badchemstudent
Harmless
Posts: 3
Registered: 25-1-2006
Member Is Offline
Mood: No Mood
|
|
hydrates-please help.
I'm horrible when it comes to chemistry so any help would be greatly appreciated.
The lab I'm doing requires us to determine the percent of water in the compound if we are given un unknown hydrate. I'm having problems with the
following pre-lab questions:
- Why do you think it is necessary to heat the evaporating dish before finding its mass?
-What is the percent of water in MgSO4 * 7H2O
Explain what effects the following errors would have on the value for the percent water in the hydrate.
a. the hydrate was not heated long enough
b. a damp crucible was used.
c. the crucible and contents were allowing to cool overnight before finding the mass.
Predict what would happen if you added a few drops of distilled water to the anhydrou salt remaining at end of this experiment
What are dessicating agents(i got this part) but what substances are used for this purpose?
thank you so much...I really wouldn't ask if I didn't need it desperatly. Hope no one is annoyed by this post :/
|
|
|
guy
National Hazard
Posts: 982
Registered: 14-4-2004
Location: California, USA
Member Is Offline
Mood: Catalytic!
|
|
"Schoolwork help and beginner questions (not a textbook substitute)"
Some of these questions all you need to do is look in a book or the internet. Search for "dessicator" for example. Others are just common sense
really! For example:
"Explain what effects the following errors would have on the value for the percent water in the hydrate.
a. the hydrate was not heated long enough".
|
|
|
badchemstudent
Harmless
Posts: 3
Registered: 25-1-2006
Member Is Offline
Mood: No Mood
|
|
I did look these up. I coudn't find jack.
|
|
|
BromicAcid
International Hazard
Posts: 3227
Registered: 13-7-2003
Location: Wisconsin
Member Is Offline
Mood: Rock n' Roll
|
|
Okay.... here we go...
| Quote: | | Why do you think it is necessary to heat the evaporating dish before finding its mass? |
Depends on the
evaporating dish, some are glass, some are ceramic or porcelin, in the case of the latter two they may contain some water absorbed within them. So,
heating them will drive off this water and lead to more accurate readings, since you will be heating them with the
MgSO<sub>4</sub>*7H<sub>2</sub>O the water lost might be attributed to the magnesium sulfate otherwise.
| Quote: | | What is the percent of water in MgSO4 * 7H2O |
What is the molecular weight of magnesium sulfate heptahydrate?
246.47 from a google search. And what is the molecular weight of water, 18.02 g/mol, there are 7 of them so..... 126.14 grams of water..... so that
would be 51.17% of the weight.
These questions sound vaguely like quant homework.
a. the hydrate was not heated long enough
*If the hydrate is not heated long enough then not enough water is removed and it would make there appear to be less water in the hydrate.
b. a damp crucible was used.
*More water comes off the hydrate leading one to believe there is more water in the hydrate.
c. the crucible and contents were allowing to cool overnight before finding the mass.
*Assuming they were not cooled in a dessicator, they will re-absorb some water from the atmosphere, in this case there will appear to be less water in
the hydrate because it will re-gain its lost weight.
Predict what would happen if you added a few drops of distilled water to the anhydrou salt remaining at end of this experiment
*The solid would suck up the water, I've never worked with anhydrous magnesium sulfate but I doubt its hydration process is violent, many people here
have more experience with magnesium sulfate.
What are dessicating agents(i got this part) but what substances are used for this purpose?
*Okay, maybe you should just google this, or if you want to just look in one place, wiki it.
Best of luck in the future.
|
|
|
badchemstudent
Harmless
Posts: 3
Registered: 25-1-2006
Member Is Offline
Mood: No Mood
|
|
thank you so much. That really helped. I was doing the percent comp. all wrong. I'm a dumbass.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
