GS105    Practicing with MOLES   KEY

 

Calculate the formula weight (in amu) for the following:

 

NaOH   ___39.99amu___             Na= 22.99 amu       O = 16 amu      H= 1 amu      22.99+16+1= 39.99 amu

 

KAlSi₃O₈    _278.35amu__     K=39.1amu;   Al= 26.96amu;   Si=28.09 amu;  O=16amu  

                                                    39.1+ 26.96 +(3) 28.09 +(8) 16= 278.35amu

 

Na₂SO₄   __142.05amu___         Na= 22.99amu       S=32.07amu    O=16amu      (2) 22.99+ 32.07 + (4) 16)= 142.05

 

How many grams are in one mole of the following:  To convert to grams you will just change the units  

 

NaOH   __39.99g______     1mol Na= 22.99g   1 mol O=16g    1mol H 1g        1mol NaOH= 22.99+16+1=39.99g

 

KAlSi₃O₈     ___278.35g___

 

Na₂SO₄   ___142.05g____

 

How many atoms are in one mole of the following?   In one mole of anything there are 6.02X10²³ atoms

 

NaOH   __6.02X10²³ ______                                           Na₂SO₄   ___6.02X10²³ ___

 

KAlSi₃O₈     ___6.02X10²³ __

 

How many moles are in:

 

200 grams of NaOH     ____5___________     1 mole NaOH = 39.99g so      200g NaOH/39.99g per mole = 5 moles

 

678 grams of KAlSi₃O₈   ___2.43____    1 mole= 278.35g   so   678g/278.35g per mole = 2.43 moles

 

56 grams of Na₂SO₄   ___0.39______    1 mole =142.05g  so  56g/142.05g per mole = 0.39 moles

 

How many atoms are in:   Use the information from above to solve

 

200 grams of NaOH     __3.01x10²⁴______      200g= 5 moles.   1 mole =6.02 x10²³ atoms.   (5) 6.02 x10²³ =

                                                                                                                                                                    3.01x10²⁴

678 grams of KAlSi₃O₈   _1.46x10²⁴____    678g = 2.43 moles    (2.43) 6.02 x10²³= 1.46x10²⁴

 

56 grams of Na₂SO₄   __2.34x10²³____   56g=0.39 moles    (0.39) 6.02 x10²³ =  2.34 x 10²³

 

How much of each would you have grams if you had:

 

3 moles of  NaOH  _____119.97g______________    1mol NaOH =39.99g    3(39.99g)=119.97g

 

5.2 moles of KAlSi₃O₈  ____1447.42g___________   1mol =278.35g          5.2(278.35g) = 1447.42g

 

1.4 moles of Na₂SO₄_______198.87g____________  1mol =142.05g      1.4(142.05g)= 198.87g

 

Calculate the mass (grams) of Iron (Fe) in a sample that is 3.2 moles

          Fe=55.85amuà 1 mole of Fe = 55.85g         3.2mol (55.85g) =         198.87g

 

Calculate the number of atoms in a sample of Calcium (Ca) that has a mass of 75 grams

           Ca= 40.08amuà 1 mole of Ca =55.85g   therefore  75gCa/55.85g per mole = 1.34mole of Ca

           1 mole of Ca = 6.02x10²³ atoms    therefore   1.34 moles (6.02x10²³atoms per mole) =    8.06 x1023 atoms