Mole  Problems  

Calcula/ng  molar  mass  

Round all masses to the 10ths place

Calculate  the  molecular  weight  of  Fe2O3  

•  Step One: two atoms of iron and three of oxygen

•  Step Two: Fe = 55.8 amu and O = 16.0 amu

•  Step Three: (2 x 55.8) + (3 x 16.0)

•  Step Four: 111.6 + 48.0 = 159.6 amu (grams) for one mole

Calculate  the  molecular  weight  of  KClO4  

•  Step One: one atom of potassium, one of chlorine, and four of oxygen.

•  Step Two: K = 39.1 amu, Cl = 35.5 amu, O = 16.0 amu

•  Step Three: (1 x 39.1) + (1 x 35.5) + (4 x 16.0)

•  Step Four: 39.1 + 35.5 + 64.0 = 138.6 amu (grams) for one mole

Calculate  the  molecular  weight  of  (NH4)2S  

•  Step One: two atoms of nitrogen, eight of hydrogen and one of sulfur

•  Step Two: N = 14.0 amu, H = 1.0 amu, S = 32.1 amu

•  Step Three: (2 x 14.0) + (8 x 1.0) + (1 x 32.1)

•  Step Four: 28 + 8.0 + 32.1 = 68.1 amu (grams) for one mole

Calculate  the  molar  mass  of  Al(NO3)3  

•  Calculate the molar mass of Al(NO3)3

•  Al(1 x 27.0) + N(3 x 14.0) + O(9 x 16.0) =

•  213.0 amu (grams) is the mass of one mole of aluminum nitrate.

You  Try  These…  

•  1. AlCl3 •  2. Ba(SCN)2 •  3. LiH •  4. Ba(BrO3)2 •  5. AlBr3 •  6. HCl

Answers  

•  1. 133.5 g/mol •  2. 253.5 g/mol •  3. 7.9 g/mol •  4. 393.1 g/mol •  5. 266.7 g/mol •  6. 36.5 g/mol

GRAMS  to  MOLES  

Round all final answers to 3 sig figs

Convert  25.0  grams  of  KMnO4  to  moles.    

•  KMnO4 = 158.0 g / mole of KMnO4

•  Now let’s solve it

•  25.0 g x 1 mole = 0.158191804 moles 158.0 g

•  0.158 moles

Calculate  how  many  moles  are  in  17.0  grams  of  H2O2.  

•  H2O2 = 34.0 g / mole

•  Now, let’s solve it

•  17.0 g x 1 mol H2O2 = 0.5 moles 34.0 g

•  0.500 moles

You  try  these…  

•  Calculate the moles present in: •  1) 2.00 grams of H2O •  2) 75.57 grams of KBr •  3) 100. grams of KClO4

•  4) 8.76 grams of NaOH •  5) 0.750 grams of Na2CO3

•  Remember to round answers to 3 sig figs

Answers  

•  1) 0.111 moles •  2) 0.635 moles •  3) 0.722 moles •  4) 0.219 moles •  5) 0.00708 moles

MOLES  TO  GRAMS  

Round all answers to 3 sig figs

Calculate  how  many  grams  are  in  0.700  moles  of  H2O2    

•  H2O2 molar mass = 34.0 grams/mole

•  0.700 moles x 34.0 grams = 23.8 g 1 mole •  23.8 grams

Convert  2.50  moles  of  KClO3  to  grams.    

•  KClO3 molecular mass = 122.6 g/mole

•  2.50 moles x 122.6 g = 306.5 grams 1 mole •  307 grams

You  try  these…  

•  Calculate the grams present in: •  1) 0.200 moles of H2S •  2) 0.100 moles of KI •  3) 1.500 moles of KClO •  4) 0.750 moles of NaOH •  5) 3.40 x 10-5 moles of Na2CO3

•  Remember to round answer to 3 sig figs

Answers  

•  1) 6.82 grams •  2) 16.6 grams •  3) 136 grams •  4) 30.0 grams •  5) 0.00360 grams

Avogadro's  Number  

6.02 x 1023 particles = 1 mole

Particles can mean atoms or molecules

One  mole  of  ANY  specified  en/ty  contains  6.02  x  1023  of  that  en/ty  

For  Example  

•  One mole of donuts contains 6.02 x 1023 donuts

•  One mole of H2O contains 6.02 x 1023 molecules

•  One mole of nails contains 6.02 x 1023 nails

•  One mole of Fe contains 6.02 x 1023 atoms

Con/nued  

•  One mole of dogs contains 6.02 x 1023 dogs

•  One mole of electrons contains 6.02 x 1023 electrons

•  One mole of Chemistry students contains 6.02 x 1023 poor, suffering (I mean happy, joyful) high school students

0.450  mole  of  Fe  contains  how  many  atoms?    

•  0.450 mole Fe x 6.02 x 1023 atoms 1 mole

•  = 2.709x1023 atoms

•  Final, rounded answer: 2.71x1023 atoms

0.200  mole  of  H2O  contains  how  many  molecules?    

•  0.200 mole x 6.02 x 1023 atoms 1 mole

•  = 1.204x1023 atoms

•  Final, rounded answer: 1.20x1023 atoms

You  try  these…  

•  1) Calculate the number of molecules in 1.058 mole of H2O

•  2) Calculate the number of atoms in 0.750 mole of Fe

•  Remember to round to 3 sig figs

Answers  

•  1) 6.37x1023 molecules

•  2) 4.52x1023 atoms

Two  Step  Problems  

Grams to particles OR particles to grams

Grams to atoms OR atoms to grams

If MOLE is not stated, it’s a two step problem

ROUND ALL ANSWERS TO # SIG FIGS

0.450  gram  of  Fe  contains  how  many  atoms?    

•  0.450 g x 1 mole Fe x 6.02x1023 atoms = 55.8 g 1 mole

•  4.8548387x1021 atoms

•  Final answer = 4.85x1021 atoms

0.200  gram  of  H2O  contains  how  many  molecules?    

•  H2O molecular mass = 18.0 g

•  0.200 g x 1 mole H2O x 6.02x1023 molecules 18.0 g 1 mole

•  6.6838888889x1021 molecules

•  Final answer = 6.68x1021 molecules

You  try  these…  

•  1) Calculate the number of molecules in 1.058 gram of H2O

•  2) Calculate the number of atoms in 0.750 gram of Fe

•  Remember to round answer to 3 sig figs

Answers  

•  1) 3.54x1022 molecules

•  2) 8.10x1021 atoms

THE  END