Chemical reactions
This Topic is About...
- I will find out that new substances form during chemical reactions.
- I will make a prediction for an investigation.
- I will make drawings of my observations.
- I will make a conclusion for an investigation.
- I will find out that we can get results by observing over time.
- I will research information to answer a scientific question.
You’re going to be a science explorer!
Key Words
- chemical reaction
- react
- rust
Tap to Learn the Meanings!
- chemical reaction: When substances mix and change to make something new.
- react: To change or combine with another substance during a chemical process.
- rust: A reddish-brown coating that forms when iron reacts with water and air.
Excellent! You’re learning how materials can change in chemistry.
Making new substances
Change of state is a physical process that changes the form of a substance. The substance does not change. But when some substances are mixed together, they change and form a new substance or material. This is called a chemical reaction. We say that the substances react together.
Lots of chemical reactions take place around us every day. For example, when builders mix cement powder with sand, water and limestone, they make a new material called concrete. It is not possible to turn concrete back into the substances that made it. This is true for most chemical reactions.
Burning wood is also a chemical reaction. When we heat the wood, it reacts with the air. A grey substance called ash and two different gases form. The ash and gases are new substances.
Have you ever noticed that old tin cans and cars turn a reddish-brown colour if they are left outside for a long time? The metal in the cans and cars reacts with other substances to form a new substance called rust. Rusting is a chemical reaction.
Let’s Investigate!
Question: Which substances/conditions make wire wool rust?
Equipment: Three pieces of wire wool, three glass jars and one lid, water, a marking pen
Method:
- Put a piece of wire wool in each jar. Number the jars 1, 2, and 3 with the marking pen.
- Pour enough water into jar 1 to cover some of the wire wool.
- Cover the wire wool in jar 2 completely with water. Put a lid on the jar.
- Leave jar 3 open (no water added).
- Predict what you think will happen in each jar.
- Leave the jars for two days. Then observe them carefully and make drawings of what you see.
Follow-up Questions:
Tap to See Answers
- 1a: Rust forms most clearly in jar 1 (water + air). Jar 2 shows little/slow rust because it has water but very little air (lid on). Jar 3 stays mostly unchanged because it has air but no water.
- 1b: Answers will vary.
- 2a: Rusting is a slow chemical reaction; time is needed for changes to appear.
- 2b: The rust in jar 1 will increase; jar 2 may begin to show slight rust; jar 3 will likely still show little change.
- 3:Conclusion: Wire wool needs both water and oxygen (air) to rust. Where only one is present, rusting is much slower or does not happen.
- 4: This was a comparative test with careful observation over time.
Great reasoning! You identified the conditions needed for rusting.
