chem 101 lab study set
Solid KOH is being dissolved in water: Identify the system and the surroundings. If this reaction is exothermic, what happens to the heat of each species?
- the system is the KOH and the surroundings are the water and the container -the reaction is exothermic (releases energy)
You sealed an Erlenmeyer flask that was determined to have a volume of 272.2 mL with a stopper. The density of air at 25 °C is 0.001185 g/mL. Air has an effective molar mass of 28.96 g/mol. What amount of air was sealed in the flask?
0.01114 mol <--- dimensional analysis to get moles
You measure NaOH by difference using an analytical balance. The initial mass of the NaOH bottle is 5.042g. After removing the NaOH, the bottle mass is 4.812 g. What is the mass of the NaOH you are using? (use correct significant figures).
0.2300. Initial mass- final mass = mass you are working with
Use the trend line A = 17453C + 0.0745 to calculate the concentration of a solution that has an absorption of 1.0, where Aand C are absorption and concentration, respectively.
5.3e-5 M
A solution absorbs 50% of a specific wavelength of light that passes through it in a spectrophotometer. What is the %transmittance and absorbance at this wavelength for this solution?
50%
Define the variables in Beer's law:
A: absorbance- the itensity of light that passes through the cuvet.ε: Molar Extincion Coefficient- how well the mixture absorbs a certain wavelength of light.ι: Path Length- for this experiment it is 1.000 cm.C: Concentration- in this case concentration of the mixture in mol/L.
what is the difference between an ideal and real gas?
An ideal gas is a theoretical gas composed of many randomly moving particles that are not subject to interparticle interactions. A real gas is simply the opposite; it occupies space and the molecules have interactions.
true or false: molecules from the liquid to the vapor phase, the average kinetic energy of the solution is lower and the temperature of the solution is higher than the original solution
As molecules escape from the liquid to the vapor phase, the average kinetic energy of the solution is higher and the temperature of the solution is lower than the original solution. (false: the opposite of the statement given)
energy of a photon equation
E=hc/wavelength
What is the name of the law that relates temperature a pressure?
Gay-Lussac's law, Amontons' law or the pressure law
Why does ice float on water?
Ice is less dense than water
After measuring the absorbance vs Concentration (and working with the same spectrophotometer), you realized you hadworked with a wrong max wavelength. Which of the following will get affected in the regression line for the calibration curve?
Slope of the absorbance vs Concentration plot
what are the characteristics of an ideal gas?
The gas particles have negligible volume. The gas particles are equally sized and do not have intermolecular forces (attraction or repulsion) with other gas particles. The gas particles move randomly in agreement with Newton's Laws of Motion.
In experiment 5, you were asked to fill up the pipet bulb with water before adding the gases. Why did you need to do this?
The water will capture and dilute the water/yeast/acid displaced by the gas bubbles you will be generating this is because oxygen gas has very low solubility in water and therefore can be collected as gas
calculating mean/average
To calculate the mean you need to add all the numbers in the set and then divide by the number of items in the set--> average
how does temperature affect the density of a solution
When a liquid or gas is heated, the molecules move faster, bump into each other, and spread apart. Because the molecules are spread apart, they take up more space. They are less dense.
what is a decomposition reaction
When something is broken down into smaller molecules (AB→A+B) ex. hydrogen peroxide decomposed by catalase.
After you finish collecting your absorbance readings on the spectrophotometer, you notice a dark smudge on your cuvette you used to blank while doing a Beer's Law experiment. How would you expect this to have affected your absorbance readings on samples you ran after the blank?
Your absorbance readings for all the others would be lower because the absorbance reading from your blank cuvette would be higher
oxidation states
a concept that provides a way to keep track of electrons in oxidation-reduction reactions according to certain rules. know how to solve for one
discrete light source
a light source with strong and distinct lines
continuous light source
a light source without strong discrete and distinct lines
would a small ΔHvap or a large ΔHvap in a larger change in temperature
a small enthalpy of radiation
What is a precipitate?
a solid that forms and settles out of a liquid mixture
Anelectronmovesfromthegroundstate(n=1)toanexcitedstate(n=5),isthisemissionorabsorbance,isthechangeinenergy positive or negative, and describe the relative stability of the electron after the transition.
absorbance, positive energy change, less stable - farther from the nucleus. emission and negative energy change when the energy state decreases
Which of the following represents possible sources of error during this experiment? (Select all that apply.) for the ideal gas experiment
air was used as a model of an ideal gas air leaks in the pressure/temperature apparatus.
systematic error
an error that always occurs in the same direction
random error
an error that occurs when the selected sample is an imperfect representation of the overall population
Explainthedifferencebetweenastoichiometricreactionandacatalyticreaction,giveoneexampleforeachthatwasnotpart of your experiments (be specific with a type of redox, combustion, or acid-base reaction).
catalytic reagents are not consumed during the reaction, whereas stoichiometric reagents are consumed during the reaction
The following reaction is an example of what type of reaction? 2H2 +O2➔2H2O
combination reaction
calculating the cv
cv = standard deviation/ sample population x 100
If the experimenter made a mistake and put lithium chloride in the beaker and silver nitrate in the buret how would theslope of the first and second lines change?
d. The slope of first line would be positive and the slope of the second line would be negative
when should you not wear gloves in the laboratory setting?
gloves should not be worn when dealing with the computer or other personal items; when taking notes
Looking through your spectroscope, you see several discrete, clearly defined lines. What is a possible source for this spectrum.
fluorescent lamp
when a species gets reduced it...
gains electrons
which noble gas is the most ideal and which is the least? why?
helium because it has a full electron shell and unlike the other noble gases, it exists as a single atom (lower dispersion)
If molecule A has an enthalpy of vaporization, ΔHvap, that is larger than molecule B, what does this imply about the intermolecular forces of molecule A relative to molecule B?
higher
define accuracy
how close a measurement is to the true value
define precision
how close a series of measurements are to one another
Does calibration using standards help to improve the accuracy or the precision of the experiment?
it provides more accurate results
density formula
mass/volume
Methanol (CH3OH) possess a larger ΔHvap than methane (CH4) due to
methanol has stronger IMFs than methane because it is a polar molecule that can form hydrogen bonding
For several molecules with the same chemical formula, how does the degree of branching influence the relative intermolecular forces? Why?
more branching decreases the surface area and there is therefore less of a chance for IMFs to form; less collision
You are taking an evening laboratory session and want to bring a snack to help you make it through the evening. When should you be allowed to have food at the bench top in the lab?
never, eating in the lab is not allowed
The Rydberg constant is a value useful for calculating the change in energy involved in electronic transitions between an excited state and a state where nf=2 in hydrogen atoms. Can the Rydberg constant be applied to determine changes in energy observed in mercury emission lines using the same relationship?
no because mercury has many electrons with many possible final energy states.
What experimental components hindered the launch of the pipet rockets in Experiment 5?
reaction c is a combustion reaction which is very exothermic and releases enough energy to fuel the rocket. this is the combination of the hydrogen and oxygen gas produced in reaction a and b
You make a solution of 0.1 M NaOH and accidentally spill the solution, covering your gloved hand and onto your arm. Your wrist was exposed, and the solution came into direct contact with your skin. What should you do?
skin contact can produce burns, so, we must (like most chemicals) rinse immediately at the water faucets at the sink where the skin was exposed to corrosive materials. If you are exposed to alot of it there is a shower at the fron of the room
standard deviation formula
sqrt(sum of squares of the deviation from the mean/n-1)
would weaker or stronger intermolecular forces have a higher change in temperature
the presence of stronger IMFs result in a high boiling point and a lower melting point and therefore a larger change in temperature
What is the definition absolute zero? What does this imply about the pressure at absolute temperature?
theoretical temp where there is no motion & no heat; no pressure
describe the behavior of a photon
they behave in a wave-like manner as well as acting as particles
Why is a catalyst needed in the decomposition of hydrogen peroxide into water and oxygen?
this process is generally very slow, especially as the presence of water increases. the catalase in the yeast makes the reaction faster
What is the purpose of blank in Beer's law experiment?
to calibrate the spectrometer by setting the absorbance of the blank cuvette
What's the purpose of a calibration curve?
to create a linear equation and r-squared value to help solve for the unknown concentration of each Gatorade and Powerade sample.
A solution containing an unknown metal ion is sprayed into an open flame, giving rise to an orange color by eye. Upon researching metal ions which burn with this color, you find several candidate ions which also burn orange and are unsure how to identify the unknown. What test(s) would you perform to identify the identity of the unknown?
use a spectrometer to the find the wavelengths corresponding to peaks in % transmittance vs wavelengths; compare that known metals to find the identity.
What volume of a 3.0 x 10-3 M solution is needed to prepare 50.0 mL of 5.0 x 10-5 M; how many moles of solute are in thissolution?
volume needed: 8.3e-4 Lmols: 2.49e-6 mols
What causes absorption?
when an electron moves to a higher energy level absorption occurs when radiation passes through a gas.
