UNIT 1 STOICHIOMETRY HW 1
Directions: For each question, provide your final answer below the question. For math-based answers,
work must be shown on a separate sheet of paper and attached to the back of this packet. Without work,
no credit will be given. Check significant figures and units.
1. Water is added to 4.267 grams of UF6. The only products are 3.730 grams of a solid containing only uranium,
oxygen and fluorine and 0.970 gram of a gas. The gas is 95.0% fluorine, and the remainder is hydrogen.
(a) From these data, determine the empirical formula of the gas.
(b)What fraction of the fluorine of the original compound is in the solid and what fraction in the gas after
the reaction?
(c) What is the formula of the solid product?
(d)Write a balanced equation for the reaction between UF6 and H2O. Assume that the empirical formula of
the gas is the true formula.
2.
An experiment is to be performed to determine the mass percent of sulfate in an unknown soluble sulfate salt.
The equipment shown above is available for the experiment. A drying oven is also available.
(a) Briefly list the steps needed to carry out this experiment.
(b)What experimental data need to be collected to calculate the mass percent of sulfate in the unknown?
(c) List the calculations necessary to determine the mass percent of sulfate in the unknown.
(d)Would 0.20-molar MgCl2 be an acceptable substitute for the BaCl2 solution provided for this
experiment? Explain.
UNIT 1 STOICHIOMETRY HW 2
Directions: Read the passage below and answer the summary questions that follow in complete sentences.
Perspiration Power: Scientists Turn Sweat Into Electrical Energy
By Richard Knox
It takes energy to work up a sweat. But now researchers have cleverly
figured out how to turn sweat into energy. Scientists have devised a small
skin patch they call a “temporary tattoo” that can transform lactate — one
of 800 or so chemicals in sweat — into electrical energy. Not much
energy, so far. Only about 4 microwatts, less than half of what it takes to
power a digital watch. But the energy alchemists are confident they can
scale up their sweat “biobattery” enough to play an iPod, power a GPS
device, or warn a marathoner when it’s time to top up her electrolytes.
The researchers think their work could also have military and biomedical
applications, if they can tweak the technology to squeeze more electricity
out of sweat. “Sweat has been largely neglected, not thought of as a
worthwhile physiological fluid.”–Researcher Josh Windmiller. “Right now
we’re working on the biofuel cell so it can get higher power,” Wenzhao Jia, of the University of California
San Diego, tells CommonHealth. She’s describing the skin-patch biobattery tomorrow at a meeting of the
American Chemical Society in San Francisco. One problem in experiments so far: People who are less fit
produce more energy from their sweat than those who are moderately fit. The fittest subjects produce
the least amount of power. The researchers are trying to figure out how to compensate for this. “We want
to integrate another electronic element such as a super-capacitor that can store the power,” Jia says.
“Ultimately, we can connect a number of cells together to make the current higher. Jia says the sweatpowered battery grew out of an earlier effort to monitor levels of lactate, a metabolic byproduct when
sugar (glucose) is broken down to produce energy — a process called glycolysis. (It’s the buildup of
lactate, or lactic acid, that makes your muscles sore after strenuous exercise.) “Lactate is a very important
indicator of how you are doing during exercise,” Jia says. High-performance athletes monitor their lactate
levels to evaluate their endurance capacity and their training program. It’s also an important marker of
heart failure, shock or generalized infection. But up to now, measuring lactate required drawing blood
and analyzing it in a laboratory. Last year Jia and her UCSD colleagues reported a new way to measure
lactate levels by analyzing sweat. They devised a lactate sensor that could be printed onto a flexible
plastic strip — the same process used in printing T-shirts. The strip can be worn like a bandage,
collecting data that can be streamed to a mobile device –- and voila, continuous monitoring of lactate in
sweat during exercise, something not possible before. The new “biobattery” takes the approach a step
farther, from collecting data through sweat to harvesting energy. Josh Windmiller, one of the researchers,
says the work shows that sweat deserves more respect. “Sweat has gotten a bum reputation,” Windmiller
said in a recent online interview. “It makes us uncomfortable, makes us smell…Sweat has been largely
neglected, not thought of as a worthwhile physiological fluid.” He’s founded a company called
Electrozyme to develop wearable sweat monitors. It’s betting that fitness buffs will pay for a device —
maybe someday a sweat-powered device — that gives them a minute-by-minute read-out of their
metabolism.
1. Are you interested in this new development in science? What aspect(s) seem the most interesting? Or,
why are you not interested?
UNIT 1 STOICHIOMETRY HW 3
2. What are some of the inherent problems with this new technology besides the problems listed in the
article?
3. Research the molecular and structural formula of lactic acid and record them below:
4. Find the molar mass of lactic acid.
5. Find the percent by mass of carbon in lactic acid.
6. Find the empirical formula of lactic acid.
7. Write the reaction for the combustion of lactic acid in excess oxygen. Make sure it is balanced.
8. If 1.265 moles of lactic acid is burned in the reaction you wrote above, what is the minimum number of
liters of oxygen needed for the complete combustion at STP?
9. If 700.0 grams of lactic acid were burned according to your equation, how many grams of water could
be formed?
10. If 330.3 grams of water is produced in the experiment outlined in the previous question, what is the
percent yield of water?