AP Chem Unit 3 and 4 Review

Question 1

What are the steps to find an oxidation number of a neutral compound? Ex. ClF3 and ZnH2

Answer 1

For ClF3; Fluorine is ALWAYS 1- so -1(3)=-3. To cancel out the 3-, Cl must be 3+
For ZnH2; Hydrogen is 1- with METALS, so -1(2)=-2. To cancel out the 2- Zn must be 2+

Question 2

What are the steps to find an oxidation number of a polyatomic? Ex. NO3 and MnO4

Answer 2

*Sum of Oxidation # must equal the ion charge. For NO3; Oxygen is 2-, so -2(3)=-6. NO3 has a charge of -1, so N must be 5+. (-6+5=-1)
For MnO4; Oxygen is 2-, so -2(4)=-8. MnO4 has a charge of -1, so Mn must be 7+. (-8+7=-1)

Question 3

How do you write a balanced net ionic equation?

Answer 3

1. Write a balanced chemical equation
2. Determine what elements are spectator ions (aqueous on both sides)
3. Write your final net ionic equation with charges and phases.
   Note* It is possible for a chemical equation to not have a net ionic equation (all are aqueous)

Question 4

What are the steps to find an oxidation number of a polyatomic and element? *Hard Ex. (NH4)2HPO4 and Na4Fe(OH)6

Answer 4

First, let’s focus on the polyatomics. For NH4, Hydrogen is 1+ since with NONMETALS so, 1(4)=4. NH4 has a charge of +1 so Nitrogen must be -3. (4-3=1). For PO4, Oxygen is 2- so, -2(4)=-8. PO4 has a charge of -3 so P must be 5+. (-8+5=-3). Now let’s focus on the singular Hydrogen must balance out the charges of NH4 and PO4. NH4 is +1(2) and PO4 is -3 so, H must be 1+ to cancel them out. (2-3=-1+1=0)

For Na4Fe(OH)6 let’s focus on the polyatomic. Oxygen is 2-. NH4 has a charge of -1 so Hydrogen must be 1+. (-2+1=-1). Na and Fe must cancel out the charge of (OH)6, -6. There are 4 Na’s so it must be 1+ 1(4)=4. So this means that Fe must be 2+. 4+2=6 and 6-6=0

Question 5

What is an Oxidization (IS Oxidized)? What about the Oxidizing Agent (Oxidant)?

Answer 5

The element being oxidized loses electrons and the oxidant is what takes their electrons away!

Question 6

What is reduction (IS Reduced)? What about the Reducing Agent (Reductant)?

Answer 6

The element being reduced gains electrons while the reductant is what gives its electrons away to the thing being reduced.

Question 8

How do you find the empirical formula?

Answer 8

1.) First you convert % into grams and convert into moles of the substance by its molar mass
2.) with the smallest number, based on mol’s, you divide it w/ every number *(there cant be no decimals so multiply until you get a whole number)
3. With the numbers you have apply it to the corresponding element

Question 9

How do you find molecular formula?

Answer 9

1.) Follow the rules to empirical
2.) Find the molar mass of the empirical formula and divide it by the actual Molar mass, so, mm molec/emp mm
3.) multiply that number to the small coefficients from the empirical formula

Question 10

How do you find the limiting reactant?

Answer 10

1.) Create your balanced equation
2.) Calculate the number of mole of different substances you have
3.) Divide by the coefficients in the balanced equation
4.) The reactant with the smallest result is the LR

Question 11

If I have my %yield and actual yield how do I find what is NEEDED to yield

Answer 11

1.) solve for theoretical yield
2.) Convert to mols
3.) Then grams

Question 12

Define Titrant and Titration

Answer 12

Titrant: substance that is added during a titration
Titration: the slow process of adding one solution that is known to another that is not known

Question 13

What is standardization?

Answer 13

It is determining the accurate concentration of a molarity

Question 14

What is the equivalence point?

Answer 14

It is when equal quantities of reactants are mixed (mol=mol)

Question 15

What is a homogeneous mixture?

Answer 15

Two substances that have the same composition and properties throughout, it is evenly mixed

Question 16

What is a heterogeneous mixture?

Answer 16

Two or more substances that have different compositions and properties, unevenly mixed

Question 17

Define a solvent

Answer 17

Typically are liquids, however can differ in states of matter. It dissolves a solute which results in a solution

Question 18

Define solute

Answer 18

A substance that is dissolved in a solution

Question 19

What is spectroscopy and how can it be used in chemistry?

Answer 19

It measures the absorbance or transmission that comes from the matter of a wavelength or frequency of the radiation. We use this in chemistry to detect, determine or quantify the molecular sample. Every molecule and atom will reflect, absorb or emit an electromagnetic radiation of its own.

Question 20

What is beers law?

Answer 20

A= εbC, where A=absorbtion, ε= molar absorptivity, b=length of light path, and C=concentration.

The more concentrated a solution the more it will absorb light. The slope of a beers law curve is y=mx+b. This line can figure out the concentration of an unknown solution

Question 21

What dictates strong/weak electrolytes and non electrolytes?

Answer 21

Strong: Solute completely disassociates into ions.
-All ionic compounds in an aqueous solution
-Strong Acids
Weak: Only a small portion of molecules disassociate into ions.
-Weak Acids and Weak Bases
Non: Does not conduct electricity
-Particles present are MOLECULES NOT IONS

Question 22

What is the difference between disassociation and Dissolution?

Answer 22

Disassociation is the separation of ions that occurs when a solid ionic compound dissolves
Dissolution is the process of solute dissolving in a solvent (physical change)

Question 23

How do you figure out how much excess is left over after a reaction?

Answer 23

1.) First figure our your limiting then excess reactants
2.) Convert however many grams of LR to grams of your ER.
3.) Minus the amount of ER that is used by the initial amount of ER

Question 24

Actual yield

Answer 24

The amount of product actually produced in a reaction- determined experimentally

Question 25

Theoretical Yield

Answer 25

The amount of product calculated that should be produced inna reaction - determined using a stoich problem