can elements lose mass?

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Clarification of Question by tapemeister-ga on 01 Jun 2006 05:13 PDT

If elements can lose mass then why is that particular abilty cited as
a property of compounds and a way of distinguishing between elments
and compounds in the famous KS3 greenium (copper carbonate)
experiment?
I am confused and yet supposed to be teaching this.

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Clarification of Question by tapemeister-ga on 01 Jun 2006 05:15 PDT

If elements can lose mass then why is that particular abilty cited as
a property of compounds and a way of distinguishing between elments
and compounds in the famous KS3 greenium (copper carbonate)
experiment?
I am confused and yet supposed to be teaching this.As far as I'm aware
carbon (an element) loses mass on heating with the production of CO2

Hi

Of course Elements can lose mass.

Have a read up pn Radioactive Decay.

And have a look at a good article on:
* http://www.btinternet.com/~j.doyle/SR/Emc2/Decay.htm

There's some technobabble on Wikipedia:
* http://en.wikipedia.org/wiki/Radioactive_decay

Or a simpler explanation, with pictures on Thinkquest
* http://library.thinkquest.org/3471/radiation_types_body.html

As Sherlock Holmes would say "Elemental, my dear Watson"

Hope this helps

Ratty

If elements can lose mass then why is that particular abilty cited as
a property of compounds and a way of distinguishing between elments
and compounds in the famous KS3 greenium (copper carbonate)
experiment?

My chemistry being rusty, I had to check that out.

The experiment does not seem that famous, well not to Gurgle, but it
appears to be demonstrating a way of determining that something is
definitely /not/ an element.

If one defines an element as a collection of atoms with the same
number of protons, then there are several ways in which it could lose
mass.

- radioactive decay - as cited
- substituting 'lighter' isotopes for heavier ones
- removing electrons

frde-ga, you can use the word Google in answers, comments, and
clarifications, just not the initial question.

"The experiment does not seem that famous, well not to Gurgle, but it
appears to be demonstrating a way of determining that something is
definitely /not/ an element"

Exactly.So does loss of mass in itself mean that it can't be an
element.That seems to be what the experiment suggests.

@Nelson

I know that, but reckoned it sensible to pound in the idea
- you have amplified it - genuinely thanks

@tapemeister-ga 
My memory is eroded, but the concept of 'significant loss of mass' comes to mind.

- you could play all sorts of tricks on a compound and it could retain
or increase mass.

Your question should be 'do atoms mutate ?'

Could you give a reference to the problematic statement on mass?

A Google search for
mass "copper carbonate" KS3 greenium

turned up this Word doc:
www.webucate.org/ourgallery/ albums/userpics/10001/Year8elements.doc
but I didn't see what you are specifically referring to.

A Google book search for:

intitle:exploring intitle:science

shows four books that might have a quote on mass that you are
referring to. If so, could you name the book and give a short quote to
permit a "Search Within This Book?"

If you are talking about changes of mass that are equal to or greater
than an atomic mass unit, this can readily happen for a compound in a
chemical reaction. Elements are characterized by their stability and
were thought to be completely stable until radioactivity was explained
about 100 years ago. Certain isotopes of heavy elements (like Uranium
and Plutonium, for example) can decay by emitting a neutron, thus
keeping the same number of protons, but weighing less by about one
AMU. Thus, elements can indeed lose mass, as others have pointed out,
but it is unusual and can be ignored unless you are dealing with known
radioactive elements.

Perhaps a more precise definition of "element" is as follows: two
atoms are the same element if and only if they have the same number of
protons.  For example, helium-5 is known to emit a neutron (helium-4
is by far the most abundant natural isotope), yet both helium-5 and
helium-4 are considered helium.  As a highly trained organic chemist,
I can safely say I have never heard of this KS3 greenium experiment,
if there is such a thing.  For the last part, I find it rather vague. 
If one heats carbon in the presence of oxygen, then depending on the
conditions, one may obtain some CO2.  Perhaps the pile of graphite one
had, for example, diminishes in mass because some has become gaseous
CO2, but in fact, there is still the same amount of carbon present in
the system.  So I don't this to be a reasonable counterexample.  I
hope this answers your question.  Perhaps if you could describe this
"KS3 experiment"?

I found this reference to greenium and copper carbonate:

Chapter 2 Non-specialist Support
© 2005 Hodder Murray
"2.5 Testing ?Greenium?
· This practical activity involves the pupils collecting evidence in
order to decide whether
?greenium? is an element or compound. Greenium is actually copper
carbonate, which is
insoluble in water. It decomposes on heating giving off carbon dioxide
and leaving black
copper oxide in the crucible. It reacts with acid, fizzing, as carbon
dioxide is given off.
· Handling crucibles and lids is fiddly and will require skilled
dexterity on the pupils?
part.
· Do not allow the pupils to wander around the room with hot crucibles
and make sure
that they are consistent in only weighing the crucible before and after hearing.
· It might be helpful for you to demonstrate heating the CuCO3 in a
test tube with a
delivery tube passing the CO2 given off through limewater. This will
also provide a focus
for interpreting the evidence that shows that Greenium is a compound."
http://www.hodderscience.co.uk/password2/nonspecdocs/Book%20B/ActivityNotes/whole.pdf

Perhaps the "mass loss" here might refer to changes that can be caused
by heating. Here the change would be from one material (copper
carbonate) to copper oxide and carbon dioxide. Since the carbon
dioxide evolves as a gas, the remaining product (copper oxide) weighs
less than the starting material. An element may change state upon
heating, but a new substance won't be formed (see below for
exceptions), and there should be no mass loss - as there is when the
copper carbonate (a compound) is decomposed by heating.

(The following is probably outside the scope of the experiment, but an
element could react with oxygen, etc,. and a new substance would be
formed; but in this case, there would be a mass gain - at least
relative to the starting element.)

heres $0.05 on this: (having done a similar experiment recently)

CuCO3 --heat--> CuO + CO2(g)
CuCO3 (heavier) > CuO

Weight lost is equal to the number of moles Cu03 X molar mass of CO2
(~44gmol-1). This weight plus the weight of remaining CuO should
roughly equal the initial mass.