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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: zerox0o on September 03, 2009, 04:36:31 PM

Title: Determine the mass of a piece of lead but does not have a laboratory balance
Post by: zerox0o on September 03, 2009, 04:36:31 PM

How do I do this? Please help me :(

A student needs to determine the mass of a piece of lead but does not have a laboratory balance. The student takes a graduated cylinder and pours water into it until the volume reading is 31.0 mL. After dropping the piece of lead into the cylinder, the volume increases to 42.6 mL. What is the mass of the lead in grams ?

Title: Re: Determine the mass of a piece of lead but does not have a laboratory balance
Post by: Lonn on September 03, 2009, 05:15:21 PM

look for the density online

Density of lead: 11.34  g*cm−3

cm-³ = mL

so your answer should be in grams

Volume = mass/density

Title: Re: Determine the mass of a piece of lead but does not have a laboratory balance
Post by: zerox0o on September 03, 2009, 06:30:02 PM

is it = 131.54 g?  ;D

Title: Re: Determine the mass of a piece of lead but does not have a laboratory balance
Post by: Lonn on September 03, 2009, 07:01:45 PM

No sorry I wrote:

 Volume = mass/density

In this case it was:

Mass = Density/Volume


You have to take the volume of water and substract it from the final volume from when you added the lead:

42.6mL - 31.0mL = 11.6mL

11.6mL is the volume of the lead

the Density of lead is 11.34 g*cm-³

remember: cm-³ = mL so just change it to 11.34 g*mL so mL gets canceled.

Now you:

Mass = Density/Volume

Mass = 11.34 g*mL/11.6mL

you divide 11.34 into 11.6 and the mL get cancelled

you get:

Mass = 0.977586

with scientific notation

Mass = 9.8 x 10^-1g

Title: Re: Determine the mass of a piece of lead but does not have a laboratory balance
Post by: zerox0o on September 03, 2009, 07:45:32 PM

Thank you so much! your explanation was so clear!  ;D
It was so confusing for me before  ???