  Finally, the outer circle is the Lewis theory which explains the acid and base properties of all chemicals and encompasses the other two theories.

Acid-Venn-1

 

In 1886, a Swedish chemist named Svante Arrhenius proposed the idea that an acid is a chemical which releases a Hydrogen Ion when it is dissolved in water and a base is a chemical which releses an Hydroxide ion when dissolved in water.

{for an animation of how this works, see also our  post on strong and weak acids}

This is a fairly detailed video about Arrhenius acids and bases and slats. Its worth watching but be sure to take notes!

 

Next comes the Bronsted-Lowry theory

Chem Unit 10: MonoDi-TriPoly-Protic Acids

Say Whhhhhhhhatt?

The Latin prefix mono, di, tri, or poly is used to show how many ‘PROTONS’ or simply H+ ions an acid will give up when its dissolved in water.

Soooo…

A Monoprotic Acid can give up or donate 1 and only 1 H+ ion.

Here are some examples of monoprotic acids;

HCl – Hydrochloric acid
HNO3 – Nitric acid
CH3COOH – Acetic Acid, sometimes written HOAc

Let’s write an ionization equation for HCl in water

HCl(aq) +H2O   -> H3O+ + Cl- ( or moresimply written H+ + Cl-)

Q: Write the ionization equations for Nitric and Acetic Acids.

Here are some examples of diprotic acids;

H2SO4 – Sulphuric acid
H2SO3 – Sulfurous acid

H2CO3 – Carbonic acid ( in soft drinks due to CO2 being dissolved in water. Carbonic acid plays an important part in our body’s blood and respiration system as This is how carbon dioxide dissolves in the blood and is taken back to the lungs to be exhaled.

H2C2O4 – Oxalic acid (driveway, concrete cleaner, wood bleach)

H2S – Hydrogen Sulfide – highly poisonous – smells like rotten eggs ( oh yeah, break open a rotten egg some time and see how it smells)  Hold your nose closed AND RUN!!!!!!  Also an atmospheric  pollutant caused by Sulfur in gasoline from low quality high sulfur crude oil.

 

Let’s write the ionization equation for a diprotic acid. This time since there are 2 hydrogens released, we need to do this in 2 steps.

Step 1:   H2SO4(aq) +  H2O  –>  HSO4-  +  H3O+  ( or more simply HSO4- + H+)

Step 2:  HSO4(aq)- +  H2O  <–>  SO4–  +  H3O+  ( or more simply HSO4– + H+).

Note that step 2 is not as energetically favorable so the arrows point both ways.

 

Now you write the ionization equations for H2SO3,  H2CO3, H2CO4, and H2S.

Next we’ll list some triprotic acids.  As a challenge, you should try to write the 3 step ionization formulas.

H3PO4 – phosphoric acid

C6H8O7 – citric acid

 

 

Start at the 2:00 minute mark.

Chem Unit 10: Citric Acid

Citric Acid

 

Citric Acid - silly

 

 

Warm up: How many protons does Citric Acid produce when it is dissolved in water?
Citric Acid: H3C6H5O7Citric Acid ball and stick model

 

Structural Formula: Identify each of the carbon, Oxygen and Hydrogen atoms.   Identify which Hydrogens are released when Citric Acid is dissolved in water.

in your notes, draw the neutral citrus acid molecule, the -1 ion, the -2 ion, and the -3 ion. Hint: you need to think about which Hydrogen atoms are release as H+ and why.

Citric Acid Structural Formula

 

 

Review Chapter 18 Assessment pg 53.

 

Unit 10 Quick Quiz

Unit 10 Quick Quiz: 5 Q x 10 pts = 50 pts max

Q1: Draw a Venn diagram showing 3 theories of acids – (5 pts)_

Write the main idea of each theory in the right part of the Venn Diagram

Q2:  What is 2×10^-7  times 5×10^-8 ?

Q3: What does pH + pOH always equal ?

Q4: What are the 2 steps to calculate pH from [OH-] ?

Q5: Write the formula for Kw.

Chemistry Unit 10: Acids and Bases S2 Wk 2-3-4

Warm up: {FM} Describe the physical properties
(taste & texture) of acids, and of bases. Give an example of each.

Agenda: 3 theories of acids and bases

What is an acid base reaction?

Math Pre-requisite:  Venn Diagrams.

Activity: draw a Venn diagram for turtles, ninjas, and those mutant ninja turtles.

Now we discuss 3 theories of acids
Arrhenius

Draw an illustration of what happens when an acid dissolves in water.  Draw another diagram for a base dissolved in water.

 

Bronsted-Lowrey

Draw a diagram of what happens in a Bronsted- Lowry Acid-Base reaction.

How is the Bronsted-Lowry Theory different from the Arrhenius theory?

Draw a Venn diagram for the Arrhenius and Bronsted-Lowry models considering the kinds of chemicals they describe.

 

 

Lewis

Describe the Lewis Acid-Base model using diagrams and words.

 

see textbook.

Exit Assessment: draw venn diagram with the 3 theories of acids, write the definition of acid and base in each theory.

Crash course – acid-base reactions – from previous lessons

Part 2: pH and pOH

 

Warm Up: {FM} Draw the Venn diagram for 3 models of acids and bases.
What is pH? what is the pH of common household chemials.

More about pH from Crash Course…..

To learn more about exponents and the log scale please see my post “Why everyone hates John Napier” under the Math tab.

 

Here’s a simple explanation of exponential notation;

Practice problems: Exponential / Scientific notation and multiplying numbers.

 

pH and pOH