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So the same properties throughout could also refer to a solution, an alloy,
or just plain old air, but not a suspension, colloid, or mixture. Then pure
substance would be only a compound or element. I still think it is an
awfully fine definition to be inflicted on physical science students,
especially if it is not agreed upon. I would tend to agree that the
definition the same throughout makes more sense.
Incidentally the book says milk is a colloid, but every dairy farmer and
older person might disagree. Soymilk is definitely a suspension. They
forgot the important adjective homogenized. The book also calls paint a
colloid, but every painter knows it settles like a suspension. Perhaps they
were thinking of something other than common house paint. Do they expect
students to memorize that paint is a colloid even when they know it settles?
No wonder students say science doesn't make sense.
John M. Clement
Houston, TX
Ah... Didn't get that distinction from your post. I can't recall if the
terms "pure substance" and "substance" have been used interchangeably
throughout the past, but just a quick referral to my (now) limited library
of old chemistry textbooks finds the same definition back into the '80s.
One states that a substance is a material that has the same properties
throughout, which is a slight variation on the theme, but is consistent
with:
element or compound = substance
everything else = mixture
Overall, I would have to say, then, that the definition you have there is
in
accordance with accepted chemistry terminology. My personal recollections
go back to the early '60s, and it seems to me that it has always been
defined this way.
----- Original Message -----
From: "John Clement" <clement@hal-pc.org>
To: "'Forum for Physics Educators'" <phys-l@carnot.physics.buffalo.edu>
Sent: Friday, March 20, 2009 3:03 PM
Subject: Re: [Phys-l] Definition of Substance
> My question was not about "pure substance" but just the work
"substance".
> The book defined "substance" as either a pure element or compound. I
> would
> agree with "pure substance" as being either an element or compound, but
> not
> just the word substance without the adjective pure.
>
> John M. Clement
> Houston, TX
>
>
>> Subject: Re: [Phys-l] Definition of Substance
>>
>> I can't speak to the origin of this terminology, but your text is in
>> agreement with the chemistry texts in New York over the last 30 years
or
>> so. I wouldn't, therefore, ascribe this terminology to a specific
>> author. "Pure substance" refers to any entity which has the same
>> particles throughout, and cannot, therefore, be separated into
>> dissimilar portions by physical means. This limits pure substances to
>> elements and compounds (and ignores differences between isotopes, >> btw).
>> I think the original intent was to focus students on the particle
nature
>> of matter by categorizing according to the particulate composition, >> and
>> those categories would obviously require different names. The choices
>> made for those names were necessarily subjective.
>>
>> A pure substance is not "opposite" to anything, merely different based
>> on composition. The other class of matter is mixture, which contains
>> dissimilar particles that have been physically combined, and which can
>> be physically separated into dissimilar portions by physical means. A
>> solution IS a mixture which has the added characteristic of being
>> homogeneous - the mixing is completely uniform. This typically
requires
>> the particles to be atomic/molecular in size. Other mixtures one >> might
>> come up with would tend to be heterogeneous and contain localized
>> "clumps" of one substance or another (even if those clumps consisted >> of
>> particles which are atomic/molecular in size). Suspensions, despite
>> being quite uniformly mixed, are still considered to be different than
>> solutions, presumably because of the larger particle size.
>>
>> I think there is ample cause/purpose for the distinction between these
>> classes of matter.
>>
>> On Fri, 2009-03-20 at 11:06 -0500, John Clement wrote:
>> > In the TX IPC book the word substance is defined essentially to mean
a
>> > "pure" compound or element. I do not remember having encountered
this
>> > definition, and the dictionary is no help here.
>> >
>> > I personally think this is one particular author's definition, or
>> possibly a
>> > definition pushed to be able to ask questions like "Is milk a
>> substance?".
>> > Since there are alternate words which do have traditional
definitions,
>> this
>> > is a vey unnecessary complication.
>> >
>> > Would anyone agree with the book definition? This is in the
>> > "chemistry"
>> > part of the text, so would a chemist agree with this? I would use
>> > "pure
>> > substance" as the opposite to a mixture, solution...
>> >
>> > Language is messy, but we don't have to burden students with
>> > unnecessary
>> > definitions. If the vast majority agrees with the book definition,
>> > then
>> it
>> > is reasonable, but merely unnecessary.
>> >
>> > John M. Clement
>> > Houston, TX
>> >
>> >
>> > _______________________________________________
>> > Forum for Physics Educators
>> > Phys-l@carnot.physics.buffalo.edu
>> > https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
>>
>> _______________________________________________
>> Forum for Physics Educators
>> Phys-l@carnot.physics.buffalo.edu
>> https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
>
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@carnot.physics.buffalo.edu
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_______________________________________________
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_______________________________________________
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