Step 1
Density is defined as:
D = mass of the platinum brick/volume of the platinum brick
D = m/V
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Step 2
Information provided:
D = 21.45 g/mL
V = 150.0 mL
m = unknown
Price per grams of Pt = 31.86 $/g of Pt
Symbol for platinum = Pt (please, look at the periodic table)
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Step 3
How much should the brick weigh if it’s is really platinum?
From D = m/V
=> D x V = m
=> 21.45 g/mL x 150.0 mL = 3218 g approx.
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And how much money?
3218 g of Pt x 31.86 $/g of Pt = $99,660 approx.
Answer:
3218 g
$99,660