Good Morning 04/21/23• Starter: You are trying to get a job and your

interviewer has asked you to do the following…– Take as many pieces of paper from a stack as

you want. Then you must leave half of the sheets plus ½ a sheet of paper on the desk. After that you must give half of the remaining sheets plus ½ a sheet to the interviewer. Once that is done you must still have 1 sheet left. But you can not rip, cut or mangle the paper. How many sheets do you take?

• Today we will be…– Working through the Physical & chemical

Changes Lab • With any remaining time we will work on the

Review.• The test is tomorrow.

Answer

• 7,

• Half the paper is 3½ plus a ½ is 4 sheets

• Half of the 3 remaining sheets is 1½ plus ½ is 2.

• You now have 1 sheet left.

To access the Lab Report

• Open up the “Shortcut to Science Shares”

• Then open the “Durand” Folder

• “PhySci B” Folder

• The word doc titled “Phys&ChemChangesLab”

• This doc has your instructions and you will type in your answers and save it when you are done.

• There will be instructions on how to save at the bottom of the word doc.

Saving your document for credit

• Click Save as under the file menu it will automatically try to save it in the “PhySci B folder, you must select your class period (1st, 2nd 3rd or 5th) Save it in the following format

• Last Name_FirstInitial_Changes Lab• Example: Durand_M_Changes Lab.• Then repeat this for each of your Lab

partners or have them type it in.

Please read the lab through very carefully and follow the instructions.• Once everyone is done we will go over the

answers.

Preparation

• Send two people up to the center desk. One will need to hold the test tubes while the other scoops the materials into the test tube.Red crystals – 2 of the small scoopsPink crystals – 2 of the small scoopsWhite crystals – 1 of the small scoops

Clean up • White Crystals – clean out as much as possible

onto a paper towel and throw it away, then clean it out with water from the squeeze bottle and wash it down the drain.

• HCl & Zinc – pour into the waste beaker on the center table labeled for the HCl & Zinc.

• Red Crystals – pour into the waste beaker on the center table labeled “Red Crystals & Water”

• Shaving Cream – throw away the paper towel and wash off the stirring rod.

• Pink crystals – pour into the waste beaker on the center table labeled “Pink Crystals & Water”

White Crystals• Observations:

• The combination turned into a clear gelatin like substance. Seeming to absorb the water.

• Physical or Chemical Change?

• Physical

• How do you know?

• no gas (like O2 or H2) was given off, which indicates that the water is still water

HCl & Zinc• Observations:• Gas bubbles were released and the metal

disappeared. • Physical or Chemical Change?• Chemical• How do you know?• A gas was given off, which tells us that

something broke down. Did you waft the gas? Did it smell like a swimming pool? If not what does that mean what do you think the gas could be?

Red Crystals• Observations:• The crystals appeared to repel the water,

and made a little globule (clumped together) when the test tube was slanted the crystals “broke through” to the surface.

• Physical or Chemical Change?• Physical• How do you know?• There was no interaction they didn’t even

mix!

Shaving Cream• Observations:• The substance turned white, became

foamy and it got much larger. • Physical or Chemical Change?• Physical• How do you know?• This one is tricky because it looks totally

different, but all we did was mix in the air. There was no gas released and no heat given off.

Pink Crystals• Observations:

• When the water was added the crystals disappeared and the liquid became a fluorescent yellow color.

• Physical or Chemical Change?

• Physical

• How do you know?

• no gas (like O2 or H2) was given off, which indicates that the water is still water.

Mysteries Revealed

• White Crystals – water absorbing particles from a diaper

• HCl & Zinc – it is what it is no mystery

• Red Crystals – Mystic Sand which is simply white sand coated with a “hydrophobic” (water fearing) chemical

• Shaving Cream – no mystery

• Pink crystals – salt with food coloring

• Now that you know please don’t tell everyone else.

Would you like a deeper explanation of Mixtures?

• Milk is an example of a specific kind of mixture called a colloid.

Colloids

• A colloid (KAH loyd) is a type of mixture with particles that are larger than those in solutions but not heavy enough to settle out.

• One way to distinguish a colloid from a solution is by its appearance.

Detecting Colloids

• Fog appears white because its particles are large enough to scatter light.

• You can tell for certain if a liquid is a colloid by passing a beam of light through it.

• A light beam is invisible as it passes through a solution, but can be seen readily as it passes through a colloid. This occurs because the particles in the colloid are large enough to scatter light, but those in the solution are not.

Detecting Colloids

• This scattering of light by colloidal particles is called the Tyndall effect.

• Some mixtures are neither solutions nor colloids. One example is muddy pond water.

Suspensions

• Pond water is a suspension, which is a heterogeneous mixture containing a liquid in which visible particles settle.

• A Solution neither scatters light or can be made more clear by filtering.

Solutions

• The table summarizes the properties of different types of mixtures.

A Quiz

Link