[c0ok1e]

Standard solution of a mixture requires 1g of MgSO4.7H2O

I cannot find MgSO4.7H2O in my lab so I use MgSO4 anhydrous. The following is my calculation used to prepare the mixture can you see if it is correct.

MgSO4.7H2O = MW of 246
MgSO4 = MW of 120

So using calculation,

246MW = 1g
120 MW = 120/246
= 0.487g

Is my method of calculation correct?

Thanks

[StarvinMarvin]

The result is correct, although according to the way sou presented it, the logic of those calculations is a bit misty. Explain please how you got to the solution.

[c0ok1e]

I dont understand what you mean by how i got the solution.. I mean its just medium preparation.. Medium consist of example 1g of A, 2g of B, 10g of C, 1g of MgSO4.7H2O then mix all of them together with distilled water and mix then autoclave.

THen my lab doesnt have MgSO4.7H2O I use MgSO4 anhydrous so i calculate according to the following..

So my method is correct? Thanks.. Im so worried i might have did the wrong thing cuz im not sure if i need to use the same amount of MgSO4 as MgSO4.7H2O because i thought the water might not have any difference on the amount needed for MgSO4

[Borek]

What StarvinMarvin means is that the way you presented your approach is barely readable - so while you are most likely correct in your thinking, it is not clear from what you wrote that you are.

120 MW = 120/246 = 0.487g

is algebraically incorrect

[c0ok1e]

Im sorry for my poor english. Do you understand now?
My main question is:

1) Is it necessary to convert the amount needed from MgSO4.7H2O if Im using MgSO4 anhydrous? or will it be the same if im using the same amount?

2) If adjustment need to be made, then is my calculation correct?
Using proportion calculation,
MgSO4.7H2O of MW 246 need 1 gram. Then MgSO4 anhydrous with MW 120 will need 0.487 gram?

[Borek]

As we told you, your result was OK and troubles with understanding your explanation had nothing to do with your English.

[StarvinMarvin]

Thing is, what I wanted you to tell me is how you formulated such a weird proportion, because even  though the result was OK, the way it was written down suggested that there was something strange about the way how you deduced it.

[c0ok1e]

Actually I dont really know the correct method to calculate the proportion. I only calculate it using normal maths. Can you teach me how the correct method should be to calculate such kind of calculation?

[Borek]

But that's the problem - what you wrote was not algebraically correct (not correct using 'normal maths' to use your words). You have probably correctly thought about proportions and the way they should be applied, but what you wrote was incorrect. Part of the text I quoted earlier is completly off, 120 MW is not equal to 0.487 g.

http://www.chembuddy.com/?left=balancing-stoichiometry&right=ratio-proportions

[c0ok1e]

Ok cool.. The way I present it was wrong.. How should I present it so that its simple to understand?

[StarvinMarvin]

I think, something along these lines would be sufficient to show the mechanism of thinking in the proportion:

120 g (of MgSO4) ---- 246 g (MgSO4*7H2O) which means "if 120 g of MgSO4 is in 246 g of hydrate...

x g (of MgSO4) ------- 1 g (MgSO4*7H2O) "then x is in 1 g"

x=(1*120)/246

The proportion should not only serve to help you calculate, but it should also depict the way of thinking.

[c0ok1e]

eh? i dont understand.. how can 120g be in 246g??120g is for MgSO4 abd 246 is for MgSO4.7h2O its different thing? Can you give a brief explanation because actually my chemistry is quite weak

thanks

[Borek]

1 mole of magnesium sulfate heptahydrate contains 1 moles of magnesium sulfate and seven moles of water. If you want to make a solution that contains 1 mole of magnesium sulfate, you can take 1 mole of anhdyrous magnesium sulfate or 1 mole of magnesium sulfate heptahydrate - you will have the same amount of magnesium sulfate in both cases. However, in the first case you need 120 g of solid and in the second 246 g of solid.

You may think about it this way - molar mass of heptahydrate is 120 (magnesium sulfate) + 7*18 (water) = 246.

[c0ok1e]

I c.. I think I kinda understand.. thanks mr borek and mr starvinmarvin