Review For Chem. Final (2017)

The Chem. Final will be divided up into 3 sections: Critical Thinking/Logical Fallacies Hydrocarbons Balancing Equations

Critical Thinking

#1 Rule of Logic? Don’t be arbitrary!

Logical Fallacies A logical fallacy is an error or flaw in reasoning that invalidates an argument

Common Fallacies you’ll need to know Red Herring (avoiding the topic) Special Pleading (double standards) Ad Hominem (attacking the person) Begging the Question (circular reasoning) Straw Man (mischaracterizing an argument, then attacking that mischaracterization instead of the actual argument)

1. Red Herring Fallacy A Red Herring is a way to avoid the question by: Changing the subject Introducing an irrelevant point Using a distraction to draw attention away from the question

2. Special Pleading Fallacy Special Pleading is when a person uses a double standard or argues for an unjustified exception. Ex: “Generally it is wrong to steal…but I really needed the money.”

3. Ad Hominem Fallacy Attacking the person instead of the argument. Latin for “against the man” or “to the man” Also called “poisoning the well” fallacy

4. Begging the Question Using circular reasoning The premise assumes the conclusion is already true (rather than the other way around) When a series of assumptions pretend to be an argument

A Classic Example of Begging the Question “Women shouldn’t be bullfighters…because a bullfighter needs to be a man. A manly man.” A Classic Example of Begging the Question

An incorrect use of the phrase “Begging the Question” “I weigh 300 pounds and am severely out of shape, which begs the question, “Why haven’t I begun exercising yet?” An incorrect use of the phrase “Begging the Question”

5. Straw Man Fallacy When you misrepresent someone’s argument so that it is easier to attack. Makes it easier to present your own position as being reasonable, but this kind of dishonesty serves to undermine honest rational debate.

Hydrocarbons

Hydrocarbons are grouped into 3 classes Alkanes Only single bonds connecting the carbon atoms in the chain Octane C8H12

Hydrocarbons are grouped into 3 classes 2. Alkenes Contain at least one double bond

Hydrocarbons are grouped into 3 classes 3. Alkynes Contain at least one triple bond

Hydrocarbon skeletal structure Sometimes, in an effort to simplify things, we only show the “skeletal structure” of an organic molecule Where are the Hydrogen’s??? Butane skeletal structure

Hydrocarbon skeletal structure When you see a naked organic skeleton, the “joints” represent carbon atoms, and the Hydrogen atoms are left out. Carbon Octane skeletal structure

Hydrocarbon skeletal structure The “lines” between the joints represent the bonds between the atoms. In this case, they are all single bonds, so this is an alkane Bonds Octane skeletal structure

Name the following molecules by identifying their skeletal structures 1 2 3 4

Hydrocarbons can form rings Hydrocarbons can form rings ***Note that the general formula won’t work on rings. You must look at the bond lines*** C5H10 C6H12 C6H6

When a hydrocarbon forms a ring, we typically use the term “cyclo” to denote it Cyclopentane Cyclohexene

Balancing Equations

What is a chemical equation? Chemical equation - Describes a chemical change. Parts of an equation: Reactant Product 2Ag + H2S Ag2S + H2 Reaction symbol

Reactants and Products Reactant - The chemical(s) you start with before the reaction. Written on left side of equation. Product - The new chemical(s) formed by the reaction. Right side of equation.

Subscripts and Coefficients Subscript - shows how many atoms of an element are in a molecule. EX: H2O 2 atoms of hydrogen (H)‏ 1 atom of oxygen (O)‏ Coefficient - shows how many molecules there are of a particular chemical. EX: 3 H2O Means there are 3 water molecules.

Law of Conservation of Mass In a chemical reaction, matter is neither created nor destroyed. In other words, the number and type of atoms going INTO a rxn must be the same as the number and type of atoms coming OUT. If an equation obeys the Law of Conservation, it is balanced.

An Unbalanced Equation CH4 + O2 CO2 + H2O Reactant Side Product Side 1 carbon atom 4 hydrogen atoms 2 oxygen atoms 1 carbon atom 2 hydrogen atoms 3 oxygen atoms

A Balanced Equation CH4 + 2O2 CO2 + 2H2O Reactant Side Product Side 1 carbon atom 4 hydrogen atoms 4 oxygen atoms 1 carbon atom 4 hydrogen atoms 4 oxygen atoms

Rules of the Game 1. Matter cannot be created or destroyed. 2. Subscripts cannot be added, removed, or changed. 3. You can only change coefficients. 4. Coefficients can only go in front of chemical formulas...NEVER in the middle of a formula. A few extra tips: Try balancing big formulas first; save free elements for last. If the same polyatomic ion appears on both sides of the equation, it’s usually okay to treat it as one unit. There is no one particular way to balance equations. Some equations are harder to balance than others and might require some creativity to solve.

Practice Question #1 Copy and balance the following equation: __ Al + ___ HCl __ AlCl3 + __H2 Practice Question #2 Copy and balance the following equation: __ H3PO4 + __ HCl __ PCl5 + __H2O

Practice #1 Answer Practice #2 Answer 2 Al + 6 HCl 2 AlCl3 + 3 H2 Practice #2 Answer 1 H3PO4 + 5 HCl 1 PCl5 + 4 H2O