Unit 3 check
Unit 3 check: Properties of Substances and Mixtures
13 questions from 13 lessons in Unit 3. Answer each one, and if you miss, follow the link back to where it is taught, then try again. Your score counts first tries.
Question 1 · from 3.1 · Rank it
All three are nonpolar hydrocarbons. Propane, CH₃CH₂CH₃, has 26 electrons. Pentane, CH₃CH₂CH₂CH₂CH₃, has 42 electrons in a chain of five carbon atoms. 2,2-Dimethylpropane, C(CH₃)₄, also has 42 electrons, with four carbon atoms bonded around a central one, which makes the molecule compact. Rank the three by the strength of the dispersion forces between their own molecules.
Strongest first
Give each one a place, 1 for first. Give two the same place if they are equal.
Your ranking: none yet
Question 2 · from 3.2 · Sort it
Potassium chloride, KCl, is an ionic solid that melts at 770 °C. Sort each sample by whether it conducts electricity. Tap a card, then its bin.
Conducts
Does not conduct
Question 3 · from 3.3 · Fill the statement
A sealed, rigid steel tank of helium is carried from a cool room into hot sunlight. The tank's volume does not change, and no helium gets in or out. Complete the description of the helium inside.
The average spacing between the helium atoms , and the atoms collide with one another and with the walls often and .
Question 4 · from 3.4 · Sketch the graph
A fixed amount of gas is held at constant temperature in a cylinder with a movable piston. At 1 L its pressure is 1200 kPa. Sketch how its pressure changes as the volume is raised one liter at a time to 6 L. The first point is placed for you; drag the others so the graph rises or falls the way the pressure does, and bends the same way along its whole length, as the pressure does.
One shape that fits
Drag a point up or down, or tap it and use the arrow keys. Only the shape is checked.
Setup for question 5
Samples of gas that differ in temperature, in the mass of their particles, or in both.
Question 5 · from 3.5 · Decide and justify
Flask X holds oxygen at 300 K, and flask Y holds oxygen at 600 K. A student claims that every molecule in flask Y is moving faster than every molecule in flask X. Is the claim correct?
Which reason supports your decision?
Setup for question 6
Four flasks each hold 1.00 mol of a noble gas in 1.00 L at 300. K, where PV = nRT predicts 24.6 atm for every one. The table gives each gas’s pressure from a model of real gases, used here as a teaching example.
| Gas | Electrons per atom | Pressure from the model (atm) | Ideal gas law (atm) |
|---|---|---|---|
| Helium | 2 | 25.2 | 24.6 |
| Neon | 10 | 24.8 | 24.6 |
| Argon | 18 | 24.1 | 24.6 |
| Krypton | 36 | 23.3 | 24.6 |
Question 6 · from 3.6 · Decide and justify
Using the table: xenon, with 54 electrons per atom, is put in a fifth flask under the same conditions. Will its pressure be above or below krypton’s 23.3 atm?
Which reason supports your decision?
Setup for question 7
A class made four sugar solutions, each in a volumetric flask filled to the mark. The data are a teaching example.
| Solution | Solute | Molar mass (g/mol) | Mass of solute (g) | Volume of solution (mL) |
|---|---|---|---|---|
| A | Glucose, C₆H₁₂O₆ | 180.16 | 27.0 | 500.0 |
| B | Sucrose, C₁₂H₂₂O₁₁ | 342.30 | 17.1 | 250.0 |
| C | Glucose, C₆H₁₂O₆ | 180.16 | 4.50 | 50.0 |
| D | Sucrose, C₁₂H₂₂O₁₁ | 342.30 | 68.5 | 500.0 |
Question 7 · from 3.7 · Calculate
Using the table: a student takes 10.0 mL of solution C. How many glucose molecules does the 10.0 mL hold? Give your answer to three significant figures, typed in e-notation (6.022 × 10²³ is typed 6.022e23).
Question 8 · from 3.8 · Spot the error
A student plans a drawing of magnesium nitrate, Mg(NO₃)₂, dissolved in water. Tap the line with the mistake.
Question 9 · from 3.9 · Multiple choice
A student pours sugar water through filter paper, and the liquid that comes through tastes just as sweet as before. Which explanation is correct?
Question 10 · from 3.10 · Fill the statement
Complete the explanation of why potassium bromide, KBr, dissolves in water but barely dissolves in hexane.
In water, the molecules around each K⁺ ion point their ends toward it, and the molecules around each Br⁻ ion point their ends toward it. These attractions pull the ions out of the solid. Hexane is .
Question 11 · from 3.11 · Fill the statement
Complete the explanation of which region of the spectrum goes with a change in a molecule's rotational level.
Of the three kinds of levels, rotational levels are the , so a step between them needs a photon with the energy. Those photons are photons.
Question 12 · from 3.12 · Calculate
Sodium streetlamps glow with yellow light of wavelength 589 nm. Using h = 6.626 × 10⁻³⁴ J·s and c = 2.998 × 10⁸ m/s, calculate the energy of one photon of this light. Give your answer to three significant figures.
Setup for question 13
Two new situations: things that can go wrong in a real measurement, and a cuvette narrower than the usual one.
Question 13 · from 3.13 · Sort it
A student made a calibration line with clean, dry 1.00 cm cuvettes at a dye's wavelength of maximum absorbance. Each card is something that went wrong with the reading of the unknown only. Sort each card by its effect on the unknown's measured absorbance.
Higher than it should be
Lower than it should be
0 of 13 answered.