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Offline defhalotones

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chemistry homework question, help
« on: January 31, 2009, 05:59:58 PM »
The question:  The density of liquid mercury is 13.6 g/mL at 25 degrees C.

A: what is the density in g/cm3(cubed)?
B: Convert the densit to English units of lb/qt.

I'm not quite understanding this stuff..

Offline Arkcon

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Re: chemistry homework question, help
« Reply #1 on: January 31, 2009, 09:04:24 PM »
Try writing it, on paper, as 13.6 g
                                    -------
                                        ml

And see if you can figure it out.  For example, what are the first units?  What do they mean?  How are they different from the question units?  Have you been asked to convert units before?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline TheJoker

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Re: chemistry homework question, help
« Reply #2 on: January 31, 2009, 09:37:29 PM »
also:    1 mL = 1 cm3(cubed)       

Offline JGK

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Re: chemistry homework question, help
« Reply #3 on: February 01, 2009, 09:09:49 AM »
The question:  The density of liquid mercury is 13.6 g/mL at 25 degrees C.

A: what is the density in g/cm3(cubed)?
B: Convert the densit to English units of lb/qt.

I'm not quite understanding this stuff..

As an Englishman I can honestly say that part b is woefully out of date. Having attended school between 1966 - 1980 I cannot remember ever using these units we were working with grams and litres all the time
Experience is something you don't get until just after you need it.

Offline Arkcon

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Re: chemistry homework question, help
« Reply #4 on: February 01, 2009, 09:38:20 AM »
As an Englishman I can honestly say that part b is woefully out of date. Having attended school between 1966 - 1980 I cannot remember ever using these units we were working with grams and litres all the time

Well, I've said it before, so I can say it again as a benefit for the latest crop of noobs -- this is how chemistry is taught.

First, you're given the simple chemistry equation D=M/V, and you're asked to convert units, metric and imperial, as examples.  Then, you're taught the "equation" that is the balanced chemical reaction, and asked to convert units -- grams of reagent, to moles, so you can use the balanced equation, to convert moles of product, back to grams.  Then you're taught the gas laws, and asked to convert again, from volumes, and pressures, and temperatures, of gas reactants and products, to moles, for the balanced reaction, and back again.

These are not trivial topics.  First of, it's much simpler math than kinetics, or thermodynamics.  I hate to sound critical of anyone, but if someone can't handle these simple conversions, no matter how hard they try, then it's pretty obvious, the rest of the chemistry course is going to go very badly for them. 

Also, conversions are important, we've had very advanced people on these boards, ask for bog-standard solution prep.  And, this is not a joke, I've worked with professionals who couldn't work out, how to make a solution, or how to convert back from instrument response, to sample signal, to concentration in sample, to extract concentration, to % active in raw material.  They may have been spoon-fed answers all their lives, and everyone else pays the price.  I mentioned before the story I'd heard in high school, about the nurse who prepared infant formula incorrectly, and every baby in the nursery that day died.  Can you say, "Who needs this BS calculation anyway", then go look at a hospital nursery, and say, "Yeah, this could be emptied, not my problem."

Quote
B: Convert the densit to English units of lb/qt.

Well, to lighten the mood here a bit, after my sad story above, even this is silly.  You know why?  Because lbs is the imperial units for weight, not mass.  The imperial units for mass is, the slug.  I'm not kidding, look it up.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

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