9/8 CW - Katie Braymiller | Library

Physical vs. Chemical changes
Substances can undergo chemical or physical changes, which affect the substances in different ways. A physical change in a substance doesn't change what the substance is. In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed. For example, if a piece of paper is cut up into small pieces it still is paper. This would be a physical change in the shape and size of the paper. If the same piece of paper is burned, it is broken up into different substances that are not paper.
Physical changes can be reversed; chemical changes cannot be reversed without extraordinary means, if at all. For example, a cup of water can be frozen when cooled and then can be returned to a liquid form when heated. If a person decided to mix sugar into water to make sugar water, this would be a physical change because the water could be left out to evaporate and the sugar crystals would remain, meaning you could change the substance back to water and sugar. However, if a person made a recipe for a cake with flour, water, sugar and other ingredients and baked them together, you could not separate the ingredients once it’s baked together. Baking the cake would be a chemical change since this can’t be reversed.

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Would water evaporating from a boiling pot be a chemical or physical change? Explain.

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Would a banana rotting be a chemical or physical change? Explain.

Answer questions 21 and 22 based on the description below:
In an investigation, a dripless wax candle is massed and then lighted. As the candle burns, a small amount of liquid wax forms near the flame. After 10 minutes, the candle’s flame is extinguished and the candle is allowed to cool. The cooled candle is massed.

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Identify one physical change that takes place in this investigation.

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State one observation that indicates a chemical change has occurred in this investigation.

Lab Activity
Station 1 – Flame
Step A. Place a few pieces of the solid labeled P onto a piece of foil, hold the foil over the Bunsen burner using the tongs.

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Is this a chemical or physical change? Explain. (provide observations of what happened)

Step B: Dip the wooden stick in water and then dip it into the solution labeled Li to pick a couple of crystals onto the stick. Then hold the stick in the flame for just a few seconds. If the stick starts on fire, place it into the cup of water.

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Is this a chemical or physical change? Explain. (provide observations of what happened

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Are your observations in this demonstration qualitative or quantitative?

Station 2 – Citric Acid

Step C. Put some water into bottom of the mixing cup.

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Use the thermometer to determine the temperature of the water.

Step D. Put one scoop of the solid labeled Ca into the water in the mixing cup.

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Use the thermometer to determine the temperature of the water.

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Is this a chemical or physical change? Explain.

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Is this a qualitative or quantitative observation?

Answer question 30 based on the following scenario:
A group of students do an activity with baking soda and vinegar. The steps of the activity are listed below.
A. Pour 100 g of vinegar into a flask.
B. Measure the temperature of the vinegar.
C. Add 10 g of baking soda to the flask.
D. Observe as the contents of the flask bubble.
E. Measure the temperature of the contents of the flask and observe any change in temperature and the bubbles that are produced.

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Describe one piece of evidence that a chemical change occurs when baking soda is added to vinegar.

Answer question 31 and 32 based on the following scenario:
At the beginning of summer, some paint was scratched off a student’s bicycle. The exposed metal where the bicycle was scratched had a shiny, silvery color. The student kept the bicycle outside all summer. By the end of summer, the exposed metal had changed to rust, which is dark orange in color. The student did some research to find out what happened to the metal and learned that the bicycle is made of steel, which contains mostly iron. The student conducted an investigation to learn more about the process that changed the steel into rust. The student placed equal amounts of iron filings (small pieces of iron) into beakers X, Y, and Z. At the start of the investigation, all of the filings were gray. The student added nothing else to beaker X, water to beaker Y, and table salt (NaCl) and hydrogen peroxide (H2O2) to beaker Z. The student’s observations over a two-day period are shown in the table.

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In which, if any, beakers did a physical change occur? Explain.

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In which, if any beakers did a chemical change occur? Explain.

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