May 29, 2016

Homework Help: Chemistry

Posted by Bryan on Thursday, January 25, 2007 at 3:41pm.

I Have Two Questions

1)How would you calculate the number of nanometers in 8.1 cm?

2)What is the equivalent of 0.35 lb in grams?

You need to learn to do deimensional analysis. It's easy.
0.35 lb to grams
We know there are 453.6 g in a lb. We take the given (0.35 lb) and multiply by a conversion factor. The factor is either 453.6 g/1 lb or 1 lb/453.6 g.

0.35 lb x factor = ??
Now all we need to do is determine which of the two factors to use? That's easy, too. We arrange the factor so the unit we don't want to keep (lbs in this case) cancels and grams is what is left.
0.35 lb x (453.6 g/lb) = ?? grams.
Note that we place lb of the factor in the denominator so that it will cancel with the given (lb in this case) and it leave g from the factor to go with the numerical value of the answer.

There are 1 x 10^7 nm in 1 cm.

given (8.1 cm) x factor.
8.1 cm x (1 x 10^7 nm/cm) = ??

Again, the cm unit cancels (that's the one we don't want to keep) but we leave the nm of the factor, so the answer is 8.1 x 10^7 nm.
This is a simple process and we need not make it complicated.

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