Saturday, September 6, 2008

Results from the Quiz

Surprisingly, I did pretty well on the test, except for the mixtures and pure substances. Can anybody tell me why milk is a mixture and sugar is a pure substance?? And is a mixture always non homogeneous and is a pure substance always homogeneous?

1 comment:

Robert Ellis said...

Milk is a mixture because it is composed of multiple substances or molecules including sugars, proteins, and fats. You can physically separate these components (by straining the fat out, for example).

Table sugar (sucrose), on the other hand, while it is composed of two different molecules (glucose and fructose), can't be manually broken down. It's a compound; glucose and fructose are bonded together. It would take a chemical reaction to separate them.

Mixtures can be homogenous (air and seawater are examples).

Whether or not a pure substance forms a homogenous mixture depends on what kind of mixture it is. You could mix iron pellets in a bucket of mud and the iron pellets would be pure (and homogenous within themselves), but not homogenous within the mud.

(Thanks for the question. I had to look at the chemistry chapter in my A&P textbook to answer it.)