Archive for the ‘Chemistry’ category

Don’t worry, it’s just a fast (oxidisation) reaction…

February 5, 2008

MarvinEvery explosion is “just” a reaction, admittedly one that progresses very quickly (Boom! Kaboom!). Oxidisation is the word used in chemistry to mean “a reaction with oxygen”. Oxidation reactions are essential because they release energy – respiration is an oxidation reaction, as is burning (combustion) and also corrosion. Respiration is good, burning can be good, and corrosion is rarely good. An example of corrosion is iron (Fe) rusting. When Iron combines with oxygen and water, iron oxide is produced:

4 Fe(s) + 3 O2 (g) + 2 H2O (l) → 2 Fe2O3·H2O

RustThe reactants (Iron, Oxygen, and Water) combine chemically to make saturated (·H2O) iron oxide (Fe2O3). Iron oxide has none of the properties that are desirable in alloys of iron – it has low strength, is friable (crumbly) and completely non conductive. We try and prevent corrosion at all times, because it degrades materials. the two most common ways of preventing corrosion are:

  1. Painting: The paint provides a protective layer that keeps the water/ oxygen from coming into contact with the iron. This stops the iron from contacting either water or oxygen, thus preventing the corrosion reaction.
  2. Sacrificial Protection: This works by coating one metal by another. The coating metal must be higher on the activity series than the coated metal. One example of this is coating Iron with Zinc (also called galvanisation). This prevents the coated metal from corroding by causing the more reactive metal to corrode first.

The activity series shows some metals are more active than others – here is a video that shows how reactive (explosive!) some metals can be:

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To be or not to be… Dichotomous keys in Chemistry

February 4, 2008

Chemicals Before we can start looking at the way individual chemicals react with each other, we have to identify the different types of “stuff” that can be used. All the physical material that exists is called “matter”. Matter can be subdivided into many different types based on its chemical and physical properties. We can use a “Dichotomous Key” to identify the various types by asking questions with “yes or no” type responses. Below is such a key, showing the division of matter into various types. You will need to include all these terms in your glossary.

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An Elemental Approach

January 27, 2008

Ion Attraction NZ The first subject for the year is Chemistry, and the topic that we are studying is Reactions. in this topic you will learn about the formation and decay of molecules, and the different ways elements can join and separate. We will be looking at this information from an atomic perspective, and learning about the role electrons play in the various reactions. Students would have been introduced to this topic last year, and the first thing we will do is review some of that knowledge and look at the structure of the Periodic table.

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