Discussion:
Confusing Homework Problem - Hydrates and Their Thermal Decompositions
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s***@gmail.com
2017-03-22 16:13:50 UTC
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Hello,
I've attempted to solve the following problem, but I'm not sure of my
answer. If correct, can someone explain why - and if incorrect, can someone
explain where I made the error?
The thermal decomposition of 1.6608 g of MgSO4 * H2O produces 1.4446 g of a
1) MgSO4 * H2O(s) -> MgSO4(s) + H2O(g)
2) MgSO4 * H2O(s) -> MgO(s) + SO3(g) + H2O(g)
Complete the following table, and then identify the correct solid product by
comparing the calculated masses of MgSO4 and MgO with the observed mass of
the product.
Formula
Substance Weight Moles Mass (g)
-----------------------------------------------------
MgSO4 * H2O __________ __________ __________
MgSO4 __________ __________ __________
MgO __________ __________ __________
Because the observed mass of the product is 1.4446 g, the product is
__________.
**************************************
** HERE'S HOW I COMPLETED THE TABLE **
**************************************
Formula
Substance Weight Moles Mass (g)
-----------------------------------------------------
MgSO4 * H2O _138.4____ _0.0120___ _1.6608___
MgSO4 _120.4____ _0.0120___ _1.4446___
MgO __40.31___ _0.0358___ _1.4446___
******************
** HOW I DID IT **
******************
http://www.encyclopedia.com/articlesnew/17182.html
My lab manual (that the question comes from) is from a different company
than my text book and for whatever reason, I was unable to find the term
"Formula Weight" in the Glossary of my text book.
Next, I entered the known mass listed in the beginning of the problem. It
said "by comparing the calculated masses... with the observed mass of the
product".
Next I attempted to calculate the number of moles of each sample based on
the Formula Weight and the Mass of each substance. Here, I used a formula
Mass (g) x ( 1 mol / Atomic Mass ) = Number of moles
16.3 g S x ( 1 mol S / 32.07 g S ) = 0.508 mol S
Because the observed mass of the product is 1.4446 g, the product is
_MgSO4____.
I said this because I know that the answer is either MgSO4 or MgO. In the
Moles column of the talbe I completed, the values for MgSO4 * H2O and MgSO4
were very close while the value for MgO seemed larger.
It seems to me though that the values from the Moles column for MgSO4 and
MgO should be smaller than that for MgSO4 * H2O, especially after the H2O is
gone.
So, am I correct? Did I make some horrible assumption or error to come to
this conclusion?
My apologies if this is the incorrect place to post this type of question.
Of all of the newsgroups on my NNTP server, this seemed the most likely to
result in an intelligent and timely response (I'd like to know your opinions
before I head to class at 4:30 PM EDT).
Regards,
Neb Okla
What qualitative test could be used to substantiate this result? and What special safety precautions have been citied in this experiment?
Dean
2017-03-22 18:39:39 UTC
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Post by s***@gmail.com
Hello,
I've attempted to solve the following problem, but I'm not sure of my
answer. If correct, can someone explain why - and if incorrect, can someone
explain where I made the error?
The thermal decomposition of 1.6608 g of MgSO4 * H2O produces 1.4446 g of a
1) MgSO4 * H2O(s) -> MgSO4(s) + H2O(g)
2) MgSO4 * H2O(s) -> MgO(s) + SO3(g) + H2O(g)
Complete the following table, and then identify the correct solid product by
comparing the calculated masses of MgSO4 and MgO with the observed mass of
the product.
Formula
Substance Weight Moles Mass (g)
-----------------------------------------------------
MgSO4 * H2O __________ __________ __________
MgSO4 __________ __________ __________
MgO __________ __________ __________
Because the observed mass of the product is 1.4446 g, the product is
__________.
**************************************
** HERE'S HOW I COMPLETED THE TABLE **
**************************************
Formula
Substance Weight Moles Mass (g)
-----------------------------------------------------
MgSO4 * H2O _138.4____ _0.0120___ _1.6608___
MgSO4 _120.4____ _0.0120___ _1.4446___
MgO __40.31___ _0.0358___ _1.4446___
******************
** HOW I DID IT **
******************
http://www.encyclopedia.com/articlesnew/17182.html
My lab manual (that the question comes from) is from a different company
than my text book and for whatever reason, I was unable to find the term
"Formula Weight" in the Glossary of my text book.
Next, I entered the known mass listed in the beginning of the problem. It
said "by comparing the calculated masses... with the observed mass of the
product".
Next I attempted to calculate the number of moles of each sample based on
the Formula Weight and the Mass of each substance. Here, I used a formula
Mass (g) x ( 1 mol / Atomic Mass ) = Number of moles
16.3 g S x ( 1 mol S / 32.07 g S ) = 0.508 mol S
Because the observed mass of the product is 1.4446 g, the product is
_MgSO4____.
I said this because I know that the answer is either MgSO4 or MgO. In the
Moles column of the talbe I completed, the values for MgSO4 * H2O and MgSO4
were very close while the value for MgO seemed larger.
It seems to me though that the values from the Moles column for MgSO4 and
MgO should be smaller than that for MgSO4 * H2O, especially after the H2O is
gone.
So, am I correct? Did I make some horrible assumption or error to come to
this conclusion?
My apologies if this is the incorrect place to post this type of question.
Of all of the newsgroups on my NNTP server, this seemed the most likely to
result in an intelligent and timely response (I'd like to know your opinions
before I head to class at 4:30 PM EDT).
Regards,
Neb Okla
What qualitative test could be used to substantiate this result? and What special safety precautions have been citied in this experiment?
I doubt anyone cares after 16 years.
Norm X
2017-03-22 19:27:07 UTC
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Post by Dean
I doubt anyone cares after 16 years.
Net News dates are not reliable.
dlzc
2017-03-22 19:47:06 UTC
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Post by Norm X
Post by Dean
I doubt anyone cares after 16 years.
Net News dates are not reliable.
They are for USENET. This is a 16 year old thread.

David A. Smith
Lusani Khubana
2021-03-18 02:31:43 UTC
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Post by Norm X
Post by Dean
I doubt anyone cares after 16 years.
Net News dates are not reliable.
They are for USENET. This is a 16 year old thread.
David A. Smith
I care

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