Overview

Lesson Procedure

60-70 minutes of class time across 5 phases.

1. Warm-Up5 minutes
2. Direct Instruction15-20 minutes
3. Guided Practice15-20 minutes
4. Independent Practice20 minutes
5. Closure5 minutes

1. Warm-Up5 minutes

   Project this invented news brief: "A new study of 40 volunteers found that people who drank green tea every day for 12 weeks lost 2 kg more than people who did not. Green tea burns fat."

   Warm-Up Prompt

   Before you accept the last sentence, what would you want to know about the study's hypothesis, its data, its analysis and its conclusion? Name one thing you could check yourself and one other source you would look for.

   Take answers and sort them into the four parts of Diagram 1. Hypothesis: was it stated before the study? Data: how were the groups chosen, and how was weight measured? Analysis: is 2 kg an average, and how much did people vary? Conclusion: "burns fat" names a cause the study did not measure. Students can check the arithmetic if the brief gives the group averages, and they can look for other studies. Tell students that this is today's skill. RST.11-12.8 asks them to evaluate the hypotheses, data, analysis and conclusions in a science or technical text, verifying the data when possible and corroborating or challenging conclusions with other sources of information.

2. Direct Instruction15-20 minutes

   Part 1: Four parts, two checks. Post Diagram 1 for the whole lesson. Students evaluate each part of a study in turn: the hypothesis (the proposed explanation and what it predicts), the data (what was measured and how), the analysis (what was done to the data) and the conclusions (what the author says it all shows). Two checks cut across the parts. To verify the data is to redo the numbers from the text's own figures. To corroborate or challenge a conclusion is to compare it with other sources: another experiment, another method, a reference value or later work. Agreement from a different method is stronger than agreement from a repeat of the same one.

   Part 2: Model with Curie (T1). In 1898 Marie Curie measured how strongly different substances made air conduct electricity, the effect of the rays we now call radioactivity. Her instrument gave a current: the larger the current, the more active the sample. Uranium compounds were known to be active in proportion to the uranium they contain. Gloss before reading: "pitchblende" is the main ore of uranium, "chalcolite" and "autunite" are uranium minerals, and "simple bodies" means chemical elements. Read T1 aloud, then show the rows of Curie's table below it and work the two examples.

   1I have examined many minerals in my apparatus; certain of them gave evidence of radio-activity, e.g., pitchblende, thorite, orangite, fergusonite, cleveite, chalcolite, autunite, monazite, &c. The following is a table giving in ampères the intensity, i, of the current obtained with metallic uranium and with different minerals:—

   [...]

   2All the minerals which showed radio-activity contained uranium or thorium: their activity is therefore not surprising, but the intensity of the action in certain cases is unexpected. Thus pitchblendes (ores of uranium oxide) are found which are four times as active as metallic uranium. Chalcolite (double phosphate of copper and uranium) is twice as active as uranium. Autunite (phosphate of uranium and calcium) is as active as uranium. These facts do not accord with previous conclusions, according to which no mineral should be so active as thorium or uranium.

   3To throw light on this point, I prepared artificial chalcolite by the process of Debray, starting with the pure products. The process consists in mixing a solution of uranium nitrate with a solution of copper phosphate in phosphoric acid and warming to 50° or 60°. After some time, crystals of chalcolite appear in the liquid.

   4Chalcolite thus obtained possesses a perfectly normal activity, given by its composition; it is two and a-half times less active than uranium.

   5It therefore appeared probable that if pitchblende, chalcolite, and autunite possess so great a degree of activity, these substances contain a small quantity of a strongly radio-active body, differing from uranium and thorium and the simple bodies actually known. I thought that if this were indeed the case, I might hope to extract this substance from the ore by the ordinary methods of chemical analysis.

   From Curie's table in T1: current produced by metallic uranium and by uranium minerals, in units of 10⁻¹¹ ampere (values as printed; thorium and rare-earth minerals left out; carnotite, a uranium mineral, is the last row of her table, after the rare-earth minerals)

   Substance	i × 10¹¹
   Uranium	2·3
   Pitchblende from Johanngeorgenstadt	8·3
   Pitchblende from Joachimsthal	7·0
   Pitchblende from Pzibran	6·5
   Pitchblende from Cornwallis	1·6
   Cleveite	1·4
   Chalcolite	5·2
   Autunite	2·7
   Carnotite	6·2

   • Evaluating a hypothesis (T1, paragraphs 2 and 5)

     State Curie's hypothesis in your own words. Is it well grounded in her data, and how carefully does she word it?

     Result: The hypothesis (paragraph 5): the very active minerals "contain a small quantity of a strongly radio-active body, differing from uranium and thorium and the simple bodies actually known," that is, an unknown element. It is grounded in an anomaly in the data: if activity depends only on the uranium present, no uranium mineral should be more active than uranium metal, yet paragraph 2 reports minerals that are. The wording is careful: "It therefore appeared probable" and "if this were indeed the case" mark it as a proposal still to be tested, not a finding. A strong hypothesis also says what would follow if it is true; paragraph 5 names that consequence in its last sentence.

   • Verifying the data (T1, paragraph 2, and the table)

     Paragraph 2 says chalcolite "is twice as active as uranium" and autunite "is as active as uranium." Check both statements against the table.

     Result: Activity is compared through the current. Chalcolite: 5·2 ÷ 2·3 ≈ 2.26, so "twice" is a fair rounding. Autunite: 2·7 ÷ 2·3 ≈ 1.17, so "as active as" is loose: autunite gave about 17 percent more current than uranium metal. Both statements are supported in direction; the second is stated less exactly than the data allow. Verifying also means noticing what the table cannot tell you: the currents come from one apparatus and depend on how each sample was spread (in a paragraph left out of T1, Curie notes that the current from orangite rose with the thickness of the layer), so small differences deserve less weight than large ones.

   Close the model by naming the pattern. Curie's hypothesis grew out of data that did not fit an accepted rule, and it is worded as a proposal. The data mostly check out when verified. What the text has not yet done is test the hypothesis; paragraphs 3-4 describe a step she took before announcing it, which students will evaluate in the quiz. Diagram 2 draws these rows of the table to scale.

3. Guided Practice15-20 minutes

   Pairs read the lab report (T2), a modern text written for this page, and mark the hypothesis, data, analysis and conclusion in the margin. Then use the reference table below it, a second source, to work the two examples as a class.

   1Hypothesis. Our unknown metal cylinder is aluminum, because it is silver-gray and feels light for its size. If it is aluminum, its specific heat should be close to 0.90 J/(g·°C) and its density close to 2.70 g/cm³. Specific heat is the energy needed to warm 1 gram of a substance by 1 °C. (The class, the cylinder and the data in this report are invented for teaching.)

   2Method. We heated the 60.0 g cylinder in boiling water for 5 minutes; the water read 100.0 °C. We then moved it quickly into a foam-cup calorimeter holding 100.0 g of water at 20.0 °C, stirred, and recorded the highest temperature. We ran three trials, drying the cylinder and starting with fresh water each time. To find the volume, we lowered the cylinder into a graduated cylinder of water.

   3Data. Highest temperatures: trial 1, 29.0 °C; trial 2, 28.7 °C; trial 3, 29.2 °C. The water in the graduated cylinder rose from 50.0 mL to 72.5 mL.

   4Analysis. The heat lost by the metal equals the heat gained by the water, so c = (100.0 × 4.18 × rise of the water) ÷ (60.0 × fall of the metal), where 4.18 J/(g·°C) is the specific heat of water. Trial 1: c = (100.0 × 4.18 × 9.0) ÷ (60.0 × 71.0) = 0.883. Trial 2: c = 0.805. Trial 3: c = 0.905. Mean: 0.864 J/(g·°C). Density: 60.0 g ÷ 22.5 cm³ = 2.67 g/cm³.

   5Conclusion. Our mean specific heat, 0.864 J/(g·°C), is within 4 percent of the value for aluminum, 0.897, and our density, 2.67 g/cm³, matches aluminum's 2.70. This proves that the cylinder is pure aluminum. The small difference in specific heat was caused by human error.

   Another source: standard reference values for six metals near room temperature

   Metal	Specific heat (J/(g·°C))	Density (g/cm³)
   Aluminum	0.897	2.70
   Magnesium	1.02	1.74
   Titanium	0.523	4.51
   Zinc	0.388	7.14
   Iron	0.449	7.87
   Copper	0.385	8.96

   • Verifying the analysis (T2, paragraphs 3-4)

     Recompute the specific heat for trials 2 and 3 and the mean. Does the report's analysis hold?

     Result: Trial 2: the water rose 28.7 - 20.0 = 8.7 °C and the metal fell 100.0 - 28.7 = 71.3 °C, so c = (100.0 × 4.18 × 8.7) ÷ (60.0 × 71.3) = 3,636.6 ÷ 4,278 ≈ 0.850, not 0.805. Trial 3: (100.0 × 4.18 × 9.2) ÷ (60.0 × 70.8) = 3,845.6 ÷ 4,248 ≈ 0.905, as reported. The corrected mean is (0.883 + 0.850 + 0.905) ÷ 3 ≈ 0.879, not 0.864. The density also checks: 72.5 - 50.0 = 22.5 cm³, and 60.0 ÷ 22.5 ≈ 2.67 g/cm³. The error is in the analysis, not the data, and fixing it moves the result closer to aluminum: 0.879 is 2 percent below 0.897.

   • Corroborating and challenging the conclusion (T2, paragraph 5, and the reference table)

     Use the reference table to judge the conclusion. Which parts are corroborated, and which are challenged?

     Result: Corroborated: two independent properties, specific heat and density, both point to aluminum, and no other metal in the table comes close on either (magnesium, the next lightest, has a density of 1.74 and a specific heat of 1.02). Agreement on two unrelated measurements is much stronger than agreement on one. Challenged: "proves that the cylinder is pure aluminum" goes beyond the data, because common aluminum alloys have almost the same density and specific heat, so these tests cannot tell pure aluminum from an alloy. "Human error" names no cause. Heat lost to the cup and the air while the cylinder is moved would make the water rise too little and c come out low, which fits the direction of the gap. A strong conclusion would say: "The data are consistent with aluminum or an aluminum alloy."

   Debrief: Which part of the report was weakest: the hypothesis, the data, the analysis or the conclusion? Students usually find that the hypothesis (it makes two testable predictions) and the data are sound, the analysis has one arithmetic slip, and the conclusion overreaches. Evaluation is part by part; one weak part does not sink the whole report.

4. Independent Practice20 minutes

   Students read Curie's account of the atomic weight of radium (T3), with its three tables, and Rutherford's account of the same work a year later (T4), and answer quiz questions 1-20. Questions 1-8 and 15-16 use T3 and its tables; questions 9-12, 17 and 20 use T4 with T3; questions 13, 14, 18 and 19 use T1 in Direct Instruction, with its table and Diagram 2. Tell students before they read: the atomic weight is the mass of an atom on the scale then in use, with hydrogen near 1; Curie found it by dissolving a weighed amount of radium chloride and weighing the silver chloride it formed, and "bivalent" or "divalent" means that each atom combines with two chlorine atoms. In the source's numbers the raised dot is a decimal point: 0·1150 means 0.1150.

   1I employed the classic method of weighing as silver chloride the chlorine contained in a known weight of the anhydrous chloride. As control experiment, I determined the atomic weight of barium by the same method, under the same conditions, and with the same quantity of material, first 0·5 grm. and then 0·1 grm. The figures obtained were always between 137 and 138. I thus saw that the method gives satisfactory results, even with a very small quantity of material.

   2The first two determinations were made with chlorides, of which one was 230 times and the other 600 times as active as uranium. These two experiments gave the same figure as the experiment with the pure barium chloride. There was therefore no hope of finding a difference except by using a much more active product. The following experiment was made with a chloride, the activity of which was about 3500 times as great as that of uranium; and this experiment enabled me, for the first time, to observe a small but distinct difference; I found, as the mean atomic weight of the metal contained in this chloride, the number 140, which showed that the atomic weight of radium must be higher than that of barium. By using more and more active products, and obtaining spectra of radium of increasing intensity, I found that the figures obtained rose in proportion, as is seen in the following table (p. 28).

   3The figures of column A must only be looked upon as a rough estimate. The calculation of the activity of strongly radio-active bodies is difficult, for many reasons which will be discussed later.

   [...]

   4A represents the activity of the chloride, that of uranium being unity; M the atomic weight found.

   5At the termination of the processes described above, I obtained, in March, 1902, 0·12 grm. of radium chloride, of which Demarçay made the spectral analysis. This radium chloride, in the opinion of Demarçay, was fairly pure; its spectrum, however, showed the three principal barium lines with considerable intensity. I made four successive estimations of the chloride, the results of which as follows:—

   [...]

   6I then re-purified this chloride, and obtained a much purer substance, in the spectrum of which the two strongest barium lines were very faint. Given the sensitiveness of the spectrum reaction of barium, Demarçay estimated that the purified chloride contained only the merest traces of barium, incapable of influencing the atomic weight to an appreciable extent. I made three determinations with this perfectly pure radium chloride. The results were as follows:—

   [...]

   7The mean of these numbers is 225. They were calculated in the same way as the preceding ones by considering radium as a bivalent element, the chloride having the formula RaCl₂, and taking for silver and chlorine the values Ag = 107·8, Cl = 35·4.

   8Hence the atomic weight of radium is Ra = 225.

   [...]

   9From its chemical properties, radium is an element of the group of alkaline earths, being the member next above barium.

   10From its atomic weight also, radium takes its place in Mendeleeff’s table after barium with the alkaline earth metals, in the row which already contains uranium and thorium.

   Curie's first table in T3 (the first [...]): activity of the chloride and atomic weight found, with her notes

   A (activity, uranium = 1)	M (atomic weight found)	Curie's note
   3500	140	Spectrum of radium faint.
   4700	141
   7500	145·8	Spectrum of radium strong, but that of barium predominating.
   Order of magnitude, 10⁶	173·8	The two spectra of almost equal intensity.
   Order of magnitude, 10⁶	225	Only a trace of barium present.

   Curie's second table in T3 (the second [...]): the fairly pure chloride of March 1902, masses in grams

   Estimation	Anhydrous radium chloride	Silver chloride	M
   I.	0·1150	0·1130	220·7
   II.	0·1140	0·1119	223·0
   III.	0·11135	0·1086	222·8
   IV.	0·10925	0·10645	223·1

   Curie's third table in T3 (the third [...]): the re-purified chloride, masses in grams

   Estimation	Anhydrous radium chloride	Silver chloride	M
   I.	0·09192	0·08890	225·3
   II.	0·08936	0·08627	225·8
   III.	0·08839	0·08589	224·0

   114. Atomic weight of radium. Mme Curie has made successive determinations of the atomic weight of the new element with specimens of steadily increasing purity. In the first observation the radium was largely mixed with barium, and the atomic weight obtained was the same as that of barium, 137·5. In successive observations with specimens of increasing purity the atomic weights of the mixture were 146 and 175. The final value obtained recently was 225, which may be taken as the atomic weight of radium on the assumption that it is divalent.

   2In these experiments about 0·1 gram of pure radium chloride was obtained by successive fractionations. The difficulty involved in preparing a quantity of pure radium chloride large enough to test the atomic weight may be gauged from the fact that only a few centigrams of fairly pure radium, or a few decigrams of less concentrated material, are obtained from the treatment of about 2 tons of the mineral from which it is derived.

   3Runge and Precht have examined the spectrum of radium in a magnetic field, and have shown the existence of series analogous to those observed for calcium, barium, and strontium. These series are connected with the atomic weights of the elements in question, and Runge and Precht have calculated by these means that the atomic weight of radium should be 258—a number considerably greater than the number 225 obtained by Mme Curie by means of chemical analysis. Marshall Watts, on the other hand, using another relation between the lines of the spectrum, deduced the value obtained by Mme Curie. Runge has criticised the method of deduction employed by Marshall Watts on the ground that the lines used for comparison in the different spectra were not homologous. Considering that the number found by Mme Curie agrees with that required by the periodic system, it is advisable in the present state of our knowledge to accept the experimental number rather than the one deduced by Runge and Precht from spectroscopic evidence.

   4There is no doubt that radium is a new element possessing remarkable physical properties. The detection and separation of this substance, existing in such minute proportions in pitchblende, has been due entirely to the characteristic property we are considering, and is the first notable triumph of the study of radio-activity. As we shall see later, the property of radio-activity can be used, not only as a means of chemical research, but also as an extraordinarily delicate method of detecting chemical changes of a very special kind.

5. Closure5 minutes

   Exit ticket: "Pick one number or conclusion from today's texts. Say whether you verified it, corroborated it, challenged it, or could not check it, and name the source or calculation you used." Sort the tickets into "checked with a calculation," "checked against another source" and "accepted without a check" to plan the next lesson.

   Teacher note on the historical texts. T1, T3 and T5 are an English translation, published in 1904, of Marie Curie's 1903 doctoral thesis; T4 and T6 are from Ernest Rutherford's textbook of 1905. Their units and values are of their time: atomic weights were measured against a scale then in use, Curie takes chlorine as 35·4 and silver as 107·8 (today 35.45 and 107.87), and wavelengths appear in µµ (today nanometers) and Ångström units. The mass of radium-226, the isotope Curie isolated, is 226.03 on today's scale. Radium is intensely radioactive and was later found to harm the people who handled it; Curie's death in 1934 is generally attributed to her long exposure to radiation. No radioactive material is used in this lesson. The texts contain no dated or offensive language.

   Homework passages. The homework compares Curie's and Rutherford's accounts of the spectrum of radium, below, with their tables of lines.

   1It was of the first importance to check, by all possible means, the hypothesis, underlying this work, of new radio-active elements. In the case of radium, spectrum analysis was the means of confirming this hypothesis.

   2M. Demarçay undertook the examination of the new radio-active bodies by the searching methods which he employs in the study of photographic spark spectra.

   3The assistance of so competent a scientist was of the greatest value to us, and we are deeply grateful to him for having consented to take up this work. The results of the spectrum analysis brought conviction to us when we were still in doubt as to the interpretation of the results of our research.

   4The first specimens of fairly active barium chloride containing radium, examined by M. Demarçay, exhibited together with the barium lines a new line of considerable intensity and of wave-length λ = 381·47 µµ in the ultra-violet. With the more active products prepared subsequently, Demarçay saw the line 381·47 µµ more distinctly; at the same time other new lines appeared, and the intensity of the new lines was comparable with that of the barium lines. A further concentration furnished a product for which the new spectrum predominated, and the three strongest barium lines, alone visible, merely indicated the presence of this metal as an impurity. This product may be looked upon as nearly pure radium chloride. Finally, by further purification, I obtained an exceedingly pure chloride, in the spectrum of which the two chief barium lines were scarcely visible.

   5The following is a list, according to Demarçay, of the principal radium lines for the portion of the spectrum included between λ = 500·0 and λ = 350·0 µµ. The intensity of each line is represented by a figure, the strongest being marked 16:—

   [...]

   6According to Demarçay, the position of radium may be among the bodies possessing the most sensitive spectrum reaction. I also have concluded from the work of concentration, that in the first specimen examined, which showed clearly the line 3814·7, the proportion of radium must have been very small (perhaps about 0·02 per cent). Nevertheless, an activity fifty times as great as that of metallic uranium is required in order to distinguish clearly the principal radium line in the spectra photographed. With a sensitive electrometer the radio-activity of a substance only 1/100 of that of metallic uranium can be detected. It is clear that, in order to detect the presence of radium, the property of radio-activity is several thousand times more sensitive than the spectrum reaction.

   Demarçay's radium lines as listed by Curie in T5 (the [...]): wavelength λ in µµ and intensity (strongest = 16)

   λ (µµ)	Intensity
   482·63	10
   472·69	5
   469·98	3
   469·21	7
   468·30	14
   464·19	4
   460·03	3
   453·35	9
   443·61	8
   434·06	12
   381·47	16
   364·96	12

   113. Spectrum of radium. It was of great importance to settle as soon as possible whether radium was in reality modified barium or a new element with a definite spectrum. For this purpose the Curies prepared some specimens of radium chloride, and submitted them for examination of their spectrum to Demarçay, an authority on that subject. The first specimen of radium chloride examined by Demarçay was not very active, but showed, besides the lines due to barium, a very strong new line in the ultra-violet. In another sample of greater activity, the line was still stronger and others also appeared, while the intensity of the new lines was comparable with those present due to barium. With a still more active specimen which was probably nearly pure, only three strong lines of barium appeared, while the new spectrum was very bright. The following table shows the wave-length of the new lines observed for radium. The wave lengths are expressed in Ångström units and the intensity of each ray is denoted by a number, the ray of maximum intensity being 16.

   [...]

   2The lines are all sharply defined, and three or four of them have an intensity comparable with any known lines of other substances. There are also present in the spectrum two strong nebulous bands. In the visible part of the spectrum, which has not been photographed, the only noticeable ray has a wave length 5665, which is, however, very feeble compared with that of wave length 4826·3. The general aspect of the spectrum is similar to that of the alkaline earths; it is known that these metals have strong lines accompanied by nebulous bands.

   3The principal line due to radium can be distinguished in impure radium of activity 50 times that of uranium. By the electrical method it is easy to distinguish the presence of radium in a body which has an activity only ¹⁄₁₀₀ of uranium. With a more sensitive electrometer ¹⁄₁₀₀₀₀ of the activity of uranium could be observed. For the detection of radium, the examination of the radio-activity is thus a process nearly a million times more sensitive than spectrum analysis.

   4Later observations on the spectrum of radium have been made by Runge, Exner and Haschek, with specimens of radium prepared by Giesel. Crookes has photographed the spectrum of radium in the ultra-violet, while Runge and Precht, using a highly purified sample of radium, observed a number of new lines in the spark spectrum. It has been mentioned already that the bromide of radium gives a characteristic pure carmine-red coloration to the Bunsen flame. The flame spectrum shows two broad bright bands in the orange-red, not observed in Demarçay’s spectrum. In addition there is a line in the blue-green and two feeble lines in the violet.

   Rutherford's table of the new radium lines in T6 (the [...]): wavelength in Ångström units and intensity (strongest = 16)

   Wave length (Å)	Intensity
   4826·3	10
   4726·9	5
   4699·6	3
   4692·1	7
   4683·0	14
   4641·9	4
   4600·3	3
   4533·5	9
   4436·1	6
   4340·6	12
   3814·7	16
   3649·6	12

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   In T3, paragraph 1, why did Curie determine the atomic weight of barium by the same method?

   ATo test the method on a known element with samples as small as hers BTo find out how much barium was mixed into each of the radium samples she weighed CTo prove that radium and barium have the same atomic weight when they are pure DTo measure how radio-active pure barium chloride is when compared with uranium

2. Question 2 of 20 · Multiple Choice

   In T3, paragraph 2, the first two samples, 230 and 600 times as active as uranium, "gave the same figure as the experiment with the pure barium chloride." How does Curie interpret this result?

   AAs evidence that radium and barium have the same atomic weight BAs a sign that only far more active samples could show a difference CAs proof that the method fails for samples that are radio-active DAs a sign that the two samples in fact contained no radium at all

3. Question 3 of 20 · Multiple Choice

   Curie says the atomic weights "rose in proportion" as the activity rose (T3, paragraph 2, and her first table). Which evaluation of this analysis does the table best support?

   AIt is fully supported: M rose by the same factor as A in every row of the table BIt is contradicted: M fell between two rows even though A rose between them CIt is untestable: the table gives no values of A, only values of M and notes DM rises down the table as A rises, but not by a fixed ratio, and A is rough

4. Question 4 of 20 · Multiple Choice

   Verify estimation I of the re-purified chloride (Curie's third table: 0·09192 g of radium chloride, 0·08890 g of silver chloride, M = 225·3). With Curie's values Ag = 107·8 and Cl = 35·4, each RaCl₂ gives two AgCl, so M + 70.8 = 2 × 143.2 × (mass of radium chloride) ÷ (mass of silver chloride). Which calculation reproduces her 225·3?

   A2 × 143.2 × 0.08890 ÷ 0.09192 - 70.8 B2 × 143.2 × 0.09192 ÷ 0.08890 C2 × 143.2 × 0.09192 ÷ 0.08890 - 70.8 D143.2 × 0.09192 ÷ 0.08890 - 35.4

5. Question 5 of 20 · Multiple Choice

   Now verify estimation II of the fairly pure chloride (Curie's second table: 0·1140 g, 0·1119 g, M = 223·0) with the same relation. What do you find?

   AThe masses give about 221.0, so the printed 223·0 does not follow from them BThe masses give about 223.0, so the printed value checks out like the others CThe masses give about 225.3, the same result as the re-purified chloride DThe masses give about 291.8, because the chlorine should not be subtracted

6. Question 6 of 20 · Multiple Choice

   The re-purified chloride gave 225·3, 225·8 and 224·0 (Curie's third table), and Curie reports the mean as 225. How well do these three values support "Ra = 225"?

   AFully: three values that agree prove that no error of any kind affected the result BWell: they agree within 1.8 units, under 1 percent, though a shared error could hide CPoorly: the three values differ from each other, so no mean taken from them can be trusted DPoorly: three determinations are far too few to report any mean or any conclusion

7. Question 7 of 20 · Multiple Choice

   Curie's result assumes radium is "bivalent" (RaCl₂; T3, paragraph 7). If radium formed RaCl₃ instead, the relation would become M + 106.2 = 3 × 143.2 × (mass of radium chloride) ÷ (mass of silver chloride). What would estimation I of the re-purified chloride give?

   AAbout 225.3 BAbout 150.2 CAbout 444.2 DAbout 338.0

8. Question 8 of 20 · Multiple Choice

   How do the last two paragraphs of T3 bear on the assumption that radium is bivalent?

   ABoth give fully independent proof that radium forms RaCl₂, so the assumption needs no further support BNeither is relevant, because they discuss the periodic table rather than the chloride CChemistry is independent support; the table placement partly rests on the 225 itself DBoth show the assumption is wrong, because uranium and thorium are not alkaline earth metals

9. Question 9 of 20 · Multiple Choice

   Rutherford (T4, paragraph 1) says the atomic weights of the mixtures "were 146 and 175" before the final 225. How does his account compare with Curie's first table in T3?

   AIt agrees on the rising pattern and on 225, but its 175 differs from Curie's 173·8 BIt contradicts Curie, because it says the atomic weight fell as the samples became purer CIt agrees exactly, because 146 and 175 are the values printed in Curie's table DIt reports a different final value, which challenges Curie's conclusion of 225

10. Question 10 of 20 · Multiple Choice

    What kind of evidence did Runge and Precht use to arrive at 258 (T4, paragraph 3)?

    AA new chemical analysis of a larger and purer sample of radium chloride than Curie's BA link between spectral line series and atomic weight, seen in calcium, barium, strontium CMeasurements of the activity of radium compared with the activity of metallic uranium DThe place that the periodic system required for a new alkaline earth metal below barium

11. Question 11 of 20 · Multiple Choice

    Marshall Watts "deduced the value obtained by Mme Curie" from the spectrum, but Runge criticized his method (T4, paragraph 3). How much should Watts's result count as corroboration?

    AAs much as a second chemical analysis, because it reaches the same number BNone, because a result taken from the spectrum can never bear on an atomic weight CMore than Curie's own result, because it comes from a newer kind of method DLittle, until Runge's criticism that the lines were not homologous is answered

12. Question 12 of 20 · Multiple Choice

    A modern source gives 226.03 for the mass of radium-226, the isotope Curie isolated. About how far is each 1904 value from it, as a percentage of 226.03?

    ACurie's 225 is about 0.5 percent low; Runge and Precht's 258 is about 14 percent high BCurie's 225 is about 1 percent low; Runge and Precht's 258 is about 32 percent high CCurie's 225 is about 0.5 percent low; Runge and Precht's 258 is about 12 percent high DCurie's 225 is about 14 percent low; Runge and Precht's 258 is about 0.5 percent high

13. Question 13 of 20 · Multiple Choice

    T1, paragraph 4, says artificial chalcolite "is two and a-half times less active than uranium." In Curie's apparatus, where uranium gave a current of 2·3 (in units of 10⁻¹¹ ampere), what current would that be?

    AAbout 5.75 BAbout 2.08 CAbout 0.92 DAbout 13.0

14. Question 14 of 20 · Multiple Choice

    Why is Curie's artificial chalcolite (T1, paragraphs 3-4) a strong test of the idea behind her hypothesis?

    AIt shows that chalcolite is not radio-active at all when it is made in a laboratory BIt proves that the unknown active substance in the ore must be the element polonium CIt shows that Debray's process makes chalcolite more active than the natural mineral DMade from pure products, it is the same compound without the ore's other contents

15. Question 15 of 20 · Short Answer

    Curie's hypothesis (T1, paragraph 5) ends: "I might hope to extract this substance from the ore by the ordinary methods of chemical analysis." What prediction does the hypothesis make, what result would have challenged it, and how does T3 show the prediction being tested?

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16. Question 16 of 20 · Short Answer

    Recompute estimation I of the re-purified chloride with today's values, Ag = 107.87 and Cl = 35.45 (so M + 70.9 = 2 × 143.32 × mass of chloride ÷ mass of silver chloride). How much does updating the constants change the result? What other cause of the remaining gap to 226.03 does T3 point to?

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17. Question 17 of 20 · Short Answer

    Evaluate the conclusion "the atomic weight of radium is Ra = 225" (T3, paragraph 8). Use at least two other sources of information on this page to corroborate or challenge it, and give your verdict.

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18. Question 18 of 20 · Short Answer

    Curie writes that some pitchblendes "are four times as active as metallic uranium" (T1, paragraph 2). Verify this against her table and Diagram 2, and evaluate how precisely she words the claim.

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19. Question 19 of 20 · Short Answer

    Curie's evidence in T1 is a set of currents from minerals. Evaluate the data themselves: name one strength and one weakness of these data as evidence for the hypothesis, citing T1.

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20. Question 20 of 20 · Short Answer

    Rutherford (T4, paragraph 3) advises accepting Curie's 225 "rather than the one deduced by Runge and Precht," because it "agrees with that required by the periodic system." Evaluate this reasoning. What kind of evidence is agreement with the periodic system, and what could have challenged it?

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These standards connect to RST.11-12.8: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: Common Core State Standards for English Language Arts & Literacy. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.