CHANGE Project

Climate Change Narrative Game Education

Teacher Notes: Chemistry Unit – Ocean Acidification

Lesson Time: 50 minutes

14 minutes slides/36 minutes lab

Instructor Note: These notes include a “sample lesson” that is intended to provide an example

of how this information could be presented to a classroom. The sample lesson is written in a

conversational tone and often does not follow the normal rules of writing (we don’t talk the way

we write). If you are very familiar with the topic, then the CHANGE team recommends that you

quickly skim through the material to make sure there are no surprises or changes. If you

relatively new to this material, then a more careful reading is in order.

Each section of the lesson includes the anticipated time that you will spend on each

subject (to the nearest minute, rounded up). The time estimates are intended as a tool to help you

manage the classroom, and are not a hard and fast rule. If your students are asking very fruitful

questions in a section that wasn’t allotted enough time, allow the questions (within reason). You

can make this time up by asking fewer questions later or by abbreviating topics that were

partially covered by the earlier questions.

Sample Lesson

Overview: (est. time: 1 min)

Today we’re going to talk about the chemistry

behind ocean acidification and then do some lab work so

you’ll see first-hand what the effects will be. The

processes behind ocean acidification are pretty

straightforward and would have been well understood by chemists 100 years ago. We’re also

going to talk about some of the basic chemistry that goes on all around us so that we can

understand the phenomenon of ocean acidification.

pH Scale: (est. time: 3 min)

QUESTION: By a show of hands, how many of you went

swimming in a pool over the summer?

ANTICIPATED RESPONSE: (most hands will raise)

QUESTION: Does anyone know what the pH of a

swimming pool is supposed to be kept at? (A few students will be responsible for caring for their

pool, but they probably don’t remember the exact numbers)

ANTICIPATED RESPONSE: Somewhere between 7 and 8

TEACHER FEEDBACK: Your pH should be between 7.2 and 7.8, and anyone that has had to

take care of a pool will tell you that you have to add chemicals about every week to keep it

where it should be.

In case you don’t know what pH is, it’s the standard scale that everyone uses to measure

acidity. We define a pH of 7 as neutral, because that’s the pH we find in absolutely pure water.

In real life, water isn’t pure though, and the ocean has a pH of 8.2. All pH numbers lower than 7

are acidic and numbers higher than 7 are called alkaline or basic. Every whole number step

means that the substance is either 10 times more acidic or basic, depending on which way you’re

going. So, I’ve given you a bunch of numbers that describe acids and bases, but did you know

that humans have a built-in ability to identify acids and bases?

We can tell how acidic or basic something is by its taste. Acids are sour and bases are

bitter. That doesn’t mean that everything that isn’t pH balanced tastes bad. Sour candies are

incredibly popular, and with the exception of a few that are just ridiculous, they taste pretty

good, right? If you look at the pH scale, you see that lemons have a pH of 2 and oranges are at 3.

The reason most people don’t just peel a lemon and eat it is that they are 10 times more acidic

and therefore 10 times more sour than an orange.

QUESTION: Someone that’s gone swimming in the ocean, on top of being salty, does the ocean

water taste sweet, sour, or bitter?

ANTICIPATED RESPONSE: Bitter

TEACHER FEEDBACK: Isn’t that interesting? Things don’t start to taste too sour to eat until

the pH gets down to about 2, but a pH of 8, which is barely alkaline already tastes pretty bitter.

QUESTION: Does anybody want to take a guess why that is?

ANTICIPATED FEEDACK: (Possible that no hands will raise, the answer isn’t obvious)

Because ocean water can kill us.

TEACHER FEEDBACK: Generally speaking, if we describe something as very sour or bitter,

we aren’t talking about something delicious that we want to eat more of. Almost everything

that’s edible by humans falls in the pH range of 2 to 8. This doesn’t mean you should go around

tasting random things, especially when you know better, because with some poisons even a taste

is enough to kill you. Most things with a pH outside the 2 to 8 range is probably going to make

you sick.

Natural Carbon Cycle: (est. time: 3 min)

In the natural world, you see a states of dynamic

equilibrium all over the place. Plants take in carbon

dioxide and water to produce oxygen and carbohydrates.

Carbohydrates are pretty much what their name suggests.

They are chains of carbon atoms bound to the chemical elements of water. We call short

carbohydrate chains sugars, and longer chains, like the ones in potatoes, are complex

carbohydrates. The ones that are extremely long are ones that humans can’t break down, and we

call them dietary fibers. Most solid plant material, like wood, is made up of densely packed

carbohydrate fibers.

Animals, do the reverse chemical reaction of plants. They take in oxygen by breathing

and eat the carbohydrates from plants. Then they release the energy from the carbohydrates by

breaking them back into carbon dioxide and water. Some animals, like koalas can survive

without having to drink water. Think about it, carbohydrates are, by definition, chemically made

up of half carbon and half water. Animals that digest dense fibers like wood and leaves are

getting a lot of their water by breaking them down.

When you look at all the inputs and outputs of carbon in the ecosystem, it gets

complicated quickly. But, in general, when plants die and are buried before they get eaten, that

carbon is sequestered from the ecosystem. When volcanos erupt, they pump carbon dioxide out

of the Earth into the atmosphere. We know that the amount of carbon dioxide and oxygen in the

atmosphere varies over geologic time periods. And, looking at the records in the rocks and

fossils, we know that a lot of this variation is due to the types and concentrations of plants and

animals, but sometimes it’s from major volcanic events, like super volcanos.

Human Caused CO2 in the Environment: (est. time: 2

min)

When we dig fossil fuels, like coal and oil, out of

the ground and burn it for fuel, we are using carbon that

had been sequestered from the atmosphere and re-

releasing it into the ecosystem as carbon dioxide. Now let me ask a question to see if you can

put it all together.

QUESTION: Because billions of people use fossil fuels to power their day, unnaturally adding

carbon dioxide to the atmosphere, what do you think is happening to the amount of carbon

dioxide dissolved in the oceans?

ANTICIPATED RESPONSE: It’s going up.

FOLLOW-UP QUESTION: Okay, that was too easy. Let’s try this one…Several countries are

trying to find economical ways of fixing carbon. Fixing carbon is where you do something to

lock it into rocks and other material, or somehow bury it to remove it from the ecosystem. Kind

of like drilling for oil, but in reverse. What will happen to the ocean if they are successful?

ANTICIPATED RESPONSE: (Give them time to think it through) The carbon dioxide in the

ocean will go down?

TEACHER FEEDBACK: Exactly! Nature will maintain its equilibrium, so if we start removing

the carbon dioxide from the air, more will come out of the ocean to re-establish equilibrium.

Ocean Acidification (est. time: 2 min)

It turns out that somewhere between a quarter and a third

of the carbon dioxide being added to the atmosphere finds

its way into the ocean. Then some of the dissolved

carbon dioxide reacts with water to make carbonic acid.

That’s the reason why CO2, which is odorless and tasteless, can change the flavor of a soda and

also drops its pH to about 3. We are slowly making our oceans more acidic. Since we started

measuring their pH about a hundred years ago, the ocean dropped its pH from 8.3 down to 8.2.

That doesn’t sound like a lot, but remember that for every whole number it goes down, it’s 10

times more acidic. Because the production rate of CO2 is increasing, scientists expect that we’ll

drop to a pH of 7.9 by the year 2100.

But, it’s not all bad news. Did you know that not all carbon dioxide is created equally?

If I grow several trees in my backyard so I can use them for firewood in the winter, the carbon in

the wood came from the atmosphere. When I burn the wood, I’m just releasing carbon dioxide

that came out of the air to begin with. In this scenario, as long as I plant as many trees as I cut

down, there are no global warming or ocean acidification concerns. If, on the other hand, I pull

oil and coal out of the ground and burn them, then there is a concern. Their carbon had been

locked out of the ecosystem for millions of years.

Effects of Ocean Acidification: (est. time: 2 min)

When the pH of the ocean changes, we have

measurable proof that we are changing our environment.

Beyond, that, why do we care? Because Corals and

crustaceans. Corals are a required habitat for at least part of the life cycle for most sea life and

crustaceans are at the base of the food web.

Building a shell that is just barely safe from dissolving is metabolically inexpensive.

Unfortunately, nature’s propensity to reward metabolically efficient species through the process

of evolution might be catastrophic for us. We’re already seeing shells and corals growing much

more slowly, and in some places outright dissolving. Unless the human civilization changes

something, we are going to find out just how resilient the oceans are during your lifetime.

Having said all that, most industrialized nations are working hard to keep the future safe.

I don’t know what the final answer will be, but it most likely will be the result of many small

steps and individual choices that we make. Maybe you demand that smokestacks get torn down

and replaced with wind and solar farms. Maybe, as a society, we decide that we’re done using

gasoline in our cars because going electric isn’t that much more expensive. Maybe one of you

has the answer.

Summary: (est. time: 1 min)

Before we move on to our lab, does anyone have

questions about ocean acidification, dynamic equilibrium

or anything else?