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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: roncarlston on February 04, 2010, 11:52:45 PM

Title: Help with density problem
Post by: roncarlston on February 04, 2010, 11:52:45 PM

Taking my first ever chemistry class and i've run into this problem:

Suppose you have two 100-mL graduated cylinders. In each cylinder there is 40.0 mL of water. You also have two cubes: one is lead and the other is aluminum. Each cube measures 2.0 cm on each side. After you carefully lower each cube into the water of its own cylinder, what will the new water level be in each of the cylinders?

we are given the following data: aluminum density = 2.70 g/cm(cubed), lead density = 11.3 g/cm(cubed)


I am really new to things like unit conversions and there are no sample problems of this type in the book...it goes from "heres how to calculate density" to this problem... i wish the book would show the answers so i could at least reverse engineer the problem and check my work... if someone could show me how to do this i would really appreciate it, thanks!

Title: Re: Help with density problem
Post by: savy2020 on February 05, 2010, 01:15:42 AM

Water level would be same in both

Title: Re: Help with density problem
Post by: DrCMS on February 05, 2010, 06:01:21 AM

As both lead and aluminium are more dense than water the cubes will sink and raise the water level by the volume of each cube.

What is the volume of a cube with 2cm sides?

What is the volume of the water + the cube?

Title: Re: Help with density problem
Post by: roncarlston on February 05, 2010, 11:05:08 AM

oh man it looks like i was really overcomplicating this!

the volume of the cube should be 2^3 = 8  correct? raising the water level to 48g/cm^3 ?

Title: Re: Help with density problem
Post by: savy2020 on February 05, 2010, 11:48:53 AM

Yes! but 48cm³ (unit of volume)

Title: Re: Help with density problem
Post by: roncarlston on February 05, 2010, 01:36:10 PM

but since the book wants to know the level of the water in the cylinder (mL) shouldn't i use the answer 48.0 mL?

Title: Re: Help with density problem
Post by: DrCMS on February 05, 2010, 03:40:09 PM

yes

Title: Re: Help with density problem
Post by: roncarlston on February 05, 2010, 05:01:15 PM

thank you guys