Learning Intention: Students will understand that rusting is another type of chemical reaction, in which the products of the reaction are different to the reactants. They will also learn about the process of planning and conducting an experiment, devising an hypothesis and using a control with variables.
Success Criteria: Students will plan and conduct an experiment that tests an hypothesis about rusting.
You will be familiar with ‘rust’ as the orange/brown corrosion that affects some metals. Farmers, engineers, sailors and car-makers are all very aware of the economic impact of rusting. Rusting is a chemical reaction that occurs when metals are exposed to moisture and the air. How Stuff Works has a good article about rust – “How does rust work?”. Read pages 60 and 61 in your text book. Your task is to devise an experiment to investigate rusting. You may like to test the effect of the saltiness of water on the time taken for an iron nail to rust. You may like to test some methods that are used to reduce or prevent rusting. Follow these steps:
Write an hypothesis – a theory about rusting that you want to test. For example, “The greater the concentration of salt, the quicker iron will rust.”
What will be the ‘control’ and the ‘variable’ in your experiment?
Write a list of materials and equipment that you will need to complete the test. Submit your list of requirements to me so we can be sure we have everything you will need.
Formulate a method that describes exactly what you need to do – make sure someone else can use this method to repeat the experiment in exactly the same way you have done.
In your method you need to include how you will record your results – will you measure mass, time, volume, temperature or some other factor/quantity?
Undertake your experiment, recording your results.
Include a discussion of your findings in your report. Were there any sources of error or unexpected results?
Write a conclusion that refers to your original aim/hypothesis. Did you prove or disprove your hypothesis? Do you need to do further experimentation?
You use stacks of paper every day but do you know how it’s made? Paper has been made since 105 AD in China, but other materials such as papyrus (in Egypt), parchment and vellum (various grades of mammal skin) were used in other parts of the world prior to this. Find out more about the history of paper at Wikipedia.
In Sri Lanka, a fair trade company is making paper from elephant pooh! In that country, humans are encroaching on elephant habitat, cutting down trees for fire wood and shooting and killing elephants that come looking for food. This company, “Mr. Ellie Pooh” aims to create employment and encourage villagers to see the elephants as an asset rather than a threat.
Compared to using virgin wood, paper made with 100% recycled content uses 44% less energy, produces 38% less greenhouse gas emissions, 41% less particulate emissions, 50% less wastewater, 49% less solid waste and — of course — 100% less wood.
This week we are making paper from grass in six steps:
Cut the grass and grind it with the mortar and pestle
Add caustic soda to release the cell contents
Wash and rinse to remove chemicals and cell contents
Add bleach and bring to the boil
Wash and rinse to remove the bleach
Form the paper
Which of these steps are physical changes and which are chemical changes?
Learning Intention: Students will understand the relevance of specific chemical reactions to everyday life and be able to describe the usefulness of those reactions to society.
Success criteria: Students will produce a poster, slideshow or video that investigates and describes a specific chemical reaction and it’s usefulness in our lives.
Your task is to research one of the following materials and how they can react to produce useful results – a release of heat, a new product or a portable source of energy for example. Find out how these materials are extracted or produced, the useful reaction that occurs and how this reaction benefits society. Are their any disadvantages of this reaction? (eg. greenhouse gases produced, finite resources being used or toxic by-products?
Fossil Fuels (oil, coal or gas – choose one) – combustion
Electrolysis to allow silver plating, copper plating etc
Thanks to Duncan Patti for producing the slideshow above, which is a good summary of what you should know about chemical reactions from Year 7 and 8 science and an introduction to Year 9 Chemistry. You need to know the difference between a physical change and a chemical reaction (what evidence is there for a chemical reaction?). You also need to know the four ways in which you can increase the rate of a reaction. It is also very helpful if you can remember the chemical formula for the first twenty elements, as well as some other common ones (iron, copper, silver and lead).
Learning Intention: To develop an understanding of acids and bases and the chemical reactions they are part of.
Success Criteria: You will be able to describe the differences between acids and bases and give several household examples of how they are used. You will perform some simple chemical reactions and identify that the colour changes indicate the pH of the mixture.
Today we will be doing an experiment with acids and bases – making a pH indicator using red cabbage and testing various household substances. PH is a measure of the acidity (ph is less than 7) or alkalinity (ph is greater than 7) of a substance.
Another experiment we will do this week demonstrates how antacids work in your stomach. We will add dilute hydrochloric acid to a conical flask, which simulates the gastric juices in your digestive system. We will then add universal indicator to show the level of acidity. We will then add an antacid (alka-seltza tablet) and show how the pH increases, which demonstrates that the solution has become less acidic. When an acid and a base are mixed together the chemical reaction that takes place is called a neutralisation. The acid and base react to form a salt and water.
When metals are placed in acid they can corrode. An acid and a metal react together to produce hydrogen gas and a salt. You can test for hydrogen gas using the ‘pop’ test – light a match at the mouth of the test tube and you will hear a ‘pop’. Acid rain is problem in the northern hemisphere, caused by air pollution. We will learn more about acid rain in class.
Students have performed several experiments to show the results of chemical reactions:
Change of colour (new products formed)
Gas production (new products formed)
Precipitate formation (new products formed)
Change of temperature (release or absorbtion of energy)
Light or sound produced (indicating energy has been released)
Students have also performed an experiment to demonstrate how grass can be turned into paper, using a series of physical and chemical reactions. Each student produced a slideshow about these reactions.
Cutting and crushing the grass (Physical)
Digesting the grass with caustisc soda (Chemical – colour change)
This a rusty tractor engine, captured at Jurien Bay, WA.
Over the next few weeks we will be doing many different experiments, including turning grass into paper. After you have finished this unit of work, you should be able to answer the following questions:
What are the two main differences between physical change and chemical reactions?
What are four signs that new products are formed during a chemical reaction?
Name four ways you can increase the rate of a reaction.
Freezing, melting, evaporation and condensation are all physical changes of state in which molecules of a substance gain or lose kinetic energy. Many common changes that occur around us are actually chemical reactions – when iron rusts, apples go brown, silver tarnishes or copper develops a green tinge, oxidation is occurring. Combustion (burning) is also a form of oxidation. In a chemical reaction new products are formed and this may result in a colour change, a precipitate being formed, the release of gases or energy in the form of light or sound. The following resources may help you to learn about chemical reactions: