Chemistry

Acids and Bases: The ocean crisis

The ocean is becoming increasingly acidic, a phenomenon that is impacting marine life around the world. Now scientists are reporting that the rate of ocean acidification is the worst it’s been in the last 300 million years.

In this lesson you will investigate:

• What are acids and bases?

• How do we measure the strength of acids and bases?

• What is ocean acidification?

• How does carbon dioxide make water more acidic?

• How is ocean acidification affecting marine life?

So put your diving gear on, plunge into this lesson and explore what’s happening beneath the surface of the seas.

This is a print version of an interactive online lesson. To sign up for the real thing or for curriculum details about the lesson go to www.cosmosforschools.com

Introduction: Acids and Bases (P1)

Our oceans are in desperate trouble. When carbon dioxide gas from the air dissolves into sea water it makes it more acidic. Andthat higher acidity has a terrible effect on marine life. Molluscs find it harder to build shells and tiny animals and coral reefs die.

We knew it was bad, but a new study by scientists shows it is worse than we thought. In fact, they say it is the worst it has been for300 million years.

The information was published by the World Meteorological Organization in its Greenhouse Gas Bulletin, which monitors theeffects of climate change. It is the first time the group has included ocean acidification in the bulletin, but the scientists said it wasimportant we look at ocean health because it is central to the Earth’s climate.

And the damage caused by acidification is also cascading through the food chain and could in the future reduce the amount of foodthe oceans can produce, just as the world’s population is growing to record numbers.

To try and work out exactly what will happen, scientists are looking back to the last time that carbon dioxide levels were high, 55million years ago, to see what we can expect to happen.

Read the original Cosmos blog post here.

Acids corrode all sorts of substances. What do you think causes the corrosion of some statues?

Question 1

Rearrange: Before exploring ocean acidification let's consolidate what you already know about acids and bases. Drag andrearrange the terms in the mind map so that they belong to either the "Acids" or "Bases" node. Then add two terms of your own.

Acids and bases

Acids

Bases

low pH

high pH

tastes bitter

tastes sour

lemon

soap

Gather: Acids and Bases (P1)

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Question 1

Recall: Your stomach is basic.

True

False

Question 2

Recall: Your blood is acidic.

True

False

Question 3

Recall: The ancient Greeks defined acids and bases by the way that they behaved. Add these behaviours into the table below.

Behaviour 1 Behaviour 2

Acids

Bases

Acids have special chemical properties. They are what give lemons their sour taste and play a key role in helping you digest yourfood.

Some of these properties include:

They are corrosive.

They have a sour taste.

Acids

They are particularly reactive with metals.

They are neutralised by bases.

Bases, like acids, have special chemical properties. Bakers use bases to help make cakes rise and they are the active ingredient inpaint stripper.

Bases have the following common properties:

They are corrosive, though the term "caustic" is more commonly used.

They have a bitter taste.

They have a soapy, slimy feel.

They are neutralised by acids.

If a base can be dissolved in water it is known as an alkali.

Bases

Question 4

Research: Use the internet to find three more examples of acids and bases that you might come across in everyday life and listthem in the table below.

Acids Bases

Acids and bases range in strength. Strong acids and bases are very reactive and dangerous while weak acids and bases aregenerally not. When something is neither acidic nor basic it is said to be neutral.

The acidity of a solution is a measure of it's hydrogen ion (H ) concentration. The higher the concentration of H , the more acidic it is.The lower the concentration of H , the more basic it is.

Measuring acidity

+ +

+

Question 5

Describe: Fill in the table below to complete the following statement:

Strong acids have _______________ H concentrations. Strong bases have _______________ H concentrations.+ +

Blank 1 Blank 2

Acidity is measured in a special unit called pH. Most acids and bases range in pH from 1 to 14. The more acidic a substance, thelower its pH. The more basic a substance, the higher its pH. Neutral substances have a pH of 7.

Question 6

Label: Label the following substances with either "strongly acidic", "acidic", "neutral", "basic" or "strongly basic". Add a star next tothe substance with the highest H concentration and a cloud next to the substance with the lowest H concentration.+ +

The acidity of a substance can be changed. For example, if you take an antacid tablet it will decrease the acidity in yourstomach. When a substance becomes more acidic it is said to be undergoing acidification, a process that is currently taking place inour oceans.

Ocean acidification

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Question 7

Recall: Over the past 250 years acid levels in the ocean have risen by

5-10%.

25-30%.

45-50%.

65-70%.

Question 8

Describe: In simple terms, explain the effect that increased atmospheric carbon dioxide has on the ocean.

Question 9

Recall: List five organisms that the video states are affected by ocean acidification.

Organism

1

2

3

4

5

Process: Acids and Bases (P1)

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Question 1

Complete: Fill in the table below to complete the following summary of the chemistry behind ocean acidification:

The amount of carbon dioxide (CO ) in the atmosphere is _______________ .

Roughly 30% of atmospheric CO is absorbed by the oceans.

When CO and water (H O) react they produce bicarbonate ions (HCO ) and _______________ (H+) as described by the followingequation:

CO + H O HCO + H

The increased H concentration in the ocean is making it more _______________ .

2

2

2 2 3-

2 2 → 3- +

+

Blank 1 Blank 2 Blank 3

The following table shows the values of ocean pH since 1875 as well as the predicted future values based on current projections.

Year Ocean pH

1875 8.16

1900 8.15

1925 8.14

1950 8.13

1975 8.11

2000 8.08

2025 8.04

2050 7.99

2075 7.93

2100 7.86

Question 2

Visualise: Visualise the change in ocean pH over time above by plotting the above data.

Hint: Make sure to label the x and y axes.

Change in ocean acidity over time

X-Axis

auto

Y-A

xis

7.81850 auto

Series 1

x y

This graph needs some data!

Question 3

Interpret: What does your graph infer about the future of ocean acidity?

Some sea creatures have shells. Shell growth requires calcium carbonate (CaCO ) which is formed by combining calcium ions (Ca )with carbonate ions (CO ):

Ca + CO CaCO

Hydrogen ions (H ) can also combine with carbonate ions to form bicarbonate ions (HCO ), which are no good for making shells:

H + CO HCO

32+

32-

2+3

2- → 3

+3

-

+3

2- → 3-

Question 4

Complete: Fill in the table below to complete the following sentence:

The _______________ hydrogen ion concentration of the oceans is resulting in _______________ carbonate ions being available for_______________ formation, a key ingredient for shell growth.

Blank 1 Blank 2 Blank 3

Question 5

Count: Examine the illustration in Question 6.

Panel A shows an array of molecules in ocean water and two carbon dioxide molecules in the atmosphere.

Panel B shows what happens when the carbon dioxide molecules react with water molecules in the ocean.

Count the number of carbon, oxygen, hydrogen and calcium atoms in each panel to make sure that there are the same number ineach. Add your tallies to the table below.

Carbon Oxygen Hydrogen Calcium

Panel A

Panel B

Question 6

Draw: In the illustration below, draw a circle around the carbonate ions that are available for calcium carbonate formation, and byextension shell growth. Note the difference between the two panels. Then draw a red box around the panel that has more acidicwater.

Question 7

Illustrate: Communicating scientific events, such as ocean acidification, to the public is important. There are many ways ofcommunicating science to the public and cartoons is just one of them. Draw and upload a three- or four-panel cartoon thatillustrates an element of ocean acidification that you would like to communicate to the public.

Apply: Acids and Bases (P2)

Experiment: Modelling ocean acidification

In this lesson you have explored the effect that increased atmospheric carbon dioxide has on our oceans. This simple experimentwill allow you to model this phenomenon right before your eyes.

To investigate the effect of carbon dioxide on sea water.

Conical flask

White tile or white paper

Sea water (or tap water if you don't have access to sea water)

Universal indicator

Straw

Background

Aim

Materials

Question 1

Order: Add the numbers 1-6 into the table below to correctly order the steps of the experiment.

Record what happens to the indicator colour and pH in the table in Question 2.

Place the flask over the white tile or paper.

Add enough drops of universal indicator solution to the water to make its colour obvious, but not too bright.

Add sea water to the conical flask until it is about a quarter full.

Record the initial indicator colour and approximate pH in Question 2.

Place the drinking straw into the water well below its surface, then blow bubbles into the water for about 1-2 minutes.

Note: You breathe out more carbon dioxide than you breathe in. When you blow into sea water, you dissolve extra carbon dioxide into it.

Results

Question 2

Record: Add your observations into the table below.

What colour is the universal indicatorsolution?

What is the approximate pH of thesolution?

Before blowing into the seawater

After blowing into the sea water

Question 3

Document: You may optionally upload photos or videos of your experiment below.

Procedure

Question 4

Summarise: What have you learnt from this experiment and what does it imply for the future of our oceans?

Discussion and conclusion

Career: Acids and Bases (P2)

Dr Sarah Cooley works on puzzles – complex puzzles. As the Science Outreach Manager at the Ocean Conservancy inWashington DC she helps piece together scientific information and use it to help find solutions to the problem of ocean acidification.

Sarah’s work centres on explaining the growing scientificunderstanding of ocean acidification to policy-makers and thepublic, so she spends a lot of her time sending emails andmaking phone calls, as well as at meetings and workshops. Shetries to figure out how humans might fare as marine ecosystemsacidify and uses these projections to work with people whodevelop state and national laws trying to find ways to help uslive sustainably. Working on lawmaking strategies is like solvinga puzzle, and Sarah loves that.

She also loves that she gets to travel a lot for her work. She hasbeen all over the world, including Hawaii, Barcelona, London,Vancouver, Paris, Monte Carlo and Greece – and that’s just inthe past three years. In London, at one of her meetings to applyfor research funds, Sarah was introduced to Prince Albert II ofMonaco. Thank goodness she had her smart phone and couldlook up how to greet him the right way first!

Sarah was drawn to science by the feeling that there werealways puzzles to solve. And since she grew up sailing off thecoast of New Jersey she naturally came to love the ocean as well.To her, the carbon cycle is the most interesting Earth processthere is. “I guess I was destined to become a marine carbonchemist!” she says. But Sarah was also fascinated by people'srelationships with the Earth and she has found new purpose inher role as a science communicator. Her favourite part of thejob is figuring out what's important to someone and thenhelping them understand how ocean acidification is connectedto that.

When she isn’t puzzling out legal strategies or rubbing elbowswith royalty, Sarah enjoys reading, singing and spending timewith her family.

Question 1

Plan: As part of her work Sarah runs workshops on ocean acidification for policy makers. Imagine that Sarah has asked you to runone of her workshops for politicians. Plan the structure of your workshop below, describing what you would cover and why.

Cosmos Lessons team

Lesson authors: Samantha Webber and Deborah TaylorProfile author: Megan ToomeyEditors: Bill Condie and Jim RountreeArt director: Robyn AdderlyEducation director: Daniel Pikler

Image credits: Kate Patterson / MediPics / Prose / Getty images /iStockVideo credits: TED-Ed / California Academy of Sciences / NOAAVisualizations / YouTube