CHM144 Final Exam

linear regression

a method used to calculate the "best fit" line that describes the mathematical relationship between two experimental variables that have a linear relationship

independent variable

the variable that one typically has control over and is manipulated; plotted on the x-axis

dependent variable

the variable that is measured during the experiment; plotted on the y-axis

a, b, c

Select all that are true about the "best fit" line with real data. a.) It may not go through all the data points. b.) It does not have to go through the origin. c.) Every data point has some experimental error associated with it.

the data they were derived from

The numbers in a linear regression cannot have more significant digits than...?

0.990

The correlation of all linear graphs should be greater than what value?

calibration curve

a graph that can be used to determine the concentration of an unknown sample of a compound for which you have measured an absorbance

known sample

The absorbance of the unknown sample should be within the range of the absorbance measurements of the ...?

interpolation

a method that involves solving for an unknown "x" value

reduce; oxidized

A more active metal will replace and ... a less active metal during a chemical reaction. The more active metal itself will become ...

scientific hypothesis

a reasoned and testable proposal predicting the causal relationship among multiple observations

measurements

form the basis of all science; critical to the development and testing of a scientific hypothesis

1.) The measuring device 2.) The individual performing the measurement.

Measurements are always accompanied by some level of uncertainty that is a function of what two things?

systematic errors

errors that are all approximately of the same magnitude and direction from the true value; can be minimized by well-designed experimental procedures, proper calibration, and maintenance of instrumentation

random errors

occur in large part because of of interpretations of measurement readings by experimenters, by random fluctuations in an experimental method, or limits of instrumentation; can be reduced by careful laboratory technique or observation

the same as the MEASUREMENT with the smallest amount of sigfigs

If a measurement is multiplied or divided, the number of significant figures will be ?

the same as the smallest number of DECIMAL PLACES in a value

If a measurement is added or subtracted, the number of significant figures will be ?

infinite

Exact numbers have an ... amount of sigfigs and should not be factored into determining how many sigfigs a calculation should have.

more

You should always carry ... significant figures through a calculation than you will need at the end.

accuracy

the degree of agreement between a measured value of a quantity and the "true" value of that quantity. (arrows hitting the bullseye)

precision

the degree of agreement among several measured values of the same quantity (arrows hitting the same spot, even if it's not the bullseye)

accuracy

Systematic errors affect the ... of the measurement.

precision

Random errors affect the ... of the measurement.

mistakes/determinate errors

accidents that result in a poor measurement; usually only affect one value in a series of repeated measurements of the same quantity

central value

the value about which the individual measured values tend to cluster

mean

the sum of data points divided by the number of data points (average)

median

the central member of a series of data points, arranged in order of magnitude; especially useful when suspecting an outlier

mode

the value that occurs most frequently in a data set

standard deviation

the most common way to express the precision of a series of measurements; the difference between the mean and the measured data point

absolute deviation

the absolute values of the difference between the mean and the data point; absolute value of standard deviations

range

the difference between the biggest and the smallest data point; another measurement of absolute precision

percent relative standard deviation

a measure of the precision of the individual data points relative to the mean of the data, expressed as a percentage

standard deviation of the mean

another measure of precision; estimates the precision of the mean of a group of n independent measurements of the same quantity; standard deviation/root of n

systematic error

As the number of individual measurements increases, what becomes the dominant source of error?

Q-test

the test that should be applied in cases of 3 to 10 repeat measurements where it appears that one data point is an outlier; can only reject one data point from a set

discarded

If the calculated Q value is greater than the critical value, the suspect value should be ....

on the high or low end of the range of data

During a Q test, only data points where can possibly discarded?

the point that is farther from its nearest neighbor

Which data point on the end of the range of values should be considered for possible removal during a Q test?

significance tests

tests that allow an experimenter to compare a measured value to a "true" or accepted value OR to compare two independently measured values of the same quantity to each other

n-1

degrees of freedom for a T test for comparison to an accepted value, and for a Q test

statistically different

If the absolute value of the difference between the accepted value and the mean is greater than t*sm, the two values are ....

statistically different

If a confidence interval does not include the value, then it is ....

2n-2

degrees of freedom for comparison of two independent measurements of the same quantity

n1+n2-2

degrees of freedom for comparison of two independent measurements of different quantities

It uses standard deviation instead of standard deviation of the mean

What is special about the t test for two independent measurements of DIFFERENT quantities?

Because popcorn was regarded as a laboratory chemical, and laboratory chemicals cannot be consumed.

Why wasn't it okay to eat the popcorn?

True

True or False: The results of individual trials often give a range of values.

statistical analysis

provides criteria for rejection of data points and for comparison of numerical quantities

to determine the moisture content of popcorn and to use basic statistics to analyze the results

What was the purpose of the popcorn/statistics lab?

starch, a variable amount of water, and a hard, moisture-sealed husk

What are kernels primarily composed of?

Unpopped kernel

Which popcorn kernel had a higher mass: the popped kernel or the unpopped kernel?

It lost mass as water escaped the kernel

Why does the popped kernel have a lower mass than the unpopped kernel?

to prevent scorching of the kernels

Why should there be substantial distance from the bottom of the flame to the bottom of the evaporating dish?

Mass of unpopped kernel-Mass of popped kernel

Calculation for mass of water (Experiment #2)

(mass of water)/(mass of unpopped corn) * 100

Calculation of percent water (Experiment #2)

They are considered laboratory chemicals, and cannot be consumed.

Why can the sugar from Experiment #3 not be consumed?

Poured down the sink

How can the sugar solutions in Experiment #3 be disposed of?

intensive physical properties

independent of the amount of substance; density, color, melting point, boiling point

extensive physical properties

dependent on the amount of the substance; volume, mass, and surface area

Since they don't change based on amount, they can be used to identify unknown substances

Why are intensive properties such as density important?

M/V

Density formula

The liquid form of water is more dense than its solid form (ice can float in water)

What is special about water when it comes to density?

The other solutes present are present in fairly small amounts compared to sucrose.

Why is the density of a beverage primarily based on sucrose content?

weight percent (w/w); volume percent (v/v); weight/volume (w/v)

three common examples of expressing percent composition of a solution

(mass solute) / (mass solution) * 100

weight percent (w/w) equation

mass of solution - mass of solute

mass of solvent equation

standard solutions

solutions where the concentration or amount of solute is known

X Axis: Percent Sugar Y Axis: Density of Solution

Which variables goes on the x axis and y axis for the density and percent sugar of beverages experiment?

Calibration curve- allows for interpolation of unknown values

What purpose does the graph of standard solutions serve in Experiment #3?

The calibration mark

When you use a volumetric flask, where are you filling to?

Water would dilute the sugar solutions and mess with the concentration

Why must you shake out excess water from the plastic bottles and make sure they are dry in Experiment #3?

Mass of solute- mass of solvent stays at 50mL

In Experiment #3, are you changing the mass of solute or the mass of solvent?

All (three decimal points)

In Experiment #3, weigh each empty bottle without their lids and use ... of the available figures from the balance.

30 mL beaker

In Experiment #3, which container is used to estimate the amount of solute (sugar) to be added to the 250mL bottles?

plastic pipet

When filling the 50-mL volumetric flask with as much water as you can, make sure to use a ... to make sure not to overshoot the etched mark on the flask.

False- mass it once and assume it is the same for the rest of the solutions

True or False: In Experiment #3, you must get the mass of the empty 100-mL and the full of water 100-mL beaker each for each solution.

weighing by difference

the standard method for obtaining the mass of a liquid or another material that would be difficult to weigh on weigh paper (mass of full container - mass of empty container)

increases

Experiment #3: As the percent sugar increases, the density ....

Beaker (0 dp), Erlenmeyer flask (0 dp) graduated cylinder (1 dp), volumetric flask (2 dp),

List the following in order from least accurate to most accurate: graduated cylinder, beaker, Erlenmeyer flask, volumetric flask

3 decimal places

How many decimal places can a balance use?

The copper chloride hydrate; hydrochloric acid

What is highly toxic by ingestion and inhalation? What is also highly toxic and can be corrosive to the skin and eyes?

reaction stoichiometry

What process is used to determine the number of moles of each of the compounds of a hydrated binary salt?

In the appropriately labeled containers; NOT in the sink

How should the copper chloride hydrate be disposed of in Experiment #4?

The Law of Definite Proportions

a fundamental component of the modern atomic theory; the mole ratios of elements in a compound will be small whole numbers

empirical formula

the simplest whole number mole ratio of the elements that make up a compound; provides the relative number of moles of each element per mole of the compound, or the relative number of atoms of each element per molecule of the compound

molecular formula

expresses the actual number of moles of each element per mole of the compound, or the actual number of atoms of each element per molecule

arrays of cations and anions

Ionic compounds do not exist as molecules, but as ....

smallest number of moles

The empirical formula can be determined by converting the mass of each component into the number of moles of each component, then dividing each by the what?

CuxCly * zH2O

What is the general formula of the hydrated compound?

the mass of the water

By measuring the mass of the sample before and after heating a sample of the compound to drive off water, what can you find?

a redox reaction; producing elemental copper

After dissolving the dried copper chloride in water, what will be conducted? What is the purpose?

reducing agent; replaces copper as the more active metal

What is aluminum's role in the redox reaction in Experiment #4?

blue-green to brown

When the chopper chloride hydrate goes from being hydrated to dehydrated, what is the corresponding color change?

If blue-green crystals remain, it means the sample hasn't been completely dehydrated.

After the initial heating, why is it important to make sure no blue-green crystals remain in the crucible?

It removes the coating on the foil, increases surface area, and exposes a reactive surface.

When aluminum is added to the solution, why is it important to sand the foil?

It may remove copper from the solution and cause a determinate error

Why can't you remove the stirring rod that you used to stir the aluminum foil into the solution?

Colorless; a small amount of aluminum should remain

After the reaction between the aluminum and the copper solution is complete, what color is the solution? And should there be any reactants remaining?

H2(g) and AlCl3 (aq)

When HCl is added to the aluminum and copper solution, which two products does it produce?

0.001 g

When you are drying and weighing the copper filtrate at the end of Experiment #4, what is the error limit that the value must be consistent within?

Mass of dehydrated sample - mass of copper

Formula for mass of chlorine in Experiment #4

Traditional indicator dye titration vs. modern pH electrode titration

In Experiment #5, what is the main comparision?

NaOH

Which solution is caustic in Experiment #5?

citric acid and carbonic acid

Which two acids are commonly present in carbonated beverages and are highest in concentration?

allowing the soda to go flat; boiling the soda

How can carbonic acid be removed from the soda?

Because of the large difference in concentration

Why can the other acids in the soda be ignored?

titrant; NaOH

the solution of known concentration in a titration; what is it in Experiment #5?

analyte; citric acid

in a titration, the solution whose concentration is trying to be known; what is it in Experiment #5?

an acid-base reaction in which a hydrogen ion (proton, H+) is transferred from an acid to a base

What is the reaction used during an acid-base reaction?

monoprotic acid

an acid that only has one proton available to react with a base; example is HCl; always react with bases with a 1/1 stoichiometry

polyprotic acid

an acid that has multiple protons that can react with a base; citric acid is an example

THREE moles of NaOH to ONE mole of citric acid

What is the stoichiometric ratio between citric acid and NaOH in Experiment #5?

similar; cannot

All three acidic protons in citric acid are of ... strength, so they all react with NaOH to a similar extent. Thus, the three reactions ... be readily distinguished from each other.

equivalence point

the point in the titration where the number of moles of base added is stoichiometrically equal to the number of moles of acid originally present in the analyte

an indicator dye that changes color at the equivalence point

What typically helps estimate the equivalence point? It indirectly measures pH

end point

the estimate of the equivalence point

Because all three protons of the acid have similar strengths

Why is there one observable end point for the citric acid titration?

pH = log[H+]

pH formula

pH electrode

a tool that allows pH to be measured directly

phenolphthalein; colorless to light pink

most common indicator used for titrations of strong acids by strong bases; what color change does it have?

overestimates

The measured end point of a titration actually ... the equivalence point slightly.

in order to see the color change of the indicator

Why must colorless sodas be used in traditional titrations?

citric acid solution in the flask; NaOH is the buret

Which solution is placed in the Erlenmeyer flask? Which solution is placed in the buret?

a magnetic stir bar

What is used in the modern titration to thoroughly mix the reactants?

the point of the most rapid pH change

The estimate of the equivalence point can be detected as what?

1.) Air bubbles may be trapped in the stopcock of the buret tip 2.) Not reading the buret volume at eye level 3.) Over or underestimating the end point color

What are the sources of error associated with the use of a buret?

Rinsing with deionized water; rinsing with the titrant

The two steps of cleaning the buret

The volume from the rapid titration can have 4 mL subtracted and immediately added to the accurate titration

How does the rapid titration help with the accurate titration?

drop by drop

After the volume from the rapid titration is added to the accurate titration, how must the NaOH be added?

Final volume - initial volume (in the buret)

formula for volume of NaOH used

1.) Calculating the moles of NaOH from mL 2.) Using the 3:1 ratio of NaOH:citric acid to find moles of citric acid 3.) Divide moles from Step 2 over liters of soda used to find molarity

What are the steps for calculating the molarity of citric acid?

with a solution of known pH (7.0)

How is the pH electrode calibrated?

1.) No indicator is used; the pH probe is instead 2.) A 250-mL beaker is used instead of the Erlenmeyer flask

What are two of the main changes in setting up the modern titration?

a pH of about 8.5

What is the estimated equivalence point for citric acid?

From 6.0 to 11.0

From which pH values is NaOH being added drop wise?

20 data points

In the pH range of 7-10 you should have about how many data points?

the peak of the first derivative (the long, tall line in the graph)

On LoggerPro, what corresponds to the volume of NaOH at the estimated equivalence point?

X-Axis: titrant volume Y-Axis: pH

In the graph of Experiment #5-2, what goes on the x-axis, and what goes on the y-axis?

Hydrochloric Acid (8M)

Which solution in Experiment #6 is highly toxic if swallowed or inhaled, or corrosive to the skin and eyes

Into the appropriately labeled containers in the fume hood

How should you dispose of the solutions in Experiment #6?

chemical reaction

occurs when a substance is converted into a different substance; the products have properties that differ from each other and the original substance

precipitation, acid-base reactions, and oxidation-reduction (redox) reactions

three most important types of reactions in general chemistry

net transfer

In redox reactions, there is a ... of electrons from one reactant to another.

combination

a redox reaction in which two or more reactants form one product

decomposition

a redox reaction in which one reactant decomposes into two or more products

displacement

a redox reaction in which the number of substances remains the same during the reaction, but atoms or ions exchange places

single-displacement reaction

a displacement reaction in which one element displaces another element from a compound; all are oxidation-reduction processes

oxidation

loss of electrons

reduction

gain of electrons

reducing agent

a substance that is oxidized and causes a reduction

oxidizing agent

a substance with is reduced and causes an oxidation

oxidation number

developed as a "bookkeeping" method to keep track of which atoms gain electrons and which atoms lose electrons in redox reactions; can be used to determine which species are reduced and oxidized, and are also helpful for balancing equations

+2, -1

In OF2, what is the oxidation number of O? In peroxides, what is the oxidation number of O?

To establish the relative chemical reactivity of several metals and hydrogen as reducing agents

What is the purpose of Experiment #6, about the reactions in the wellplate?

no

If a metal is less active than the one it is trying to replace, ... reaction will occur.

molecular equation

the equation that shows all the reactants and products as if they were intact, undissociated compounds

total ionic equation

shows all of the soluble ionic substances dissociated into their component ions

spectator ion

an ion that is not involved in the chemical reaction; same on both sides of the total ionic equation, not present in the net ionic equation

net ionic equation

an equation that eliminates all spectator ions and shows the chemical reaction in its simplest form

a color change; deposition of the displaced metal on the surface of the reactive metal

signs of a chemical reaction in Experiment #6

Fe is more active than Pb; Fe is a stronger reducing agent

What does Fe>Pb mean?

it allows one to make predictions regarding metal displacement reactions without having to actually conduct the experiment

Why is an activity series a useful tool?

microscale laboratory techniques

techniques that involve much smaller volumes of solutions that allow you to carry out the experiments quickly, safely, and with less waste than with traditional laboratory methods; a microplate was used in Experiment #6

color changes, solid formation, solid dissolution, gas formation, and whether the reaction is slow or vigorous

What should be included in observations written in your notebook for Experiment #6?

False- some occurred immediately, and some took up to 20 minutes to occur

True or False: All reactions occurred at the same speed during Experiment #6.

It gets rid of excess aluminum so the amount of elemental copper can be determined

Why is HCl used in Experiment #4?

quantitative transfer

a method of transferring a solution to another container that involves rinsing the original container with deionized water and adding the rise to the new container with the rest of the solution; prevents loss of sample

NO2

Nitric acid reacts with metals to form this poisonous brown gas that stains the skin yellow/brown

NH3 (concentrated ammonia)

Which chemical in Experiment #7 is corrosive?

2.50%

The percentage of copper in a penny authorized by Congress is now what?

nitric acid

Since Cu is less active than H, a stronger oxidizing agent is required to oxidize Cu. What is this agent?

Nitrogen dioxide gas, and two complex ions: [Cu(NH3)4(H2O2)]2+ and [Zn(NH3)4(H2O2)]2+

What three things does the oxidation of copper and zinc with nitric acid produce?

Cu ion: deep blue Zn ion: colorless

What are the colors of the complex ions in Experiment #7?

To determine the concentration of copper without interference from the much larger concentration of zinc found in the penny

The colorlessness of the Zn ion provides an opportunity for what?

different

Compounds and ions that have color absorb visible light at ... wavelengths.

spectroscopy

uses the interactions of matter and light to determine the concentration of colored solutions

spectrometer

an instrument that measures how much light energy, of a particular wavelength, is absorbed or transmitted by a sample placed in the light beam of the instrument.

directly; identification

Absorbance is ... proportional to the concentration of the light-absorbing species in a sample at a particular wavelength. It can be used for ... purposes.

transmittance

the fraction of the original light intensity that is not absorbed by the sample; has a range from zero to one

smaller

The more light the sample absorbs, the ... the percent transmission.

A = abc

Beer-Lambert Law

less

More concentrated/more intensely colored solutions will transmit ... light.

calibration curve; interpolation

In Experiment #7, the spectrometer will be used to measure the absorbance of known concentrations of solutions containing the complex copper ion. This establishes a ... and allows for the ... of the unknown value of copper in the penny.

increase

As the amount of Cu2+ increases in the solutions, I expect the absorbance values to...

fume hood

Because of the toxicity of dinitrogen oxide, where must the reaction between nitric acid and the penny take place?

concentrated ammonia; blue to colorless

After the penny-HNO3 solution has been transferred out of the beaker in Experiment #7, still in the fume hood, add 14 mL of what to the volumetric flask? What color change does this produce?

Five, plus the blank solution

How many solutions/calibration standards were made during Experiment #7 to determine the amount of copper in the penny?

1.) A unique amount of stock Cu2+ solution (zero for the blank solution) 2.) 3 mL of concentrated ammonia 3.) Deionized water to the fill line

Each volumetric flask that was prepared in Experiment #7 contains which three things?

To get rid of any fingerprints or liquids on the outside that may mess with light transmission and accurate readings

Why do you wipe the outside of the cuvettes?

least; most

In Experiment #7, you'll take absorbance measurements from ... concentrated to ... concentrated.

X-Axis: concentration Y-Axis: absorbance

In the experiment to determine the percent copper in a penny, what goes on the x-axis, and what goes on the y-axis?

g Cu (penny) = [measured concentration of Cu g/L] * [L of measured soln in volumetric flask]

Equation for mass of Cu originally in your penny

(mass of Cu) / (mass of penny)

Equation for mass percent of Cu in the penny

delta E + P*deltaV

delta H equals... (in terms of internal energy, pressure, and volume)

the heat gained or lost by a system at constant pressure

delta H = q where q is...

lost; increase; exothermic

If delta H is less than 0, heat is ... by the system to the surroundings, the surroundings ... in temperature, and is ....

remove; decrease; endothermic

If delta H is greater than 0, the reaction would ... from the surroundings, the temperature of the surroundings would ..., and the reaction is said to be ....

calorimeter

a device that can measure the amount of heat given off or absorbed by a reaction

heat capacity

The temperature change experienced by an object when it absorbs or loses heat is determine by what?

specific heat capacity

the amount of heat required to raise the temperature of 1 gram of the material by 1K/degree C

m*C*delta T ; C*V*d*delta T

q = ?

water

The calorimeter that we used in Experiment #8 uses what are the medium that absorbs or loses heat?

Same numerical value, but opposite signs (-qrxn = qaq

What is the relationship between the heat absorbed the calorimeter and the heat generated by the reactoin?

exothermic

In Experiment #8, if the temperature of the solution increased during the reaction, the reaction was what?

endothermic

In Experiment #8, if the temperature of the solution decreased during the reaction, the reaction was what?

being inside multiple polystyrene coffee cups and having air space between the coffee cups and the beaker

What allowed the calorimeter to be well-insulated in Experiment #8?

qualitative; quantitative

In Experiment #8, we performed both ... and ... evaluations.

exothermic

The best candidates for hot packs are ... salts.

endothermic

The best candidates for cold packs are ... salts.

The salts readily absorbed water from the air and would have been changed.

When obtaining the salt to test for Experiment #8, the salt containers had to be capped quickly; why was this?