I need a bit of help with my chemistry assignment... the prof pulled some questions out of his ass that no one in my class has seen before, and I was hoping that a few of you may be able to help me out.

There's 2 questions, they're both about density (I know d=m/v, don't bother saying that.)

1. A solution containing 47.15 g of liquid A and 16.53 g of liquid B has a density of 1.025 g mL-1. On adding a further 16.09 g of liquid B to the mixture, the density drops to 0.968 g mL-1. Assuming that the volumes are additive, calculate the density of liquid B in g mL-1.

2. Equal masses of two liquids are mixed to give a solution of density 1.0735 g mL-1. If the density of the first liquid is 1.32 g mL-1, calculate the density of the second liquid in g mL-1 and round to the correct number of significant digits. Assume that the volumes are additive.

Any help to figure these out would be greatly appreciated...

Wish I could help you. Its been 2 years since Ive taken Chemistry. I can remember doing problems exactly like this, but I just can't remember what that formula was. I can sort of see it, but not really. I'll try to figure it out.

Sorry I couldn't be of any help.

Come on ELEMENT. Help me with my CHEMISTRY.

I hate science so much, especially chemistry which I am currently taking but in high school not college.

Think of this as a math problem. 2 number. Equal weight.

1.0735 = Mean of two numbers, 1.32 and an unknown.

1.0735 x 2 = 2.147

2.147 - 1.32 = 0.827 g (and that is w/ sig figs)

Yeah, that's what I had for an answer, but it said it was wrong... (all our assignments are online, no teacher involved)...

I'd help you out man, but I slept through chemistry.

chemistry major to the rescue...hold on while i work out the first one

First thing you should do is to list what you know..

A-47.15g
B-16.53g

density-1.025 g/mL

later 16.09g of B is added to the solution changing the density to 0.968 g/mL

-you would want to start by finding the total volume of the first solution
(A+B )/X = 1.025g/mL (or 1.025g / 1mL)

63.68g/X = 1.025g/1mL
-Cross multiply and solve for X
---->X=62.13mL<----
keep that number in mind

-then find the volume of the second mixture
(A+B+16.09g)/X = 0.968g/1mL

---->X=82.41mL<----


the difference between the two volumes is the volume of the additional amount of B that was later added...

so... 16.09g/(82.41mL-62.13) = 0.793mL

and there's your answer for the first one

Que? And that is all the info they gave you? What?

DUDE im adding you to Buddies, expect a lot of PMs from me

even though he was wrong..... :rolleyes:

*Hugs* I love you.

How sweet :P

THE QUESTION WAS FLAWED!!! :lol:


Come one wf, question 2, I want to know the answer now!

once again, state what you know

the mass of the total solution is twice whatever one of them is
density is 1.0735 g/mL
A-1.32 g/mL


right now, a safe assumption would be that there is only one mL of A added in the solution making the mass of A 1.32g (which makes B 1.32 also)

so in your equation...

(1.32g+1.32g)/(1mL+X) = 1.0735g/ 1mL
X= the volume of B
cross multiply

2.64g(1mL) = 1.0735g(1mL) +1.0735g(X)
subtract 1.0735g(mL) from both sides

1.57g(mL) = 1.0735g(X)
divide both sides by 1.0735g

X=1.46mL

now you have your volume and mass of B

1.32g/1.46mL=0.904g/mL

your answer...0.904g/mL

Ding ding, that's the answer it said was right. Well, it had .9046, but you're close enough. I <3 WF.

Oh. I get it now. Don't know how I missed that one....

Under sig figs, that would be wrong, because they only gave you 3 digits in 1.32.

Answer should be .905 w/ correct sig figs.

^^ hes right. i learned that this morning in chem ..

first thing you should always do is to state what you already know and whatever you can find from that...

sometimes what you find is irrelevant, sometimes it's not, but it helps a lot

I still plan on stapling my prof's nut sack to his desk for not teaching us this, or putting it in our textbook. I shouldn't have to ask people on a baseball forum for help on an assignment...

That reminds me of an Eminem song.

dude element, you should put up a homework help forum, just for tihngs like this. thatd be great for the schookl year, and obviously theres some genious people here..

Pfft, I've got a nasty little stapler 12 inches infront of me, and I'm not afraid to use it!

Ok, let me say this right now. I'm not stupid. In fact, I'm very smart. It's just that I haven't done sig figs or densities for over 2 years, and I'm rusty! I SHOULDN'T be asking for help on a regular basis. And if I see someone needs help with something I understand well (like Calculus or stoichiometry) then I'll be willing to help.

exactly. im going to go suggest a homework forum.

yeah good idea.

i'm having the most horrible time with Geometry

ayo ill help you


10th grade?

I'm in Algebra II :P

Pre-calc bitches

algebras a little harder, but thats easy stuff too.

im in pre calc next year. im in math "b" this year, or 11th grade..

yo im in grade 11. i can help with math crap.

I'm in pre calc later on this year *beer*

I hate math, I can't understand anything about it.

I get straight A's in everything else though :huh:

its so easy, especially geometree to me.

yeah geometry is very easy.

lucky for you, i get tortured by my teacher cause i can't get anything.

she thinks if she forces it into me illl know it :)

nope

University calculus *flexes*.