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Goswami Example 305.11


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#1 owiewave

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Posted 02 April 2011 - 05:23 PM

I was reviewing example 305.11 of the Goswami Book, and have a question. I understand the problem, other than where it says that Magnesium Bicarbonate requires 0 moles of Na2CO3. reviewing the equations on page 592, it appears that one mole of magnesium bicarbonate is needed for one mole of Na2CO3, just as it is needed for MgSO4.

Please let me know what I may be missing!

#2 civilized_naah

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Posted 02 April 2011 - 09:53 PM

QUOTE (owiewave @ Apr 2 2011, 01:23 PM) <{POST_SNAPBACK}>
I was reviewing example 305.11 of the Goswami Book, and have a question. I understand the problem, other than where it says that Magnesium Bicarbonate requires 0 moles of Na2CO3. reviewing the equations on page 592, it appears that one mole of magnesium bicarbonate is needed for one mole of Na2CO3, just as it is needed for MgSO4.

Please let me know what I may be missing!

According to the last reaction on page 591, in order to treat 1 mole of magnesium bicarbonate, you only need 2 moles of calcium hydroxide, no Na2CO3. This removes all the calcium and magnesium ions as precipitate

#3 Jacob_PE

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Posted 16 August 2011 - 06:13 PM

QUOTE (owiewave @ Apr 2 2011, 12:23 PM) <{POST_SNAPBACK}>
I was reviewing example 305.11 of the Goswami Book, and have a question. I understand the problem, other than where it says that Magnesium Bicarbonate requires 0 moles of Na2CO3. reviewing the equations on page 592, it appears that one mole of magnesium bicarbonate is needed for one mole of Na2CO3, just as it is needed for MgSO4.

Please let me know what I may be missing!

I think another way to answer this question is that Soda Ash (Na2CO3) is used to remove noncarbonate hardness only, not carbonate hardness, carbonate hardness removal is performed using lime (Ca(OH)2); interestingly enough lime is also used for noncarbonate hardness. 'Magnesium Bicarbonate requires 0 moles of Na2CO3' because it is carbonate hardness, not non-carbonate hardness.
And I think you have the wording turned around as written: one mole of magnesium bicarbonate is needed for one mole of Na2CO3. Its either lime or soda ash that is needed for removing x moles of something, not the other way around.
Looking at the last equation on page 591, 2 moles of lime are needed for removing 1 mole of Mg(HCO3)2, and as far as MgSO4 (magnesium sulfate), non-carbonate hardness, you need one mole of lime (Ca(OH)2) and one mole of soda ash (Na2CO3) as shown in the equation on page 592 under 'Magnesium NonCarbonate Hardness Removal'. With all that said, the solution to problem 305.11 appears consistent with the equations.
Someone please let me know if i'm off base here.




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