Studied by 35 peoplelinear 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
Note
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