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cherrie asked in 科學及數學化學 · 1 decade ago

20marks~F.3chem about crystal

My teacher has mentioned that Copper(II) sulphate crystal is an example of

compound and its chemical symbol is CuSo4.nH2O

But I wonder why it wasn't a mixture. CuSo4 is definitely a compound but it

contains water which has not been chemically compound together.

So can u plz guys explain why is it a compound?

Also are all kinds of crystal compound?

Do all crystal contain water?

What is the definition of crystal?

I am juz a beginner. I hope you guys can use simple form of words to explain for me. Besides, it is better to use english to explain. but chinese is also okay...

20 marks will be rewarded for detailed explaination~

Thanks for helping~~ I have been bothered by this question for a long time!


Thank you for answering Renee J. Yeung !

So do u mean that crystallisation is a kind of chemical change?

i ask because refer to my book, it stated that the definition of compound is two or more element combined together by "chemical methods".

Update 2:

I can't define whether crystallisation is a kind of "chemical change" or "physical change"...

In the crystallisation, the solvent evaporates and the solute gather together to form crystal,right? but originally, the solution is a mixture.Therefore, i has a doubt about it...

Update 3:

Besides, you have mentioned that "The definition of crystal, in scientific means, is always a solid. The atoms/molecules/ions are arranged in a pattern with makes it 3-D shaped. "

" CRYSTALS can be made up of ANYTHING, ranging from compounds to elements on their own"

Update 4:

So does it mean that crystals are anything that are in solid with molecules that are arranged in a regular pattern? must it be a compound or element? is glass or metal a kind of crystal?

i understand my questions are quite silly, but they really bother me a lot~

2 Answers

  • Anonymous
    1 decade ago
    Favorite Answer

    1) Why is CuSO4 a compound?

    The definition of a compound is that it is made up of other elements. For example, NaCl (table salt). It is made up of sodium(Na) and chlorine(Cl). It is a common compound in daily life. Others are H2O and CH4 (methane).

    CuSO4 is an ionic compound, like table salt. Ionic means being made up of ions, which have an electrical charge, making them unstable. When combined together, they become stable as they lose or gain electrons from each other. Cu is 2+ and SO4 is 2-. Combining them together makes it the ionic compound CuSO4. The water in it is from the crystallisation process. So it is not a mixture, it is part of the crystal itself.

    2) Are all kinds of crystals compounds?

    Mostly all of the crystals found in the universe are compounds. These crystals are usually ionic compounds, as mentioned above. Compounds such as diamond, graphite (the black thing in your pencil) are crystal compounds too. Even snowflakes are crystals, water crystals.

    3) Do all crystals contain water?

    No, not all crystals contain water. But there are some that do. The water inside them are called water of crystallisation. It is called that way, because during the process of turning a compound into a crystal, you heat up the compound mixture and then let it slowly cool down. Of course, the mixtures have water in it, that is why the water formed in the crystal is called that. Not all crystals are made from that process, but usually most of the ones done in the lab.

    4) What is the definition of crystal?

    The definition of crystal, in scientific means, is always a solid. The atoms/molecules/ions are arranged in a pattern with makes it 3-D shaped.

    So, to not get you confused, CRYSTALS can be made up of ANYTHING, ranging from compounds to elements on their own.

    However, COMPOUNDS are made up of different elements, they can be crystals, but they can never be only one group of elements.

    Work hard!

    Source(s): Myself and wikipedia
  • 1 decade ago

    ---Not all crystals are compound. There are some crystals wnich are form by pure element.

    ---CuSO4.nH2O is a compound with water in it.

    ---Crystallisation is physical change, because the solute only GROUP together but NOT COMBINE together.

    ---Formation of compound is a chemical change, because the elements COMBINE together.

    ---All crystals are solid, but not all solids are crystals.

    ---All crystals have regular shape.

    ---Metal is NOT a crystal.

    ---Glass is also NOT a crystal.

    Source(s): My own chem knowledge
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