Brittany M. answered • 09/04/20
Chemistry PhD | 5+ Years of Helping Students Succeed
It sounds like you may be missing some information. There should be a table in your book, or provided by your teacher, that you can use to find the densities of these metals.
You may also find it helpful to find the information online from a reputable source. Once you have the densities, you'll need to find out the mass of lead that you have.
Lead has a density of 11.4g/cm^3 and iron has a density of 7.87g/cm^3.
Using dimensional analysis, the mass of lead that you have is:
2.20 cm^3 * (11.4 g / cm^3 ) = 25.08 grams of lead.
Now in order for the balance to be balanced you'll need to have the same mass of iron.
Again, using dimensional analysis,
25.08 g Fe * ( 1cm^3 / 7.87 g ) = 3.187 cm^3 Fe. Using significant figures, you would want to round to 3.19 cm^3.
Notice how we used the inverse of the density (flipped it upside down) when solving for the volume of iron. This is because we want to make sure that the units we don't want will cancel out and we'll be left with the units we're looking for.
