Chem 144 Lab Final
What is the purpose of the "Which Salts Make Good Cold Packs or Hot Packs?" lab?
- to identify salts that serves as reactants in cold and hot packs - to determine the heats of solution for different salts - to determine patterns between the heat evolved or absorbed and the mass of the salt utilized.
What is the concentration of Cu2+ (g/L) in the standard solution you will produce using 0.00 mL of the stock Cu2+ solution? (use correct sig figs)
0.00 g/L BECAUSE 0.00mL: (5.00g/ml)(0.00 L) / 0.05L = 0.00 g/L
What is the concentration of Cu2+ (g/L) in the standard solution you will produce using 2.00 mL of the stock Cu2+ solution? (use correct sig figs)
0.200 g/L BECAUSE 2.00mL: (5.00g/ml)(0.002 L) / 0.05L = 0.200 g/L
What is the concentration of Cu2+ (g/L) in the standard solution you will produce using 4.00 mL of the stock Cu2+ solution? (use correct sig figs)
0.400 g/L BECAUSE 4.00mL: (5.00g/ml)(0.004 L) / 0.05L = 0.400 g/L
What is the concentration of Cu2+ (g/L) in the standard solution you will produce using 6.00 mL of the stock Cu2+ solution? (use correct sig figs)
0.600 g/L BECAUSE 6.00mL: (5.00g/ml)(0.006 L) / 0.05L = 0.600 g/L
What is the concentration of Cu2+ (g/L) in the standard solution you will produce using 8.00 mL of the stock Cu2+ solution? (use correct sig figs)
0.800 g/L BECAUSE 8.00mL: (5.00g/ml)(0.008 L) / 0.05L = 0.800 g/L
What is the concentration of Cu2+ (g/L) in the standard solution you will produce using 10.00 mL of the stock Cu2+ solution? (use correct sig figs)
1.00 g/L BECAUSE 10.00 mL: (5.00g/ml)(0.010 L) / 0.05L = 1.00 g/L
how do monoprotic acids react with bases?
1/1 stoichiometry
What is the angle for a Tetrahedral EPA?
109.5
What is the angle for a Trigonal Planar EPA?
120
How many valence electrons are present in the CS2?
16
What is the angle for a linear EPA?
180
single bonds represent how many valence electrons being used?
2 per single bond
Describe the modern calorimeter process.
2 polystyrene cups were placed inside of each other with a lid, a rubber stopper, a temperature probe, and a glass stirring rod. The calorimeter was placed in a beaker for support. The temperature probe was connected to LabQuest and this program recorded the temperature every 15 seconds until the temperature was stable. We added 100 mL of distilled water into the calorimeter measured the stable temperature, and then added the salt and stirred the solution measuring the temperature every 15 seconds until the temperature was stable.
Describe the traditional calorimeter process.
2 polystyrene cups were placed inside of each other with a lid, a rubber stopper, a thermometer, and a glass stirring rod. The calorimeter was placed in a beaker for support. We added 100 mL of distilled water into the calorimeter measured the stable temperature, and then added the salt and stirred the solution measuring the temperature every 15 seconds until the temperature was stable.
For Part 2, Gay-Lussac's Law, the initial water bath should be ~ ______ K
273
In the acid base reaction of aqueous citric acid with aqueous sodium hydroxide. How many moles of base are needed to react with (neutralize) one mole of citric acid?
3
Citric acid is a triprotic acid (polyprotic) which means what?
3 moles of base are needed to completely neutralize one mole of citric acid 1/3 stoichiometry
Explain the penny lab
3 pennies were weighed and qualitatively observed. In the fume hood, each penny was placed in a 150 mL beaker and 25 mL of 6 M HNO3 was added to the pennies. They dissolved in the fume hood. Next, 0.00, 2.00, 4.00, 6.00, 8.00, and 10.00 mL of stock Cu2+ solution was measured into volumetric flasks. 3 mL of 15 M ammonia was added to each volumetric flask. The dissolved pennies were quantitatively transferred into 3 separate 100 mL volumetric flasks. 14 mL of ammonia was added to the volumetric flask using a graduated cylinder and was then swirled. The swirling created a dark blue color. Each penny sample was put in a cuvette. Blank solution was used to calibrate the spectrometer. Then all the solutions of Cu2+ were placed in the spectrometer and the absorbance wavelength was recorded. This was then performed on the penny cuvettes too. Interpolation was used to determine the amount of Cu in each penny sample. The grams of Cu in the original penny was then calculated.
During part 3, Charles' Law, what is the Vtubing ?
4.0 mL
The Cs of dH20 is?
4.184
In Part 1, Boyle's Law, for each reading, the volume of air in the syringe should be decreased by ____ mL
5
Including both rapid and accurate titrations, how many trials will you conduct in week 1, Procedure 1 (Traditional Titration Using an Indicator Dye)?
5
Explain Part 1, qualitative heat studies, of the salt lab.
5 salts were obtained in 5 separate test tubes. 7-8 mL of water was added to each test tube and the contents were swirled to ensure mixing. We touched the outside of each test tube to see if it got warmer or colder or if there was no change. We recorded our observations in a table. Salts that felt cold to touch got a + sign and salts the felt warm to touch got a - sign in the table. Results were compared with other groups.
These six solutions are prepared by diluting a Cu2+ stock solution of _______ g/L
5.00
In Part 1, Boyle's Law, the initial volume of the air in the syringe is set to ______ mL
55
What is the pH for the endpoint of a strong acid (HCl) being titrated by a strong base (NaOH)?
7.0
For the acid-base reaction of citric acid and sodium hydroxide, the equivalence point occurs at which pH?
8.5
What is the angle for a Octahedral EPA?
90
What is the angle for a Trigonal Bipyramidal EPA?
90, 120
What happened during the Boyle's Law (Part 1) experiment?
A 60-mL syringe containing air attached to a ring stand was examined as a pressure sensor read the varying pressure at different volumes of air in the syringe.
For polyatomic ions, the total number of valence electrons must be adjusted for the charge of the ion. _______ one electron for each negative charge
Add
What elements often have FEWER electrons than required by the octet rule?
Be & B
How and why were pennies changed in 1982?
Before 1982, pennies were 95% copper. In 1982, the cost of copper increased so the cost to produce the penny ended up being higher than the face value. So in 1982 and after, the pennies are now made primarily of zinc and the percentage authorized by Congress is now 2.5% by mass.
What elements should always be assumed to satisfy the octet rule?
C, N, O, and F.
Typically what elements are depicted with multiple bonds?
C, N, and O
What is the molecular formula of citric acid?
C6H8O7
In this experiment, you will assign formal charges to individual atoms in your Lewis structures. Equation for Formal Charge is:
FC = # of VALENCE electrons in the neutral atom - (# of NON-BONDED electrons + 1/2x number of BONDING electrions
Explain the Titration calculated by the pH electrode
First the LabQuest device was set up and the pH electrode was calibrated. The buret was cleaned with the same cleaning procedures from the traditional titration. The sodas being titrated were either Orange Crush or Jones Green Apple. 20.00 mL of the soda was measured out and dH20 was added to the soda totalling 100 mL. The soda solution was put in a 250-mL beaker. The beaker was placed in the center of a magnetic stir plate and under the buret with a clean magnetic stir bar placed in the solution. The pH electrode was placed in the solution about 3 cm from the bottom of the beaker and the buret was filled to 0.00 mL with 0.0465 NaOH solution. For the first accurate titration trial, the NaOH was added to the soda solution until the pH reached 6.0 and the volume of the buret was recorded. Next, the NaOH was added in 0.2-0.3 increments and the pH of the soda solution and volume of NaOH was recorded on the LabQuest device in notebooks at every addition. The NaOH was added to the solution until the pH reached 10.5. The Labquest was saved for trial one. The next 2 trials were performed the same. The data from LabQuest was uploaded into Logger Pro into graphs. The titrant volume was calculated using Logger Pro. The molarity of citric acid was then calculated for each trial. The mean and standard deviation was then calculated from the molarity values.
What is one of the most important sources of error in calorimeter experiments? Explain.
Heat loss into the surrounding environment is an important source of error during calorimeter experiments. Since heat is the primary measurement it is an important error. There are many opportunities to lose heat to the environment: - when you add the salt with the lid off - the hole in the lid where the stirring rod is
Why is it important that these reactions are run in 2 polystyrene cups nestled in a beaker?
It acts as an effective insulator and the airspace between the two cups insulates the solution. This is important because the calorimeter needs to be properly insulated to produce accurate measurements.
qaq is also known as what?
Joules
What temperature scale must be used to express the relationships between variables in the gas law experiments?
Kelvin
How do you convert C to K?
Kelvin = Celsius + 273.15
If some of the penny solution had been spilled before transfer to the volumetric flask and dilution to 200. mL the apparent amount of Cu in the penny would have been:
Less than calculated in problem
What is the formula used to find the concentration of each standard solution?
M1V1 = M2V2
How is the number of valence electrons calculated?
On the periodic table, there is an "A" section from IIIA - VIIIA. That tells you the number of valence electron per element in the compound. Add one electron for each negative charge and subtract one electron for each positive charge.
Which soda from set #2 CANNOT be titrated using the traditional (phenolphthalein) method?
Orange Crush
A plot of pressure (P) vs. temperature (T) for an ideal gas shows a linear relationship with a positive slope and an intercept of zero. The equation for this relationship is:
P = mT, because y=mx where y = P, x = T, P=mT (b is zero) (P and T are directly proportional form PV=nRT)
For Gay-Lussac's Law, what is the mathematical relationship?
P1/T1 = P2/T2
For Boyle's Law, what is the mathematical relationship?
P1V1 =P2V2
What is the most common indicator used for titrations of strong acids by strong bases (we used this)?
Phenolphthalein
What happened during the Gay-Lussac's Law (Part 2) experiment?
Pressure changes were examined as a pressure sensor read the varying pressure of air in a sealed 25-mL Erlenmeyer flask in differing temperatures of water.
For polyatomic ions, the total number of valence electrons must be adjusted for the charge of the ion. ________ one electron for each positive charge.
Subtract
∆T = ?
Tf-Ti
Titrations that employ an indicator dye such as phenolphthalein have an inherent limitation to their accuracy because
The end point detected by the titration is not identical to the equivalence point.
calorimetry
The experimental measurement of enthalpy changes for chemical reactions
Explain the traditional titration.
The pH of the citric acid endpoint was calculated by using phenolphthalein indicator dye. The traditional titration was used with a colorless soda (either 7-Up or Sprite). The buret was cleaned with dH20 & 0.0465 NaOH solution. Once the buret was cleaned, the buret was filled above the 0.00 mL mark with the 0.0465 NaOH solution. The volume of the NaOH solution in the buret was adjusted to a little bit below the 0.00 mL mark. 40.00 mL of the soda was measured an poured into a 250-mL Erlenmeyer flask. DH20 was added to the soda in the Erlenmeyer flask until the solution reached 100 mL. Five drops of phenolphthalein indicator dye was then added to the soda solution and the Erlenmeyer flask was placed under the buret. The initial rapid titration began as the 0.0465 NaOH solution was added to the Erlenmeyer flask soda solution in 2 mL increments. The flask was being swirled during the additions of 0.0465 NaOH solution. A pink color persisted once the 0.0465 NaOH solution reached a certain amount of NaOH (near 20 mL). The titrant volume reached the end point and was then calculated. In order to perform the 4 accurate titration trials, 4 mL was subtracted from the titrant volume reached at the endpoint for the initial rapid titration. The 4 accurate trials proceeded like the initial trial did. After all 4 trials were done, a Q-test was performed to see if any needed to be rejected. Next the molarity for the citric acid was calculated for each trial. Lastly, a mean and standard deviation was calculated from molarity values.
Give background on the physical behaviour of an ideal gas.
There are gases all around us. In fact, air is a combination of various gases and each gas has a distinct chemical behavior. Despite their differing chemical behavior, all gases have extremely comparable physical properties, which include four variables. Those variables are temperature (T), volume (V), and pressure (P) and the amount of the gas. The amount of the gas is noted as the number of moles, or n. All four variables are able to be examined by holding two variables constant, while the other two variables' relationship is examined. For this experiment, the relationship between three variables: temperature, volume, and pressure were able to be determined. The number of moles, (n), was constant for all three parts of the experiment. There was a total of three relationships between variables in this experiment, and each relationship is acknowledged as a specific gas law. These gas laws are complementary and able to be united into one relationship, the ideal gas law. The ideal gas law relationship is written as PV=nRT, where (R) is known as the gas constant.
Why do you use 2 polystyrene coffee cups during calorimetry?
This lab will make use of a calorimeter to measure the amount of heat given off or absorbed by a reaction. The calorimeter needs to be well-insulated in order to obtain accurate measurements
For Charles' Law, what is the mathematical relationship?
V1/T1 = V2/T2
What happened during the Charles' Law (Part 3) experiment?
Volume changes of air in a bottle caused by a 20-mL syringe were examined in different temperatures of water while a constant pressure was exerted.
For Charles' Law, what is the formula to calculate Vtotal in the bottle?
Vtotal = Vbottle + Vsyringe + Vtubing
What was the equation for proportionality constant values (k) for Charles' Law?
Vtotal/(T)^n
Water should be carefully excluded from the apparatus used in the properties of gases experiment (#9) because
Water vapor behaves non-ideally at ordinary temperatures and pressures
Explain Part 2, quantitative heat studies, of the salt lab.
We were assigned one exothermic salt and one endothermic salt. We studied these salts at two different masses (4g & 8g) each. We studied one salt with the traditional calorimeter and one salt with the modern calorimeter.
The large excess of Zn present in the penny does not interfere with the measurement of the Cu content of the penny because
Zn(NH3)42+ does not absorb at the wavelength at which the Cu(NH3)42+ is detected.
What is a standard solution?
a known concentration
For the AXmEn notation, what does the n represent?
a nonbonded electron pair on the central atom.
how can pH be measured directly?
a pH electrode/probe
What is the endpoint for citric acid
a pH of about 8.5
Endothermic reactions
absorb heat and have positive enthalpy changes.
A UV-vis spectrophotometer is an instrument that measures how much light energy, of a particular wavelength, is __________ by a sample placed in the light beam of the instrument.
absorbed
u
accepted value
In all of the gas law experiments, why is the number of moles (n) held constant?
all experiments will be conducted on an ENCLOSED sample of air
NH3
ammonia
during the penny lab experiment, when __________ is added to the solution of dissolved Cu and Zn, the solution will turn a deep _______ color. The species responsible for this color is [Cu(NH3)4(H2O)2]2+.
ammonia (NH3); blue
what is a polyprotic acid?
an acid that has multiple acidic protons that can react with a base
what is a monoprotic acid?
an acid that only has one proton available to react with a base
In the calorimetry experiment, why couldn't the Tf be measured directly?
because a small amount of heat is "lost" from the calorimeter
Why will there be only one observable end point for citric acid?
because all three protons of the acid have similar strengths
Your group will need to calibrate the spectrophotometer during the experiment. Which standard solution will be used?
blank solution
Which device is used to both deliver and measure the volume of sodium hydroxide (NaOH) to the citric acid solution?
buret
During part 3, Charles' Law, how is the Vbottle measured?
by disassembling the apparatus, filling the bottle with water, and measuring that volume using a 100-mL graduated cylinder.
what is an example of a polyprotic acid?
citric acid
what was the analyte for the acid base titration lab?
citric acid
The absorption of light energy by a molecular species can be of use for quantitative analysis because the amount of light energy absorbed at a particular wavelength by a compound in solution is proportional to its __________________ in that solution.
concentration
For Charles' Law, what is the proportionality of relationship between the two variables being measured?
directly proportional
For Gay-Lussac's Law, what is the proportionality of relationship between the two variables being measured?
directly proportional
According to the Beer-Lambert law, absorbance is what of the absorbing species in the solution
directly proportional to the concentration
How do you go from mL to L?
divide by 1000
If the temperature of the water decreases when a reaction takes place in aqueous solution, the reaction was ____________.
endothermic
In an experiment, a student measured the initial temperature of 100.0 mL of water to be 22.0 C. By graphical analysis, they found Tf = 16.1 C. Based on the change in temperature, is this an exothermic or endothermic reaction?
endothermic
In an acid-base titration, the _______________ ____________ occurs when the number of moles of acid is stoichiometrically equal to the number of moles of base added to neutralize the acid.
equivalence point
In the data analysis of the quantitative studies you will graph your data using Logger Pro. The initial temperature (Ti) is the temperature at time 0 seconds. The final temperature (Tf) cannot be measured directly and must be obtained by ________________ to time zero.
extrapolation
For Part 2, Gay-Lussac's Law, the temperature of the water bath is varied for each new reading by using ice and/or hot and cold tap water. The goal is to create ______ additional water baths that differ from each other and the original water bath by approximately ____ K
four; 10
Because nitrogen dioxide is produced during the penny lab, the dissolving of the penny must be carried out in the
fume hood
∆H = qp where ∆H is the change in enthalpy and qp is the _____________ gained or lost by a system at constant pressure.
heat
what is qp
heat gained or lost by a system at constant pressure
what are examples of a monoprotic acid?
hydrochloric acid (HCl) & Acetic acid
Before beginning this experiment, each student must write a hypothesis for the pair-wise behavior of an ideal gas for each of the following pairs of variables: pressure-volume (P-V), volume-temperature (V-T), and pressure-temperature (P-T). To do this, use the _____ ______ _____ to predict how the two coupled variables will vary with each other in an experiment in which the other two variables are held constant.
ideal gas law
If the volume of an enclosed gas at constant temperature is decreased the pressure of the gas will:
increase, because they are inversely proportional
Double or triple bonds are used to connect atoms when there are _____________ valence electrons remaining to complete the octets of all atoms.
insufficient
Outside of lab, students will use the equation of the line from the calibration curve and the absorbance values for each penny solution from the group to ______________ the concentration of Cu (g/L) in each penny sample from the group.
interpolate
For Boyle's Law, what is the proportionality of relationship between the two variables being measured?
inversely proportional
When looking at a graph, how do you determine the endpoint in an "S" curve?
it corresponds to the steepest part of the "S" curve
What was the equation for proportionality constant values (k) for Boyle's Law?
k = P/(V)^n
What was the equation for proportionality constant values (k) for Gay-Lussac's Law?
k= P/T(T)^n
exothermic reactions
loses heat and has negative enthalpy changes
Xm
mean
because citric acid is used for tartness what is the concentration compared to other acids?
much higher concentrations, except for carbonic acid
In Experiment #6 you learned that Zn will dissolve in acidic aqueous solutions as Zn2+, but Cu will not dissolve because Cu is less active than H2. A stronger oxidizing agent than H+ is required to oxidize Cu. Aqueous solutions of ________________ are strong oxidizing agents that are capable of oxidizing a number of less active metals, including Cu.
nitric acid
The oxidation of both Cu and Zn (both present in a penny) with nitric acid generates complex ions of Cu and Zn in solution. It also produces ________ _________a brown, toxic gas.
nitrogen dioxide
n
number of measurements
After connecting the atoms, complete the _____ of atoms by adding nonbonded lone pairs to each, beginning with the most _________________ atoms. Be sure not to use more electrons than are available!
octets; electronegative
Any titration requires that the reaction be monitored to determine when the equivalence point has been reached. For acid-base titrations and the experiment you will conduct, the most common methods rely on measuring the:
pH
how can the amount of citric acid be determined once carbonic acid is removed?
quantitatively by acid-base titration
After counting the number of valence electrons, the atoms of the molecule or polyatomic ion should be written/drawn to show the correct connectivity, using __________ bonds to connect adjacent atoms.
single
what was the titrant we used for the acid-base titration lab?
sodium hydroxide or NaOH
When carrying out a chemical reaction in aqueous solution, you can easily monitor the temperature of the water (surroundings). By noting the change in temperature (Tf - Ti), you can calculate the amount of heat (q) that was either lost or gained by the water. To do this, you must also know the mass (m) of the water, and the ________________________ (Cs) of water. The equation is: q = Cs∙m∙(Tf - Ti)
specific heat capacity
The instrument will be used to measure the absorbance of known concentrations of solutions containing the copper complex ion. These are called ___________ solutions and will produce a linear calibration curve.
standard
Sx
standard deviation
Sm
standard deviation of the mean Sm = Sx/square root of n
For Expt 2, Gay-Lussac's Law, the independent variable is __________ and the dependent variable is __________.
temperature; pressure
For Expt 3, Charles' Law, the independent variable is ___________ and the dependent variable is __________
temperature; volume
What does titrating the sodas with NaOH help determine?
the concentration of citric acid present in each soda
What is the estimate of the equivalence point called?
the end point
For the AXmEn notation, what does the m represent?
the number of atoms attached to the central atom
In all of the gas law experiments, what will be held constant?
the number of moles (n)
most acid-base titration methods rely on measuring what?
the pH
What is an equivalence point of a titration?
the point where the number of moles of base added (the titrant) is stoichiometrically EQUAL to the number of moles of acid originally present in the analyte
In an exothermic reaction, does heat go to the system of to the surroundings?
the surroundings
In an endothermic reaction, does heat go to the system of to the surroundings?
the system
how can pH be measured indirectly?
the use of an indicator dye that changes color at the desired pH
Only elements of the _________ period or higher on the periodic table may exceed the octet rule in some of their structures.
third
Using a solution of known concentration to determine the concentration of another solution through a monitored reaction of known stoichiometry that goes to completion is called a ________
titration
what is citric acid used for in carbonated beverages?
to add tartness in otherwise sweet drinks
What was the purpose of the gas properties lab?
to conduct a series of experiments, where each will examine the relationship between two fo the four variables in the ideal gas law while the other two are held constant.
What is the purpose of "The Quantitative Determination of an Acid in Carbonated Beverages" lab?
to find the amounts of citric acid present in two different sodas
How do scientists typically ESTIMATE the equivalence point?
using an indicator dye that changes color to signal that the amount of titrant added is equal to the analyte in a sample
Lewis structures are a simple shorthand representation of the bonding of atoms and the distribution of ___________ electrons in molecules and polyatomic ions of the main-group elements.
valence
In Part 2, Gay-Lussac's Law, what variable is held constant and what variable relationship is being studied?
variable relationship: pressure & temperature constant: volume
In Part 1, Boyle's Law, what variable is held constant and what variable relationship is being studied?
variable relationship: pressure & volume constant: temperature
In Part 3, Charles' Law, what variable is held constant and what variable relationship is being studied?
variable relationship: volume & temperature constant: pressure
For Expt 1, Boyle's Law, the independent variable is ________ and the dependent variable is ________
volume; pressure
A neutralization reaction between HCl (aq) and NaOH (aq) produces
water and a salt
a calorimeter must be what so no heat escapes?
well-insulated
What is the formula for a T-test?
| u - xm | > (t)(Sm)