CHM145 Final Exam Review

1.) To understand colligative properties

2.) To measure the boiling point elevation of water caused by the dissolved compounds salt and sugar.

1.) To understand colligative properties

2.) To measure the boiling point elevation of water caused by the dissolved compounds salt and sugar.

What is the purpose of Experiment 1: Colligative Properties?

Boiling aqueous solutions can cause severe burns

Why should caution be exercised in Experiment 1: Colligative Properties?

Salt lowers the freezing point of water, so it will freeze and make ice on the roads only at very cold temperatures.

Why is salt added to icy roads in the winter?

non-volatile solutes

substances with no volatile solutes; change vapor pressure, boiling point, freezing point, and osmotic pressure

colligative properties

changes in properties are dependent on the number of dissolved particles, and the collective effect of the number of solute particles, not the kind or identity of the solute particles

vapor pressure, boiling point, freezing point, osmotic pressure

four examples of colligative properties

lowers the vapor pressure

Adding a non-volatile solute does what to the vapor pressure of the solution?

raises the boiling point

Adding a non-volatile solute does what to the boiling point of the solvent?

normal boiling point

the temperature at which the vapor pressure equals 1

the concentration of solute particles; molality

What is boiling point elevation a function of, and what units is it typically expressed in?

moles of solute particles / kg of solvent

molality formula

particles; chemical compound

Boiling point depends on the number of moles of ________, not on the number of moles of a _________________.

They don’t dissolve; matches the moles of nonelectrolytes

How do nonelectrolytes dissolve in water? What is the Van Hoff factor for nonelectrolytes?

dissolve into individual ions; the Van Hoff factor matches the number of moles of individual ions

How do electrolytes, such as ionic compounds, dissolve in water? What is the Van Hoff factor for these electrolytes?

Vernier temperature probe; hot plate

What tool is used to measure temperature in Experiment 1: Colligative Properties? What tool is used to heat and stir the water?

an aluminum foil lid

What is put on top of the beaker during Experiment 1: Colligative Properties, before temperature measurements are made?

the volume of water will change dramatically and the calculated molalities will be affected; concentration will be larger and the boiling point will be higher than it is supposed to be

If the water in the beaker is boiled too vigorously in Experiment 1: Colligative Properties, what will happen?

x-axis: time

y-axis: temperature

During Experiment 1: Colligative Properties, what goes on the y-axis and what goes on the x-axis when plotting the data from the salt and sugar samples?

salt

Experiment 1: Colligative Properties: I expect that the _________ (salt/sugar) will have the higher boiling point elevation since it contains more moles of particles.

First plateau: boiling point of solvent

Second plateau: boiling point of solution (solvent + solute)

The graphs from Experiment 1: Colligative Properties will have two plateaus; what do each one represent?

100 mL graduated cylinder

In Experiment 1: Colligative Properties, what measurement tool limits the significant figures in molality measurements?

1.) Filled in dots

2.) A title

3.) Labeled axes

4.) Connect the dots turned off

5.) Linear fit

6.) Autoscaled

7.) Correlation should not be zero

What are the requirements for graphs?

To monitor the rate of a chemical reaction, to determine the kinetic order of a reaction, to understand the molecular components of the rate limiting step, and to determine the energy of activation of the reaction from the temperature dependence

What is the purpose of Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide?

Hydrogen peroxide is a strong oxidant and can irritate skin and eyes

What is a safety concern for Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide?

rate of a chemical reaction

how quickly reactant concentrations decrease and product concentrations increase; how rapidly a chemical reaction occurs

False. (Some take millions of years, others take seconds)

T or F: All chemical reactions proceed at the same speed.

chemical kinetics

the area of chemistry that is concerned with the speeds, or rates, of reactions

reaction rate

defined as the change in the concentration of reactants or products per unit of time

reactant concentrations

Reaction rates depend on what?

catalysts

can speed up decomposition reactions; increase the rate of a reaction without undergoing a net change in their own structure

KI (potassium iodide)

What was the catalyst in Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide?

O2; monitoring change in pressure so the decomposition occurs as a function of time

The decomposition of hydrogen peroxide generates what as a product? What does this allow for in terms of monitoring the solution?

slope of pressure vs. time

What measures the rate of the reaction in Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide?

a short lag phase near the beginning that does not provide accurate information

What do you need to watch out for on the graphs in Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide?

rate law/ rate equation

centerpiece of any kinetic study; expresses how the rate depends on the concentrations of reactants

temperature

The magnitude of k changes with _______________ and therefore determines how it affects the rate.

how a reaction occurs; which molecules collide with which other molecules

Knowing the order of the reaction provides insight into what?

pressure/time

concentration/time

Ideal Gas Law and molarity

In Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide, what were the units of the initial rate measurements? What were these units converted to? How was this conversion done?

rate limiting step

The order of the reaction indicates which molecular components, and the numbers of those components, that are present during the _____________________ of the reaction.

increases

The rate of most chemical reactions increases as the temperature ___________.

energy of activation

the minimum energy required to bring about the reaction; energy barrier that the reactants must traverse in order to react; found with the Arrhenius equation

False

T or F: The slope depends on the units of k in Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide.

reaction mechanism

a sequence of possible single reaction steps that sum to the overall reaction, or a hypothesis of how a reaction occurs

elementary steps

individual steps of a reaction mechanism

Concentration of H2O2: varied

Concentration of KI and temperature: kept constant

To find the kinetic order of hydrogen peroxide, what should be done to the concentration of H202, and what should be done to the concentration of KI and the temperature?

10 mL graduated cylinder

What measurement tool is used to prepare solutions of H202 and KI?

10 K

Temperature difference of approximately how much is required for the trials involving varied temperature?

to find the energy of activation

In Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide, why are experiments where the temperature is varied necessary?

True

T or F: An airtight system is crucial to the success of Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide

+/- 1K

The average temperature of all of the trials in Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide following the standard trial should be within _______ of the standard trial’s average temperature.

H2O2 and KI dilute each other; M1V1=M2V2

Why are the final concentrations of H2O2 and KI not the same as their initial concentrations in Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide? What equation should be used to find the final, new concentrations?

decreases

As the concentration of KI decreases, the reaction rate ____________.

increases

As the temperature of the reaction increases, the rate of the reaction ___________.

decreases

As the concentration of H2O2 decreases, the reaction rate _________.

False

T or F: Over the course of the 300 second experiment in Experiment 2: Kinetics of the Decomposition of Hydrogen Peroxide, the temperature does not have to be consistent.

5 minutes in hot; 8 minutes in cold

How long must the test tubes incubate in the hot water bath? How long must the test tubes incubate in the cold water bath?

Plot rate (M/s) vs. final concentration and examine the shape of the plot

method for finding the order of the reactants graphically

2 mL H2O2; 1 mL KI; 3 mL

How much H2O2, regardless of concentration, should be put in the reaction flask for trials 1-9? How much KI? What is the total volume in every test tube?

to observe a system under chemical equilibrium, to observe changes in the state of equilibrium, to apply Le Chatelier’s Principle, and to measure an equilibrium constant

What are the purposes of Experiment 3: Determination of an Equilibrium Constant?

Fe(NO3)3 solutions are strong oxidizing agents and are corrosive; gloves are required. SCN- is a moderately toxic ion

What are safety concerns in Experiment 3: Determination of an Equilibrium Constant?

All solutions must be disposed of in the labeled waste containers.

What are waste disposal rules for Experiment 3: Determination of an Equilibrium Constant?

equilibrium

occurs in a chemical reaction when the rates of the forward and the reverse reactions are equal; concentrations of all species involved no longer change with time, but do not all have to be equal

Keq (equilibrium constant)

the ratio of the forward and reverse rate constants

True

T or F: Equilibrium condition is dynamic.

Le Chatelier’s Principle

predicts how an equilibrium system will change when it is disturbed; when a chemical system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the compounds, it re-attains equilibrium by undergoing a net reaction that reduces the effect of the disturbance

the reaction will shift right and produce more product to consume the excess reactant

If additional reactant is added to a reaction at equilibrium…

the reaction will shift left and produce more reactants to consume the excess product

If additional product is added to a reaction at equilibrium…

will favor the endothermic reaction direction and shift in the opposite direction to use up the heat

An increase in temperature for a reaction at equilibrium…

favors the product of the exothermic reaction

A temperature decrease for a reaction at equilibrium…

Nothing

What happens to a reaction with delta H = 0 when a temperature change happens?

qualitatively; quantitatively

In Experiment 3: Determination of an Equilibrium Constant, the extent of the formation of the complex ion could be measured both ___________ and ______________.

complex ion has an orange color, while Fe3+ and SCN- are colorless

How could the complex ion formation be estimated qualitatively in Experiment 3: Determination of an Equilibrium Constant?

Beer’s Law

absorbance is directly proportional to the concentration of a light-absorbing species in a sample at a particular wavelength

to prevent precipitation of Fe3+ as Fe(OH)3.

Why do Fe3+ solutions contain 1M HNO3 in Experiment 3: Determination of an Equilibrium Constant?

Neither H+ nor NO3- are involved in the reaction of interest.

In Experiment 3: Determination of an Equilibrium Constant, how does the addition of HNO3 have no effect on the reaction of interest?

increase

If the concentration of Fe3+ is held constant and the concentration of SCN- is increased, I expect that the absorbance of the complex ion (FeSCN2+) will ___________.

10 mL graduated cylinder

All solutions in Experiment 3: Determination of an Equilibrium Constant were made in what measurement tool?

to improve precision

Why was the same graduated cylinder used to prepare each solution in Experiment 3: Determination of an Equilibrium Constant?

Add deionized water, then Fe3+ solution, then SCN- solution

What was the order of addition of liquids when preparing solutions in Experiment 3: Determination of an Equilibrium Constant?

covers the top of measurement tools and allows for inversion and mixing

What is the purpose of Parafilm?

one

How many different cuvettes were used for absorbance measurements in Experiment 3: Determination of an Equilibrium Constant?

3 mL

How much of the solution should be put into the cuvette for an absorbance measurement in Experiment 3: Determination of an Equilibrium Constant?

Pat the outside of the cuvette dry with a Kimwipe, but do not dry the inside. Do not the touch the clear sides of the cuvette.

What is proper procedure for cleaning/preparing a cuvette?

two to four minutes

Measurements need to be made quickly in Experiment 3: Determination of an Equilibrium Constant because the color fades slowly from solutions in the cuvette after how long?

Fe3+; same

Excess _____ is used in solutions so that all the SCN- is converted into the complex ion. Therefore, we can assume that the concentration of the complex ion is the _______ as that of the initial concentration of SCN-.

blank solution; slight yellow

Which solution is put into the cuvette to calibrate the LabQuest? What color might it have that calibration accounts for?

the one with the highest SCN- concentration; the approximate wavelength of maximum absorbance

After calibration, which solution should be placed in the spectrometer first? Which value should this produce?

True

T or F: The final concentrations of Fe3+ and SCN-, after being mixed in the 10mL graduated cylinder, are not the same as their initial concentrations since they are diluted by each other and by water in Experiment 3: Determination of an Equilibrium Constant.

concentration of complex ion (x-axis); absorbance (y-axis)

What is on the x-axis and the y-axis for the calibration curve created during Experiment 3: Determination of an Equilibrium Constant?

not; significant concentrations

In Experiment 3: Determination of an Equilibrium Constant, the equilibrium constant is measured under conditions in which there is _____ a large excess of one reactant over the other, so that at equilibrium there are ____________________ of all species present.

Blank absorbance reading - absorbance of unknown solution

How do you obtain the net absorbance in Experiment 3: Determination of an Equilibrium Constant?

labeled waste containers

Where should all solutions be discarded in Experiment 3: Determination of an Equilibrium Constant?

interpolation of net absorbance using the slope and y-intercept obtained through linear regression

How is the concentration of the complex ion in the unknown solution calculated in Experiment 3: Determination of an Equilibrium Constant?

Keq (equilibrium constant)

Once all three equilibrium concentrations have been calculated in Experiment 3: Determination of an Equilibrium Constant, what are these values used for calculating?

To understand the concept of the ionization constant Ka; to measure Ka for weak acids using pH measurements and absorbance measurements

What is the purpose of Experiment 4: Ionization Constants of Weak Acids?

phenol red indicator can be a skin irritant

What is a safety concern for Experiment 4: Ionization Constants of Weak Acids?

Arrhenius Theory

Acids dissociate in water to yield H3O+; bases dissociate in water to yield OH-

Bronsted-Lowry Theory

Acids donate protons; bases accept protons

Lewis Theory

acids accept an electron pair to form a bond; bases donate an electron pair to form a bond

conjugate acid-base pair

an acid and a base that differ only in the presence or absence of a proton