Question H7a

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A Raab 1K
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Joined: Sat Aug 24, 2019 12:16 am

Question H7a

Postby A Raab 1K » Tue Oct 01, 2019 8:43 pm

H7a. Write a balanced chemical equation for each of the following reactions. (a) Calcium metal reacts with water to produce hydrogen gas and aqueous calcium hydroxide.
For calcium hydroxide, how would one know if the molecule is CaOH or Ca(OH)2? (and for other molecules that include hydroxide too)

EvanWang
Posts: 101
Joined: Sat Sep 07, 2019 12:16 am

Re: Question H7a

Postby EvanWang » Tue Oct 01, 2019 8:49 pm

Calcium is in the second group of the periodic table so calcium ions are Ca2+. Hydroxide ions have a -1 charge, so you need 2 OH to make the overall charge neutral. So Calcium hydroxide is Ca(OH)2.

SnehinRajkumar1L
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Joined: Thu Jul 11, 2019 12:15 am

Re: Question H7a

Postby SnehinRajkumar1L » Tue Oct 01, 2019 8:50 pm

Hydroxide has a -1 charge. Group 2 elements (including calcium), always have a +2 charge. So, for the charges to balance you would need 2 hydroxide molecules for the calcium ion. This applies to Group 1 elements where they always have a +1 charge. Elements in group 13, 14, 15, 16, and 17 have a +3, +4, -3, -2, and -1 charges respectively. Use this rule to determine the number of hydroxides in a compound.

A Raab 1K
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Joined: Sat Aug 24, 2019 12:16 am

Re: Question H7a

Postby A Raab 1K » Tue Oct 01, 2019 9:23 pm

Along that same theme, how would I know what to do for metal solids such as magnesium or for a nitrogen atmosphere? Magnesium is just Mg, whereas the nitrogen atmosphere is N2.

Vanessa Chuang 4F
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Joined: Sat Aug 24, 2019 12:18 am

Re: Question H7a

Postby Vanessa Chuang 4F » Tue Oct 01, 2019 10:54 pm

Generally, if you're given a solid metal, it will stand by itself (ex: Mg, Cu, Ni, etc) unless the question states otherwise. However, for gases such as nitrogen and oxygen, those just happen to exist in the atmosphere as molecules (N2, O2, etc) which is why they need to be noted as so.

Amir Bayat
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Joined: Sat Sep 07, 2019 12:16 am

Re: Question H7a

Postby Amir Bayat » Wed Oct 02, 2019 2:38 pm

How do you know that hydroxide has a -1 charge?

Is this due to hydrogen being in the first row? Then what charge does oxygen have?

MinuChoi
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Joined: Wed Sep 18, 2019 12:15 am

Re: Question H7a

Postby MinuChoi » Wed Oct 02, 2019 2:54 pm

Hydroxide has -1 charge because of oxidation numbers. O's oxidation number is -2 and H's oxidation number is -1.
You can also think of when water ionizes; it splits into a hydrogen ion (acidic) and hydroxide ion (basic). Hydrogen ions have charge +1 and water is neutral charge, so hydroxide has charge -1.


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