For those of you absent Friday 1/9/15 here is the link to a YouTube on hydrogen bonding and the lab we did at the end of the hour

The review for the 2nd quarter final is also available in a different file on this web site (don’t cheat and look at the answers until you try the problems). A hard copy of the review will be given out in class on Monday

Friday, 1/09/2015Learning Target: SWBAT draw and explain Hydrogen Bonds between molecules

-Open your desk top textbook to p. 423 (our home book it’s page 412-415)

-In your Notebook:

  • Write:INTERMOLECULAR FORCES HYDROGEN BONDS
    ELECTRON DENSITYPARTIAL CHARGE

-Watch Hydrogen Bonding video (see link above)

  • Take notes, in your notebook.

-Lab: Surface Tension

  • Surface tension is the result of intermolecular forces, including hydrogen bonds.
  • How much of each liquid can you stack on a penny? How would you describe the differences between the liquids?

-Due today: Word web / Flow chart

-Extra credit that is on the web site is also due by Tuesday before finals (this is the last week to cook)

Definitions for Friday, 1/09/15

-Intermolecular forces – Forces that act between molecules

-Hydrogen bonds – Attractive intermolecular force, specifically between an H attached to an O, F, or N to another molecule’s O, F, or N.

-Electron Density – Probability that an electron will be at a particular location. Higher electronegativity means higher electron density, and partial negative charge.

-Partial charge – Charge that is less than a full electron or proton’s charge. Results from differences in electron density.

Name: ______period: ____ date: ______

Surface Tension and Intermolecular Forcesver 2

Background: The attractions between molecules are called intermolecular forces. There are three main types of intermolecular forces: dispersion forces, dipole-dipole interactions, and hydrogen bonding. Dispersion forces are the weakest form of intermolecular attraction, dipole-dipole interactions are the second weakest, and hydrogen bonding is the strongest form of intermolecular attraction.

Surface tension is caused by forces between molecules (intermolecular forces) that form cohesion between molecules. Stronger attractions between liquid molecules result in higher (stronger) surface tension of the liquid.

Questions: Do different liquids have different degrees of surface tension? Why?

What role does polarity play in the surface tension of water?

How are intermolecular forces related to surface tension?

Procedure:

Move around the lab to collect data at 4 different lab stations: water, oil, alcohol, and soapy water.

  1. Go to a station and check your materials. Each station should have a couple of pennies and one of the four liquids. Each liquid will have a pipette to measure drops. You will also have a plastic tray to keep it all neat. Don’t move the pipettes between stations (to avoid cross contamination)
  2. Place your penny on the counter; put a brown paper towel under your penny to help clean up when it spills.
  3. Use the pipette and count how many drops of the liquid you can add to the penny until the liquid drips off the penny. Try to keep the drop size as consistent as possible(the more freely the drops fall through the air they more uniform they will be; keep angle of pipette consistent as well).
  4. Do three trials for each liquid; find an average. Record your data in the table below.
  5. Repeat steps 2 and 4 using the different solutions
  6. Water
  7. Oil (baby oil)
  8. Alcohol (isopropyl)
  9. Soapy water

Data Table:

# of drops / Pure water / Oil (baby oil) / Alcohol water / Soap water
Trial 1
Trial 2
Trial 3
Average of trials

Questions and Conclusions:

  1. Which liquids have the strongest surface tension? The weakest?
  1. How do dissolved substances affect the surface tension of water?
  1. Which solution had the greatest intermolecular forces holding it together? What types of forces were they?
  1. Which solution had the weakest intermolecular forces holding it together? What types of forces might they have been?