For candy in my kitchen!

And its true.  My favorite people to cook with are other scientists, its a lucky by-product of graduate school friends.

Unfortunately, making candies and baked goods doesn’t always translate well in the classroom (except, of course, for homeschoolers) but here’s another chance to use something you’re going to do anyway (right?) to teach the kids around you.

Today: TOFFEE (aka physical and chemical changes)

Recipe:

Materials (Recipe)

• 1c. butter
• 1 1/3 c. sugar
• 3 T. water
• 1 T. light corn syrup
• 1/8 t. salt
• 1 t. vanilla
• 1 c. Chocolate chips or milk chocolate for top
• Hot plate
• Pot
• Candy thermometer
• Wooden spoon or heat resistant rubber spatula
• 9×13 inch pan
• Measuring cups and spoons

Grade Level 1-6 (up to adult)

State Indicator (s) (Ohio)
Doing Scientific Inquiry – 1.1, 1.3, 3.4, 5.5
Nature of Matter – 1.3, 1.4, 4.2, 4.4, 6.2, 6.3, 6.4
Math-
Use Measurement Techniques and Tools – K.2, 2.6, 3.5, 3.6

Goals and Objectives for Student Learning

• The objective of this lesson is to show examples of physical and chemical changes by making toffee and to give the students an opportunity to determine if a change is physical or chemical.
• Making the toffee can be done as a demonstration for the class. The melted mixture can be placed into smaller containers and distributed to lab groups for chocolate melting.

Students can draw a cartoon strip or before and after pictures to describe the processes that were used to make the toffee rather than writing traditional responses.

Safety

The hot toffee mixture is very dangerous for children/students to handle and can result in severe burns. Reinforce the idea that some experiments require immediate adult supervision.

I recommend having at least one other person in the room for this demonstration.

Learning Activities

While making the toffee, have students take notes (or draw pictures of) the steps you are doing to make the toffee.

The recipe is as follows: Grease a 9×13 pan with butter. Mix sugar, butter, water, salt, and corn syrup together and bring to a soft crack stage, 300-310 degrees Fahrenheit. Pour into pan, cover with chocolate bars and spread chocolate when melted. Cut into pieces once cooled.

As the toffee is cooling, walk around the room and have students answer the following questions about physical and chemical changes:

1. What type of change happened to the butter? Physical or chemical. Describe. {melting is physical, browning is chemical}
2. Which ingredients were solids when we started?
3. What type of change happened when we mixed all the ingredients together and heated it? Physical or chemical. Describe. {butter melting – physical, sugar heating to soft crack stage – chemical (technically, its decomposition)}
4. What type of change happened when we poured the toffee onto the greased pan? Physical or chemical? Describe. {physical – it changed shape, physical – it hardened from a liquid to solid}
5. List any other changes you saw occur while making the toffee. {Students may have noticed carmelization of the sugar – chemical change. Melting chocolate is a physical change.}

What’s Going On

Making toffee is a fun and easy cooking activity that demonstrates several physical and chemical changes. Physical and chemical changes present in this lesson include:

Physical changes:

1. Butter melting (change of state)
2. Sugar, salt, and corn syrup dissolving in water.
3. Toffee hardening from liquid to solid
4. Chocolate melting and spreading out on top of toffee and then hardening again in different shape.
5. Cutting toffee into smaller pieces

The Chemical Change of Sugar:

The heat causes the sugar to caramelize and change colors: first to a yellow color, then to a darker and darker caramel color as the sugar is oxidized. The brown color comes from complex chemical reactions involving the element carbon. The other chemical change that happens is that when basic table sugar, sucrose, is heated with water, the heat causes the sucrose molecules to react with that water molecules and break down into the more simple sugars, fructose and glucose, that make up sucrose.

What do you enjoy making with the children in your life?