I took chem. and i'm confoozled

[mflo]

(7.99 g/mL)(25000 mL) = 199750 (?)

 

[nintendofreak]

1) grams
2) grams
3) not sure about the numerical part (too lazy to reach for calculator) but the unit is right
4) it would be cm^5. When you multiply them, they add. its when you have it like (cm^3)^2 where you would multiply.

 

[mflo]

oh ic, Thank you so much

 

[nintendofreak]

g/mL * mL/1

Think of it as a multiplication problem, with g's having value 2, and mL having value 3. So the 3's would cancel leaving the 2 (g).

cm^2 is like cm*cm so when you divide it by cm, one of them cancels out!

 

[Quantum]

The first two should be grams. Units of measurement can be treated exactly the same way as variables. Just like (x/y)(y) = x, (g/mL)(mL) = g. For the first one, if you know how many grams are in each milliliter, and how many milliliters you have, then you know how many grams you have because it's the remaining unknown.

It might be easier to understand if you think of an analogous situation. Let's say you know that you can fit five apples in a basket and you have four baskets. So, (5 apples/basket)(4 baskets) = 20 apples.

Hope this helps.

 

[miikes]

ah so you're stuck on the basic math of chem

if you're having trouble there you should try org chem, that shit will kill you.

anyways, multiplication and division in chem is mostly the cancellations of labels. in doing so, I'd suggest using a yellow pad or a lined paper.

for the first one, I'm guessing that's a solution with a density of about 7.99 g/ml, then you have 25000ml of that solution and you want to get the mass of the solution. since one ml is above the division bar and one is under they cancel out so you're left with g.

pretty much just write out equations long on two rows such as this scan so you can easily cancel out labels.

for the last, remember diving is the same as multiplying the reciprocal (am I right?) of the number. so dividing by 4 is the same as multiplying by 1/4

Also, don't forget significant figures!! in the scan, the number of ? is the number of SFs you should use.

 

[mflo]

Thank you everyone, I understand it now.