The purpose of this site is to help with a few highschool chemistry problems. I will provide one example for each case. Let me know if this helps and I will probably use this method in the future.
Determine the percentage composition for the compounds listed in assignment 10-5
There are 3 different kinds of chemical formulas you will be dealing with in this section. I will do an example for each
Step 1: Find the molar mass for each element
This is done by looking up each element on the periodic table. In this case you are looking up sodium (Na) and Fluorine (F). The molar mass is the number below each of these entries in the periodic table, which should be 22.990 grams/mol for Na and 18.998 grams/mol for F.
Step 2: Find the total mass of the compound
Since there are no subscripts, in this compound there is only 1 mol of sodium (Na) per 1 mol of fluorine (F). Since there is only 1 mol of each, calculating how much mass is in each is easy and done as follows:
1 mol F * (18.998 grams F / 1 mol F) = 18.998 grams F
1 mol Na * (22.990 grams Na / 1 mol Na) = 22.990 grams Na
Now you just add these together to get the total, which will be 41.988
Step 3: Find percent composition of each element in the compound.
Percent composition is the percentage each element contributes to the entire compound. Percent composition is how much of each element is in the compound. In the example of NaF, we're trying to find the percentage of sodium (Na) and fluorine (F) in the entire compound (NaF). The calculations are done as follows:
Percent of Sodium: 22.990 grams Na / 41.988 grams NaF = 0.5475 * 100 = 54.8% of NaF is Na
Percent of Fluorine: 18.998 grams F / 41.988 grams NaF = 0.4524 * 100 = 45.2% of NaF is F
And the above two lines are your final answer!
Step 1: Find the molar mass for each element
Exactly the same as example 1. Find the molar mass for carbon (C) and oxygen (O).
Step 2: Find the total mass of the compound
Close to the same as example 1, with one difference. Now, instead of 1 mol of each element, you have 1 mol of carbon (C) and 2 mols of oxygen (o). So the calculation is:
1 mol C * (12.011 grams C / 1 mol C) = 12.011 grams C
2 mol O * (15.999 grams O / 1 mol O) = 31.998 grams O
Now you just add these together to get the total, which will be 44.009
Step 3: Find percent composition of each element in the compound.
Now you do the same thing you did in example 1!
Percent of Carbon: 12.011 grams C / 44.009 grams CO2 = 0.2729 * 100 = 27.3% of CO2 is C
Percent of Oxygen: 31.998 grams O / 44.009 grams CO2 = 0.7270 * 100 = 72.7% of CO2 is O
And the above two lines are your final answer!
Step 1: Find the molar mass for each element
Exactly the same as example 1 and 2. Find the molar mass for Aluminum (Al), Chromium (Cr), and oxygen (O).
Step 2: Find the total mass of the compound
Close to the same as example 2, with one difference. You have to do a ton of multiplication to figure out how many moles of each element are in this compound.
For Al2, the subscript is 2, which means there's only 2 moles. For Cr, it has no subscript, and the subscript outside the parentheses is 3, so there are 3 moles of Cr. Finally, for O, the subscript is 4 and the subscript outside the parentheses is 3, so the number of moles of O is 3 x 4, which is 12. The calculation is as follows:
2 mol Al * (26.982 grams Al / 1 mol Al) = 53.964 grams Al
3 mol Cr * (51.996 grams Cr / 1 mol Cr) = 155.988 grams Cr
12 mol O * (15.999 grams O / 1 mol O) = 191.998 grams O
Now you just add these together to get the total, which will be 401.95
Step 3: Find percent composition of each element in the compound.
Now you do the same thing you did in example 1 and 2!
Percent of Aluminum: 53.964 grams Al / 401.95 grams Al2(CrO4)3 = 0.1342 * 100 = 13.4% of Al2(CrO4)3 is Al
Percent of Chromium: 155.988 grams Cr / 401.95 grams Al2(CrO4)3 = 0.3880 * 100 = 38.8% of Al2(CrO4)3 is Cr
Percent of Oxygen: 191.998 grams O / 401.95 grams CAl2(CrO4)3 = 0.4776 * 100 = 47.8% of Al2(CrO4)3 is O
And the above two lines are your final answer!
Mixed Practice. Follow the directions for each problem
There are 6 kinds of questions in this section, and I will generally explain all of them.
This is the same as 10-5
I believe we did this in 10-1. Basically you find the molar mass, flip it around so that the number is 1/(molar mass), and multiply it by the number of grams you're given.
In the case of question 11, ml is the same as grams
Same as above, but instead of flipping the molar mass around, leave it alone and multiply the number of moles you're given by the molar mass, and that should be it!
This is what I taught you with Avagadro's number, where you take the number of moles and multiply it by 6.022 x 10
So I don't know if you're given a table of densities or not, but the density of barium fluoride is 4.89 grams / 1 mL, and the density of C6H12O6 is 1.54 grams / 1 mL. So you would have to take the moles, multiply it by the molar mass, and then multiply it by the flip of the densities. Make sure all of the units cancel out and you're left with mL. Once you have the number of mL, multiply it by 0.001 to get the number of liters. Confusing I know, but try it first and then ask me for help if you need it!
See explanation for 10-6
Dude I have no idea, if you have notes on this pls.