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With mouth wide open, vibrating air coming up the throat from the vocal chords leaving the open mouth and spreading in all directions. Hi, I am Janice VanCleave, author of 50+ best-selling science experiment books for children ages 4 through high school. I taught science for 27 years and now am creating this science website.   My scream was not staged. The picture was to be of two adult cats, which I was holding. A microsecond before the camera snapped, the two cats dug their claws into my skin as they prepared to leap out of my arms. A picture like this is great for making inferences. Kids could make "guesses" as to why I am screaming. They would be drawing on facts from the photo, such as I look like I am in pain or maybe I am just pretending.

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Home » Chemistry: Density

Chemistry: Density

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teaching-math2

Notes from Janice’s Desk

Density is a physical property describing the mass of one unit volume of a substance. If the mass is measured in grams, generally the volume is measured in milliliters or cubic centimeters. (NOTE: 1 ml = 1 cm3)

black-round-bullet1 A pure substance is an element, such as copper or gold  or a compound, such as water or sodium chloride (table salt).

black-round-bullet1 The density of pure substances is constant. This means that they do not change as long as other materials are not mixed with them.

black-round-bullet1 Memorize the density of water, which is: density of water = 1g/1ml.
This means that 1 gram of water occupies a space of 1 ml.

Since density is a constant, it can be used as a conversion factor, which is a ratio used in math calculations to change units.

Dimensional analysis is the math process in which one or more conversion factors are used to solve a problem.

DON’T PANIC! IT SOUNDS HARDER THAN IT IS.

Problem:

1. The density of a liquid is 4 g/ml. What is the mass of 3 ml of the liquid?

ARE YOU THINKING, “I CAN DO THIS PROBLEM IN MY HEAD. THE MASS IS 12 g.  SO WHY BOTHER WITH DIMENSIONAL ANALYSIS?”

TRUST ME. IF YOU PLAN TO DO WELL IN YOUR CHEMISTRY CLASS, YOU NEED TO BE A WHIZ AT DIMENSIONAL ANALYSIS.

For step-by-step instructions for using dimensional analysis to solve the problem, see MATH: DIMENSIONAL ANALYSIS

More Later,

Janice