Chemistry - 2nd Problem Set, #4-6
4. How many molecules of HCl are in 4.91 L of HCl acid at 25 ºC if the density
equals 1.096 g/mL?
d = 1.096 g/mL; vol = 4.91 L = 4910 mL; molar mass = 36.45 g/mol
a. Convert volume to mass using density: density x volume = mass
• (1.096g/mL) (4910mL HCl) = 5381 g HCl
b. Convert mass to moles: grams / molar mass = mol
• (5381g HCl) / (36.45g/mol) = 148 mol HCl
c. Convert moles to molecules: (moles) (Avo. #) = molecules
• (148mol HCl) (6.02 x 10^23 molecules/mole) = 8.89 x 10^25 molecules
volume --> mass --> moles --> molecules
Continued: Copy in journal.
5. If a 1.000 gallon (3.785 L) bottle were filled with bleach (NaClO), how many Cl atoms
would be in the bottle? dbleach = 1.090 g/mL. Hint: (First find the mass of the NaClO.)
• Mass NaClO = (3785 mL) (1.090 g/mL) = 4126 g NaClO
• Mol NaClO = (4126 g) / [(23+35.45+16) g/mol] = 55.4 mol NaClO
• 1 mol Cl atoms per 1 mol NaClO; So 55.4 mol NaClO = 55.4 mol Cl atoms
• (55.4 mol Cl atoms) (6.02 x 10^23 atoms/mol) = 3.34 x 10^25 atoms
6. At 25º C, the density of water is 0.997 g/ml. At -10º C, the density of ice is 0.917 g/cm3.
If a bottle with a volume of 275 mL were filled fully with water at 25º C and then frozen to
-10º C, could the ice still be contained in the bottle? What would the volume of the ice be?
• At 25ºC, mass of water = (0.997 g.mL) (275 mL) = 274.2 g H2O
• At -10ºC, volume of ice = (274.2 g) / (0.917 g/mL) = 299 mL ice
• 299 mL > 275 mL, capacity of bottle. Bottle would NOT contain all of the ice.