[hiddenlife5009]

Hi guys, I was just wondering if anyone could explain these questions to me in-depth a bit more and possibly the method.

1. Consider the reaction
HCl + Mg(OH)2 –> MgCl2 + 2 H2O
How many grams of magnesium chloride are made from 2.5 grams of magnesium hydroxide?

2. Consider the reaction
C6H12 + 9 O2 –> 6 CO2 + 6 H2O
How many grams of O2 are consumed when C6H12 is burned to yield 1.8 grams of CO2

Thanks.

[Mitch]

You need to show you've attempted the problem first.

[hiddenlife5009]

Ok, well, from what I understand:

1. Balance the equation, therefore,

2HCl + Mg(OH)2 -> MgCl2 + 2H2O

2. It is then required to convert the known coefficient into moles. The molar mass of Mg(OH)2 is 58.32 and the mass shown is 2.5g. Because N = m/M:

2.5g/58.32 = 0.043

3. This is the part where I get confused. I believe it is required to construct two ratios - one from the problem and one from the equation and set them equal.

The way I see it is,

0.043/1 = x/1

From examples I have seen, I am required to cross multiply and convert back to moles, but that just leads me back to 2.5g (starting number for Mg(OH)2).

I think the answer is 4.09? Or so I've heard. Could anyone explain to me what I'm doing wrong or missing?

Sorry for my first post being so 'leechy', I now understand how these forums work  .

[AWK]

2.5g/58.32 = 0.043

3. This is the part where I get confused. I believe it is required to construct two ratios - one from the problem and one from the equation and set them equal.

Since stoichiometry of reaction shows the same nuber of moles for Mg(OH)₂ and MgCl₂ this is sufficient to multiply this number (0.043) by molar mass of MgCl2

[hiddenlife5009]

2.5g/58.32 = 0.043

3. This is the part where I get confused. I believe it is required to construct two ratios - one from the problem and one from the equation and set them equal.

Since stoichiometry of reaction shows the same nuber of moles for Mg(OH)₂ and MgCl₂ this is sufficient to multiply this number (0.043) by molar mass of MgCl2

Ah thankyou for that. No wonder I couldn't get it right, I needed to multiply the molar mass of the unknown coefficient.

Thankyou very much for clearing that up.