yet another... Density to Moles

Just when you think all the conversions are over, from moles to atoms to atoms to moles, we still have one more!

But don't worry! It's pretty easy! Today in class we learned about converting from Density to Moles.

Density is a measure of Mass per volume.

D= M/V

It is usually measured in g/L (grams per liter) or g/ml (grams per milliliter)

Lets try a few Questions shall we?

A 2.5 g sample of an unknown metal has a volume of 32 mL. Determine the metal's density.

Since we are given grams and mL, we simply divide 2.5g/32mL to get 0.078g/mL

Remember density can be measured in g/mL!

(DENSITY-MOLES)

How many moles are in a 25.0mL sample of Iron if the density of Iron is 7.87 g/mL?

start with the given density:

7.87g/mL x 25.0 mL = 196.75g x 1 mol/55.8g = 3.53 mol

(GIVEN VOLUME/MOL- FIND DENSITY)

If a gold ring has a volume of 7.50 mL and contains 0.736 mol of Gold determine the density of Gold.

You are given the volume in mL so you must find the mass!

Take 0.736 mol and use it in this equation:

0.736mol x 197.0g/1 mol = 144.992 g

Now since you've figured out grams, the formula for density is d=m/v

You have mass= 144.992g

You have volume= 7.50mL 

now divide the two to get

19.3 g/mL

(DENSITY-ATOMS)

Copper has a density of 8.96 g/mL. Determine the number of atoms in copper key that has a volume of 20mL.

8.96 g/ml x 20ml = 179.2 g x 1mol/63.5g = 2.82 mol x 6.02 x 10^23 atoms/1mol 

= 1.7 x 10^24atoms

We also learned about the Density of gases!

The Density of gases varies with temperature!

New formula:

Lets try some questions!

Determine the density of Methane (CH4) at STP

Molar mass->16.0g/mol

Molar volume->22.4L/mol

= .714 g/L

An unknown diatomic gas has a density of 1.25 g/L at STP. Determine the Molar mass for this gas then write the chemical formula for it.

1.25 g/L x 22.4 L/1mol 

= 28 g/mol

= 28g/mol

2

(You divide by 2 because we are looking for an "unknown diatomic gas")

Once you divide by 2, you get 

14 g/mol

What element on the periodic table has a molar mass of 14g?

Nitrogen!

N2!

And that is all we learned :)

Post by REN