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