CHM 144 Final
For the t-test inequality (from the question earlier), you were asked to compare two groups of data. What is the numerical value for the right-side of the inequality? Report your answer to one decimal place.
1.8
Experiment #4: What volume of 95% ethanol will be used to wash the copper you collect on the filter paper?
10 mL
If a 10 mL volumetric flask is used to measure its maximum volume, what is the measurement recorded to the correct number of significant figures?
10.00 mL
A "normal distribution" (see Ch. 4, Figure 4-3 of the lab manual) occurs when approximately 68.3% of data falls within plus or minus one standard deviation of the mean (xm ± 1sx); especially if the data set has greater than 20 data points. Use the following set of % water values (these are the same as the previous question): 14, 7.6, 9.5, 12, 8.0, 6.8 Answer the following: xm + 1sx 12.5 and xm -1sx [ Select ] ["10.7", "6.9", "12.5", "8.7"] the number of data points within the range of xm ± 1sx 4/6 data points are in the range Is this considered to be a "normal distribution"? [ Select ] ["No, this is NOT a normal distribution since the percent of data points in the range is not equal to 68.3%.", "Yes, this is a normal distribution since 68.3% of data points are in the range."]
12.5, 6.9, 4/6 are in range, No, this is NOT a normal distribution since the percent of data points in the range is not equal to 68.3%
Though you did the Q-test in your lab notebook, here's another example (at the 95% confidence level). Use the following set of % water values: 9.3, 14, 7.6, 7.8, 10., 9.5, 12, 8.0, 8.6, 6.8 TIPS: see Appendix I for the equation and an example; examine the data points on the low end and high end of the data set, but perform the Q-test on the one number furthest from its nearest neighbor. Possible outlier to be tested: [ Select ] ["7.8", "12", "7.6", "10.", "6.8", "14"] Q-critical value from Table 4-1: [ Select ] ["0.47", "0.97", "0.49", "0.53", "0.63"] Q-calculated value: [ Select ] ["7.2", "0.47", "0.11", "0.49", "2.0", "0.28"] Conclusion: since Qcalculated < Qcritical keep data point, it's not an outlier
14, 0.47, 0.28
A group of students, at a different university, did a similar experiment with the following results for % water: xm = 9.5, sx = 1.7, n = 10 TIPS: see Appendix I for the equations; make sure that your answers are rounded to the correct number of significant figures. % Relative standard deviation (%RSD): Standard deviation of the mean (sm):
18, 0.54
Experiment #3: If hydrochloric acid (HCl) is sold as a 28% solution, this means that the reagent contains 28 grams of HCl per 100 grams of the solution. What is the mass of the solvent in grams?
72 g
Experiment #5: For the acid-base reaction of citric acid and sodium hydroxide, the equivalence point occurs at a pH of:
8.5
In Experiment #4, you will perform the following reaction as part of the experimental procedure to determine the empirical formula of an unknown copper chloride hydrate. 3Cu2+ (aq) + 2Al (s) → 3Cu (s) + 2Al3+ (aq) What is the reducing agent in this reaction?
Al (s)
Expt #4: What are the products formed when the aluminum was dissolved by aqueous acid in this experiment? Choose all that apply!
AlCl3 (aq) H2 (g)
Which formatting options should be applied to all graphs made in CHM 144/145? Select all that apply.
All graphs should have a linear fit (if applicable). Graphs should be autoscaled. All graphs should have labeled axes with units (where applicable). Connect the dots turned OFF. All graphs should have a title. Filled symbols should be used so that data points are visible.
itric acid is a triprotic acid. Why is it that there is only one observable end point if there are three acidic protons?
All three acidic protons are of similar strength
One of the objectives of Experiment #4 is to use reaction stoichiometry to determine the number of moles of each of the components of a ______ binary salt.
hydrated
Goggles and gloves must be worn at all times for Experiment #4. Which substance, used in the experiment, is highly toxic by ingestion or inhalation and corrosive to the skin and eyes?
hydrochloric acid
A substance can be characterized by physical properties such as mass, volume, color, and density. Density is an example of an intensive property meaning; it is ________ of the amount of substance present. An extensive property like volume is _______ on the amount of substance present.
independent, dependent
Place the instructions for Experiment #2 in order
measure the mass of several unpopped popcorn kernals, pop the corn by allowing the water inside to steam and expand the kernals, and measure the mass of the popped corn
Any titration requires that the reaction be monitored to determine when the equivalence point has been reached. For the experiment you will conduct (Part II), the most common methods rely on:
measuring the pH
What are the units of molarity?
mol/L
In Experiment #5, students will determine the concentration of citric acid in carbonated beverages, using a solution of sodium hydroxide (NaOH) of known concentration. 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(n) ________________.
titration
Expt #5-2: What is the purpose of calculating and showing the first derivative along with your titration curve (see Figure 7-8 of the lab manual)?
to identify the estimated equivalence point of the titration
Students will be measuring the density of aqueous solutions. "Aqueous" means that the solvent that makes up the solution is __________.
water
Unlike a solid, a liquid cannot be weighed on a balance unless it's contained. The standard method for obtaining the mass of a liquid is described in the manual and is called:
weighing by difference
When does the equivalence point occur in an acid-base titration?
when the number of moles of acid is stoichiometrically equal to the number of moles of base added.
Linear regression (also called linear least-squares regression) is a method used to calculate the ___________ that describes the mathematical relationship between two experimental variables that have a linear relationship.
"best fit" line
Expt. #5-1: Why are all of the answers for moles (NaOH and citric acid) reported to three significant figures? Select all that apply. (2)
-Because the concentration of NaOH is reported to three significant figures -Because the volumes from the graduated cylinder are reported to three significant figures.
For the traditional titration method (Part 1), the volume of NaOH used in your molarity calculations was the total volume added (Vf-Vi). Why should the total volume not be used in the calculations for Part 2 (titration with the pH electrode)?
-Vtotal is beyond the equivalence point since the titration doesn't stop until after pH 10 -Vtotal represents the total amount of NaOH added not the volume where the moles of acid equal the moles of base -If Vtotal was used, the molarity would be larger than it should be.
Expt. #5-1: Carbonated sodas (like Sprite® or 7-Up®) contain carbonic acid in addition to citric acid. How is it possible that the reported results are only for the molarity of citric acid and do not include other acids that are present in sodas? Select all that apply. (2)
-citric acid is present in much higher concentrations than other acids. -carbonic acid is removed when sodas are flattened.
Expt #4: How would your experimental formula (CuxCly⋅zH2O) have been affected if the final products were not dried completely before weighing it? (2)
-incomplete drying is calculated as increased amount of copper or Cu in the formula -"x" would have been larger than it should be
The analytical method for this experiment is the acid-base titration. Which of the following are true regarding the acid-base titration you performed for this experiment?
-one solution of known concentration is used to determine the concentration of another solution -the stoichiometry of the reaction must be known -the buret contains the sodium hydroxide -the reaction is monitored and goes until completion (or neutralization)
Expt. #4: Why is it important to sand the aluminum foil before it was added to the 150-mL beaker in step #10 of the procedure? (3)
-sanding removes the coating on the foil -sanding increases the surface area -sanding exposes a reactive surface
Which of the following explain the difference between the equivalence point and the end point of a titration?
-the end point is the point at which a titration is stopped -the equivalence point is the point of stoichiometric equivalence of moles of acid and base -the end point is the point at which the color change happened -the end point is an estimate (or overestimate) of the equivalence point
In both the traditional titration (Part 1) and the titration using the pH electrode (Part 2), you reached an estimated equivalence point. Which method gives results that align more closely to the true equivalence point and why?
-the pH electrode titration because it doesn't rely on humans determining where light pink is -the pH electrode titration because it shows the region of the most rapid pH change
If 25.31 mL of 0.0500 M NaOH solution are required to reach the equivalence point of an acid-base titration of 40.0 mL of 7-Up, how many moles of NaOH were required? Make sure your answer has the correct number of significant figures.
0.00127
Experiment #4: At the end of the experiment, you will be drying your copper sample under a heat lamp. The procedure states to dry and weigh the copper until the mass is constant within the error limit of the balance. What's the error limit in grams?
0.001g
Experiment #4: A student calculated the following masses for their experiment: 0.181 g water, 0.376 g copper, 0.438 g chlorine. Use these masses to calculate: moles of water in their sample of copper chloride hydrate ______ moles moles of copper in their sample of copper chloride hydrate ______ moles moles of chlorine in their sample of copper chloride hydrate ______moles
0.0100, 0.00592, 0.0121
For the t-test inequality (from the previous question), you were asked to compare two groups of data. What is the numerical value for the left-side of the inequality? Report your answer to one decimal place.
0.1
Experiment #4: To find the empirical formula... Based on the calculated moles of Cu, Cl and water (from the previous question), divide each by the smallest numbers of moles and then round off to obtain the smallest whole number. Given that the general formula is: CuxCly ⋅ zH2O The whole number for x is [ Select ] ["3", "2", "number not listed", "1"] , the whole number for y is [ Select ] ["number not listed", "3", "1", "2"] and the whole number of z is [ Select ] ["number not listed", "2", "1", "3"] .
1, 2, 2
Two groups of students, at a different university, did a similar experiment with the following results for % water: group 1: xm = 9.5, sx = 1.7, n = 10 group 2: xm = 9.4, sx = 2.2, n = 10 Is the % water in popcorn kernels statistically different between the two groups at the 95% confidence level? Conduct a t-test to find out (see Appendix I for the equation and an example and be careful, there are two types of t-tests). t-value used: Conclusion:
2.10, the difference is NOT statistically significant
One online source claims that optimum moisture content (or, % water) of popcorn is 14%. Is there a statistical difference between this accepted value and group 2's data (xm = 9.4, sx = 2.2, n = 10) at the 95% confidence level? Conduct a t-test to find out (see Appendix I for the equation and an example and be careful there are two types of t-tests).
2.26, Yes, the difference is statistically significant
Experiment #5: In the acid-base reaction of aqueous citric acid with aqueous sodium hydroxide, how many moles of the base are needed to react with (neutralize) one mole of citric acid?
3
In experiment #3: A group of students at another university conducted a similar density experiment where they found the mean % sugar of triplicate "unknown" trials as 11.98% (sx = 0.98). They identified the "unknown" as Cranberry Juice, since the Nutritional Label lists 12.16% sugar. Does the % sugar differ significantly (at the 95% confidence level) from the accepted value? Conduct a t-test to find out. t-value used: Conclusion:
4.30, The difference is NOT statistically significant since the left side of the inequality is NOT greater than the right side.
In experiment #3: Part I (Preparation of Standard Solutions), students will be preparing solutions that each have a different w/w% of sugar (range 0%-20%). How many solutions will be prepared?
5
Use the following set of % water values for the calculations listed below. 14, 7.6, 9.5, 12, 8.0, 6.8 TIPS: see Appendix I for the equations; make sure that your answers are rounded to the correct number of significant figures; the units for all answers are % and do not need to be entered. Mean (xm): Median: Mode: (hint: if there is no mode, put "no mode" or "N/A") Standard deviation (sx):
9.7, 8.8, N/A, 2.8
Expt #5-1: Why must a colorless soda be used for the traditional titration method?
Because colorless sodas allow you to see a color change to faint pink.
Expt #5: Which soda(s) cannot be titrated using the traditional (phenolphthalein) method (Part I)?
Jones green apple, orange crush
Expt #4: Why was it important that the solution be colorless after the aluminum foil was added to the beaker?
The lack of color indicates that the reduction of Cu2+ (aq) is complete
Which device is used to deliver and measure the volume of sodium hydroxide to the citric acid solution for both parts of Experiment 5?
buret
Figure 4-1 of the lab manual shows the apparatus for popping popcorn. The distance from the flame to the bottom of the evaporating dish should be about 8-10 inches so as to prevent ___________ of the kernels
burning
Experiment #4: The original copper chloride sample (from the bottle) was [ Select ] ["brown", "silver", "colorless", "blue"] . After using the Bunsen burner, the sample turned [ Select ] ["silver", "brown", "colorless", "blue"] . The sample changed color because [ Select ] ["it was dehydrated by heating", "it was hydrated by heating"] .
blue, brown, it was dehydrated by heating
Experiment #4: When the unknown copper chloride hydrate is heated, its color changes to _________
brown
Experiment 3 introduces the concept of density, specifically, you'll be finding the density of a liquid. Students will be making a [ Select ] ["trajectory", "logarithmic", "calibration", "simple"] curve of known [ Select ] ["soda", "sugar", "salt"] concentration. This curve will help to determine the sugar content of an "unknown" commercial beverage.
calibration, sugar
When the redox reaction between Al (s) and Cu2+ (aq) is complete , the solution will be __________.
colorless
In experiment #4: What is the name of the vessel in which you will place your unknown copper chloride hydrate sample for heating?
crucible
What term is used to describe the liquid accumulated in the filter flask during vacuum filtration?
filtrate
When 12 oz. cans of regular Coke and Diet Coke are placed in a large container of water, some float while others sink. Diet Coke will _____ in a large container of water because ["it contains a lot of sugar", "it contains no sugar"] and therefore has ["a lower density than water", "a higher density than water"].
float, it contain's no sugar, a lower density than water
Expt 5-1: Classify the following experimental objectives as pertaining to "Part 1", "Part 2" or "both": to learn how to perform an acid-base titration [ Select ] ["part 1 objective", "part 2 objective", "pertains to parts 1 & 2"] to detect the end point of a titration based on a visual observation [ Select ] ["pertains to parts 1 & 2", "part 2 objective", "part 1 objective"] to calculate the molarity of citric acid [ Select ] ["part 2 objective", "part 1 objective", "pertains to parts 1 & 2"] to learn how to use pH to monitor a titration [ Select ] ["part 2 objective", "part 1 objective", "pertains to parts 1 & 2"] to learn about acid-base indicators part 1 objective
parts 1&2, part 1, part 1&2, part 2, part 1
Your group needs 8 kernels that are all popped to about the same size (you can then extinguish the Bunsen burner). Next, to determine the mass of water, subtract the mass of _____ corn from the mass of ______ corn. The percent water is determined by dividing the mass of water by the mass of unpopped corn and multiplying by 100.
popped, unpopped
