Help with another chem. unit conversion problem?

Question

Given that basalt seems to well up when the ocean crust pulls apart at Mid-Ocean ridges, you might decide that maybe the entire Earth is made of basalt. On your bathroom scale, a 64 in^3 (4 in * 4in * 4in) block of basalt weighs 116 oz. Use this information to calculate whether the average density of the Earth (5.5 g/cm63) can be explained by an Earth made completely of basalt.

Thanks for answering! I'm just stumped...

And if in general could you explain how to convert between a number with two units (miles per hour, grams per cubic cm, etc.)

Thanks!

Answer 1

Well, in general, you need to convert both parts of the unit.

so for above, you have 116 oz / 64in^3, or 1.8125 oz/in^3  (by simple division).

first convert ounces to grams, so

1.8125 oz = 1.8125 x 28.349 = 51.3835 g

then convert in^3 to cm^3, so

1 in^3 = 16.387 cm^3

Now you have 51.3835 g/16.387 cm^3 or 3.1356 g/cm^3

This is less than the density of the earth, so the earth can NOT be made entirely of basalt.