Chem 1Al Exam

Front 1

Molarity

Back 1

Molarity = # moles solute/ Liters of solution

-Way of measuring the concentration of a solution

Front 2

Ionic bonding

Back 2

Usually between a metal and a non-metal - One atom (the non-metal) takes an electron from the other (metal)
- This causes one atom to be positively charged and the other to be negatively charged
o Atoms or molecules with a charge are known as ions
- A strong interaction forms based on the opposite charges attracting, thus making the ionic bond.

Front 3

Covalent bonding

Back 3

Usually between two nonmetals - Bond formed by atoms sharing electrons.
- No positively charged and negatively charged ions formed since electrons are shared o However small partial positive and negative charges can form

Front 4

Electronegativity

Back 4

- Some elements have a stronger affinity for electrons than others o This property is called electronegativity and these elements are called more
electronegative.

Front 5

Electronegativity trend

Back 5

As you go from the bottom left of the periodic table to the top right electronegativity increased

Front 6

Nonpolar bonds occur between:

Back 6

Two of the same atom (same electronegativity so electrons are equally shared) o Different atoms with similar electronegativity
- A good example of this is the C—H bond which has no significant dipole since carbon and hydrogen have very similar electronegativities.

Front 7

Intermolecular forces

Back 7

Weaker forces exist which cause molecules to interact with and stick to each other.
o These allow solid and liquid states to exist.

Front 8

Dipole-dipole

Back 8

Interactions between polar molecules (ie. Molecules with dipoles) - Partial positive and negative charges are attracted to each other causes the molecules
to be drawn together.

Front 9

Hydrogen bonding

Back 9

Subset of dipole-dipole interactions is Hydrogen Bonding:
o o
Strongest type of dipole-dipole interaction Only happens between H—N, H—O, and H—F bonds
 Large difference in electronegativity between the two atoms causes a more powerful dipole

Front 10

Water and H-bonding

Back 10

Many of waters important properties are due to hydrogen bonding. This includes the fact that it is a liquid of room
temperature, even though it is a very small and light molecule.

Front 11

LDS

Back 11

Interaction between nonpolar atoms and molecules o Just because something in non-polar doesn’t mean it won’t interact with other
atoms and molecules Instantaneous dipoles can form which induce dipoles in nearby atoms and molecules.

Front 12

LDS and size of molecule

Back 12

Larger molecules/atoms have less tightly held electrons which can form
instantaneous and induced dipoles more easily.

Front 13

copolymer

Back 13

- Polymers made up of more than one monomer

Front 14

cross-linking

Back 14

- -
Bonds that link one polymer chain to another Crosslinking causes chains to lose some of their flexibility.

Front 15

Controlled experiments

Back 15

Controlled Experiments involve changing only one variable at a time.

Front 16

Independent variable

Back 16

The “thing” we are changing.

Front 17

Dependent variable

Back 17

What is being affected as a result of the
Independent Variable.

Front 18

Control variable

Back 18

Remains constant throughout the experiment

Front 19

Structure

Back 19

Structure is the microscopic make up. The atoms, electrons, and bonds and orientations.

Front 20

Property

Back 20

Property is what we visibly can observe and test.

Front 21

H-bonding, LDS, dipole-dipole (order of strength)

Back 21

– – –
Hydrogen Bonding: Strongest Dipole-Dipole: Medium London Dispersion Forces: Weakest

Front 22

Density

Back 22

Density=Mass/Volume
Similar to the Biofuels Lab: More/stronger IMFs will typically lead to a denser substance.
Denser objects sink when placed in less dense objects/fluids.

Front 23

Mixed densities

Back 23

D=(V1D1+V2D2)/(V1+V2)
This is basically just saying Density equals the sum of the masses divided by the sum of the volumes – The definition of density!

Front 24

You want to make 50mls of a solution with a density of 1.2g/ml.
You have a solution of density 1g/ml and another of density 2g/ml.
How much of each solution do you need to make the 1.2g/ml solution?

Back 24

Set up the equation. (Units omitted in subsequent lines) 1.2g/ml=(1g/ml*x+2g/ml*(50-x))/50ml
Make sure you understand why the “x” and “50-x” are there. 60=1x + 100 – 2x
–
-40=-1x x=40ml

Front 25

Resonance

Back 25

Resonance is the movement of electrons/bonds only. The new structure follows all the same rules, but differs in electron arrangement

Front 26

Functional groups

Back 26

Different parts of a molecule which can endow certain reactivities or properties (Relates back to structure- property relationship)

Front 27

Isomers

Back 27

Different forms of the same molecular formula. They can differ in bond connectivity or 3 dimensional orientation

Front 28

Enantiomer

Back 28

A type of Stereoisomer which is the same in connectivity and 3-dimensional orientation – however they are mirror images of each other and are not super-imposable (can not be “stacked”).
–
This is a specific example from lab 4 and is referred to as “chiral” and can differ in their reactivity to other chiral molecules and in their rotation of plane polarized light.

Front 29

Absorbances at the same wavelength..

Back 29

Absorbances at the same wavelength add directly. (E.G. 1+1=2)

Front 30

Concentrations of substances (dyes) can be determined using..

Back 30

using the Beer Lamber Law and absorbance values at specific wavelengths

Front 31

Transmittance

Back 31

Transmittance= Final Intensity/Initial Intensity

Front 32

Absorbance

Back 32

Absorbance = -log(T)
Keep in mind that absorbance is a unit-less number. (Things that come out of logs are unit- less.)

Front 33

Transmittance differs at...

Back 33

Transmittance differs at different wavelengths of light.

Front 34

Beer Lambert Law

Back 34

Absorbance = єbc
є=molar absorptivity (extinction coefficient differs in units)
b=path length
c=concentration of dye
Important: molar absorptivity is a constant value only at a constant wavelength. Changing the wavelengths gives different molar absorptivity values!