Lesson 2

Lesson 2: Acids and Bases

I can Explain the pH scale.

I can Calculate pH and ion concentrations in acidic and basic solutions.

I can Predict the products from a reaction of an acid and a base.

I can Describe how a buffer works.

Review from lesson 1

Multiple Choice

Acid or Base?

Contains H+ or H30+ ions.

• Acid

• Base

Multiple Choice

Acid or Base?

Contains OH- ions.

• Acid

• Base

Multiple Choice

Acid or Base?

NaOH

• Acid

• Base

Multiple Choice

Acid or Base?

HCl

• Acid

• Base

Multiple Choice

Acid or Base?

pH of below 7 on the pH scale.

• Acid

• Base

Multiple Choice

Acid or Base?

pH of above 7 on the pH scale.

• Acid

• Base

Lesson 2 Part 1: The pH scale

I can Explain the pH scale.

I can Calculate pH and ion concentrations in acidic and basic solutions.

Your Stomach

What type of acid does your stomach contain?

What do you think you could do to help calm a sour stomach?

Multiple Select

What do you think are some common properties of acids? (pick 3)

• Bitter tasting

• Sour tasting

• Corrosive

• Slippery

• Burn

Acid Properties

Acids are sour, they burn, and they are corrosive.

When some sulfur- and nitrogen-based pollutants from car emissions get into the air, they mix with water to form acid in the clouds. This causes the rain to become slightly acidic; in other words, it causes acid rain.

A forest in the Czech Republic that has been destroyed by acid rain.

Multiple Select

What do you think are some common properties of bases? (pick 3)

• Bitter tasting

• Sour tasting

• Corrosive

• Slippery

• Burn

Base Properties

Bases are slippery, bitter, and corrosive.

Bases react with oil and grease. That is why so many cleaning products — like soap, drain cleaner, and bleach — are bases. Bases feel slippery to the touch because they actually dissolve a small number of skin cells, leaving behind a slippery feeling as skin cells slip off.

Can you eat or drink most bases?

Open Ended

Explain in your own words the difference between a strong and a week acid or base.

Differing Acidity or Basicity

Strong vs Weak Acids

Strong vs Weak Bases

Multiple Choice

Lab Review: What color did the litmus (pH) paper turn when an acid was detected?

• Red

• Blue

• yellow/green

Multiple Choice

Lab Review: What color did the litmus (pH) paper turn when a base was detected?

• Red

• Blue

• yellow/green

Multiple Choice

Lab Review: What color did the litmus (pH) paper turn when a neutral substance was detected?

• Red

• Blue

• yellow/green

pH

pH is the measure of how acidic or basic a solution is.

What would the pH number be for

Which do you think is considered a stronger base...Bleach or blood? Why?

Try this!

on your whiteboard,

put these in order from most acidic to least acidic.

Open Ended

What is one way you can easily figure out if something is an acid, base or neutral?

Indicators

A common, quick way to check pH is with an indicator.

Open Ended

If I had a solution that had a pH of 5 and I added an extremely strong acid HCl to it. What do you think would happen to the pH? why?

Calculating pH

The pH scale is based on the concentration of H+ ions in a solution.

pH = –log[H⁺]

Multiple Choice

Try this: find the pH if your H+ concentration is 1.00 x10^-7

• 8

• 7

• 4

• 12

• the correct answer isn't an option on here

Calculating pOH

pOH can be calculated from the OH– concentration.

pOH = –log[OH^–]

14= pH + pOH

Water

H₂O <--> H⁺ + OH^–

K_w = [H⁺][OH^–]

[H⁺] = 1 × 10^–7 M, and [OH^–] = 1 × 10^–7 M

These concentrations give water a pH of 7 and also a pOH of 7, which is why water can act as an acid or as a base. Since there is always an equal number of H⁺ and OH^– ions in water, the solution is neutral.

complete pH practice worksheet

Lesson 2 Part 2: Acids, Bases and Buffers

I can Predict the products from a reaction of an acid and a base.

Review of Yesterday's Lesson

Open Ended

What are some ways sink holes can form?

How did acids cause this?

In 1981, in the city of Winter Park, Florida, an unexpected disaster occurred: A sink hole.

The ground suddenly collapsed. Throughout the day, an enormous hole formed. It was 320 feet wide and 90 feet deep! It swallowed an entire two-story house and destroyed a car dealership and a public swimming pool.

Carbonic acid dissolves limestone.

H₂CO₃ + CaCO₃  <--> Ca(HCO₃)₂

The ground in Winter Park, Florida, contained a lot of limestone. Limestone is made of calcium carbonate (CaCO₃), which acts as a base when dissolved in water.

Rainwater falls and mixes with carbon dioxide in the atmosphere, forming carbonic acid (H₂CO₃). 

Open Ended

Why does acid rain happen? What causes it? Explain your thinking.

Acid rain results from pollutants mixing with water.

Acid rain is caused when sulfur oxides or nitrogen-based oxides mix with water in the air and then come down as rain. The main source of these oxides is the exhaust of car engines or power plants that are burning coal. The main form of acid rain is sulfuric acid (H₂SO₄).

Multiple Select

What types of materials are made in the product?

• Acid

• Base

• Salt

Acid Rain and Aquatic Ecosystems

Acid rain can be very damaging to all kinds of ecosystems, particularly to animals in aquatic ecosystems. Some animals tolerate acid rain better than others, however. To the right is a chart that shows the range of pH that different animals can tolerate.

Which animals have the best tolerance for acid rain?

Acids and bases react to produce a salt and water.

Acid + Base <-->  Salt +Water

How would I make salt and water from mixing the acid HCl and the base NaOH?

Multiple Choice

Think back to last semester.

What kind of reaction is the acid-base reaction?

HCl + NaOH --> NaCl + H₂O

Acid + Base --> Salt + Water

• Synthesis

• Decomposition

• Double replacement

• Single replacement

Try this on your white board

How do acids/bases work in your body?

Open Ended

Think back to yesterday.... What would you want to eat to calm a sour stomach? Why would we do that?

Neutralization

When acids and bases react, they can neutralize each other.

A neutralization reaction is one that removes essentially all H⁺ and OH^– ions from a solution. The products of an acid-base neutralization reaction are neutral — they are neither acidic nor basic.

Acid + Base --> Salt + Water

Blood pH

The pH of blood must stay constant.

When you play basketball or soccer, run, swim, or even just walk, your increased breathing rate causes more H⁺ ions to move into your bloodstream. In other words, physical activity makes your blood become more acidic. So is it dangerous to exercise? Could you get "acid poisoning"?

Open Ended

What do you think we have in our blood that makes it stay consistently at a 7.4 pH?

Begin Project 2 Part 1

Part 3: Buffers

I can Describe how a buffer works.

Buffers

Buffers resist a change in pH.

When you exercise, additional acid — H₂CO₃ — moves into your bloodstream. However, the pH of your blood doesn't change. This is because there is a buffer in your blood.

A buffer is a conjugate acid-base pair in a solution. The buffer resists a change in pH when additional acid or base is added to the solution.

How does a buffer resist a change in pH? Observe for yourself by adding some acid (HCl) and base (KOH) to water and then to a buffer solution of acetic acid (CH₃COOH). 

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