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HOw do i measure in grams without an expensive scale?


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#1 AZNchemist

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Posted 11 November 2007 - 09:55 PM

For a chemistry experiment, i have to measure in grams, but i don't have a scale at home, what do i do instead of buying one?:-( Please help me
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#2 ydoaPs

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Posted 11 November 2007 - 09:57 PM

Make a balance and use a box of paperclips. One paperclip is roughly a gram.
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#3 insane_alien

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Posted 12 November 2007 - 07:23 AM

making your own instrumentation is probably about the cheapest way to do it.

another way is water displacement. you have a glass(modify this for whatever size you need) full to the brim of water, a small floatingcontainer to hold your sample(make sure it will float WITH the sample in it) and something that can measure volume(a measuring cylinder, jug, what ever, i've even calibrated pint glass for similar purposes).

fill the big glass with water, place the sample container in gently(so as not to spill more water than it takes) then put the measureing device under the big glass. add your sample to the sample container and collect all the water that runs off. every cubic centimeter is roughly a gram(IS a gram if you do it a 25*C)
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#4 HallsofIvy

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Posted 14 November 2007 - 07:37 PM

making your own instrumentation is probably about the cheapest way to do it.

another way is water displacement. you have a glass(modify this for whatever size you need) full to the brim of water, a small floatingcontainer to hold your sample(make sure it will float WITH the sample in it) and something that can measure volume(a measuring cylinder, jug, what ever, i've even calibrated pint glass for similar purposes).

fill the big glass with water, place the sample container in gently(so as not to spill more water than it takes) then put the measureing device under the big glass. add your sample to the sample container and collect all the water that runs off. every cubic centimeter is roughly a gram(IS a gram if you do it a 25*C)

That measures volume. a cubic centimeter of WATER is approximately a gram. It doesn't follow that the mass of the object you were using the water to determine the volume of has that same mass.
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#5 MrMongoose

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Posted 14 November 2007 - 09:56 PM

How about putting a large mass on your existing scale, connecting the top of the mass to a rod which passes over a pivot with the other end connected to a small container. Have the pivot a lot closer to the scale end of the rod than it is to the container end and use the moments to calculate the mass of whatever you put in the container from the decrease in mass measured by the scale.
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#6 gcol

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Posted 14 November 2007 - 10:05 PM

I made two simple weighing devices when I was into very light model aircraft and I needed to weigh very small pieces of balsawood. one was a simple balance arm where both the sample and weight could be moved along the graduated arm. This was so sensitive I could weigh small feathers, and it had to be in a draft-proof container. The slightest breath would disturb it. The second was based on a torsion wire, about 22SWG as I remember. About 25 grammes deflection on a 3" diameter circular scale.
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#7 insane_alien

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Posted 14 November 2007 - 11:14 PM

That measures volume. a cubic centimeter of WATER is approximately a gram. It doesn't follow that the mass of the object you were using the water to determine the volume of has that same mass.


no but that doesn't apply, you are trying to get the weight in grams, so however many cm^3 of water it displaces is how many grams it weighs.
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#8 Cap'n Refsmmat

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Posted 14 November 2007 - 11:19 PM

That depends on it having a density of 1 g/mL.
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#9 insane_alien

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Posted 14 November 2007 - 11:24 PM

no it doesn't. thats what the sample float is for.

it just needs the working fluid(water) to have a density of 1 g/ml

the density of the sample is irrelevant.
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#10 Sisyphus

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Posted 15 November 2007 - 12:18 AM

It doesn't have to have the same density as water, but it does have to have a density less than or equal to water. If it's more dense, it just sits on the bottom.
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I think you'll find it's a bit more complicated than that.

#11 insane_alien

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Posted 15 November 2007 - 08:45 AM

It doesn't have to have the same density as water, but it does have to have a density less than or equal to water. If it's more dense, it just sits on the bottom.


that is why the sample is placed into a floating container as i said before. several times. why does everyone think i just said chuck the sample into the water.
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#12 tvp45

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Posted 18 November 2007 - 02:22 PM

For a chemistry experiment, i have to measure in grams, but i don't have a scale at home, what do i do instead of buying one?:-( Please help me

If all your work will be in mass rather than volume, make a home-made balance beam (popsickle stick, 3 holes, 3 strings, 2 bottom ends of coffee filters). Use the paperclip calibration mentioned earlier. If you are doing only mass, actual units don't matter, only the proportions, so a paperclip accuracy is quite good enough.
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#13 MrMongoose

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Posted 18 November 2007 - 09:22 PM

I just re-read this and realised you don't have a scale... Naturally my methods will only work for what I initially thought I read, i.e. you don't have a sensitive enough scale.

sorry
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#14 insane_alien

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Posted 19 November 2007 - 08:39 AM

thats why i suggested the volume displacement scale. it can be quite accurate. you could also put the scale on the sample float. the thinner it is the more accurate it will be although it won't be able to hold as much. you could probably get down to tenths of a gram reasonably easily. with some more tweaking it should be possible to get hundredths.
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#15 MrMongoose

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Posted 19 November 2007 - 06:09 PM

...and a good method it is too! Its almost worth forgetting whatever experiment required a mass measurement and just getting excited about the hydrostatics!
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#16 insane_alien

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Posted 19 November 2007 - 06:57 PM

hydrostatics are boring. when it is a dynamical system is where it gets interesting.
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#17 John Cuthber

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Posted 19 November 2007 - 07:11 PM

Spoken like a man with a water pistol. ;-)
On the other hand, hydrostatics is where it might answer the original poster's question.
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#18 insane_alien

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Posted 19 November 2007 - 08:26 PM

super soaker monster XL actually.
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