CHM144 Final Exam

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260 Terms
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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...?
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 ...?
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
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 ?
Exact numbers have an ... amount of sigfigs and should not be factored into determining how many sigfigs a calculation should have.
You should always carry ... significant figures through a calculation than you will need at the end.
the degree of agreement between a measured value of a quantity and the "true" value of that quantity. (arrows hitting the bullseye)
the degree of agreement among several measured values of the same quantity (arrows hitting the same spot, even if it's not the bullseye)
Systematic errors affect the ... of the measurement.
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
the sum of data points divided by the number of data points (average)
the central member of a series of data points, arranged in order of magnitude; especially useful when suspecting an outlier
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
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?
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
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
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 ....
degrees of freedom for comparison of two independent measurements of the same quantity
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 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?
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)
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?
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?
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.
a redox reaction in which two or more reactants form one product
a redox reaction in which one reactant decomposes into two or more products
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
loss of electrons
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?
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
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?
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?
Compounds and ions that have color absorb visible light at ... wavelengths.
uses the interactions of matter and light to determine the concentration of colored solutions
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.
the fraction of the original light intensity that is not absorbed by the sample; has a range from zero to one
The more light the sample absorbs, the ... the percent transmission.
A = abc
Beer-Lambert Law
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.
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 ....
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 = ?
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?
In Experiment #8, if the temperature of the solution increased during the reaction, the reaction was what?
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.
The best candidates for hot packs are ... salts.
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?