Question

How mant grams are in 1.25x 10^24 atoms of calcium?

Answer 1

This is 83.5 grams calcium

Explanation:

Most chemistry problems can be expressed as equations which are products of the starting quantity multiplied by natural constants and conversion factors to get the answer. So you need to determine what natural constants you need and the conversion factors.

We see that the answer has units of "atoms". Generally when you see any quantity with "atoms" or "molecules" in it, you will probably need Avogadro's Number . 1 mole of atoms OR molecules is `6 * 10^23` atoms or molecules

Now when you see "grams" of a compound/element, and you might need to relate it to moles, you need the formula or atomic or molecular weight of that. Since we are talking about calcium, we need its atomic weight, which is 40.1 g/mol

Now let's set up the product (multiplication of factors):

`(1.25 * 10^24 " atom Ca")((1 " mol Ca")/(6 * 10^23 "atoms Ca"))((40.1 " g Ca")/(1 " mol Ca"))=83.5 " g Ca"`

Notice that in the setup of the product, you arrange the dimensions in numerator-denominator fashion so they cross out (atoms Ca cross out, mol Ca cross out) and you are left with the dimensions of the answer you want in the numerator. In setting up this multiplication of factors, be careful if you have to invert a constant or conversion factor!

In this computation, we used no conversion factor (like `(1000 " ml")/(1 " L")`) and we used two natural constants