Re-cap of all that we have learned depicted through this picture:
A blog dedicated for the love and learning of Chemistry.
27.12.10
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
Mole to Atom/Molecule conversions
Today we learned how to convert from moles to atoms or from moles to molecules
Pretty basic stuff if I do say so myself!
Determine the number of atoms that are in 1.25 mol of O2
1.25mol x 6.02x10^23 atoms/ 1 mol = (7.53 x 10^23)
But since we're looking for Oxygen gas (diatomic) we times our answer by 2.
= (7.53 x 10^23) x 2
= 1.51 x 10^24 atoms
Determine the number of atoms that are in 0.58 mol of Se
0.58mol x 6.02 x 10^23 atoms/ 1 mol = 3.5 x 10^23 atoms
2. FROM ATOMS TO MOLES
How many moles are present in 3.9 x10^25 Nitrogen atoms?
3.9x10^ 25 Nitrogen atoms x 1 mol/6.02x10^23 atoms= 64.8 moles
A cylinder of Helium contains 4.6 x 10^30 atoms. How many moles of Helium is this?
4.6 x 10^30 atoms x 1 mol/ 6.02 x 10^23 atoms = 7.6 x 10^6 mol
Are you slowly realizing that conversions aren't at all that difficult like this fellow right here?
GOOD lets try another one, but this time even more complicated!
How many water molecules are there in 0.65 mol? How many hydrogen atoms are there? How many oxygen atoms are there?
If your initial reaction looks something like this^..... than follow the steps below!
First step: Do not panic after reading this question! Lets take it STEP BY STEP!
Let us first find how many water molecules is in 0.65 moles
0.65 mol x 6.02 x 10^ 23 molecules / 1 mol
You are trying to find molecules/atoms so put that on top!
Cancel out units of moles and times 0.65 and 6.02 x 10^23 and you will get
3.9 x 10 ^ 23 molecules
How many hydrogen atoms are there?
Remember they are asking for water molecules, and the chemical equation for water is H20
In this equation we see 2 Hydrogen atoms so...
(3.9x10^23atoms) x 2 = 7.8 x 10^23 atoms of Hydrogen
How many oxygen atoms? There is no subscript next to Oxygen so we assume its 1
(3.9x10^23atoms) x 1= 3.9 x 10^23 atoms of oxygen
Yay! You did it!
Post by Ren Flores
Pretty basic stuff if I do say so myself!
- FROM MOLES TO ATOMS:
Determine the number of atoms that are in 1.25 mol of O2
1.25
But since we're looking for Oxygen gas (diatomic) we times our answer by 2.
= (7.53 x 10^23) x 2
= 1.51 x 10^24 atoms
Determine the number of atoms that are in 0.58 mol of Se
0.58
2. FROM ATOMS TO MOLES
How many moles are present in 3.9 x10^25 Nitrogen atoms?
3.9x10^ 25 Nitrogen
A cylinder of Helium contains 4.6 x 10^30 atoms. How many moles of Helium is this?
4.6 x 10^30
GOOD lets try another one, but this time even more complicated!
How many water molecules are there in 0.65 mol? How many hydrogen atoms are there? How many oxygen atoms are there?
First step: Do not panic after reading this question! Lets take it STEP BY STEP!
Let us first find how many water molecules is in 0.65 moles
0.65 mol x 6.02 x 10^ 23 molecules / 1 mol
You are trying to find molecules/atoms so put that on top!
Cancel out units of moles and times 0.65 and 6.02 x 10^23 and you will get
3.9 x 10 ^ 23 molecules
How many hydrogen atoms are there?
Remember they are asking for water molecules, and the chemical equation for water is H20
In this equation we see 2 Hydrogen atoms so...
(3.9x10^23atoms) x 2 = 7.8 x 10^23 atoms of Hydrogen
How many oxygen atoms? There is no subscript next to Oxygen so we assume its 1
(3.9x10^23atoms) x 1= 3.9 x 10^23 atoms of oxygen
Yay! You did it!
Post by Ren Flores
14.12.10
MOLAR VOLUME!!!
Today we learned about Moles to Volume conversions.... ooooo sounds complicated? Well it's actually not too shabby! (Does anyone use that word anymore?)
Before we start please note:
At a specific pressure and temperature one mole of any gas occupies the same volume!
Note: *at 0 degrees Celsius and 101.3 kilo Pascals, 1 mole : 22.4 Litres
This temperature and pressure is called STP which stands for Standard Temperature Pressure.
22.4 L/mol is the molar volume at STP
Lets try some examples shall we.....
How many liters will 2.5 mol of H2 occupy at STP?
Start with what you're given... which is 2.5 mol
You want to find how many liters are in 2.5 mol of H2!
Your equation will look like this:
2.5mol x 22.4 L/ 1 mol = 56 L
Lets try some more! Isn't this fun
-----> A certain gas is found to occupy 11.6 L at STP. How many moles?
11.6 L x 1 mol / 22.4 L = .518 mol
------> At STP an unknown gas is found to occupy 150mL. How many moles of gas must there be?
First off, we see that the volume is measured in mL. We must change it to liters!
First step: 150mL x 1 L / 1000 mL = 0.150 L
Second step: 0.150 L x 1 mol/ 22.4 L = 0.00670 mol
Remember significant digits! In this case, we round to 3 sig figs!
Getting there? GOOD! :)
alright so let's try one more example and lets see if you get the gist of it all!
A certain amount of Chlorine gas occupies 1.6 L. Find the # of moles present and then determine the mass of chlorine.
So in this specific equation, we are asked to find 2 things. The number of moles present and the mass of chlorine. We shall start off with what we're given!
1.6L x 1 mol / 22.4 L = 0.71 mol
You figured out the number of moles! Now find the mass of chlorine!
0.71 mol x 71 g/ 1 mol = 5.1 g
Dont forget Chlorine is diatomic so the equation on the top would be 2(35.5) which gave us the number 71!
And das it! Good job everyone!
Post by Ren Ren
Before we start please note:
At a specific pressure and temperature one mole of any gas occupies the same volume!
Note: *at 0 degrees Celsius and 101.3 kilo Pascals, 1 mole : 22.4 Litres
This temperature and pressure is called STP which stands for Standard Temperature Pressure.
22.4 L/mol is the molar volume at STP
Lets try some examples shall we.....
How many liters will 2.5 mol of H2 occupy at STP?
Start with what you're given... which is 2.5 mol
You want to find how many liters are in 2.5 mol of H2!
Your equation will look like this:
2.5
Lets try some more! Isn't this fun
-----> A certain gas is found to occupy 11.6 L at STP. How many moles?
11.6
------> At STP an unknown gas is found to occupy 150mL. How many moles of gas must there be?
First off, we see that the volume is measured in mL. We must change it to liters!
First step: 150
Second step: 0.150 L x 1 mol/ 22.4 L = 0.00670 mol
Remember significant digits! In this case, we round to 3 sig figs!
Getting there? GOOD! :)
alright so let's try one more example and lets see if you get the gist of it all!
A certain amount of Chlorine gas occupies 1.6 L. Find the # of moles present and then determine the mass of chlorine.
So in this specific equation, we are asked to find 2 things. The number of moles present and the mass of chlorine. We shall start off with what we're given!
1.6
You figured out the number of moles! Now find the mass of chlorine!
0.71 mol x 71 g/ 1 mol = 5.1 g
Dont forget Chlorine is diatomic so the equation on the top would be 2(35.5) which gave us the number 71!
And das it! Good job everyone!
Post by Ren Ren
6.12.10
MOLAR MASS
Molar mass: The molar mass is the mass, in grams, of one mole of a substance. The molar mass is numerically the same as the formula mass (found in the periodic table) but with units of grams mol-1.
We use grams per mol = g/mol
To calculate the molar masses:
Here are some other examples:
Calculate the molar masses of:
Mg(OH)2
24.3 + 2(16) + 2(1) = 58.3 g/mol
(NH4)2SO4
2(14.0)+8(1.0)+32.1+4(16.0)= 132 g/mol
Now let's try some Molar Conversions...
Mr. Doktor gave us a handy chart we can refer to when we are doing our conversions! Look below:
Now let us try shall we...
oh yeah before I forget, remember to use Avogardo's top secret number when you are trying to find the number of atoms, formula units, or moles! Whats his secret number?
Highlight the bottom space under this to find out....
6.02 x 10²³
Now dont tell anyone and use this number to your advantage.... haha
A sample of Carbon contains 2.47x10²5 atoms. How many moles of carbon is this?
2.47x10²5atoms x 1 mol/ 6.02 x 10²³ atoms = 41.02990033 moles
*Round to sig figs
= 41.0 moles
How many atoms are there in 1.5 mol of Iron?
(If your stuck, start off with what you're given!)
1.5mol x 6.02 x10²³atoms/1 mol= 9.03 x10²³ atoms
... but you only get 1/2 marks because you forgot sig figs! so remember your sig figs and you get....
= 9.0 x 10²³ atoms
12.5 moles of 0² represent how many molecules?
12.5mol x 6.02x10²³molecules/ 1mol = 7.52 x ²4 molecules
Find the mass of 0.159 mol of SiO2
0.159mol x 60.1 g/1mol = 9.5559g
=9.56g
Get the drift? If yes than good for you now go away! If no, then lets do one more with a more detailed explanation. Lets try the a similar example to the last example I did.
Find the mass of 3.66 mol of N²
Write what you're given:
3.66 mol
Now you want to get rid of moles and you want to find the mass. Mass is measured in grams (g) and since N (nitrogen) is diatomic (which you can also depict from the subscript 2 however that 2 should not be on the top right it should be on the bottom...) then you can write your equation like this:
3.66 mol x 28 g / 1 mol
28 grams came from Nitrogens Atomic mass in the periodic table which is 14 but times 2! 14x 2 = 28!
3.66mol x 28g/ 1 mol
Cancel your units....
(3.66) x (28)
and you get ....
102 grams!
Now you know how to convert mole conversions! More coming later!
-Post by Ren Flores
We use grams per mol = g/mol
To calculate the molar masses:
Here are some other examples:
Calculate the molar masses of:
Mg(OH)2
24.3 + 2(16) + 2(1) = 58.3 g/mol
(NH4)2SO4
2(14.0)+8(1.0)+32.1+4(16.0)= 132 g/mol
Now let's try some Molar Conversions...
Mr. Doktor gave us a handy chart we can refer to when we are doing our conversions! Look below:
Now let us try shall we...
oh yeah before I forget, remember to use Avogardo's top secret number when you are trying to find the number of atoms, formula units, or moles! Whats his secret number?
Highlight the bottom space under this to find out....
6.02 x 10²³
Now dont tell anyone and use this number to your advantage.... haha
A sample of Carbon contains 2.47x10²5 atoms. How many moles of carbon is this?
2.47x10²5
*Round to sig figs
= 41.0 moles
How many atoms are there in 1.5 mol of Iron?
(If your stuck, start off with what you're given!)
1.5
... but you only get 1/2 marks because you forgot sig figs! so remember your sig figs and you get....
= 9.0 x 10²³ atoms
12.5 moles of 0² represent how many molecules?
12.5
Find the mass of 0.159 mol of SiO2
0.159
=9.56g
Get the drift? If yes than good for you now go away! If no, then lets do one more with a more detailed explanation. Lets try the a similar example to the last example I did.
Find the mass of 3.66 mol of N²
Write what you're given:
3.66 mol
Now you want to get rid of moles and you want to find the mass. Mass is measured in grams (g) and since N (nitrogen) is diatomic (which you can also depict from the subscript 2 however that 2 should not be on the top right it should be on the bottom...) then you can write your equation like this:
3.66 mol x 28 g / 1 mol
28 grams came from Nitrogens Atomic mass in the periodic table which is 14 but times 2! 14x 2 = 28!
3.66
Cancel your units....
(3.66) x (28)
and you get ....
102 grams!
Now you know how to convert mole conversions! More coming later!
-Post by Ren Flores
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