Chem 1C Lab Final

Identify the factors that affect the rate of a reaction

Temperature of the chemical system

Concentration of the reactants

Presence of a catalyst

Nature of the reactants

Surface area of the reactants

The rate law for the elementary reaction,

A+2B⟶Products, is written as

rate = k [A] [B]^2

Which changes can be made to a chemical reaction in order to increase the rate constant?

Increase the temperature

Add a catalyst

How does a catalyst impact the rate of a chemical reaction?

It lowers the activation energy of a reaction.

Consider the rate law

Rate=k[NO]2[O2]

.

The rate law is (blank) order with respect to

NO and

(blank) order with respect to

O2

Overall, the rate law is

(blank) order and is considered a

(blank) rate law.

second, first, third, termolecular

Identify the term represented by each of the variables in the Arrhenius equation,

k=Ae−EaRT

R=gas constant

k=rate constant

Ea=activation energy

T=temperature

A=frequency factor

In any organic redox reaction, you can recognize the reduced and oxidized organic molecules by

(blank) between products and reactants.

Reduction corresponds to

(blank)

Oxidation corresponds to

(blank)

looking at the structures, gaining C-H bonds, losing C-H bonds

Identify characteristics of a pseudo first order experiment.

One reactant is present in great excess over another.

The change in concentration of one substance is monitored closely, while the effect of changing the concentration of the other is assumed to be negligible.

In a kinetic experiment with multiple reactants, the general form of the rate law is

Rate=k[A]x[B]y

To study the order of each reactant, you might add a large excess of one reactant, A, and plot the concentration of the other, B, over time.

What rate constant information is directly reflected in the plot of [B] versus time?

k[A]^x

According to the Beer-Lambert Law (Beer's Law), the absorbance of a sample is directly related to which of the following?

The molar absorptivity constant for the material at a specific wavelength (ε).

The distance the light travels through the sample (path length, b).

The concentration of the chemical species in the sample (c).

The relationship between absorbance of light by a solution and its concentration should be

(blank) so that when concentration increases, absorbance

(blank)

linear, increases

If you plot the absorbance measurements of solutions vs. their concentrations, what is the slope equal to?

Molar absorptivity, if the path length is 1 cm

Suppose you prepare a

5μM solution of red dye and a

5μM solution of blue dye and observe them in two identical test tubes. Why might the blue dye solution appear more intensely colored than the red dye solution?

The molar absorptivity of the blue dye is greater than the molar absorptivity of the red dye.

Suppose you measure the absorbance of a yellow dye solution in a 1.00 cm cuvette (b=1.00 cm). The absorbance of the solution at 427 nm is 0.74 . If the molar absorptivity of yellow dye at 427 nm is 27400 M-1cm-1, what is the concentration of the solution in M?

0.000027

What is the correct net ionic equation to describe this precipitation reaction?

Co(NO3)2(aq)+2NaOH(aq)⟶2NaNO3(aq)+Co(OH)2(s)

Co2+(aq)+2OH−(aq)⟶Co(OH)2(s)

What visible sign does NOT indicate a precipitation reaction when two solutions are mixed?

Bubbling in the test tube

Determine the type of each chemical equation describing a precipitation reaction.

Ca2+(aq)+SO42−(aq)⟶CaSO4(s)

(blank)

Ca2+(aq)+2Br−(aq)+2Na+(aq)+SO42−(aq)⟶

2Na+(aq)+2Br−(aq)+CaSO4(s)

(blank)

CaBr2(aq)+Na2SO4(aq)⟶2NaBr(aq)+CaSO4(s)

(blank)

net

full ionic

full molecular

Suppose you are studying an unknown solution based on its precipitation reactions with other solutions, resulting in this data table.

Unknown Precipitate: Na2SO4 No reaction: NaCl Precipitate: Na2CO3

Which compounds might be your unknown?

Ca(NO3)2

Ba(NO3)2

Sr(NO3)2

If crystal growth does not start on its own after the solution in the flask returns to room temperature, identify the best ways to promote this process.

Scratch the bottom of the flask gently with a stirring rod.

Add a bit of solid as a seed crystal.

After a recrystallization, a pure substance will ideally appear as a network of (blank) (blank). If this is not the case, it may be worthwhile to reheat the flask and allow the contents to cool more (blank)

large, crystals, slowly

Students are investigating a solvent for use in freezing point depression experiments. They measured the freezing point of the solvent as −12.6 ⁰C. The solution they made by dissolving 0.484 g of the non-electrolyte ethanol (46.07 g/mol) in 8.254 g of the solvent has a freezing point of -18.3 ⁰C.

Determine the freezing point depression constant, Kf, for the solvent.

4.5

∘C⋅kg/mol

Colligative properties are dependent on (blank) a solute, but are not dependent on (blank) the solute.

the amount of, the nature of

Identify the ideal value of the van't Hoff factor for aqueous solutions of each solute.

Na2SO4

NH4Cl

CaCl2

C12H22O11

NaCl

C2H6

3

2

3

1

2

1

For freezing point depression, the concentration of the solute is most conveniently expressed in units of molality (m) which is defined as:

moles of solute divided by kilograms of solvent.

A certain amount of a nonvolatile solute is added to a pure solvent. Which of the following statement regarding this situation is incorrect?

The boiling point of the solution will be lower than that of the pure solvent.

Suppose you are measuring the freezing point depression due to the presence of a non-electrolyte in solution using the equation

ΔTf=iKfm

Which value in the equation do you know because the solute is a non-electrolyte?

i

What is the freezing point (in degrees Celcius) of 4.20 kg of water if it contains 208.1 g of

CaBr2

? The freezing point depression constant for water is 1.86 oC/m and the molar mass of

CaBr2

is 199.89 g/mol.

-1.383

What is the freezing point (in degrees Celcius) of 4.09 kg of water if it contains 186.4 g of butanol,

C4H9OH

?

The freezing point depression constant for water is 1.86 oC/m and the molar mass of butanol is 74.12 g/mol.

-1.144

An aqueous solution appears violet. What color of light is absorbed most strongly by the solution?

yellow

What is the typical coordination number for platinum(II) ion?

4

Identify the coordination chemistry term described by each phrase.

Capable of making one bond to a transition metal (blank).

The compound is used to remove metal ions from solutions (blank).

General term for a transition metal cation bonded to a small molecule or anion (blank).

Small molecule or anion with at least one lone pair to bind to a transition metal (blank).

monodentate

chelating agent

coordination compound

ligand

Identify the donor atom in the following ligands:

Bromide ion:

Oxalate ion:

Hydroxide ion:

Br

O

O

What is the coordination number for iron(III) in the following complex?

K3[Fe(C2O4)3]

6

What is the oxidation state and d electron count of Co in [Co(H2O)3(NH3)3]Cl3?

3+, six d electrons

The value referred to as Δo is the energy difference between which set of molecular orbitals?

t2g & eg

Identify the reagents that are used in the synthesis of aspirin.

Salicylic acid

Acetic anhydride

Acid catalyst

Identify the safety concerns that appear in the synthesis of aspirin experiment.

One of the reagents is very bothersome to the nose.

Irritating vapors are produced when water is added to the reaction mixture.

If crystal growth does not start on its own in the cooling aspirin reaction mixture, what should you do?

Scratch the inside wall of the flask gently with a stirring rod.

A method for testing the presence of unreacted salicylic acid in your aspirin synthesis is to add a 1% FeCl3(aq) solution to observe a color change (or not). If a magenta color forms, what has occurred?

The phenol group was deprotonated and reacted with free Fe3+ in solution.

Suppose you start with a 1.70 g sample of aspirin. After recrystallizing the sample, you have 1.28 g of aspirin.

What is the percent recovery of aspirin in this recrystallization experiment?

75.3

Consider a mixed sample of 70% of compound Y and 30% of compound X in which Y melts at a higher temperature than X.

In this sample, (blank) As heat is applied, (blank) starts to melt first, which is when (blank) Then, (blank) melts later.

X is an impurity in Y

compound X

melting is first observed

compound Y

How do you know when the endpoint of the titration is reached?

The phenolphthalein indicator will change the solution color to pale pink.

When filling a burette for titration, adjust the burette so that (blank), preferably over a sink. Then, (blank) to add the titrant into the burette. The titrant should be filled

(blank).

the opening is near or below eye level

use a funnel

almost to the zero mark

What is the equivalence point in an acid-base titration experiment?

The point at which the moles of base equals the moles of acid

What appearance of an acidic analyte solution containing phenolphthalein indicates the endpoint of titration with a basic solution?

A persistent pale pink color throughout the solution.

Identify the correct equation for the equilibrium constant

Ka

for the weak acid dissociation of acetic acid.

HC2H3O2(aq)+H2O(l)−⇀↽−H3O+(aq)+C2H3O2−(aq)

Ka=[H3O+][C2H3O2−]/[HC2H3O2]

Why must a solution of NaOH be standardized using a primary standard, such as KHP?

Solid NaOH absorbs water readily from the air.

Identify possible errors that could affect the quality of your titration and calculations.

Select one or more:

The titrant volume is incorrectly calculated and recorded in the lab notebook.

Some KHP is spilled from the weigh boat as the analyte solution is prepared.

Titrant is added beyond the light pink endpoint of the analyte solution.

A beaker containing 0.400 g KHP was titrated with NaOH solution. The pale pink end point was reached after 17.89 mL of NaOH solution was dispensed. What is the molarity (in mol/L) of the NaOH solution?

0.1095

Suppose you are standardizing a sodium hydroxide solution with

KHP

(molar mass=204.2 g/mol) according to the equation

KHP+NaOH⟶H2O+NaKP

You prepare the standard solution from 0.300 g of

KHP

in 30.0 mL of water. If the NaOH solution is approximately 0.1 M, what is the approximate volume (in mL) of NaOH solution you will need for the titration?

14.69

To activate the eyewash, push the ________________ towards the wall.

lever

If a large amount of a caustic chemical spills on your clothes, or if your clothing catches on fire, you need to use the:

safety shower

Determine when you should remove your goggles in the lab room.

When everyone in the room is done handling any chemicals or glassware

To handle a hot glass beaker, it is best to use (blank).

If you burn yourself, immediately rinse the area with (blank).

Acids and bases, such as NaOH and HCl, are strong and can cause burns. In case of contact with your skin, rinse immediately with (blank).

tongs

water

water

What should be done if a chemical gets in one of your eyes? Select any applicable answer.

Use the eyewash station, being careful not to rub your eye.

Use a flexible hose on a faucet to rinse your eye, being careful not to rub your eye.

What precautions should you take with long hair?

Long hair must be secured with a rubber band, barette, or headband.

How do you dispose of broken glassware, such as a broken test tube or beaker that contains a chemical residue?

place in the red can labeled "glass only"

All chemical waste in the lab is disposed of in an appropriate waste jar located in the (blank)

Before you pour chemical waste into a waste jar, you must first read the (blank).

How will you dispose of non-toxic waste? (blank)

fume hood

label

trash

What should you do with chemical waste when the waste jar in the hood is filled to the bottom of the neck?

Ask the stock room personnel to bring another waste jar

The lid on a waste jar should never be tight, and a waste jar should not be filled past the bottom of the neck. Why not?

To ensure that the waste can be easily accessed, and that there is ample room for the waste and its vapors

Are shorts allowed in the lab?

no

What do you do if a strong acid is spilled on a counter or in the fume hood?

Notify the TA

Use sodium bicarbonate to neutralize the acid and notify the TA

What precautions should you take if you boil or heat a solution?

You should never leave the solution unattended.

As long as you watch the solution closely, you can work on other parts of the experiment.

When boiling a solution, you should use boiling chips to prevent splattering.

You should always wear eye protection and secure long hair.

You should make sure the beaker or flask rests securely on the ring stand or hot plate.

To activate the safety shower, pull down on the ______________________.

handle

To isolate a single variable when rearranging equations, move all other variables to the (blank) of the equation by using (blank) on them and remembering to perform that operation (blank).

Make sure the rearrangement has the target variable (blank).

other side

opposite function

both sides of the equation

in the numerator, not the denominator

When heating a solution to boiling on a hot plate, start by (blank). Then, turn the heat to (blank) to start. If necessary, (blank) after waiting about ten minutes without seeing boiling.

starting and stabilizing the stir function

a medium heat setting

turn up the heat setting

Which procedure cannot be performed on a hot plate, requiring a Bunsen burner instead?

Heating a crucible to remove water from a hydrate

While setting up a beaker to boil a solution on a hot plate, you notice that the stirring is erratic and unstable. What should you do to stabilize the stirring solution?

Move the beaker to the center of the hot plate.

Turn down the stirring speed.

Identify tools that are ideal for cleaning glassware.

Brushes

Detergent and water

When cleaning a buret, begin by coating the inside with (blank). Empty most of it out, then drain the rest by (blank). Rinse with (blank), then hang upside-down on a buret rack.

detergent solution

opening the stopcock

deionized water

Water used to rinse detergent out of a flask:

Acid solution used to clean a crucible:

The solvent used to rinse chemicals out of a beaker:

sink

waste container

waste container