You must use unit analysis to solve density problems in chemistry (NOT THE FORMULA & ALGEBRA). Remember you are learning the process of unit analysis, not simply finding the correct answer!
Use the technique you have learned in problem solving: what are you looking for, what are you given, put the units together to cancel and solve.
Example #1
A sample of a known metal is dropped into a graduated cylinder with 25.0 mL of water. The level rises to 31.5 mL. If the given density of the metal is 2.56 kg/L, what is the mass of the sample in grams?
Possible Questions
Where did 6.5 mL come from? A substance displaces its volume when immersed in water. The water level rose from 25.0 to 31.5 mL.
Why are there only 2 sig dig in the final answer? When you multiply and divide, you use the least number of sig dig. 2.56 kg/1L has 3, 6.5 mL has 2, and the conversions for L and kg are exact values with an infinite number of sig dig.
Example #2
Where did 6.5 mL come from? A substance displaces its volume when immersed in water. The water level rose from 25.0 to 31.5 mL.
Why are there only 2 sig dig in the final answer? When you multiply and divide, you use the least number of sig dig. 2.56 kg/1L has 3, 6.5 mL has 2, and the conversions for L and kg are exact values with an infinite number of sig dig.
Example #2
What is the volume of a sample of aluminum in L that weighs 56.7 g? The density of aluminum is 2.71 g/mL.
Possible Questions
Why flip the density? To make sure the units of volume will be in the numerator.
I got a different answer (0.153657), why? Remember that 2.71 is in the denominator. You must divide, not multiply. You can either input 56.7 first, divided by 2.72, divided by 1000
OR start with 1 divided by 2.71, times 56.7, divided by 1000.
OR start with 1 divided by 2.71, times 56.7, divided by 1000.
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