# ››Stoichometry problems?   (05/11/2012, 11:06 PM)

Change the following masses to number of particles by:
A) dividing by the molar mass to get the number of moles, and then
B) multiplying number of moles by Avogadro's number
1. How many molecules are in 54.0 grams of water?

1.81 x 1024 molecules of water.

2. How many molecules are in 24.0 grams of CO2?
3. How many atoms does 3.0 grams of carbon represent?

3.0 g CO2 x (1 mole C / 12.0 g C) x (6.022x10^23 molecules / mole) = 1.5x10^23 atoms C

* 4. How many formula units does 300.0 grams of calcium carbonate represent?

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Determining the Molar Mass

Determine the molar mass for the following:
1. H2O
18.0 g/mole

2. F2

38.0 g/mole
3. CaI2

294 g/mole

4. Pb(NO3)2

331 g/mole

Changing Mass to Number of Moles

Change the following masses to moles, by dividing the mass by the molar mass.
# of Moles = mass given/molar mass
1. How many moles does 70.0 grams of H2O represent?
3.47 moles

2. How many moles does 55.0 grams of C6H12O6
represent?

55 ÷ 180.16 = .31 moles
3. How many moles does 27.0 grams of CO2 represent?

27 ÷ 44.01 = 0.61 moles

4. How many moles does 46.0 grams of N2 represent?

1.64 moles
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Changing Moles to Mass

Round answers correctly and show proper units.
Change the following number of moles to mass by multiplying the number of moles by the molar mass.
mass of sample = # of moles x molar mass
1. What is the mass of 4.0 moles of LiOH ?

95.79 grams

2. What is the mass of 5.8 moles of Ba(CN)2 ?

1098.3 grams
3. What is the mass of 8.5 moles of water?

153.13 grams

4. What is the mass of 2.75 moles of CuSO4 ?

438.92 grams

Changing Number of Moles to Number of Particles

Round answers correctly and show proper units.
Change the following number of moles to number of particles by multiplying by Avogadro's number.
# of particles = # of moles x (6.02 x 1023)
1. How many atoms does 2.0 moles of He represent?

1.2x10^24 He atoms

2. How many sodium ions are in 5.0 moles of NaCl?
3. How many molecules are in 2.25 moles of CH4?

* 4. How many total atoms are in 1.0 moles of H2O ?

1.8x10^24 atoms

Changing Number of Particles to Number of Moles

Round answers correctly and show proper units.
Change the following number of particles to number of moles by dividing by Avogadro's number.
# of moles = # of particles / (6.02 x 1023)
1. How many moles of water does 6.02 x 1023molecules represent?

6.02x10^23 molecules H2O x (1 mole / 6.022x10^23 molecules) = 1.00 mole H2O
2. Convert 3.01 x 1023 molecules of C2H6 to moles.

3.01x10^23 molecules C2H6 x (1 mole / 6.022x10^23 molecules) = 0.500 moles C2H6
3. How many moles of glucose does 1.2 x 1024molecules represent?
1.2x10^24 molecules glucose x (1 mole / 6.022x10^23 molecules) = 2.0 moles glucose

4. How many moles of CaCl2 does 2.41 x 1024formula units represent?

2.41x10^24 units CaCl2 x (1 mole / 6.022x10^23 units) = 4.00 moles CaC2

Changing Number of Particles to Mass

Round answers correctly and show proper units.
Change the following number of particles to masses by:
A) dividing by the number of particles by Avogadro's number to get number of moles, and then
B) multiplying number of moles by the molar mass
1. What would be the mass of 1.20 x 1024molecules of water?

1.20x10^24 molecules x (1 mole / 6.022x10^23 molecules) x (18.0 g / mole) = 36.0 g H2O

2. What would be the mass of 2.41 x 1024 formula units of barium hydroxide?

2.41x10^24 units x (1 mole / 6.022x10^23 molecules) x (171.3 g / mole) = 342 g Ba(OH)2
3. How much mass does 1.51 x 1022 atoms of neon represent?

1.51x10^22 atoms x (1 mole / 6.022x10^23 atoms) x (20.18 g/mole) = 0.503 g Ne

4. How much mass does 7.53 x 1022 molecules of CH4 represent?
7.53x10^22 molecules x (1 mole / 6.022x10^23 molecules) x (16.04 g/mole) = 2.00 g CH4

 Current Thread... 05/11/2012, 11:06 PM Stoichometry problems? 07/28/2014, 9:33 AM Re: Stoichometry problems?