chem 107 exam 1 sansom

Color wheel

The color that you see is what is transmitted, the color opposite on the color wheel is the color that is absorbed

The shorter the wavelength, the higher the

energy

Beer's Law definition

relates the absorbance of a solution to its concentration

Beer's Law Equation

A = εcl

ε

is the molar absorption coefficient, how strongly the molecule absorbs a certain color of light, depends on identity of substance

c

is the concentration in molarity

-Most important that they know it's proportional to concentration.

l

is the path length, how far the light has to pass through the solution

Absorbance depends on 1.

The substance—each substance will have a unique spectrum, and a strength of absorbance (molar absortivity constant, epsilon)

Absorbance depends on 2.

The concentration—the more molecules are there, the more light will be absorbed.

Absorbance depends on 3.

The path length—how far the light has to pass through the solution—this is almost always 1 cm for UV-Vis spectroscopy.

qrxn

n∆H

qsol

mc∆T

∆H =

−mc∆T/n

Collision Theory

In order to react, molecules must Collide, With enough energy, In the correct orientation in space

-If any 3 of the collision things don't happen, collision won't happen.

Factors that affect reaction rates: (4)

Nature of reactants, Concentration of reactants, Temperature, Catalyst

If step 1 is slow step

rate1 = k1[A][B]

- A 1st, B 1st, D 0th

If step 2 is slow step and step 1 is in rapid equilibrium

rate2 = k2[C][D], There is an intermediate so set k1[A][B] = k-1[C], Then rate2 = (k1k2/k-1)[A][B][D]

--A 1st, B 1st, D 1st.

to figure out the rate limiting step in ex. 4

There will be a data table compare D in the table, see which order it is in the table.

If its first order, the second step will be the rate limiting

KI and NaOCl...

have a 3:1 Ratio

Percent Error

(Measured-Theoretical)/Theoretical x 100

Q test for

extreme values

Spectrophotometry uses

light (UV-Vis in our case) to identify and quantify the presence of chemicals that absorb light during electronic transitions.

transmission vs absorption color

Whatever is transmitted the opposite is absorbed.

If the solution is blue, orange is absorbed

ROYGBP

WRITE THESE OUT ON MY PAPER...

"if solution is yellow, purple is absorbed"

red vs violet energy

Red is Relaxed (lower energy)

Violet is violent (higher energy)

Discuss the ground and excited energy levels -

electrons are normally in the ground state, but it can be excited with heat, light, or electricity. We will use light

-Absorbance: marriage (THREE FACTORS AFFECT ABSORBANCE!!!)

Epsilon: cuteness, more likely to get married

C: more BYU kids, more likely to get married

L: increase pathlength. Walk around campus more. Meet more people, more likely to get married

how to find the concentration of something in a different sample

c1v1=c2v2. use the volume they give you and the molarity given for c1v1. use the total volume (water+other thing) times c2 to find c2.

how to solve for the epsilon

E= A/cl. the c is the c2 value that we calculated using c1v1=c2v2

You are given a new cobalt nitrate sample of unknown concentration. You find that it's A520 is 0.76. Find the concentration of the sample.

1. c1v1=c2v2 to find the concentration

2. use the absorbance in the table and the new concentration and the path length of 1 cm to find the epsilon value.

3. use the absorbance in the question, the epsilon from step 2, and a path length of 1 to find this concentration.

C1V1=C2V2

C1= og concentration.

C2= new solution

V2= total

Lower Energy (stability)

More Stable

-delta H on the exo/endo graphs.

energy released or absorbed at end

"products are more stable than reactants..."

endo or exo?

-products are lower. Draw graph. See it's exo

endo graph

reactants energy lower than products

exo graph

products energy lower than reactants

for balancing equations practice stuff, the peak is

the most ideal ratio

limiting reactant graph

Write reaction. 2 reactants are the x and y axis. Always needs to equal the total amount. Perfect ratio: no limiting reactants.

limiting to the left of the peak

thing on the X axis:

limiting to the right of the peak

thing on the y axis

q=n(delta)h

only unknown and bleach are part of the system

n is number of moles of the limiting reactant divided by its stoichiometric coefficient

1,3,4 - these are for this experiment

qsol=mc(delta)T

-things in equation

c is specific heat (4.184). m is the TOTAL mass. Always 10 grams for us. Delta T is change in temp, likely given to us.)

N

N: number of moles of limiting reactant (always NaOCl in 107)/ stoichiometric coefficient (1,3,4)

(delta)H = −mc(delta)T/n

-heat of reaction per one mole of reactant.

When 5.0 mL of 1 M NaOCl reacts with 5.0 mL of 1 M KI, the ΔT is 15.4 ˚C, what is the change in enthalpy?

(assume the specific heat is 4.184 J/g˚C ,and the density is 1.00 g/mL)

Know the full balanced equation. 3 NaOCl + 1 KI 3:1 ratio. Peak at 7.5

Draw the graph out and see if it's the ideal ratio.

Delta h is -mcAt/n

10x 4.184 x 15.4 / (n)

N= # moles NaOCL/ st. coef. 5mL(1M/1000mL) = .005 M / 3 =

percent error

Measured - theoretical / theoretical

found: measured

Accepted: theoretical

Nature of reactants w/collision

(identity- similar sizes)

Concentration of reactants: w/ collision

increase, increases reaction rates. more around to collide

Temperature w/ collision

increase, increase energy, increase collisions,

Catalyst: w/ collision

ORIENTATION!

catalase

Biological enzyme found in many living things

Enzymes lower activation energy by orienting the molecule correctly in space

Specific 3D structure, affected by

Temperature

A = ecl

in experiment 4

e is the slope!

Find rates w. respct to each thing.

0: c x2 rate no change

1: C x2 rate x2

2: c x2 rate x4

The test will be straight forward enough to not use the equation.

Q-test

Difference between two closest numbers divided by the range.

Only exclude extreme values for Q test

(highest or lowest)

Extreme # - nearest number / total range (highest - lowest)

(this is the Qexp)

how to find Q critical

Q critical is on the chart. Always use 90%.

N is the number of data points

Throw the Q exper out

if it's greater than the Q crit.

- Need to order the data points on the test!!!

balanced chemical equations experiment 2

1,1->,1,1

3,1,->1,3

4,1,2->,2,4,1

safety symbol: !

acutely toxic (harmful)

- sensitizers, irritants, acute toxicity

safety symbol: skull

acutely toxic