CHEM 111 Lab Practical
Does not contain a polyatomic ion
-Sodium phosphide -SO3
What statements are always true about limiting reactants?
-The limiting reactant is completely used up in the reaction -The limiting reactant dictates the amount of product -There will be an excess of other reactants at the end of the reaction
What is the correct reading of the volume in the pictured buret?
39.95 mL -always go one estimated digit past the smallest marking noticing where the bottom of the meniscus falls between the tick marks
Balance equation: Choose a coefficient for every compound, even if the coefficient is one. ___ MgCl2 + ___ KOH —> ___ Mg(OH)2 + ___ KCl
1, 2, 1, 2
What is the correct net ionic equation to describe this precipitation reaction? Co(NO3)2 (aq) + 2NaOH (aq) —> 2NaNO3 (aq) + Co(OH)2 (s)
CO2+ (aq) + 2OH- (aq) —> Co(OH)2 (s)
Identify resources that can be used to obtain reliable chemical info
Encyclopedias and tables, peer-reviewed journal articles, reference handbooks
Before lab, students should
Set up their lab notebooks to record data during lab
To use a spectroscope, position the tool to allow light to enter through the ________. The light will reflect off the _________________, which separates it into colors. View the results on the ___________.
Slit, diffraction grating, wavelength scale
Identify the main reason for adding solvent slowly to a volumetric flask
So that the liquid does not exceed the volume marking on the flask
After using a match and putting it out in lab, what should you do next?
Soak the match in a beaker of water
Solution A contains 1.0 moles of MgCl2. Solution B contains 1.0 moles of NaOH
Solution A has greater conductivity
Solution A contains 1.5 moles of C6H12O6, Solution B contains 1.5 moles of NaCl
Solution B has a greater conductivity
Contains a polyatomic ion
-KCN -Calcium hydroxide -NH4Cl -Magnesium sulfate
Scientific Process
the investigation of rational concepts that can be evaluated by observation and experimentation
A sample prepared for measurement in a spectrophotometer that contains both solute and solvent
Sample solution
Why is it important not to leave fingerprints or scratch the sample cells in spectrophotometric measurements?
Scratches and fingerprints on the surface of the cell can decrease the amount of light that reaches the detector
What chair components will be leftover after making as many chairs as possible?
Seats and backs
Consider the balanced equation for the combustion of benzene, C6H6. 2 C6H6 + 15O2 —> 12CO2 + 6H2O What molar ration will appear when calculating the amount of O2 needed to react with a given amount of C6H6?
(15 mol O2)/(2 mol C6H6)
Identify techniques to be used for accurate solution preparation using a volumetric flask.
-after the solvent is added, stopper and invert the flask to mix the solution -read the liquid volume at eye level from the bottom of the meniscus
Electron microscopes
-allow for greater magnification -use electrons to create an image
What protocols are suggested to best perform the color test of different compounds in flame?
-keep wood handle of the applicator away from the flame -be prepared to observe the flame by eye and with the spectroscope
When lighting a candle, which part undergoes each listed change? -Provides the energy to start the burning: ___________ -Starts to melt from solid to liquid: _________ -Where the flame appears: _________
-match -wax -wick
relates to frequency
-often measured in units such as Hertz (Hz) -increases as energy increases -a measure of cycles per unit time
relates to wavelength
-often measured in units such as nanometers (nm) -increases as energy decreases -a measure of distance
Optical microscopes
-optical microscopes use light to create an image -optical microscopes generally tend to be simpler and less expensive
Keeping a lab notebook
-record maximum number of significant figures -write down all pertinent experimental observations -record info neatly, top to bottom in notebook -correct any errors as soon as possible
Possible issues if a sample in a spectrophotometer gives no reading
-the sample may be placed improperly in the cuvette holder -there may be an issue with composition of the sample -there may be an issue with the spectrophotometer -the wrong wavelength may be set
Identify the aspects of the pictured graph that are missing or contain errors.
-x-axis label (need specific measurements) -title (need one) -y-axis numeric range (didn't start at 0)
A certain type of light has a wavelength of 256 nm. What is this value in meters?
0.000000256 -256 nm x 1m/1 x 10^9 nm
How many moles of HCL are in 47.3 mL of a 1.65 M HCL solution?
0.078 mol -M= moles/V -moles = MV -1.65 M x 47.3 mL x 1L/1000 mL
Glucose (molar mass=180.16 g/mol) is a simple, solvable sugar. Glucose solutions are used to treat patients with low blood sugar. Suppose you prepare a glucose solution using the described procedure -step 1: dissolve 221.4 g to glucose in enough after to make 500.0 mL of solution -step 2: transfer 20.8 mL of the solution to a new flask and add enough water to make 250.0 mL of dilute solution What is the concentration (in M) of the glucose at the end of the procedure?
0.205 M -moles of glucose = 221.4 g glucose x 1 mol sugar/180.16 g sugar -volume in liters = 500.0 mL solution x 1L/1000mL -M1V1=M2V2 -(molarity from step 1)(20.8 mL)=(M2)(250.0 mL) -M2= (molarity from step 1)(20.8 mL) / 250.0 mL
Suppose you prepare a spectrophotometer sample by adding enough water to 5.14 mL of the stock solution to make 100.0 mL of solution. If the spectrophotometer experiment indicates the dilute sample has a concentration of 0.0108 M, what was the concentration of the stock solution?
0.21 M -(M1)(5.14 mL) = (0.0108 M)(100.0 mL) -M1= (0.0108 M)(100.0 mL)/(5.14 mL)
The molar absorptivity of a compound at 500 nm wavelength is 252 M-1cm-1. Suppose one prepares a solution by dissolving 0.00140 moles of a solute in enough water to make a 500.0 mL solution. What would be the absorbance in a 3.00 mm path-length cell?
0.212 -0.00140 moles/0.500 L = 0.00280 M -A= Ecl -A= (252 M-1cm-1)(0.00280M)(3.00mm x 1cm/10mm)
A sample of limestone contains 0.980 g CaCO3. The sample is crushed and placed in a beaker with 10.0 mL of 1.00 M HCl. Predict the yield, in grams, of CaCl2
0.555 g -0.980 g CaCO3 x 1mol/100.087 g = 9.79 x 10^-3 mol CaCO3 -10.0 mL HCl x 1L/1000mL x 1.00 M = 0.01 mol HCl -CaCO3 + 2 HCl —> CaCl2 + H2CO3 -0.01 mol HCl x (1mol CaCl2/2mol HCl) x (110.98 g CaCl2/1 mol CaCl2) = 0.555 g CaCl2
The absorbance of a solution is 0.255. What is its transmittance?
0.556 -A= -log10(I/I^0) -10^-0.255= 0.556
What would be the absorbance of the solution having a transmittance of 1.500%
1.82 -transmittance = I/I^0 -A= -log10(I/I^0) -A= -log0.01500
Suppose you measure the absorbance of a yellow dye solution in a 1.00 cm cuvette (b=1.00cm) The absorbance of the solution at 427 no is 0.54. If the molar absorptivity of yellow dye at 427 nm is 27400 M-1cm-1, what is the concentration of the solution in M?
1.97x10^-5 -A= Ebc -c=A/Eb -c= 0.54/27400 M-1cm-1 x 1.00 cm
In the Imaging and Sizing Gold Nanoparticles procedure, you will begin the measurement process by first setting the scale bar to _________. Next, you will draw a line _____________ of the particle you want to measure. Press _________, and record the value in the __________ column.
100 nm, across the longest edge, m, length
How many chairs can you make with the 12 seats, 15 backs, and 44 legs?
11
Examine the given Beer's law standard curve for an unknown dye measured in a 1.0 cuvette. What is the molar absorptivity (in M-1cm-1) of the unknown dye at 542 nm?
15200 -A=Ebc -A=(slope x c) + y-intercept -slope=Eb
When each formular unit of potassium carbonate, K2CO3, dissociates into ions in solution, there is ____________ of the ___________ cation and ____________ of the _____________ anion
2 ions, potassium, 1 ion, carbonate
Suppose you measure the absorbance of a yellow dye solution in a 1.00 cm cuvette (b=1.00 cm). The absorbance of the solution at 427 nm is 0.77. If the molar absorptivity of yellow dye at 427 nm is 27400 M-1cm-1, what is the concentration of the solution of the solution in M?
2.8x10^-5 M (c=0.77/27400 M-1cm-1 x 1.00 cm)
Calculate the grams of ethane in a sample containing 0.6697 moles if the molar mass of ethane is 30.067 g/mol.
20.14 g -mass of substance = moles of substance x (molar mass in grams/1 mol of substance)
Suppose a student starts with 2.3702 g of a sand mixture and separates the components into 1.3012 g of NaCl, 0.5072 g SiO2, and 0.4503 g of CaCO3. -based on the amount of recovered, what is the percent of SiO2 in the starting mixture?
21.40% -% composition = (mass of mixture of mixture component/total mass of mixture) x 100% -% of SiO2 = (0.5072 g/ 2.3702 g) x 100
Light Emmison
2nd lab
Consider the structure of methyl orange, which is a monosodium salt in the solid form. What is the molar mass of the solid methyl orange?
327.32 g/mol -C14H14N3O3S- -(1 x 23.00 g/mol) + (14 x 12.01) + (14 x 1.01) + (3 x 14.01) + (3 x 16.00) + (1 x 32.01) = 327.32 g/mol
Indicator
A reagent added to the analyte solution that changes color when the reaction is complete
Components of Bunsen burner
A: (top) barrel B: (middle) air inlet C: (side valve) gas inlet D: (bottom) gas regulator
What type of plot can be used to determine lambda max of a solution?
Absorbance vs. wavelength
When an electron moves up to higher energy levels, the atom ____________ a photon of light whereas the atom __________ a photon of light when an electron drops to a lower energy level. -the photons emitted from an atom appear as _________________.
Absorbs, emits, a line spectrum
When diluting acid with water, it is important to always as the __________ to the __________
Acid, water
Oil floats on top of water
Added oil joins the top layer
Titration: completely open
At the beginning
A sample prepared for measurement in a spectrophotometer that contains only the solvent
Blank solution
When a Bunsen burner is properly adjusted, what should the flame look like?
Blue with no gap between the burner and the flame
Solution A is 10.0 mL of 0.1 M ethylene glycol. Solution B is 25.0 mL of 0.1 M ethylene glycol
Both solutions have the same conductivity
When observing color bands across a spectrum, the intensity corresponds to the ____________ of the band. If no band is visible in a region, record the region as having ______ intensity.
Brightness, no
In order to use a piper, place a ___________ at the top of the pipes. Use this object to fill the pipes that the ___________ of the liquid is even with the volume line. Release the liquid, touching the tip of the pipet to the sude of the container if necessary to release the last drop ________ the pipet tip.
Bulb or pump, meniscus, outside
Light scattering occurs when incident light hits a material and ______________. When light hits a homogeneous solution, light tends to ____________, and when light hits a sample with particles, light tends to ___________.
Changes its path to a new direction, pass through, scatter
Titration: partially open
Close to be calculated endpoint of a titration
Observations not necessary to record
Color of work surface, number of participants in lab
How should you prepare a buret for titration before loading it with titrant?
Condition the buret with titrant solution
Titration: completely closed
Conditioning the buret with titrant, filling the buret with the titrant
Identify the items needed to run a spectrophotometry experiment.
Cuvette, blank solution, sample solutions, spectrophotometer
Then, the light travels to the ____________, which measures the intensity of light reaching it.
Detector
The spectrophotometer includes a light source, which is passed through a ___________, which isolates a single wavelength to pass through an aperture to reach the ____________.
Diffraction grating, sample cuvette
What should be done if a spectrophotometer reports an absorbance that is too high?
Dilute the sample
What should be done is a spectrophotometer reports an absorbance that is too high?
Dilute the sample
Buret
Glassware that allows a solution to be precisely and slowly added to another solution
Some elements produce distinct colors in flame. What is the cause of this phenomenon?
Heat excites an electron from the element into a higher energy state. The electron then returns to its ground state, releasing energy corresponding to the wavelength of the color seen.
What relationship between frequency and wavelength of electromagnetic radiation?
Inverse
What qualifies a particle to be considered a nanoparticle?
It has a diameter in the nanometer range
In the process of resting nanoparticles, you will use both a reducing agent and an oxidizing agent. The reducing agent reduces _____________ and causes the ___________ of nanoparticles. The oxidizing agent oxidizing agent oxidizes ______________ and causes the __________ of the nanoparticles.
Metal ions to solid metal, growth, solid metal to metal ions, capping
If you double the wavelength of light, what happens to the energy of the photons?
It will decrease by one-half
Identify the products for the reaction of lead (II) nitrate (Pb(NO3)2(aq)) and potassium iodide (KI(aq))
KNO3 (aq), PbI2 (s)
What action is NOT necessary before lighting a Bunsen burner?
Leave the gas cock open for a few minutes before lighting to clear the line
Suppose that you need to build as many chairs as possible. Each chair requires one seat, one back, and four legs. If you have 12 seats, 15 backs, and 44 legs, which of the chair components limits the number of chairs you can make?
Legs
Observations that should be recorded
Length of time, appearance, color or temperature, mass or volume
The relationship between absorbance of light by a solution and its concentration should be ___________ so that when concentration increases, absorbance ____________
Linear, increases
The relationship between absorbance of light by a solution and its concentration should be ____________ so that when concentration increases, absorbance increases
Linear, increases
When working with laser pointers, what is the most important safety consideration?
Looking directly at the laser beam can damage your eye and vision
After clamping a buret to a ring stand, you notice that the set-up is tippy and unstable. What should you do to stabilize the set-up?
Move the buret clamp to a ring stand with a larger base
What is the expected size scale of the gold particles in the TEM images?
Nanometers
Food dye dissolves in water but not in oil
Only the bottom layer becomes colored
Identify the color absorbed by a solution that appears the color given
Orange — blue Red — green Green — red Blue — orange
What should students use when writing in their lab notebooks
Pen
Titration
Process of slowly adding a solution to react with another solution and determine the concentration of one of the solutions based on the reaction between them
A powdered drink is made up of citric acid, salt, modified cornstarch, red 40, and calcium phosphate. If you prepare a solution from the powder and place it in a spectrophotometer, which mixture component has the biggest impact on the absorbance reading from the instrument?
Red 40
Consider the given plot of absorbance vs. competition. Which line is the best-fit line to represent the black data points?
Red line (B) -(middle one)
What role(s) does citric acid plat in the reaction used to produce the gold nanoparticles?
Reducing agent and capping agent
Determine what color of light is being absorbed based on the appearance of the solution
Solution appears red — green light is absorbed Solution appears blue — orange light is absorbed Solution appears violet — yellow light is absorbed Solution appears green — red light is absorbed
Analyte
Solution of an unknown concentration that has another solution slowly added to it
Titrant
Solution of known concentration that is slowly added to a solution of unknown concentration
What is the best way to correct an incorrect entry in lab notebook?
Strike through the entry with a single line
To perform the conductivity titration, you will need both a conductivity probe and a buret set up with the reaction mixture. In the proper set-up, the end of the conductivity probe should be ____________, and the tip of the buret should be _________________. Make sure that both the probe and buret are ___________________ so that they are ____________________.
Submerges in the solution, just above the solution's surface, slightly off center of the beaker, not hit by the stir bar
In a spectrophotometer, both absorbance and transmítanse indicate _____________ passing through a sample. A high absorbance corresponds to a _________ transmittance.
The amount of light, low
Why must you use purified water when growing nanoparticles in solution?
The number of ions in solution must be carefully controlled
When filling a burst for a titration, first adjust the buret in the clamp so that ______________. Then, ______________ to ass the titration into the buret. The titration should be filled ____________________.
The opening is near eye level, use a funnel, almost to the zero mark
Why should you always condition a buret before running a titration?
To ensure there is no dilution from water that remains from cleaning
What is the purpose of the candle burning experiment?
To use observations to better understand how candles work
During a lab experiment, which senses should you use to evaluate what is happening?
Touch or feel, smell, hearing, sight
Identify the first step in preparing a spectrometer for use
Turn on the light source and the spectrophotometer
Identify the first step in preparing a spectrophotometer for use.
Turn on the light source and the spectrophotometer
Oil and water do not form a solution when mixed
Two layers are visible
Which has a greater energy, long wavelength red light or short wavelength UV light?
UV light
Arrange the colors of visible spectrum from highest to lowest energy
Violet, blue, green, yellow, orange, red
Endpoint
When the required amount of one solution has been added to the second solution to complete the reaction
Before burning a candle, you might expect to see a _________ and feel a corresponding sensation of ___________. You might also ___________ crackling and __________ burning. While the candle burns, carefully record your _______________ for your specific candle.
a small flame, heat, hear, smell, observations
Fluorescence is the ____________ of a photon of light a substance in ___________ state, returning it to the ____________ state.
emission, an excited, ground