[ankara55t]

Hello,
The question is to find the number of atoms in 52.5g of calcium metal. Do we need to have the molar mass of Ca an once we get the number of molecules how do we determine the # of atoms?

[kp2171]

Hello,
The question is to find the number of atoms in 52.5g of calcium metal. do we need to have the molar mass of Ca an once we get the number of molecules how do we determine the # of atoms?

Its good to ask this question if you are struggling. We won't do your work for you, per site rules, but ill talk you through it and you can post your answer or where you are struggling. When taking any basic chem class it is really important to spend time on the early work dealing with formulas and calculations... those who don't often don't make it through the later work. Not to scare you too much... I've just taught students who thought they could skip the early work and it never turns out well...

Boy, do I ramble or what...

First thing is the molar mass is grams/mol... "ounces" are not involved in this question as you have worded it. Just to clarify the language.

So you know how many grams there are you are thinking about using the molar mass to get to get "molecules" and you want to know about atoms versus molecules.

You need to look at the formula of whatever you are talking about. In the case of calcium metal, its really just one atom... to contrast, a molecule of water (H2O) has two atoms of hydrogen. We don't usually talk about calcium as being a "molecule"...

So calcium metal really isn't a molecule, its just a bunch of calcium atoms.

So... take the weight and use the molar mass to get the moles of calcium... then use avogadro's number to get the number of atoms per mole...

Avogadro's number doesn't mean # of molecules per mole... it means # of "whatever" per mole...

I could ask you how many eggs would you have if you had 2 moles of eggs. Thatd be one helluva breakfast...

So... use molar mass to get moles... then use avogadros number to convert moles to atoms.

Post your answer if you'd like

[Perito]

The question is to find the number of atoms in 52.5g of calcium metal. Do we need to have the molar mass of Ca an once we get the number of molecules how do we determine the # of atoms?

Yes, you need to know the "molar mass" (molecular weight where I live) of calcium.

1. Determine the number of moles of calcium. Note this relationship:



The molecular weight is in grams/mole.

2. One mole of any substance contains Avogadro's number of molecules. If there's only one atom per molecule, as in the case of calcium, it's the number of atoms.

Let me google Avogadro's number for you

[ankara55t]

52.5g divided by 40.08 g/mol = 1.31 moles

1 mole contains 6.02 x 10^23


and therefore 1.31 moles contain 1.31 X 6.02 X10^23 = 7.89 X 10^24

[Unknown008]

Perito? I think you did a mistake there. The OP has tried to answer his/her own question...

And BTW, ankara55t, yes, that's the answer.

[Perito]

Oops. Sorry ankara55t. Unknown008 is quite right (got me again).

As Unknown008 said, you're quite right.