Ch.11 Questions 42,42,44(1-3)

These are questions that I did for chemistry to improve me being able to find out the percent of an element in a compound.

1. Calcium Chloride
1. first i find the atomic mass of each compound(Ca and Cl)
1. Ca=40.08
2. Cl=35.45
2. Now since there are two Cl we 35.35x2=70.9
3. we than add 70.9+40.08=110.98
4. CaCl2 has a mass of 110.98
1. to find out the percent of Ca and Cl we simply divide the individual mass by the total mass
1. 40.08/110.98=36.11%
2. 70.9/110.98=63.88%
2. Sodium Sulfate
1. find the total mass of Sodium Sulfate
1. Na2So4
1. Na=22.990x2=45.980
2. S=32.066
3. O=15.999x4=63.996
2. add all the individual masses together
1. Na2SO4=142.042
3. divide each individual mass by the total
1. Na(45.980/142.042=32.37%)
2. S(32.066/142.042=22.58%)
3. O(63.996/142.042=45.05%)
3. Which has a larger % of Sulfur H2SO3 or H2S2O8
1. find the total mass of 
1. H2SO3
1. H=1x2=2
2. S=32.066
3. O=15.999x3=47.997
2. add all the individual masses together
1. H2SO3=82.063
3. divide each individual mass by the total
1. S(32.066/82.063=39%)
4. find the total mass of
1. H2S2O8
1. H=1x2=2
2. S=32.066x2=64.132
3. O=15.999x8=127.992
5. add all the individual masses together
1. H2S2O8=194.124
6. divide each individual mass by the total
1. S(64.132/194.124=33.03%)

H2SO3 has a larger sulfur percent.

Empirical Formula and Molecular Formula

The empirical formula of a chemical compound is the simplest positive integer ratio of atoms of each element present in a compound. Using the ration you can identify the name of an unknown compound. In this blog i am going to demonstrate my understanding on how to use this formula. Lets start with some problems:

1. You have 70% of Fe(Iron) and 30% of O(Oxygen) is the compound FeO or Fe2O3.
1. Assume that one rock of Iron Oxide is 100g.
1. you can than say that there is 70g of Fe and 30g of O
2. next is to find the number of moles in 70g of Fe and the number of moles in O
1. 70gFe=              mol/Fe, 30gO=             mol/O
3. to figure this out you would look at the atomic mass of each element
1. Fe has an atomic mass of 56 and O has an atomic mass of 16
2. taking each atomic mass you divide by the number of grams
1. 70/56=1.25, 30/16=1.875
3. the answer will be the number mole in each element.
1. 70gFe=  1.25  mol/Fe, 30gO=   1.875  mol/O
4. you than take the lower number in this case 1.25 and divide 1.875 and 1.25 by 1.25
1. 1.25/1.25=1, 1.875/1.25=1.5
2. When you get a decimal like 1.5 you will multiply both answers by two
1. 1.25/1.25=1x2=2, 1.875/1.25=1.5x2=3
5. you than have your ration for every two iron there are three oxygen
1. 2:3

This next problem I will not only use the empirical formula but to find the right answer when given to compounds that can work for the ratio I will than use the Molecular Formula.

Empirical Formula part 1

1. YOu have 2.34g of N(Nitrogen) and 5.34g of O(Oxygen) you need to find out if this compound is No2 or N2O4? Weight is 92g/mol
1. First find the number of moles in each
1. 2.34gN=      mol/N, 5.34gO=      mol/O
2. the atomic mass of N is 14 while the atomic mass of O is 16 divide the grams by the mass
1. 2.34g/14=0.167, 5.34/16=0.334
3. 2.34gN= 0.167  mol/N, 5.34gO=  0.334  mol/O
1. divide by the lowest number(0.167)
1. 0.167/0.167=1, 0.334/0.167=2
4. you have a ratio of 1 nitrogen for every 2 oxygen
1. 1:2
5. Now find the weight simple add 16x2+14=46g/mol the weight doesn't match what we were given.
2. Find out if the compound is N2O4 we have to use the molecular formula. You are given the weight of 92g/mol to get the answer you simply do the following.
1. n x46=92g/mol
1. 2x47=92g/mol
1. answer is N2O4

The Mole

The mole is a unit of measure used in chemistry to show the amount of a chemical substance. One mole is always shown as the equation of 6.02X10²³ or 602 billion trillion. A mole is abbreviated as mol, g/mol.-grams per mole. The number of a mole is always the same only the mass s different.When you are looking for the number of moles in an element for example 1 mol. of antacid Al(OH)3 would equal 78g/mol. this is because the mass of 1 mol of Al is 27, you than look at the other elements 1 mol of O is 16 but if you look at the compound it has Al(OH)3. You take the 3 and multiply it by the 1 mol. of O which gives you 48. You do the same with H and 1X3 which is 3. You than add all of them together 27+48+3=78.  There are other ways to solve a mole. Here are some of them:

1. How many moles are in 15 grams of lithium(Li)
1. to find out you first have to find out how much grams are in one mole of lithium.
1. 7g/mol.
2. Once found you than divide the number of grams so 15 by 7 to get the number of moles which is 2.13g/mol.
2. How many grams are in 2.4 moles of sulfur
1. now this is different we are looking for grams not moles so you really just to the opposite that you did to find moles.
1. there is 32g/mol in 1 mole of Sulfur
2. You than take the 32 and multiply by the number of moles you should get 76.8g/mol.
3. How many moles are in 22 grams of argon
1. 1 mol. Ar=40g/mol
1. 22/40=0.55g/mol
4. How many grams are in 88.1 moles of magnesium
1. 1 mol Mg=24
1. 24*88.1g=2114.4g/mol.
1. *-multiply
2. /-divide
5. Now here are some with compound elements
1. How many grams are in 4.5 moles of sodium fluoride, NaF
1. to solve this you first have to figure out how many grams are in one mole of NaF to do this you find the mass and add them together
1. Na=23g/mol., F=19g/mol.
1. Na+F=42g/mol.
2. taking the 42g/mol you would then multiply by 4.5 to equal 189g/mol.
1. 42*4.5=189g/mol.
2. How many moles are in 98.3 grams of aluminum hydroxide, Al(OH)3
1. Al=27g/mol, O=16*3, H=1*3, than add Al+O+H=78g/mol.
2. divide 98.3 by 78 to equal 1.26g/mol.
1. 98.3/78=1.26g/mol

Hope this post helped you to understand the mole better bye!