specific gravity... problem wrong?

[Zurfacej]

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Basic as they get... but for some reason I have no idea how they're getting this. Weight of substance/weight of aqueous liquid equal in weight of water.


How many grams does a 4 fl oz object weigh if it has a specific gravity of .844

I'm using Mosby's PTCB exam book for this (which I've heard has incorrect math problems). The book says the answer is 103. Now... setting up an equation for this...

4 fl oz equals 120 milliliters, 1 ml is equal to 1 gram of weight. So, if I'm correct, would I just do: 0.844/120 = .007033?

Any advice? even if I set up a formula using X, which is what the book advises... I still can't figure this one out... 0.844 = x/120 = 101.28

 

[matt48]

I'm not gonna do the problem for you but here is how you approach it. Specific gravity = density of liquid/density of water at a specific temperature. Look up the density of water at the indicated temperature, then find the density of the liquid. When you have the density of the liquid, calculate the mass of the liquid by multiplying density and volume of that liquid (which is given).

 

[Passion4Sci]

Hi there, it's really confusing... But once you get the hang of it it gets easier. Let me walk you through it how I learned it. Your mistake was going to mL (that whole 4 fl.oz = 120mL thing)

First, we know that 1 ounce = 29.5mL right? OK good.
Now, we know that 1 fluid ounce of water weighs 1.0357 ounces.
We also know that the substance's S.G. is .844.

So, the equation is like this:

4 (floz) * 1.0357 (ounce weight h2o) * .844 (s.g. substance) * 29.5mL (oz equivalent)

4 * 1.0357 * .844 * 29.5 = 103.147, or rounded down, to 103g.

 

[JJVmom]

I'm not gonna do the problem for you but here is how you approach it. Specific gravity = density of liquid/density of water at a specific temperature. Look up the density of water at the indicated temperature, then find the density of the liquid. When you have the density of the liquid, calculate the mass of the liquid by multiplying density and volume of that liquid (which is given).

I just passed the PTCB from strictly studying Mosby's book. The don't get into density. It's much simpler than that.