Re: How to test malachite for hydrogen

On Nov 4, 2:39 am, Marvin <physc...@xxxxxxxxxxx> wrote:
Albert wrote:
I've been given an assignment to prove the chemical name of malachite
only using certain experiments.

One of the experiments is a flame test where I dilute malachite into
hydrochloric acid and direct the Bunsen burner flame directly onto it
and check out the new colour. The previous time I did that test was
for sodium, copper, lithium, potassium and calcium carbonates and I've
recorded those colours.
This should show that copper is present in malachite.

The second experiment is simply heating malachite and seeing the
change. Once again, I've already heated and recorded carbon, copper,
magnesium, red phosphorus, calcium, sodium and sulfur. This should
show that copper is again present in malachite.

The third experiment involves diluting malachite into hydrochloric
acid in a test tube with a stopper and tube connected to an open test
tube with limewater in it. Our teacher has told us all that limewater
turns to a milky colour when compounds which are carbonates release
the necessary gas. Therefore, it will show that malachite is a
carbonate and therefore contains carbon and oxygen.

I happened to do a google search on malachite finding out that its
chemical name is copper carbonate hydroxide.

The question: how do I determine malachite has hydrogen in it?

If it is a hydroxide (i.e., it contains water) it has
hydrogen as a constituent of the water. No free hydrogen is
expected. You can heat the malachite to drive off the
water, and collect the water and weigh it to determine how
much water it holds.

Well today I did the experiment. In the heat test the malachite turned
into a black liquid, gas was emitted and there seemed to be vapour
around the top of the test tube - is this water? (from what I had
previously done, this could have been sodium or copper) In the test
where acid was added, the limewater bubbled and turned milky,
indicating carbon and oxygen and the malachite and acid turned cyan.
In the flame test, the blue flame (micro-Bunsen burner) turned light
green confirming it contained copper and not sodium.

From google malachite has 4 elements: copper, carbon, hydrogen and
oxygen. Was there any way concluding that hydogen is also in malachite?

.

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