Lesson 14

Scientists use chemistry to make products that you use every day. They test properties to find out which materials will do the best job.

Metals are good conductors of heat. Good conductors of heat also make good cooking pots. The most common metals used for cooking pots are aluminum, copper, and cast iron. Some metals are also mixed with other elements to form alloys such as stainless steel and carbon steel.

In order for cookware to be useful it must distribute the heat evenly and not react with the food.

Why would cookware reacting with food cause problems?

In cases where the metal works well as a conductor but is too reactive, the pot will be made out of the good conducting metal and then coated with another that is unreactive.

Aluminum Aluminum is a lightweight

metal that conducts heat very well.

It does not rust and it is resistant to corrosion.

Some acidic foods or eggs can react with aluminum leaving the food with an altered taste.

Anodized Aluminum has a naturally formed layer of aluminum oxide which is then thickened by an electrolytic process.

This makes the metal harder and non-reactive.

CopperCopper pan are known for the best heat

conductivity which means more even heating.

But they need to be coated so that they do not react with the food.

Copper pans are normally heavier, more expensive and used at the commercial level.

Cast Iron Cast iron has a is slow to heat up but once it up to

temperature it provides even heating that can withstand very high temperatures.

Cast iron pans are also chemically reactive and they will react with tomato sauces and wine.

Some foods such as spinach will even turn black due to chemical reactions. Cast iron pans rust and because of this they need a thin layer of fat or oil that helps to protect the metal and prevent sticking.

Stainless Steel Stainless steel is an iron alloy that contains

nickel and chromium. It is very hard, resists corrosion, resists

scratches and does not react with food. Stainless is a poor heat conductor and

because of this most pots and pans have a copper disk in the bottom of them to help distribute the heat.

Carbon Steel Carbon steel can be made very thin making

it good for heating foods quickly. It does not conduct heat well and because

of this its cooking uses are limited to specialized cookware.

Like cast iron it also corrodes and needs to be coated in fat or oil.

You have just been hired to work at a local restaurant. The establishment plans on replacing all of their cookware. They hear that you are taking a science class and ask you to decide what pot is going to have the best heat conductivity for perfect cooking. All of the pans are identical in size, thickness and all of them have the same non-stick coating on them that will not react with the food or corrode.

You have been given the following materials to make your decision: ◦ three 15 cm strips of different metals◦ 9 thumb tacks◦ tongs◦ stopwatch ◦ candle.

Design an experiment that will allow you to test the heat conductivity of the metals.

(HINT – use the melted wax from the candle to stick the tacks to the metal strips)

Question:◦ Which metal conducts heat the fastest?

Variables ◦ Control: All of the metal strips are the same and

the heat from the candle is the same. ◦ Independent: The three types of metals◦ Dependent: The time it takes to conduct the heat

through the metal.

Experimental design◦ Design a method of comparing the three metals.

Use all the materials listed above in the design.

Results ◦ Design a table that can record your data obtained

from your experiment.