To be or not to be… Dichotomous keys in Chemistry

Chemicals Before we can start looking at the way individual chemicals react with each other, we have to identify the different types of “stuff” that can be used. All the physical material that exists is called “matter”. Matter can be subdivided into many different types based on its chemical and physical properties. We can use a “Dichotomous Key” to identify the various types by asking questions with “yes or no” type responses. Below is such a key, showing the division of matter into various types. You will need to include all these terms in your glossary.

Dichotomous Key

 

 

 

1. a) the contents have mass and take up space go to Question 2
  b) the contents do not have mass or does not take up space it is ENERGY
2. a) the contents have a variable composition, a sample of this material is not uniform or different samples could differ in the proportions of the things that make it up it is a MIXTURE; go to Question 3
  b) the contents have a definite composition; every sample of this material will have the same composition it is a PURE SUBSTANCE; go to Question 6
3. a) the contents are uniform throughout, although their proportions could differ from one sample to another. it is a HOMOGENEOUS MIXTURE; go to Question 5
  b) the contents vary in composition or traits from one part of the sample to another; they do not appear uniform or are known to vary from one part of a sample to another or to settle out over time it is a HETEROGENEOUS MIXTURE; go to Question 4
4. a) the contents may appear uniformly distributed, but solid particles will settle out of the liquid portion of the mixture it is a SUSPENSION
  b) the contents visibly vary in composition. it is a HETEROGENEOUS MIXTURE
5. a) the particles of the homogeneous mixture are atoms, ions, or molecules; in a transparent mixture they will not scatter a beam of light it is a SOLUTION
  b) the particles of the homogeneous mixture are larger than molecules, they make the mixture appear cloudy or milky or they scatter light in a transparent mixture it is a COLLOID
6. a) the substance is made up of a single type of atom that has a symbol and appears on the Periodic Table of the Elements it is an ELEMENT
  b) the substance is made up of two or more atoms chemically combined in a fixed ratio it is a COMPOUND
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4 Comments on “To be or not to be… Dichotomous keys in Chemistry”

  1. Lynette Says:

    The table isn’t aligned properly with the rest of the page. ‘Tis hard to read.
    =[

  2. Mark L Says:

    Hi Mr G,

    I am kind of confused with the deifnition of heterogenous mixture. Which one is the correct one? Or are they both correct?

    By the way, the B&W periodic table was very useful in my quest to remember the first 20 elements.

    Mark
    10m

  3. mrgrichting Says:

    Unfortunately, the table is a microsoft word implant, and it’s not playing nicely with the blogging software.

    Mark, both of them are correct – solutions are a subtype of Heterogenous mixtures; everything that is not a solution is just called a heterogeneous mixture. It’s sort of like saying some soups are tomato soups, but all soups (including tomato soups) are soup. It’s sort of confusing!

  4. Mark L Says:

    Thank you for that clarification.

    Mark


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