UNIT 1.4 COMPOSITION OF MIXTURES
Chemistry is the study of matter and interactions. Chemistry overlaps with many other sciences.
Below is the contents for this sub unit. This will allow you to jump to any section you desire. If you have taken Chemistry 1, this should all be review but it is always good to brush up on the basics (significant figures especially).
PURE SUBSTANCE VS. MIXTURE
Pure substance contain molecules or formula units of a single type of set proportions.
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Example: Water always has 2 hydrogen and 1 oxygen.
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Mixtures contain molecules or formula unites of 2 or more types with varying proportion.
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Example: Steel can have varying amounts of iron, carbon, chromium, etc. depending on the company that makes it and what properties they want the steel to have.
ELEMENTAL ANALYSIS
There are several instruments that can be used to help break down what a substance or mixture is composed of. We have already talked about mass spectrum that allows us to see the ions of a substance. In section 1.6 we will talk about photoelectric spectroscopy that will help us see what electrons are doing on an atom.
Composition by mass in a substance:
You put a sample into a machine and it separates the atoms and then absorbs the different elements. The output is 11.2% hydrogen and 88.8% oxygen. What is the compound?
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If you had a 100 gram sample,
take each element and divide by molar mass
11.2 g would be H / 1.008 = 11.11 H
88.8 g would be O / 15.999 = 5.55 O
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Divide by the smallest number:
11.11 / 5.55 = 2 H
5.55 / 5.55 = 1 O
Formula H2O
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Composition of substances in mixture:
There are several different ways a mixture composition is calculated:
Molarity: mol solute / L solvent
Molality: mol solute / Kg solvent
% volume composition: % listed of volume each (or sometime only 1) substance
% weight composition: % listed of mass each (or sometime only 1) substance
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For review check out the Solution chemistry section on the Chem 1 tab
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