1. Unknown White Powder Lab
Purpose:
In this lab we are investigating the physical and chemical properties of 4 unknown white powders. A B C D
density
solubility
luster/sheen
Physical properties
melting point
color
TEACHER NOTES
Beforehand:
Go through a perform each test yourself. Doing this lab without having done the tests yourself this will leave you quite unprepared.
Materials per group: 4 unknown white powers (baking soda, salt, sugar, and crushed white chalk) and 4 weighing trays (or small cups) to put their unknown powder in. Rulers- for drawing straight lines when setting up their paper. Additionally, see notes area of next slide for materials students will need to test each property.
Safety: This lab uses fire. Therefore, students WILL wear goggles the entire day, and you need to be familiar with where your safety equipment is and how each item works. Before students begin working, remind them how dangerous loose hair, clothing, and paper is around fire. Also, you’ll want to stay near where there’s fire for most of class, to keep an eye on things.
Procedure: (*note- this lab takes 1 ½ days to do; ½ day for students to set their papers up and to explain how each test works, and the other full day for students to perform the tests)
Have students take out a sheet of notebook paper, and go through slide 1 with them (above) listing the properties that will be tested. This could have been made a handout that you simply give students, but having them do this brings more attention to the tests that will be done, and gives you the occasion to say a few words about each. Have them use rulers to draw the lines. We’ll write the ‘Purpose’ first because things are going to get quite busy, and we don’t want to lose track of what this is all about.
When papers are set up, go through slide 2, explaining what they’ll do to test each property and what kinds of things they’ll be writing for observations. As you explain, walk to that station- if there is one- and give a quick demonstration, so you’re clear as can be. You’re going to be busy enough managing this lab without having to re-explain how to do something. Also tell students the order of stations doesn’t matter, so if one’s full, just do another test.
Once students are grouped, have them begin by getting a sample of each powder and putting them in weighing trays or small cups that have been marked with letters A, B, C, and D. Each group needs just a teaspoon of each powder to test all properties.
(Teacher Notes continue below slide 2)
smell
texture
flammability
Chemical
properties
reactivity with vinegar

2. Here’s what you’re going to DO
Unknown White Powder Lab
Purpose:
In this lab we are investigating the physical and chemical properties of 4 unknown white powders. A B C D
density
Put exactly 1 mL in a small graduated cylinder and weigh
solubility
Now put on goggles and get working
Does it dissolve in water?
luster/sheen
Is it shiny? Dull?
Physical properties
“Low” if it melts quickly (<5 sec.), “Medium” if it melts between 5-10 sec., “High” if it doesn’t melt after 10 sec.
melting point
color
Compare all 4 next to each other
With materials and stations already set up, talk through this slide so students are clear on how each test is performed. Be especially clear on safety issues. Leave this slide on your screen while students work.
Here’s a list of tests, their materials in parenthesis, and what to do. Have students write observations/results on their papers.
Density: (small graduated cylinder, balance or scale) Put exactly 1 mL of each powder in the cylinder and weigh; subtract out mass of cylinder. What you’re left with is it’s density in grams/mL
Solubility: (beaker, water, spoon or stirring rod) Does each powder dissolve in water?
Luster/sheen: (no add’l materials) Lining up the 4 powders side-by-side for comparison helps. What’s one or two words that best describes the appearance of each powder?
Melting point: (aluminum foil, flame from candle or burner, scissors, test tube clamp) Students will cut a small square of foil (about 3 inches by 3 inches) and wrap it over the end of their finger to make a small bowl. Add a bit of the first powder to it. Hold the foil bowl over flame with the test tube clamp and see if it’s melting point is low (melts in less than 5 seconds), medium (between 5-10 seconds), or high (hasn’t melted after 10 seconds). Make another bowl for the other powders. DO NOT HEAT IT LONGER THAN 10 SECONDS OR IT WILL SMOKE. STAY NEAR THIS STATION ALL CLASS PERIOD. (We’re not doing an exact melting temp. with thermometers at this station because that would complicate things much more than needed; we’re just focused here on the physical property of whether it melts or not.)
Color: (no add’l materials) Line up the 4 powders side-by-side for comparison. They may all be ‘white’, but they’re not all the exact same hue.
Smell: (no add’l materials). In chemistry the proper way to smell is to hold it away from your nose and use your hand to waft in the odor. When you smell each powder, is it’s smell familiar or remind you of something?
Texture: (no add’l materials). Rub some of each powder between your fingers. What’s one or two words that best describes how each feels?
Flammability: (foil, scissors, wood splint) Cut a piece of foil long enough that you can put a sample of each power on the foil, then bring a burning splint up to each powder. Besides being flammable, does the flame causes it to scorch or produce a certain odor? STAY NEAR THIS STATION, AND MAKE SURE ALL FLAMMABLES- PAPER, ETC- ARE KEPT AWAY FROM FLAME.
Reactivity With Vinegar: ideally you have micro well plates for this; if not, just put a sample of each on a long piece of foil and add some drops of vinegar to the powders.
Each group will also need a small metal spatula to scoop samples of each powder (at half of the stations). If you don’t have those, baby spoons would also work.
NO you don’t have to do each test; just those you want to. YES there are other tests not listed you can add in. And YES there are other ways you can do the tests in this lesson; feel free to make those changes (all text in this ppt is editable).
Questions to answer for homework when finished: (which point back at the original purpose of the lab- learning what phys./chem. properties are)
Which 2 or 3 properties would be most helpful in identifying the substance? Explain. (Clarify by saying to students- ‘telling me you have a white powder is nearly useless because they all were; however, which tests seemed to give different results?’)
How are chemical properties different from physical properties? Use examples from this lab in your answer. (Example answer- Physical properties are characteristics you can observe without changing what the substance is. When we melted powder B, it didn’t become something new; it was the same substance. The same is true for color. Chemical properties, however, are observed when the substance changes into something new that wasn’t there before. When substance C reacted with vinegar, it changed into a new substance.)
smell
Any odor? Smell like something familiar?
texture
Feel them- Sicky? Rough? Gritty? Smooth?
Set a small sample of each on foil and bring a burning splint up to each.
flammability
Chemical
properties
reactivity with vinegar
Small sample of each on foil and add a few drops of vinegar