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# Group 2 elements watch

1. Hi! I have a chemistry question that I'm not sure about. Answers and how to do it would be appreciated!

0.1g of an unknown group 2 metal (which we shall call M) was dropped into distilled water in a conical flask. Some effervescence, and a small amount of white precipitate, was observed. The resulting mixture required 22.8cm3 of 0.1 moldm-3 hydrochloric acid to neutralise. Calculate the Ar of the metal, and deduce its identity.
a. Equation for reaction of M with water:
I guessed it would be:
M + H2O ------> MO + H2
b. Equation for reaction of resulting mixture with HCl:
I again guessed it would be this:
MO + 2HCl ------> MCl2 + H2
c. Ar and identity of metal.
I have no idea how to get this answer.

2. By the looks of it, ork out the mols of HCL and using your equation, you know the molar ratio and can work out the mols of the metal. Then rearrange mols = Mass/mr to work out ar.
3. (Original post by cassie05)
Hi! I have a chemistry question that I'm not sure about. Answers and how to do it would be appreciated!

0.1g of an unknown group 2 metal (which we shall call M) was dropped into distilled water in a conical flask. Some effervescence, and a small amount of white precipitate, was observed. The resulting mixture required 22.8cm3 of 0.1 moldm-3 hydrochloric acid to neutralise. Calculate the Ar of the metal, and deduce its identity.
a. Equation for reaction of M with water:
I guessed it would be:
M + H2O ------> MO + H2
b. Equation for reaction of resulting mixture with HCl:
I again guessed it would be this:
MO + 2HCl ------> MCl2 + H2
c. Ar and identity of metal.
I have no idea how to get this answer.

Your equations are incorrect. Do you remember what is formed when a group 2 metal is added to water? (Only one product)

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4. You get a metal hydroxide, not an oxide and hydrogen gas. E.g. M (OH)2

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5. (Original post by Manexopi)
By the looks of it, ork out the mols of HCL and using your equation, you know the molar ratio and can work out the mols of the metal. Then rearrange mols = Mass/mr to work out ar.
Okay, I think I understand. Thank you
6. So the first equation will be M + H2O ------> M(OH)2? And the second one will remain the same?
7. (Original post by cassie05)
So the first equation will be M + H2O ------> M(OH)2? And the second one will remain the same?
The second one will be M(OH)2 + HCL and then the products of neutralisation (salt and water).

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8. Has everyone forgotten how to balance an equation?
M + H2O -> M(OH)2

Where did the extra O come from?

M + H2O -> M(OH)2 + H2

Which would explain the effervescence in the OP.

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