Chemistry - NSTA Learning Center - National Science Teachers

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May 20, 2013

6:30 p.m. – 8:00 p.m. Eastern time

Chemical Change – Introducing a Free

Online Resource for Middle School

Chemistry

Presented by: James Kessler

http://learningcenter.nsta.org

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Introducing today’s presenter…

Introducing today’s presenters

James Kessler Manager, K-8 Science Education

American Chemical Society

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Assisting in the chat:

Patti Galvan Program Manager, K–8 Science Education



Middleschoolchemistry.com Big Ideas about the Very Small

Chapter 6: Chemical Change

American Chemical Society 6

Welcome

Free online resource for teaching

basic concepts in chemistry at the

middle school level.

Six chapters of activity-based lesson

plans which align with state standards

in physical science and inquiry.

Two main goals:

• Help students understand common

every day observations on the

molecular level.

• Help students to design and

conduct scientific experiments.

What is middleschoolchemistry.com?


What’s in a Chapter?

• Lesson Plans (5E):

– Hands-on activities

– Student Activity Sheets

– Multimedia

– Extra Teacher Background

• Student Reading

• Test Bank


Goals of the Webinar

• Demonstrate selected activities and

animations from the lessons in Chapter 6

to show how they can be used with

students

• Review some basic chemistry concepts

covered in the lessons


Big Idea for Chapter 6:

Have never

thought about it

and happy that

way

Willing to listen if

it doesn’t take too

long

Stay up nights

pondering this

What happens on the molecular level, during a chemical reaction, that

makes reactants turn into products?

Use the “Fascination Number Line” to indicate your level of

fascination with this question.

0 10 5


Lesson 6.1 What is a Chemical Reaction?

Extend Explore Explain Evaluate Engage

Is a burning candle a chemical reaction?

As a demonstration, light a candle and tell students that

in a chemical reaction:

• substances combine and react to create something

new.

• the substances that combine are called the reactants.

• the substances that are made are called the

products.

Ask students if they think a burning candle is a chemical

reaction and if they can guess what the reactants are.

Give them a hint by placing a jar over the candle.


Methane Reacting with Oxygen Extend Explore Explain Evaluate Engage

The reactants are wax from the

candle and oxygen from the air.

The wax is a long chain of carbon

and hydrogen atoms and is called

a hydrocarbon.

The smallest hydrocarbon is

methane (CH4) which we can use

to make a model of the reaction.

The methane reacts with oxygen

and becomes carbon dioxide and

water.

But how did the methane and

oxygen become carbon dioxide

and water?


Breaking and Making Bonds Extend Explore Explain Evaluate Engage

In a chemical reaction, the bonds between

the atoms in the reactants break.

The atoms rearrange and bond to form the

products.

The products are different substances than

the reactants, but they are made up of the

same atoms, just bonded in different

arrangements.

Explain the subscripts and coefficients.

You can count the atoms on both sides of

the equation and see that they are the same

type and the same number.

This is a balanced chemical equation.

Balanced Chemical Equations


Extend Explore Explain Evaluate Engage

On the Activity Sheet:

Have students count and

record the number of atoms in

the reactants and products.

They will see that there are

the same number of each

type of atom in the reactants

and the products.

What Does a Chemical Equation Tell You?


If the chemical equation needs

to be balanced, why can’t it be

written like the second one?

The chemical equation shows

the molecules of the reactants

and the actual molecules they

turn into as products.

How am I supposed to predict or

know what the products will be?

You don’t need to. The reactants

and products will be included.

You just need to interpret what it

means.

What Does a Chemical Equation Mean?


The equation shows how many of one

molecule reacts with how many of

another to produce how many of each

type of molecule in the products.

In a reaction between methane and

oxygen, one molecule of methane reacts

with two molecules of oxygen.

In this reaction, they always react in the

ratio of 1:2. One molecule of methane

with two molecules of oxygen. Or 100

molecules of methane with 200

molecules of oxygen.

Will an equation be balanced if there is a

lot more of one reactant than another in a

particular reaction?

6.2 - Controlling the Amount of Products in a Chemical Reaction


As a demonstration, add vinegar to

baking soda and ask students if

this is probably a chemical

reaction.

Yes, because the reactants were a

liquid (vinegar) and a solid (baking

soda) and a gas was produced.

The product, carbon dioxide gas

(CO2), is chemically different from

the reactants.

Controlling the Amount of Products


Do another demonstration with 10

milliliters of vinegar, 1 drop of

detergent solution, and ½

teaspoon of baking soda to show

a rough measure of the amount of

carbon dioxide produced.

Challenge students to combine

amounts of vinegar and baking

soda to make a foam that

reaches the top but does not

overflow.

Discuss idea that both reactants

are necessary: that lots more of

one will not necessarily produce

more product.

6.3 - Forming a Precipitate


As a demonstration, combine a

sodium carbonate solution with a

magnesium sulfate (Epsom salt)

solution.

The clear colorless solutions

combine to make a white

precipitate. Ask students if they

think this is a chemical reaction.

Yes, because the products are

different than the reactants. The

magnesium carbonate is the white

precipitate.

NaCO3 + MgSO4 → MgCO3 + NaSO4

Sodium

carbonate Magnesium

sulfate

Magnesium

carbonate

Sodium

sulfate

Making a Chalk Precipitate


Students make a calcium chloride

solution and sodium bicarbonate

solution and combine them.

A gas is produced and a precipitate

is formed. The precipitate is calcium

carbonate which is the substance

that makes up chalk, egg shells and

sea shells.

Chat Discussion and Questions


Have you done chemical change activities

similar to these ones?

Have you used them to help kids see that the

equation for the reaction is balanced?

Do you have any questions?

6.4 – Temperature Affects the Rate of a Reaction


As a demonstration, place one glow stick

in hot water and another identical glow

stick in cold water.

Explain that a glow stick contains two

reactants that mix when you bend and

break the little vial inside.

Ask students:

If the reactants in one glow stick are

cooled and the reactants in another glow

stick are heated, which do you think will

be brighter? Why?

6.4 – Temperature Affects the Rate of a Chemical Reaction


Ask students how they could design an

experiment to see if temperature

affects the rate of the chemical reaction

they did using calcium chloride and

sodium bicarbonate solutions.

• Use two sets of solutions.

• Heat one set and cool the other.

• Pour the cooled reactants together

and the heated reactants together at

the same time.

See which one foams and forms a

precipitate the fastest.

6.5 – A Catalyst Increases the Rate of a Reaction


Hydrogen peroxide (H2O2)

decomposes very slowly to form

oxygen (O2) and water (H2O).

The process can be speeded up

tremendously by adding yeast to the

hydrogen peroxide.

This works because yeast contains

a catalyst which catalyzes the

decomposition of the hydrogen

peroxide.

Speeding Up a Chemical Reaction


A piece of aluminum foil is placed in a

copper II sulfate solution.

No reaction is observed.

Salt is added and a reaction takes place.

One theory is that the salt compromises

a protective coating on the aluminum

which allows the copper II sulfate and

aluminum to react.

In this reaction, electrons leave the

aluminum and join the positively

charged copper ions (Cu2+) making

neutral copper atoms or copper metal.

Hydrogen gas is also produced.

6.6 – Using Chemical Change to Identify an Unknown


As a demonstration, place two

similar-looking white powders

(baking soda and corn starch) in

two separate cups.

Tell students that you are adding

the same solution (dilute tincture

of iodine) to both cups.

One solution will remain the

original light brown but the other

will turn a very dark purple.

Ask students if the powders were

the same or different. How do

they know?


Testing the Powders Can chemical change be used to identify an unknown?

Students will test four similar-looking

white powders (baking powder,

baking soda, cream of tartar, and

corn starch) with four different liquids

(water, vinegar, dilute tincture of

iodine, and universal indicator) to see

the reactions, if there are any.

Show students the testing sheet and

ask how the testing should work.

After observing and recording any

reactions, students will test an

unknown powder with the four liquids

to see if the reactions of the unknown

match the reactions of any of the

known powders.


QUESTIONS?

6.7 – Energy Changes in Chemical Reactions


Students place 10 milliliters of vinegar in a

cup and add a thermometer.

After recording the initial temperature,

students add ½ teaspoon of baking soda

and watch the thermometer.

Why does the temperature go down?

Endothermic Reaction


We know that in a chemical reaction,

the bonds of the reactants are broken,

atoms rearrange and bond in new

ways to form the products.

It takes energy to break the bonds of

the reactants.

Energy is released when new bonds in

the products are formed.

If it takes more energy to break the

bonds of the reactants than is

released when the bonds of the

products are formed, the reaction is

endothermic.

Calcium Chloride and Sodium Bicarbonate Solutions


Students place 10 milliliters of baking

soda solution in a cup and add a

thermometer.

After recording the initial temperature,

students add ½ teaspoon of calcium

chloride and watch the thermometer.

Why does the temperature go up?

Exothermic Reaction


If more energy is released when the

bonds of the products are formed

than was used to break the bonds

of the reactants, the reaction is

exothermic.

Conversions Between Kinetic and Potential Energy


The energy changes in endothermic and exothermic

reactions are really conversions between the kinetic

energy (KE) of motion and the potential energy (PE) of

attraction.

In bond-breaking, KE is used to break the bonds between

atoms, so KE goes down. But if KE goes down and atoms

are separated, the PE goes up.

So bond-breaking always converts KE to PE and is

endothermic.

Then, when the newly-separated atoms attract each other

and bond, the PE goes down. But if the PE goes down,

the KE has to go up.

So bond-making always converts PE to KE and is

exothermic.

The sum of these energy conversions determines whether

the overall reaction is net endothermic or exothermic.

Energy Diagrams


Endothermic and exothermic reactions

can also be modeled using energy

diagrams.

Kinetic energy is used to break bonds

between atoms in reacting molecules.

This converts KE to PE.

The atoms rearrange and bond again.

This converts PE to KE.

The difference between these processes

determines whether the reaction is net

endothermic or net exothermic.

Acids, Bases, and pH


Many chemical reactions involve changes in

pH. What is pH?

A small fraction of water molecules naturally

interact to produce H3O+ and OH- ions.

pH refers to the concentration of H3O+ ions.

Because of the units used to measure pH, as

the concentration of H3O+ ions increases, the

number on the pH scale decreases.

A solution with a pH of 4 (acid) has a greater

concentration of H3O+ ions than a solution

with a pH of 6 (base).

6.8 - pH and Color Changes


Demonstrate the color changes when

universal indicator is added to citric

acid and sodium carbonate.

Students test different concentrations

of citric acid and sodium carbonate to

try to get as many different colors as

possible.

Adding an Acid or a Base to an Indicator


An acid is a proton donor. An acid

donates a proton to water creating more

H3O+ ions. These protons can be

transferred to the indicator, resulting in

a color change.

A base is a proton acceptor. A base

accepts protons from water which

makes more OH- ions. Protons are then

transferred from H3O+ ions and from the

indicator to the OH- ions, resulting in a

color change.

Ready to Try it?


Any final questions?

What content or activities would be useful to you in your classroom?

Thanks to today’s presenter!

Introducing today’s presenters

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James Kessler Manager, K-8 Science Education


Assisting in the chat:

Patti Galvan Program Manager, K–8 Science Education


Thank you to the sponsor of

tonight’s web seminar:

This web seminar contains information about programs, products, and services

offered by third parties, as well as links to third-party websites. The presence of

a listing or such information does not constitute an endorsement by NSTA of a

particular company or organization, or its programs, products, or services.

Thank you to the sponsor of tonight’s web seminar—1 of 6

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Thank you to NSTA administration—2 of 6

National Science Teachers Association

David Evans, Ph.D., Executive Director

Zipporah Miller, Associate Executive Director, Conferences and Programs

NSTA Web Seminar Team

Al Byers, Ph.D., Assistant Executive Director, e-Learning and Government Partnerships

Brynn Slate, Manager, Web Seminars, Online Short Courses, and Symposia

Jeff Layman, Technical Coordinator, Web Seminars, SciGuides, and Help Desk

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Chemistry - NSTA Learning Center - National Science Teachers