# The Naked Scientists Forum

#### AlicexxDoll

• First timers
• Posts: 2
« on: 21/09/2008 18:56:42 »
Okay, so I'm horrible at chemistry (grr.) I'm usually awesome at science but this year's teacher expects us to know everything [xx(]But that just means I have to try harder!
Anyways for one question (it just the beg. of the year, so these are the basics, yet I can't figure them out!)
We have a m-V graph...

It then asks 'if you put 10.0 mL of A in one balance pan, how much mass of B would you need in the other pan to make it balance? Explain your reasoning'.
'if you have 35.0 mL of B in one balance pan what volume of A would you need in the other pan to make it balance? Explain your reasoning'.
Then, 'Determine whether substance A and B will sink or float'.
Then it tells me to 'defend your answer (sink/float) using a m-V graph' it already gave me the one above so I don't know how to make it different to answer the question!

One more question please: Then it asks me to graph many substances on a m-V graph for example, Aluminum has a density of 2.70 so to graph it would I just put it in fraction form and then the num. is mass and the dem. volume?

Thank you so much for taking the time to help me!! ♪♥♪♥♪♥
« Last Edit: 21/09/2008 18:58:49 by AlicexxDoll »

#### RD

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« Reply #1 on: 21/09/2008 19:55:23 »
A bigger version of your graph, (so the old gals & geezers can read it  )

#### blakestyger

• Guest
« Reply #2 on: 21/09/2008 20:26:27 »
Old gals and geezers indeed! Do your own homework.

#### RD

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« Reply #3 on: 21/09/2008 20:41:49 »
Density = mass / volume.

From the coordinates you have given
The density of substance  A is 18/10 = 1.8 grams per millilitre (g/ml)
The density of substance  B is 19/35 = 0.54 grams per millilitre (g/ml)

Q1. “if you put 10.0 mL of A in one balance pan, how much mass of B would you need in the other pan to make it balance? Explain your reasoning“.

The ratio of the density of substance A to substance B is 1.8 : 0.54 = 3.33 : 1 ,
i.e. substance A is 3.33 times as dense as substance B.

10.0 ml of A will be balanced by  3.33 x 10.0 ml of substance B,
i.e.  33.3ml of B is required to balance 10.0ml of A,
(B is less dense than A so a greater volume of  B is required to balance).

Q2.“if you have 35.0 mL of B in one balance pan what volume of A would you need in the other pan to make it balance? Explain your reasoning“.

Use the above ratio of densities  A : B = 3.33 : 1

35ml of B would be balanced by 35 / 3.33 of A
i.e. 10.5ml of A is required to balance 35ml of B,
(A is more dense than B so a smaller volume of  B is required to balance).
« Last Edit: 21/09/2008 20:57:59 by RD »

#### AlicexxDoll

• First timers
• Posts: 2
« Reply #4 on: 23/09/2008 03:38:06 »
Thank you so much RD~! ♥
I was so close to being right. Just .5 off of Q2! Thank you for the explanations, those were the 2 things I really did not understand, but now I do!