HS-PS1-3: Investigating Bulk Properties to Infer Forces Between Particles
In plain English: HS-PS1-3 is the NGSS high school performance expectation that asks students to plan and conduct investigations of bulk properties, such as melting point, boiling point, vapor pressure and surface tension, and use the evidence to infer how strongly the particles of a substance attract one another. It is usually taught in Chemistry or Physical Science.
Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
Clarification Statement: Emphasis is on understanding the strengths of forces between particles, and not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.
Assessment Boundary: Assessment does not include Raoult's law calculations of vapor pressure.
Next Generation Science Standards · Disciplinary Core Idea: Matter and Its Interactions · Official standard
Students cannot see particles, but they can measure what a large sample of a substance does: the temperature at which it melts or boils, how fast it evaporates, how high its vapor pressure is and how strongly its surface holds together. In this lesson they plan and carry out investigations of these bulk properties and use the results to infer how strong the electrical attractions between the particles are. A substance whose particles attract strongly melts and boils at higher temperatures, evaporates more slowly, has a lower vapor pressure and usually a higher surface tension. Students compare substances made of different kinds of particles: ions, atoms, molecules and networked materials.
The NGSS Clarification Statement says: "Emphasis is on understanding the strengths of forces between particles, and not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension." The Assessment Boundary says: "Assessment does not include Raoult's law calculations of vapor pressure." This page therefore compares forces as stronger or weaker without naming force types, uses vapor pressure only to rank substances, and never calculates the vapor pressure of a mixture. Melting points, boiling points, vapor pressures and surface tensions quoted as reference values are standard rounded values; all classroom measurements are invented and labeled as such.
Learning Objectives
By the end of this lesson, students will be able to:
Plan an investigation of a bulk property that names the independent, dependent and controlled variables, the number of trials and the safety steps
Conduct an investigation safely, record data in a table and summarize repeated trials with a mean and a range
Infer the relative strength of attractions between particles from melting point, boiling point, evaporation rate, vapor pressure and surface tension
Compare substances made of ions, atoms, molecules and networked materials using bulk-property evidence
Critique an investigation plan and explain how a flaw would affect the conclusion
Prior Knowledge Required
Students should already be comfortable with:
A particle model of solids, liquids and gases, and what happens to particle motion when thermal energy is added MS-PS1-4
Opposite charges attract, and ionic and covalent bonding from outer electrons HS-PS1-1
Independent, dependent and controlled variables in an experiment
Put one drop of water and one drop of acetone (nail polish remover) on a dry surface at the front of the room, away from any heat source. Students watch for two minutes.
Warm-Up Prompt
"The acetone drop disappears long before the water drop. Both are made of molecules too small to see. What does the difference tell you about how strongly the molecules in each liquid hold on to each other? What else could you measure to test your idea?"
List students' measurement ideas on the board (temperature, time, number of drops, boiling point). Label the list "bulk properties": properties of a sample large enough to handle, used as evidence about particles.
Direct Instruction15-20 minutes
From bulk properties to particle attractions. To melt a solid or evaporate a liquid, particles must be pulled apart against the electrical attractions between them. The stronger those attractions, the more energy it takes, so the higher the melting and boiling points and the slower the evaporation. At a given temperature, a liquid whose particles attract weakly lets more of them escape into the gas, so its vapor pressure is higher. Particles at a liquid surface are pulled inward by their neighbors; stronger attractions give a higher surface tension, so drops hold together and bead up more. The kind of particle matters too: ions with opposite charges attract strongly in every direction, atoms in a networked material are joined by bonds throughout the sample, and separate molecules or single atoms usually attract each other much more weakly. Diagram 2 models these four structures.
Melting points and kinds of particles
Reference melting points: argon (single atoms) -189 °C, paraffin wax (molecules) about 55 °C, sucrose (molecules) about 186 °C, sodium chloride (ions) 801 °C, silicon dioxide as quartz (network) about 1,710 °C.
Result: The order of melting points ranks the attractions that must be overcome: weakest between argon atoms, stronger between wax and sugar molecules, much stronger between ions, strongest in the network, where melting means breaking bonds throughout.
Vapor pressure and boiling point
Reference values at 20 °C: acetone vapor pressure 24.6 kPa, ethanol 5.9 kPa, water 2.3 kPa. Boiling points at 1 atm: acetone 56 °C, ethanol 78 °C, water 100 °C.
Result: The highest vapor pressure goes with the lowest boiling point. Both rank the attractions the same way: acetone weakest, then ethanol, then water strongest.
Surface tension
Reference surface tensions at 20 °C: water 72.8 mN/m, ethanol 22.3 mN/m.
Result: Water's surface tension is more than 3 times ethanol's (72.8 ÷ 22.3 ≈ 3.3), so water molecules pull on their neighbors at the surface more strongly. This agrees with the vapor pressure evidence.
Repeated trials
Invented class data, drops of liquid added to a penny before it overflows: water 34, 31, 34; ethanol 12, 11, 13.
Result: Means: water 33 drops (range 3), ethanol 12 drops (range 2). The difference of 21 drops is far larger than the spread within either liquid, so the result is strong evidence that water has the stronger surface attractions.
Networked material
Graphite (layers of carbon atoms bonded in a network) does not melt at ordinary pressure and only turns to vapor above about 3,600 °C. Solid iodine, made of I2 molecules, melts at 114 °C.
Result: Both are nonmetal solids, but melting iodine only separates whole molecules, while vaporizing graphite means breaking the bonds that hold the network together. The forces holding graphite together are far stronger.
After each example ask: "Which measurement is the evidence, and which way does it point: stronger or weaker attractions?" Remind students that they do not need names for the types of forces; they need to rank the strength of the attractions and support the ranking with data.
Guided Practice15 minutes
The class plans an investigation together for the question: "Do the particles in water attract each other more strongly than the particles in 91% isopropyl alcohol?" The method is evaporative cooling: a thermometer bulb wrapped in a filter paper sleeve is dipped in a liquid, pulled out, and its temperature is read as the liquid evaporates.
Independent variable: which liquid is tested. Dependent variable: the drop in temperature over 2 minutes after the thermometer is taken out.
Controlled variables: the same starting temperature of both liquids (room temperature, checked with the thermometer), the same size of filter paper sleeve, the same dipping time (10 s), the same air movement (no fans), and the same thermometer.
Trials: at least 3 for each liquid, with a fresh sleeve each time. Record a data table with columns for trial, starting temperature, lowest temperature and temperature drop.
Prediction and reasoning: if the alcohol particles attract each other more weakly, the alcohol evaporates faster and the temperature drops more.
Safety: goggles, no flames or hot plates in the room because the alcohol is flammable, and wipe up spills at once.
Independent Practice10-15 minutes
Students analyze invented results from a different method: a 0.10 mL spot of each liquid was placed on a paper towel and timed until it was no longer visible.
Evaporation times of 0.10 mL spots (invented data)
Liquid
Trial 1 (s)
Trial 2 (s)
Trial 3 (s)
Water
600
580
620
91% isopropyl alcohol
190
210
200
Glycerin
still visible at 1,800
still visible at 1,800
still visible at 1,800
Students compute the means (water 600 s, isopropyl alcohol 200 s), rank the three liquids by strength of attractions (glycerin strongest, then water, then isopropyl alcohol), and check the ranking against reference boiling points: isopropyl alcohol 82 °C, water 100 °C, glycerin about 290 °C. They write one sentence on why the alcohol sample, which contains some water, still gives a fair comparison.
Closure10 minutes
Exit ticket: "Liquid A boils at 35 °C and liquid B boils at 118 °C. Which liquid has stronger attractions between its particles, and which would evaporate faster from an open dish at room temperature? Explain." (B has stronger attractions; A evaporates faster.) Return to the warm-up list and have students circle the measurements they now know how to use as evidence.
Differentiation Strategies
For Struggling Students
Provide a planning template with labeled boxes for question, independent variable, dependent variable, controlled variables, trials, data table and safety
Give a one-line key: "higher melting point, higher boiling point, slower evaporation, lower vapor pressure, higher surface tension: stronger attractions"
Use two liquids with a large difference (water and acetone) before asking students to compare three
For Advanced Students
Ask students to find a case where two bulk properties seem to disagree and to explain what else about the particles (such as their size) could account for it
Have students design a way to test whether a data difference is larger than the spread of the trials before drawing a conclusion
Ask students to predict and then test how dissolving table salt in water changes the number of drops a penny can hold, and explain the result in terms of particles
Assessment Guidance
What to Look For
Check that plans change one variable, name what is measured, and keep the starting temperature, amount and surface area the same. Look for conclusions that cite a mean or a reference value and state the direction of the inference (for example, "lower vapor pressure, so stronger attractions"). Watch for students who think evaporation or melting breaks the bonds inside molecules, who confuse fast evaporation with strong attractions, and who draw conclusions from a single trial.
02
Classroom Activities
3 Activities
1
Evaporative Cooling Lab
30 minGroups of 3
Groups carry out the evaporative cooling method with water, ethanol and acetone, run three trials for each liquid, and use the temperature drops to rank the attractions between the particles.
Procedure
Safety: goggles on. Ethanol and acetone are flammable: no flames or hot plates in the room, small capped bottles only, and open windows or a fume hood. Wash hands afterward.
Wrap a 2 cm by 6 cm filter paper strip around the thermometer bulb and hold it with a small rubber band.
Dip the bulb in the liquid for 10 s, lift it out, lay the thermometer across a pencil so the sleeve touches nothing, and record the starting temperature and the lowest temperature reached within 2 minutes.
Use a fresh sleeve for each of 3 trials per liquid. Check that all three liquids start at room temperature.
Sample Data (invented)
Temperature drop in °C, trials 1-3. Water: 2.3, 2.6, 2.3. Ethanol: 7.6, 8.1, 7.7. Acetone: 15.0, 15.6, 15.0.
Discussion Questions
Find the mean drop for each liquid. The acetone mean is more than 6 times the water mean. What does that tell you about the attractions between acetone molecules?
Is the difference between the ethanol and water means larger than the spread of the trials for either liquid?
Compare your ranking with the reference vapor pressures in Direct Instruction. Do the two kinds of evidence agree?
Modification for Distance Learning
Students analyze the sample data in a spreadsheet, and at home compare how fast a drop of water and a drop of rubbing alcohol disappear from a plate, with an adult present and no flames nearby.
2
Solids on a Hot Plate
20 minGroups of 3-4 (teacher-supervised)
Groups heat four white or colorless solids side by side and record which melt and how quickly. Each solid stands for a different kind of particle: paraffin wax (molecules), table sugar (molecules), table salt (ions) and clean sand (a network of silicon and oxygen atoms).
Procedure
Safety: goggles and heat-resistant gloves; the teacher sets the hot plate to medium-high and stays at the station. Keep the room ventilated, and turn the plate off as soon as the sugar starts to brown or smoke.
Fold an aluminum foil tray and place a pea-sized sample of each solid in its own corner, equal distances from the center.
Start the stopwatch when the tray goes on the plate. Record the time each solid starts to melt, up to 5 minutes.
Let the tray cool completely before handling; move it with tongs.
Sample Data (invented)
Paraffin wax started to melt at 20 s. Table sugar started to melt at 150 s and browned soon after. Table salt and sand showed no change after 300 s.
Discussion Questions
Rank the four solids by the strength of the attractions that hold their particles in place. Why can you not rank salt and sand from these data alone?
Reference melting points are about 55 °C for wax, 186 °C for sugar, 801 °C for salt and 1,710 °C for quartz sand. Does the order of the reference values match your observations?
Wax and sugar are both made of molecules. What does their difference tell you about using particle type alone to predict attractions?
Modification for Distance Learning
Show a recorded version of the hot plate test with a visible timer. Students record the melting times from the video and answer the questions in a short written report.
3
Critique a Plan, Then Run It
25 minGroups of 3-4
Groups critique a flawed plan for comparing surface attractions in water and 91% isopropyl alcohol using drops on a penny, write an improved plan, and then carry it out with five trials per liquid.
The Flawed Plan
"Count how many drops of water fit on a penny using a dropper. Then use a different dropper for the alcohol and count on a second penny, heads side up for one and tails side up for the other. Do it once for each liquid. More drops means stronger attractions."
Procedure
List every flaw in the plan and explain how each could change the result (different droppers give different drop sizes, different penny faces have different surfaces, one trial cannot show spread).
Write the improved plan: one dropper type, rinsed and dried between liquids, the same penny face, pennies cleaned and dried, 5 trials each, drops added from the same height.
Carry out the improved plan. Safety: goggles; the alcohol is flammable, so no flames in the room.
Find the mean and range for each liquid. Is the difference in means larger than either range?
Which flaw in the original plan would have had the biggest effect on the result, and why?
Write a claim about the attractions between particles, with the data as evidence.
Challenge Variation
Groups add a third liquid of their choice from the approved list (such as a sugar solution), predict its drop count from its particles, then test the prediction.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Vapor Pressure and Boiling Point of Five Liquids
Standard reference values, rounded, drawn to scale: vapor pressure at 20 °C against boiling point at 1 atm. The liquid with the highest vapor pressure (acetone) has the lowest boiling point, and water has the lowest vapor pressure and the highest boiling point. Both properties rank the attractions between particles in the same order.
Diagram 2: Four Kinds of Particles in Solids and Liquids
Schematic particle models, not to scale. In sodium chloride, oppositely charged ions attract in every direction; in graphite, bonds join the atoms of each layer into one network. Separate argon atoms and separate I2 molecules attract each other much more weakly, which is why argon and iodine melt at far lower temperatures than sodium chloride or graphite.
04
Homework Assignment
~30 min
HS-PS1-3 Homework: Planning Investigations and Inferring Particle Attractions
Directions: For planning problems, name the independent, dependent and controlled variables, the number of trials and the safety steps. For data problems, state which way the evidence points (stronger or weaker attractions) and cite the numbers. Reference values are standard rounded values; all other data are invented.
Part 1: Plan and Critique (Problems 1-2)
Your teacher gives you two clear, colorless liquids, L and M, and says to treat both as flammable. Plan an investigation, using a method other than the evaporative cooling plan from class, to decide which liquid has stronger attractions between its particles. Include the variables, at least three trials, a data table, the safety steps, and the result that would mean L has the stronger attractions.
A student compared evaporation by putting 5 mL of water in a dish on a sunny windowsill and 2 mL of ethanol in a dish of the same size in a shaded cupboard. The ethanol was gone first, and the student concluded that ethanol has weaker attractions. (a) Identify two flaws. (b) Explain how each flaw could produce the result even if the conclusion were wrong. (c) Rewrite the plan.
Part 2: Analyze Bulk-Property Data (Problems 3-4)
Reference boiling points of the halogens are: fluorine (F2) -188 °C, chlorine (Cl2) -34 °C, bromine (Br2) 59 °C, iodine (I2) 184 °C. Melting points are bromine -7 °C and iodine 114 °C. (a) Rank the attractions between the molecules. (b) Use the data to state whether each halogen is a solid, liquid or gas at 25 °C. (c) Describe how the strength of the attractions changes as the molecules get larger.
Three white solids were tested in a melting-point apparatus that reaches 300 °C: solid P melted at 80 °C, solid Q at 146 °C, and solid R did not melt. R dissolves in water, and the solution conducts electricity; P and Q do not conduct. (a) Rank the attractions between particles. (b) Infer the kind of particles in each solid and explain. (c) What further test would give a melting point for R?
Part 3: Conduct and Conclude (Problems 5-6)
Liquids X, Y and Z were each placed in a sealed flask at 20 °C with a pressure sensor, and the vapor pressure was recorded after it stopped changing: X 3.1 kPa, Y 12.4 kPa, Z 0.5 kPa. (a) Rank the liquids from strongest to weakest attractions. (b) Predict the order of their boiling points. (c) How many times larger is the vapor pressure of Y than that of X?
A group measured the evaporative cooling of water four times and got temperature drops of 2.5, 2.3, 6.9 and 2.4 °C. Their notes say the sleeve on trial 3 was wrapped much more loosely. For 91% isopropyl alcohol they got 9.8, 10.4, 10.1 and 9.7 °C. (a) Find the mean for water with and without trial 3, and decide which to report. (b) Find the mean for the alcohol. (c) Write a claim, evidence and reasoning statement about the attractions between particles.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Investigation Plan
One independent variable, a measured dependent variable, at least three relevant controls, repeated trials and safety steps
Plan missing controls or repeated trials, or safety is incomplete
Data Analysis
Means, ranges or comparisons are correct and the difference is compared with the spread of the trials
One calculation error, or the spread of the trials is ignored
Inference About Attractions
Ranks the attractions in the direction the evidence supports and names the bulk property used
Correct ranking with no evidence cited, or one inference in the wrong direction
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Reference values are standard rounded values and all other data are invented. You only need to say whether attractions are stronger or weaker, not name the type of force. Pick an option to check it, and use Reset quiz to clear your answers.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
At 1 atm, liquid A boils at 65 °C and liquid B boils at 140 °C. Which conclusion do the data support?
Answer: C
Boiling pulls particles apart into the gas, so the liquid that needs the higher temperature (B, 140 °C) has the stronger attractions. Choice A reverses the inference. Choice D is wrong: boiling point is one of the bulk properties the standard uses as evidence.
Question 2 of 20 · Multiple Choice
At the same temperature, liquid J has a much higher vapor pressure than liquid K. What does this suggest?
Answer: A
A higher vapor pressure means more particles escape from the liquid at that temperature, which happens when the attractions holding them in are weaker. Choice B reverses the inference, and choice C is the opposite of the usual pattern: higher vapor pressure goes with a lower boiling point.
Question 3 of 20 · Multiple Choice
A student compares surface attractions by measuring how high each of three liquids climbs up a narrow glass tube dipped into it. Which variable must be kept the same for all three liquids?
Answer: B
A narrower tube makes any liquid climb higher, so the tube width must be controlled or the heights cannot be compared. Choice A is the independent variable, and choice C is the dependent variable that is measured. Choice D does not affect the result if the tube is cleaned and dried between liquids.
Question 4 of 20 · Multiple Choice
In an investigation that counts how many drops of a liquid fit on a penny before it overflows, what is the dependent variable?
Answer: D
The dependent variable is the result that is measured: the number of drops. The type of liquid (choice A) is the independent variable, and the dropper size and penny face (choices B and C) should be controlled.
Question 5 of 20 · Multiple Choice
Three trials of evaporative cooling with one liquid gave temperature drops of 5.8, 6.3 and 6.1 °C. What is the mean drop, to one decimal place?
Answer: A
The mean is (5.8 + 6.3 + 6.1) ÷ 3 = 18.2 ÷ 3 ≈ 6.07, which rounds to 6.1 °C. Choice B is the sum without dividing. Choice C is the range (6.3 - 5.8), and choice D is the largest single trial.
Question 6 of 20 · Multiple Choice
A hard, colorless solid does not melt at 1,000 °C, does not dissolve in water and does not conduct electricity. Which kind of particle structure best fits this evidence?
Answer: C
A very high melting point means very strong forces must be overcome, and no conductivity rules out ions free to move. A network of atoms bonded throughout, like quartz, fits all three observations. Choices A and B would melt at low temperatures.
Question 7 of 20 · Multiple Choice
Silicon carbide, used in sandpaper, does not melt below about 2,700 °C. Which inference about its structure is best supported?
Answer: B
Only a structure in which melting requires breaking strong bonds throughout the sample explains such a high melting point, so silicon carbide is a networked material. Choices A and C describe substances with low melting points. Choice D is impossible for a solid that holds together.
Question 8 of 20 · Multiple Choice
Magnesium oxide (ions Mg2+ and O2-) melts at about 2,852 °C, and sodium chloride (Na+ and Cl-) melts at 801 °C. Which explanation best fits the data?
Answer: D
Both solids are made of ions, but the charges in magnesium oxide are twice as large on each ion, so the electrical attraction between neighboring ions is stronger and more energy is needed to melt the solid. Choice C reverses the charges, and choices A and B misidentify the particles.
Question 9 of 20 · Multiple Choice
A student compares evaporation by putting 5 mL of water in a wide, shallow dish and 5 mL of ethanol in a narrow cup. What is the main flaw?
Answer: A
Evaporation happens at the surface, so a wider dish speeds it up regardless of the attractions between particles. Choice B is false: both are 5 mL. Choice C is false: the liquid is the independent variable.
Question 10 of 20 · Multiple Choice
A steel paper clip laid gently on water floats, but the same paper clip sinks in rubbing alcohol. What does this suggest?
Answer: C
The clip is held up by the surface, not by buoyancy: the stronger pull of water particles on each other gives water the higher surface tension. Choice A is false and would help the clip float, not sink. Choice D is not supported by any evidence.
Question 11 of 20 · Multiple Choice
Why should an investigation of a bulk property include several trials for each substance?
Answer: B
Repeated trials show how much results vary by chance, so a difference between substances can be judged against that variation. Choice C is not true in general, and choice D misunderstands the mean.
Question 12 of 20 · Multiple Choice
The mean evaporation times of 0.10 mL spots of three liquids were: liquid L 95 s, liquid M 400 s, liquid N 1,200 s. Which liquid has the strongest attractions between its particles?
Answer: D
The liquid that takes longest to evaporate holds on to its particles most strongly, so N (1,200 s) has the strongest attractions and L the weakest. Choice A reverses the inference by treating fast evaporation as strong attraction.
Question 13 of 20 · Multiple Choice
Of four liquids, one has much stronger attractions between its particles than the others. Which set of properties would you predict for that liquid?
Answer: C
Strong attractions make particles harder to separate, which raises the boiling point, lowers the vapor pressure and slows evaporation. Choices A, B and D each describe the liquid with the weakest attractions.
Question 14 of 20 · Multiple Choice
A student proposes to compare the boiling points of ethanol and water by heating each in a beaker over a Bunsen burner. What is the best response?
Answer: A
Ethanol vapor catches fire easily, so an open flame near it is a serious hazard; reference data or a flameless method answers the same question safely. Choices B and C make the hazard worse (a sealed container can also build up pressure), and choice D mixes the liquids, so neither boiling point could be measured.
Question 15 of 20 · Short Answer
Plan an investigation that uses a gas pressure sensor to compare the attractions between particles in two liquids at room temperature. Name the independent variable, the dependent variable, three controlled variables, the number of trials, and the result that would show stronger attractions.
Independent variable: which liquid is in the flask. Dependent variable: the vapor pressure reading once it stops changing. Controls: the same flask size, the same volume of liquid (for example 1.0 mL), the same temperature (flasks sitting in the same room-temperature water bath). At least 3 trials per liquid with a clean, dry flask each time. The liquid with the lower vapor pressure has the stronger attractions. Safety: goggles, and no flames if either liquid is flammable.
Question 16 of 20 · Short Answer
Two liquids were tested with drops on a penny. Liquid P: 25, 27, 26 drops. Liquid Q: 24, 29, 22 drops. Find each mean and range, and decide whether the data show a difference in surface attractions.
P: mean 26 drops, range 2. Q: mean 25 drops, range 7. The difference in means (1 drop) is much smaller than the spread of Q's trials, so the data do not show a clear difference. More trials or a more sensitive method would be needed.
Question 17 of 20 · Short Answer
Solid S melts at 1,418 °C and conducts electricity when melted but not as a solid. Solid T melts at 122 °C and does not conduct when melted. Infer the kind of particles in each and compare the strength of the attractions.
S is most likely made of ions: its high melting point shows very strong attractions, and conducting when melted shows charged particles free to move. T is most likely made of molecules: its low melting point shows the attractions between its particles are much weaker, and it has no free ions. The attractions in S are far stronger.
Question 18 of 20 · Short Answer
Methane (CH4) boils at -162 °C and water (H2O) at 100 °C, although their molecules are about the same size. What can you infer, and how large is the difference in boiling points?
The boiling points differ by 100 - (-162) = 262 °C. Since the molecules are similar in size, the difference must come from how strongly they attract each other: water molecules attract each other much more strongly than methane molecules do. (Naming the type of force is not required.)
Question 19 of 20 · Short Answer
A student reports that liquid X cooled the thermometer by 9 °C and liquid Y by 4 °C, and concludes that X has weaker attractions. You learn that X started at 25 °C and Y at 18 °C. Explain why the conclusion is not yet valid and how to fix the investigation.
Starting temperature was not controlled. A warmer liquid evaporates faster, so X could have cooled more simply because it started 7 °C warmer, not because its particles attract more weakly. Fix: let both liquids reach the same room temperature (checked with the thermometer) before dipping, and repeat each test at least three times.
Question 20 of 20 · Short Answer
Liquid J has a vapor pressure of 3.0 kPa at 20 °C and a surface tension of 60 mN/m. Liquid K has a vapor pressure of 18 kPa and a surface tension of 24 mN/m. Write a claim, evidence and reasoning statement about which liquid has stronger attractions.
Claim: J has stronger attractions between its particles. Evidence: J's vapor pressure is 6 times lower (3.0 vs 18 kPa) and its surface tension 2.5 times higher (60 vs 24 mN/m). Reasoning: fewer particles escape from J at the same temperature, and J's surface particles pull on each other more strongly; both point to stronger attractions, so the two kinds of evidence agree.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-PS1-3 mean?
HS-PS1-3 asks students to plan and conduct investigations of properties they can measure in a sample, such as melting point, boiling point, vapor pressure and surface tension, and use the results to infer how strongly the particles of the substance attract each other. The code stands for High School, Physical Science, core idea 1 (Matter and Its Interactions), performance expectation 3.
Do students have to name intermolecular forces for HS-PS1-3?
No. The Clarification Statement puts the emphasis on the strength of the forces between particles, not on naming specific intermolecular forces such as dipole-dipole. Students should be able to say which substance has stronger attractions and support it with bulk-property evidence.
What is the assessment boundary for HS-PS1-3?
The only official limit is that assessment does not include Raoult's law calculations of vapor pressure. Students can compare vapor pressures and use them to rank attractions, but they do not calculate the vapor pressure of a solution or mixture.
What are bulk properties in chemistry?
Bulk properties are properties of a sample large enough to handle and measure, rather than of a single particle. The ones named for this standard are melting point, boiling point, vapor pressure and surface tension; evaporation rate is a practical classroom measure linked to vapor pressure.
How does boiling point show the strength of attractions between particles?
A higher boiling point means stronger attractions. To boil, particles must separate from each other and enter the gas, and stronger attractions need more energy, which means a higher temperature. Boiling does not break the bonds inside molecules; the molecules stay whole.
Why do ionic compounds and networked materials have such high melting points?
In an ionic solid, every ion is attracted to many oppositely charged neighbors, and in a networked material such as graphite or quartz, bonds join the atoms throughout the sample. Melting either one means overcoming very strong forces, so it takes a very high temperature.
What labs work well for HS-PS1-3?
Evaporative cooling with a thermometer and filter paper sleeve, counting drops of liquid on a penny, timing the evaporation of small spots, and comparing solids on a hot plate are safe and inexpensive. Use goggles, keep flames away from flammable liquids, and have the teacher supervise any heating.
What mistakes do students make when inferring forces from data?
A frequent one is reading fast evaporation or a high vapor pressure as a sign of strong attractions, when it means the opposite. Other common mistakes are thinking that boiling breaks molecules apart into atoms, and drawing a conclusion from one trial without checking the spread of the data.
How does HS-PS1-3 connect to the periodic table standards?
The kinds of bonds predicted in HS-PS1-1, ionic or covalent, decide whether a substance is made of ions, molecules or a network, and that in turn shapes its bulk properties. HS-PS1-3 is where students gather the bulk-scale evidence for those particle-level ideas.
What comes after HS-PS1-3?
HS-PS2-6 asks students to communicate why molecular-level structure matters in the function of designed materials, which uses the same link between particles and bulk properties. HS-PS1-4 and HS-PS3-2 extend the ideas to energy stored in bonds and in the arrangement of particles.
07
Related Standards
5 standards
These standards connect to HS-PS1-3: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-PS1-4Prerequisite
Model how particle motion, temperature and state change when thermal energy is added or removed
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