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Author Topic: ice cube in water = heterogeneous mixture?  (Read 6809 times)

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philonossis

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ice cube in water = heterogeneous mixture?
« on: April 14, 2010, 02:47:18 AM »

"Classify the following as 1) a heterogeneous mixture, 2) heterogeneous, but not a mixture, 3) homogeneous mixture, or 4) homogeneous, but not a mixture.
(a) an undissolved sugar cube in water
(b) a partially dissolved sugar cube in water
(c) a completely dissolved sugar cube in water
(d) an ice cube in water

The book's answers:
a an undissolved sugar cube in water= heterogeneous mixture
b a partially dissolved sugar cube in water= heterogeneous mixture
c a completely dissolved sugar cube in water= homogeneous mixture
d an ice cube in water= heterogeneous mixture. PROBLEM

My answer: d = heterogeneous, but not a mixture.

The book (Intro. to Chemical Principles, Stoker) states that "A heterogeneous mixture contains two or more visually distinguishable phases..." p. 92  

It also states: "A mixture is a physical combination of two or more substances."

So, an ice cube in water cannot be a mixture according to the book's own definition, since water and ice are the same substance.

Can anyone explain who is right here?


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Borek

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Re: ice cube in water = heterogeneous mixture?
« Reply #1 on: April 14, 2010, 03:08:23 AM »

How does the book define substance?

But I agree with you that it is a little bit fishy.
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joinforfun8909

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Re: ice cube in water = heterogeneous mixture?
« Reply #2 on: April 14, 2010, 11:02:38 AM »

Since the ice cube and liquid water are two distinct phases, the book seems correct to state the system as a Heterogeneous mixture.
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JGK

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Re: ice cube in water = heterogeneous mixture?
« Reply #3 on: April 14, 2010, 11:11:22 AM »

Ice in water meets the first criteria:

"A heterogeneous mixture contains two or more visually distinguishable phases..."

You have Ice which is H2O(s) and water which is H2O(l) so you have a mixture of liquid and solid = 2 visually distinguishable phases

It's pretty bad wording in the book the second statement "A mixture is a physical combination of two or more substances" is a poor use of english

Ice and water are not necessarily the same substance in the literal dictionary definition of the word and therefore do fit the second description of a mixture.
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philonossis

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Re: ice cube in water = heterogeneous mixture?
« Reply #4 on: April 18, 2010, 09:40:50 PM »

How does the book define substance?

The book defines substance as follows: "Substance is a general term used to denote any variety of matter.  Pure substance is a specific term that applies only to matter that contains a single substance." (p. 90 Intro. to Chemical Principles, Stoker.)

Elsewhere the book states: "In addition to its classification by physical state, matter can also be classified in terms of its chemical composition as a pure substance or a mixture.  A pure substance is a single kind of matter that cannot be separated into other kinds of matter using physical means. all samples of a pure substance contain only that substance and nothing else....

A mixture is a physical combination of two or more substances. It has variable composition. Its properties may vary as composition varies. Its components can be separated using physical means.

A compound is a pure substance that can be broken down into two or more simpler pure substances using chemical means. Water is a compound. Hydrogen peroxide is a compound.
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