General Chemistry
Many metals corrode.
An experiment is carried out to see if magnesium ribbon wrapped around a piece of iron rod has an effect on the rate at which the iron rod rusts.
The apparatus is shown in Figure 4.
The method used is
an iron rod, with magnesium ribbon wrapped around it, is placed in a boiling tube labelled A
10 cm3 water from a measuring cylinder is poured into this boiling tube
an identical rod but with no magnesium ribbon wrapped around it is placed in a second boiling tube labelled B
Both boiling tubes are left for a few days.
(i) Explain why iron rod rather than stainless steel rod is used in this experiment.
(ii) State why it is not necessary to use a pipette to measure out 10 cm3 water in this experiment.
(iii) After a few days the two boiling tubes were examined.
Verified
General Chemistry
15.9 g of CaCO3 decomposed and 7.31 g of CaO are obtained what is the percent yield of CaO obtained
\mathrm{CaCO3}(\mathrm{s}) \rightarrow \mathrm{CaO}(\mathrm{s})+\mathrm{CO} 2(\mathrm{~g})
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General Chemistry
(20). After completing a titration, you determined 0.52 mol of sodium hydroxide were required to reach the endpoint of sulfuric acid sample of unknown concentration. Your acid sample was 45 mL. What is the concentration of your acid? (Hint: is the reaction balanced?)
\mathrm{H} 2 \mathrm{SO} 4(\mathrm{aq})+\mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{Na2SO4}(\mathrm{aq})+\mathrm{H} 2 \mathrm{O}(1)
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General Chemistry
(18). Find the mass of a metal object (in grams) that was heated to 105°C and placed in 27 g of water at 13°C The final temperature of the water is 40°C. The C water = 4.184 J/g°C and C metal = 0.184 J/g°C.
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General Chemistry
(17). Determine the molarity of a solution formed by dissolving 48.9 g LiBr in enough water to yield a total solution volume of 750.0 mL.
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General Chemistry
(12). A metal cube has an edge length of 2.44 cm and a mass of 16.28 g. Calculate the density of the metal.
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General Chemistry
A lab technician had a sample of radioactive Americium. He knew it was one of the isotopeslisted in the table below but did not know which one. The sample originally contained 0.008g of the isotope, but 120 minutes later it contained 0.004 g. Use this information to answerthe following questions. (3 points)
A. How many half-lives have passed?
B. What is the half-life of the sample?
C. Which isotope did he have? (
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General Chemistry
A. Name three kinds of radioactive decay and provide the symbol for each that is used to represent the product given off. (3 points)
\text { i. } a \text { - decay (1 point) }
\text { iii. Y - decay (1 point) }
\text { ii. } \beta \text { - decay (1 point) }
{ }_{1}^{2} \mathrm{H}+{ }_{1}^{2} \mathrm{H} \rightarrow \frac{3}{2} \mathrm{He}+{ }_{0}^{1} \mathrm{n}
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General Chemistry
A. What two competing fundamental forces are at work inside the nucleus of an atom? (1point)
B. How can the ratio of number of protons to neutrons in the nucleus be used to predict thestability of a nucleus? (2 points)
C. How much energy would be released if 0.00023 kg of plutoniumthrough radioactive decay? (2 points)were converted to energy
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General Chemistry
Use the emission spectra shown to answer the following questions (note the direction of thewavelength scale):
A. A high school student acquired an emission spectrum of an unknown sample. He knewthe unknown sample contained one of the elements, whose spectra are shown above. Theemission spectrum of his sample showed a strong emission at 610 nm but not at 480 nm.Which element did his unknown sample contain? (2 points)
B. Element A above has a strong emission around 670 nm. Does this emission line representa lower energy or higher energy transition than the emission line at 428 nm? Explain youranswer. (2 points)
C. Why does each element have its own unique emission spectrum? (2 points)
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General Chemistry
A. Write a set of four possible quantum numbers for the circled electron. (There could bemore than one correct answer.) (4 points)
n =| =m, =II
B. The electron in a hydrogen atom can undergo a transition from n = 6 to n = 1, emitting aphoton with energy 2.11 x 10-18 J. (2 points)
i. What is the frequency of this transition? (1 point)
ii. How does this transition show that the energy of a photon is quantized? (1 point)
C. Why is it impossible for an electron to have the quantum numbers n = 3, | = 0, m, = 1, m, =
+\frac{1}{2} ?(2 \text { points })
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