Observing Changes In Matter Today’s Objective: Investigate and describe properties of materials.

First… Let’s Review

Types of solutions- different substances that make it up are not separately visible. Solid dissolved in a liquid… sugar in hot coffee. Liquid dissolved in a liquid… acetic acid in water (to create vinegar) Gas dissolved in a liquid… carbon dioxide gas in water (to create carbonated pop) Gas dissolved in a gas… oxygen and smaller amounts of other gases in nitrogen (happens in the atmosphere) Solid dissolved in a solid… copper in silver (to create sterling silver)

Which of the following changes is an example of a physical change? A. Melting ice B. Rusting iron C. Burning paper D. Photosynthesis

A A physical change is easily reversible and does not involve the formation of a new form of matter. The melting of ice is easily reversible and does not result in a new compound.

Use the following information to answer the next question. Isabella watched her mother crack eggs into a frying pan. She noticed that the transparent liquid surrounding the yolks of the eggs became solid and the white when the pan was placed over the burner of the stove.

Which of the following statements best describes the changes that occur to the egg during frying? A. The changes are physical because a change in state occurs and an odour is detected. B. The changes are chemical because heat is absorbed and a new substance is formed. C. The changes are chemical because an odour is detected and heat is released. The changes are physical because a new colour appears and heat is absorbed.

B When an egg is fried, it undergoes a chemical change because a new substance with new properties is formed. This is not reversible. For example, if you remove the added heat by putting the egg in the refrigerator, it will not return to its original state.

The combination of cement and gravel is know as: A. An alloy B. A solution C. A pure substance D. A mechanical mixture

The difference between a compound and a mixture is that a compound ___ and a mixture ___. A. Is made of elements/Is not made of elements. B. Has properties that are always the same/Does not have properties that are always the same. C. Can dissolve/Cannot dissolve D. Is colourless/Is visible

D A mechanical mixture is a mixture of 2 or more substances. The addition of the gravel to the cement strengthens the mixture by making it harder.

B The properties of a compound such as water are always the same, whereas the properties of a mixture can vary. For example, the strength of concrete can vary depending on how much cement is mixed with the gravel.

How long will it take Andrew to separate a mechanical mixture? A. A long time cause Andrew was mean to me yesterday so I picked really small substances. B. A long time cause Andrew’s mechanical mixture separating abilities are not well developed. C. A long time cause Andrew will get really worked up and excited, yell loudly, freak out and waste precious mechanical mixture separating seconds. D. Not long cause Andrew is a ninja.

Doesn’t matter The point is that you can separate a mechanical mixture into the original substances. And that Andrew was mean to me yesterday. Was Andrew’s mixture and example of a homogenous or heterogeneous mixture?

Your life could be worse… I could be a teacher who sings to you! Solutions Song

Observing changes in matter Some changes in matter are easy to see: watching the ice and snow melt in the spring- solid water becoming liquid water; watching heated water in a kettle vaporize as steam. Not so easy to see that hemoglobin, which carries oxygen in your blood, changes colour when carbon dioxide and oxygen are exchanged in your lungs. Oxygen Transport

Physical Change Is one in which a material changes from one state to another. Material can also physically change back into its original state. When frozen apple juice is thawed, it melts from a solid into a liquid. If you refreeze the juice, it will turn back into a solid. Its composition will remain the same in all states.

Chemical Change Occurs when 2 or more materials (substances) react and create new materials. The new materials have completely different properties from the original substances. How can you tell when a chemical change is underway or has taken place? The main pieces of evidence to look for are changes in colour, odour, state, or thermal energy during, or as a result of the reaction between the original substances.

Change in colour

Change in Odour/Smell

Formation of a solid or gas/CO2

Release or absorption of heat energy

Sometimes it is unclear whether a material’s change in state means that a chemical or physical change occurred. In such situations, chemical analysis in the lab is required to confirm the nature of the change.

Controlling changes in matter to meet human needs. Freeze-drying foods? Can be eaten months, even years later; easy to prepare; just add water! Freeze-drying process: food is frozen to covert water content in food to ice; frozen food is put in a pressure chamber and pressure is reduced until the ice sublimes. What does “sublime” mean?? What term describes the opposite process?

Deposition… the change from a gas to a solid! The result of freeze-drying is that about 98% of the water in the original food item is removed. That leaves a food that is about 10% of its original mass- and that once packaged, does not have to be refrigerated. Can you think of an example of when it might be important to keep your supplies as light as possible?

Freeze-Fracturing a cell

In this process, a plant or animal cell is rapidly frozen. The ice formed within each cell is then removed by various evaporation techniques. The result is a clearly revealed cell structure: nucleus, pores, and membrane.

MRE Meal, Ready to Eat Instead of having to be heated, a freeze-dried food is heated in a special package called a “Flameless Ration Heater”. Pouch contains magnesium, iron, and salt. When water is added to these chemical, the resulting chemical change releases enough heat to warm the freeze-dried contents.

How can scientists use chemical change to transform common materials into other useful products?

Corn is put through a chemical change called fermentation Once the chemical process is complete, the new substances are recovered, purified, and made into biodegradable plastics, solvents, and gasohol. Biodegradable plastics are better for the environment because they can be decomposed by bacteria. Corn-based solvents and nail polishes are not as harmful to the environment as other types of solvents. Gasohol provides a renewable type of fuel for automobiles.

Problems? Food versus fuel debate. Deforestation and soil erosion. Impact on water resources. Loss of biodiversity. Pollution: many aldehydes are toxic to living cells.

Check & Reflect Page 109, #1, 3, 5, 7 – In your groups work together to answer. Page 110 & 111, #1, 3, 5, 6, 9, 15, 17, 18 – Individual work, hand in- this will count toward your mark.