Overview

Lesson Procedure

65-70 minutes of class time across 5 phases.

1. Warm-Up5-10 minutes
2. Direct Instruction20 minutes
3. Guided Practice15 minutes
4. Independent Practice20 minutes
5. Closure5 minutes

1. Warm-Up5-10 minutes

   Students take their own resting pulse with this three-line procedure, then answer the prompt.

   Pulse procedure and explanation (written for this page)

   Part	Text
   Procedure	Sit still for 2 minutes. Press two fingers (not the thumb) lightly on the inside of the wrist below the thumb. Count the beats for 15 seconds and multiply by 4.
   Explanation	A resting pulse for teenagers is usually 60-100 beats per minute. Activity raises the pulse for several minutes. Because the count is multiplied by 4, each beat miscounted changes the result by 4 beats per minute.

   Warm-Up Prompt

   Maya ran up two flights of stairs, sat down and at once counted 27 beats in 15 seconds. What rate does the procedure give, and what does the explanation tell you about that number? Which step did she skip?

   Take answers. The procedure gives 27 × 4 = 108 beats per minute, but the explanation shows why that is not her resting pulse: she skipped the 2 minutes of sitting, and activity "raises the pulse." Point out the two jobs the standard asks for: follow every step precisely, then use the text's own explanation to say what a specific result means.

2. Direct Instruction20 minutes

   Part 1: Two halves of a technical text. Many procedures contain a procedure (what to do) and an explanation (why the results should look a certain way, and what patterns mean when they do not). Keep this table up for the lesson.

   Analyzing results with the explanation in the text

   Question to ask	Where the answer comes from	Example in T1
   What should the results look like?	The explanation's model or rule	A straight line; F ÷ x the same for every load (paragraph 6)
   Does this result fit the model?	Compare the specific numbers with the prediction	Is each point on the line? Did the pointer return to zero?
   If not, which explanation fits the pattern?	The "other patterns" the text names	Curve at the end: elastic limit. Offset line: misread zero (paragraphs 6-7)
   What does the text say to do?	The procedure step tied to that pattern	Use the slope, not F ÷ x (paragraphs 5 and 7)

   Part 2: Model the spring test (T1). Read paragraphs 1-5 as a procedure and have students name each quantity and its unit. Then read paragraphs 6 and 7 as the key to the results: each sentence says what a pattern in the data means. Work the three examples, and ask the class after each one which sentence in paragraphs 6-7 explains it. Diagram 1 plots the first two examples.

   1Purpose: to find the spring constant k of a steel spring, in newtons per meter. Materials: a ring stand clamped to the table; a steel spring; a 50 g mass hanger and five 50 g slotted masses; a meter stick clamped upright beside the spring; a small paper pointer taped to the bottom of the spring; safety goggles. Wear goggles throughout: a loaded spring can slip off its hook.

   2Zero reading. Hang the spring alone from the clamp. With your eye level with the pointer, read its position on the meter stick to the nearest 0.1 cm. This is the zero position.

   3Loading. Hang the empty hanger (50 g) on the spring. When the spring has stopped bouncing, read the pointer again. The extension x is this reading minus the zero position. Add one 50 g mass at a time, up to 300 g in all, and record the extension after each. Do not load the spring beyond 300 g.

   4Unloading. Remove the masses one at a time, reading the pointer after each, and finish by removing the hanger. Record whether the pointer returns to the zero position within 0.2 cm.

   5Calculation. For each load, the force is F = mg, with m in kilograms and g = 9.8 m/s². Plot F in newtons against x in meters, draw the best-fit straight line and find its slope. The slope is the spring constant k. Do not force the line through the origin.

   6What the results mean. While a spring stays within its elastic limit, its extension is proportional to the force on it: doubling the load doubles the extension. The points then fall on a straight line, the ratio F ÷ x is the same for every load, and the pointer returns to its zero position when the load is removed. Past the elastic limit, the coils bend permanently. The extension then grows faster than the force, the last points curve away from the line toward larger extensions, and after unloading the pointer stays lower than its zero position. Readings from a spring stretched past its limit do not give its spring constant.

   7Other patterns. If the zero position was misread, every extension is off by the same amount. The points still form a straight line with the correct slope, but the line does not pass through the origin, and F ÷ x changes from load to load; this is why k is found from the slope. Readings taken while the spring is still bouncing scatter the points to both sides of the line instead of bending it.

   • Following the procedure, then reading the result

     A group follows T1 and records these extensions for loads of 50, 100, 150, 200, 250 and 300 g: 2.5, 4.9, 7.4, 9.8, 12.3 and 14.7 cm. The pointer returns to within 0.1 cm of zero. What is k, and what does the text say the result shows?

     Result: Paragraph 5: F = mg gives 0.49, 0.98, 1.47, 1.96, 2.45 and 2.94 N; with x in meters, the best-fit line has slope 20.0 N/m and passes within 0.01 N of the origin. Paragraph 6 explains the pattern: the points "fall on a straight line" and the pointer returns to zero, so the spring stayed within its elastic limit and the slope is its spring constant.

   • A result that the explanation rules out

     Another group ignores the 300 g limit in paragraph 3. Their first six extensions match the first group's, but at 350 g and 400 g they read 17.9 cm and 21.6 cm, and after unloading the pointer stays 1.4 cm lower than its zero position.

     Result: With k = 20.0 N/m, the line predicts 17.2 cm and 19.6 cm, so the last two points lie to the side of larger extension, and the gap grows. Paragraph 6 matches every detail: past the elastic limit, the points "curve away from the line toward larger extensions" and the pointer "stays lower than its zero position." The spring is damaged; its later readings "do not give its spring constant," so the spring must be replaced before the next class.

   • Why the procedure uses the slope

     A third group misreads the zero position by 0.6 cm, so every extension is 0.6 cm too large: 3.1, 5.5, 8.0, 10.4, 12.9 and 15.3 cm. One student reports k as the mean of F ÷ x.

     Result: F ÷ x now rises from 15.8 N/m at 50 g to 19.2 N/m at 300 g, as paragraph 7 predicts ("F ÷ x changes from load to load"). The best-fit slope is still 20.0 N/m, and the line crosses the force axis at -0.13 N instead of at the origin. Following paragraph 5, "Do not force the line through the origin," gives the right k; the student's average of F ÷ x does not.

3. Guided Practice15 minutes

   Pairs read the colorimeter procedure (T2). First they number the actions in paragraphs 2-5 and underline each rule of order ("from the most dilute to the most concentrated," "rinse ... before each one"). Then they write one sentence for each pattern the explanation names in paragraphs 6 and 7: what it looks like in the data and what causes it. Work the example together, pausing at each reading to ask whether it fits the line. Diagram 2 plots the result.

   1Purpose: to find the concentration of blue dye in a sports drink, as a percent of a standard dye solution, from how much red light the drink absorbs. Materials: a colorimeter set to 635 nm (red light); plastic cuvettes; lens tissue; two 10 mL plastic syringes without needles; small cups; distilled water; the standard dye solution, made by the teacher from blue food coloring; the sports drink.

   2Dilutions. Make five solutions of 10.0 mL each by mixing the standard solution with distilled water: 2.0 mL of standard with 8.0 mL of water (20%), 4.0 mL with 6.0 mL (40%), 6.0 mL with 4.0 mL (60%), 8.0 mL with 2.0 mL (80%), and 10.0 mL of standard alone (100%). Use one syringe only for the standard and the other only for the water, and stir each cup.

   3Calibration. Fill a cuvette three-quarters full with distilled water. Hold it only by its ridged sides, wipe the clear sides with lens tissue and place it in the colorimeter with a clear side facing the arrow. Press CAL. The display should read 0.000. This cuvette is the blank.

   4Measuring. Measure the solutions from the most dilute to the most concentrated. Before each one, rinse the cuvette with a small amount of the new solution and pour the rinse away. Fill, wipe and insert the cuvette as in paragraph 3, and record the absorbance.

   5The unknown. Measure the sports drink in the same way three times, refilling the cuvette each time, and find the mean absorbance. Plot absorbance against percent concentration for the five standards, draw the best-fit straight line through the origin, and read the drink's concentration from the line.

   6What the results mean. For the same dye and the same cuvette, absorbance is proportional to concentration, so the standards should lie on a straight line through the origin. On this colorimeter the relationship holds only up to an absorbance of about 1.0. Above that, so little light passes through the sample that the readings fall below the line, and a concentration read from them is too low. If a sample reads above 1.0, dilute it with an equal volume of distilled water, measure it again and double the concentration you read from the line.

   7Other patterns. Fingerprints, scratches or bubbles on the cuvette scatter light, and the colorimeter counts scattered light as absorbed, so a smudged cuvette gives a reading that is too high. A cuvette that was not rinsed with the new solution still holds drops of the previous, more dilute one, so its reading is slightly too low.

   • Analyzing a result with the text's limit

     A pair measures the five standards in T2 and gets 0.192, 0.378, 0.574, 0.826 and 0.951. They re-wipe the 80% cuvette and get 0.764. The sports drink reads 1.30, 1.32 and 1.31; diluted with an equal volume of water, it reads 0.69, 0.70 and 0.70. The best-fit line through the origin has slope 0.0095 per percent.

     Result: The first 80% reading was above the line (the line predicts 0.76), which paragraph 7 explains: a smudge makes a reading "too high." The drink's mean, 1.31, is above 1.0, so paragraph 6 applies: read directly, 1.31 ÷ 0.0095 gives about 138%, which is "too low." Diluted, the mean is 0.697, and 0.697 ÷ 0.0095 = 73.4%; doubled, the drink is about 147% of the standard. The line predicts 1.40 at 147%, so the undiluted reading of 1.31 fell below it, as the text says.

   Debrief: Why does paragraph 4 say to measure from the most dilute to the most concentrated? (With that order, any drops left in an unrinsed cuvette are more dilute than the new solution, so the error is small and its direction is known: paragraph 7 says the reading is "slightly too low.") A text that explains the order of its steps lets a reader predict the effect of breaking it.

4. Independent Practice20 minutes

   Students read the potato osmosis procedure below and use it, with the invented results in the table, to answer quiz questions 1-20 on their own. They do not carry out the experiment during the quiz.

   1Purpose: to estimate the concentration of dissolved substances in potato cells by finding the salt solution in which potato tissue neither gains nor loses water. Materials: potato cylinders about 1 cm across and 4 cm long, cut by the teacher with the skin removed; five cups holding 50 mL each of salt (sodium chloride) solution at 0.0, 0.1, 0.2, 0.3 and 0.4 mol/L; plastic wrap; paper towels; forceps; a balance that reads to 0.01 g; a timer.

   2Before soaking. Blot three cylinders for each cup by rolling each one once across a dry paper towel, without squeezing. Weigh the three together and record the initial mass for that cup.

   3Soaking. Put each set of three cylinders into its cup at the same time and cover every cup with plastic wrap. Soak all the cups for the same time, between 45 and 60 minutes.

   4After soaking. Remove the cylinders with forceps, blot them exactly as in paragraph 2, weigh each set of three together and record the final mass.

   5Calculation. For each cup, find the percent change in mass: (final mass - initial mass) ÷ initial mass × 100. Plot percent change against salt concentration, draw the best-fit straight line and find where it crosses zero percent change. That concentration is your estimate.

   6What the results mean. Water moves by osmosis across cell membranes, from the side with less dissolved solute to the side with more. In a solution weaker than the cell contents, the cells take in water and the cylinders gain mass; in a stronger solution, they lose water and mass. Where the line crosses zero, the solution matches the cell contents, and there is no net movement of water. Percent change is used rather than change in grams because the sets do not all start at the same mass.

   7Other patterns. Water left on the surface adds mass that never entered the cells, so a set blotted less after soaking than before shows a change that is too high: a gain that is too large or a loss that is too small. Potato skin slows the movement of water, so a cylinder with skin on it changes less than it should. Mass keeps changing for about the first hour, so a set soaked for a shorter time also changes less. An uncovered cup loses water by evaporation, which makes its solution stronger and the loss of mass larger.

   Invented results from one group that followed T3 (three cylinders per cup, soaked 50 minutes)

   Cup	Salt concentration (mol/L)	Initial mass (g)	Final mass (g)
   A	0.0	10.24	11.04
   B	0.1	10.51	10.84
   C	0.2	9.87	9.71
   D	0.3	10.12	9.51
   E	0.4	10.36	9.39

5. Closure5 minutes

   Exit ticket: "Choose one result from today (a curved spring graph, a smudged cuvette or a drink reading above 1.0). Quote the sentence in the text that explains it, and write what the procedure tells you to do next." Sort the tickets into "names the pattern and the cause," "names the cause but not the action" and "describes the result without the text."

   Teacher note on safety and the science. The procedures use no heat, flames or hazardous chemicals: food dye, table salt, potatoes, springs and an LED lamp. Students wear goggles for the spring test, and the teacher cuts the potato cylinders. The science in the texts is simplified in two ways worth discussing afterward. Beer's law holds for dilute solutions, and the 1.0 limit in T2 is a property of a typical school colorimeter, not a universal constant. In the solar panel text, reflection at large angles is one reason outputs fall below the cosine; the panel's design and the lamp's beam shape also play a part.

   Homework passage. The homework uses the solar panel procedure below. A small panel of this size typically gives around 100 mA in full sunlight, and a desk lamp gives only a few percent of full sunlight, so currents of a few milliamperes are expected; the numbers in the homework are invented on that scale.

   1Purpose: to measure how the current from a small solar panel changes as the panel is tilted away from a light. Materials: a small solar panel about 6 cm by 8 cm; a digital multimeter set to measure direct current in milliamperes (mA); two connecting leads; an LED desk lamp; a protractor; a ruler; a stack of books. Use an LED lamp: other bulbs can get hot enough to burn skin, and they warm the panel.

   2Setup. Darken the room: close the blinds and switch off the room lights. Connect the panel's leads directly to the multimeter. Place the lamp so that its beam points at the center of the panel from 30 cm away, measured along the beam. The tilt angle is the angle between the beam and a line straight out from the face of the panel, so at 0° the panel faces the lamp directly.

   3Readings. Set the panel at 0°, wait 10 seconds and record the current. Repeat at 15°, 30°, 45°, 60° and 75°. Turn the panel about its own center each time; do not move the lamp.

   4Final check. Return the panel to 0° and read the current again. If it differs from the first 0° reading by more than 5%, the lamp or the panel has shifted or warmed up: find the cause and repeat the whole series.

   5Calculation. Divide each current by the first 0° current to get the relative output. Compare each relative output with the cosine of the tilt angle.

   6What the results mean. A tilted panel presents a smaller area to the beam, so it intercepts less of the light, and the current falls in proportion to the cosine of the tilt angle. At 60° the panel should give about half of its 0° current. At large angles, measured outputs usually fall below the cosine, because more of the light is reflected from the panel's glossy surface instead of entering it.

   7Other patterns. Light from windows or room lights reaches the panel at every tilt, so it adds a current that does not depend on the angle. It makes the relative outputs at large angles too high, above the cosine. To test for it, cover the lamp: the current should drop to almost zero.

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   According to paragraph 2, how is each cylinder blotted before it is weighed?

   APressed firmly between two paper towels BRolled once across a dry paper towel, without squeezing CLeft on a paper towel to air-dry for a minute DShaken gently, then patted with a towel

2. Question 2 of 20 · Multiple Choice

   Which condition in paragraph 3 must be the same for every cup?

   AThe mass of the cylinders BThe concentration of the solution CThe soaking time DThe number of times each cylinder is weighed

3. Question 3 of 20 · Multiple Choice

   Why does the procedure use percent change instead of change in grams?

   APercent change is easier to plot BThe balance reads only to 0.01 g CThe sets do not all start at the same mass DChange in grams would be negative in some cups

4. Question 4 of 20 · Multiple Choice

   Using the results table, what is the percent change in mass for cup A?

   A7.81% B7.25% C0.80% D-7.81%

5. Question 5 of 20 · Multiple Choice

   In which cups did the results show a net movement of water into the potato cells?

   ACups A and B only BCups C, D and E only CCup A only DAll five cups

6. Question 6 of 20 · Multiple Choice

   Using the results table, what is the percent change in mass for cup D?

   A-0.61% B-6.41% C+6.03% D-6.03%

7. Question 7 of 20 · Multiple Choice

   Between which two concentrations does this group's line cross zero percent change?

   A0.0 and 0.1 mol/L B0.1 and 0.2 mol/L C0.2 and 0.3 mol/L D0.3 and 0.4 mol/L

8. Question 8 of 20 · Multiple Choice

   Cup B changed by +3.14% and cup C by -1.62%. Estimating along a straight line between the two cups, at what concentration is the change zero?

   A0.15 mol/L B0.13 mol/L C0.20 mol/L D0.17 mol/L

9. Question 9 of 20 · Multiple Choice

   According to paragraph 6, what does the concentration where the line crosses zero tell you?

   AThe salt solution has the same solute concentration as the potato cells BThe potato cells contain only salt, the same substance as the solution CWater has stopped crossing the cell membranes in both directions DThe potato has lost all the water its cells are able to give up

10. Question 10 of 20 · Multiple Choice

    A student in this group forgot to blot cup E's cylinders after soaking. How did that affect cup E's result?

    AIts loss of mass looks larger than it really was BIts loss of mass looks smaller than it really was CIt had no effect, because blotting is done before soaking DIt turns the loss into a gain of about the same size

11. Question 11 of 20 · Multiple Choice

    Another group left cup D uncovered in a warm, dry room. How does paragraph 7 say this changes cup D's result?

    AThe solution gets weaker, so the cylinders lose less mass BThe cylinders dry out and gain mass CNothing changes, because the time is the same DThe solution gets stronger, so the cylinders lose more mass

12. Question 12 of 20 · Multiple Choice

    One cylinder in cup A still had a strip of skin on it. According to paragraph 7, how would that change cup A's result?

    AThe gain would be larger, because skin holds water BThe gain would be smaller, because skin slows the movement of water CThe cylinder would lose mass instead of gaining it DThere would be no effect, because only three cylinders are weighed together

13. Question 13 of 20 · Multiple Choice

    A group soaked cup C for only 20 minutes and the other cups for 50 minutes. What is the best judgment about cup C's result?

    AIt is valid, because 20 minutes is enough time for osmosis to begin BIt is valid, as long as percent change is used CIt is not comparable: it broke paragraph 3, and paragraph 7 says a shorter soak changes less DIt shows that cup C's solution matches the cell contents almost exactly

14. Question 14 of 20 · Short Answer

    Calculate the percent change in mass for cup E. Then describe the pattern across all five cups and explain it with paragraph 6.

    Show model answer

15. Question 15 of 20 · Short Answer

    Explain, using the osmosis explanation in paragraph 6, why cup A gained mass and cup E lost mass. Use the words "solute" and "net movement" correctly.

    Show model answer

16. Question 16 of 20 · Short Answer

    Another group reports that their line crosses zero at 0.31 mol/L. You find that they did not blot cup D after soaking. Explain how that mistake could move their crossing point, using paragraph 7.

    Show model answer

17. Question 17 of 20 · Short Answer

    Set X starts at 6.20 g and gains 0.40 g. Set Y starts at 12.40 g and gains 0.62 g. A student says set Y responded more strongly. Evaluate the claim with a calculation and paragraph 6.

    Show model answer

18. Question 18 of 20 · Short Answer

    Why must the cylinders be blotted in the same way before and after soaking? Answer with paragraphs 2, 4 and 7.

    Show model answer

19. Question 19 of 20 · Short Answer

    To save time, a classmate plans to weigh all fifteen cylinders together before soaking and then weigh each cup's three cylinders separately after soaking. Will this plan let them follow paragraph 5? Explain.

    Show model answer

20. Question 20 of 20 · Short Answer

    Suppose the experiment is repeated with sweet potato, whose cells hold more dissolved sugar than ordinary potato cells. Predict where the line would cross zero, and justify the prediction with paragraph 6.

    Show model answer

These standards connect to RST.11-12.3: 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.