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SMS+TMSC Middle School Science
Chemistry 2016-17
Study Guide
Test on Tue Jan 24, 2017
Grade 7 - Petroleum Chemistry & Lab Work
This is only a framework - refer to teachernotes, lab sheets and your own notes!
Vocabulary
petroleum - a liquid fossil fuel carrying a mix of hydrocarbons of varying weights and thicknesses.
cracking - the process used to separate the different hydrocarbons in petroleum
ester - a chemical made from combining a carbon-based acid and an alcohol.
acid - a chemical that donates H+ (hydrogen ions or protons).
base - a chemical that donates OH- (hydroxide ions).
alcohol - a hydrocarbon with an added OH group.
prefixes - the first part of a hydrocarbon name that tells you how many carbons are in it: meth=1
eth=2 prop=3, but=4, pent, hex, hept, oct, etc...
hydrocarbon - a chemical made of linked carbon and hydrogen molecules.
alkane - a hydrocarbon that contains only single bonds
alkene - a hydrocarbon that contains double bonds
alkyne - a hydrocarbon that contains triple bonds
aliphatic - a hydrocarbon with the carbons linked in a chain.
aromatic - a hydrocarbon with the carbons linked in a ring.
Concepts
Carbon is unique among elements since it has 4 valance electrons that combine with other
elements in more possible ways than other elements.
Carbon can make a large number of compounds - it can make chains or rings of atoms and add
hydrogen, oxygen and other elements to make new chemicals.
Carbon chains are called aliphatic and rings are called aromatic.
Hydrocarbons are named for the number of carbon atoms in them and the types of bonds. 1
carbon with hydrogens on the 4 valance sites is called methane: METH=1 and alkANE = single
bonds. 2 carbons with a double bond is ethane: ETH=2, alkENE = double bonds. See the table
in the TeacherNotes.
Each compound has different characteristics. Propane (3 carbons, single bonds) is grill gas.
Polyproplyene (a repeating “poly” chain of 3-carbons with double bonds) is fleece.
For a given hydrocarbon, you can add an OH group to it and you have created an alcohol.
Propane can be made into propanol, used as rubbing alcohol.
Carbon-based acids can be reacted with alcohols to create a new compound, ester, and water.
Esters are chemicals responsible for many of the food smells you enjoy. By picking the right acid
and alcohol, you can make artificial “flavors” even though you actually don’t taste them, you smell
them.
Labs
In the silver nitrate lab, you mixed silver nitrate with one of four salts - potassium bromide,
potassium chloride, potassium iodide and potassium sulfide into 11 wells. In each reaction, the
silver ion and the potassium ion changed places, so that you ended up with potassium nitrate and
one of four salts - either silver bromide, sulfide, chloride or iodide. To do this, there has to be a
matching sliver nitrate molecule for each molecule of the potassium salt.
Each pair was mixed in ratios ranging from 1:11 (1 part silver nitrate to 11 parts potassium salt)
then 2:10, 3:9, 4:8, 5:7, 6:6, 7:5, 8:4, 9:3, 10:2, 11:1
With each reaction, some precipitate was formed and observed. The matching sliver and
potassium salts needed to be at the same level of concentration as each other. Therefore the well
with the same number - a 1:1 ratio - of salts would make the most complete reaction. 6:6
simplified is 1:1, the other wells should all be less of a reaction, since there is either too much or
too little silver salt to match the potassium.
Concentration and proper ratio are important for rate of reaction - a reaction is weaker at lower
concentrations and you don’t get much result if there is too much or too little of one of the
chemicals.
If you did not get the best result of 6:6, then you need to look at what was done and identify
possible sources of error. Measuring? Technique? Observations wrong? Simple math errors?