Homework Solutions
Chapter 4
3. a. There is twice as much sugar in solution A as in solution B.
b. The volumes are equal
c. The concentration of sugar in solution A is twice the concentration of sugar in solution B.
8. Everything except 'c'. The definition of molarity is moles salt per Liter solution. You need to know the # of moles of salt which requires knowing both the mass of salt added and the molecular mass of the salt. You need to know the final total volume of the solution. Knowing the volume of water added does not help you because volumes are not additive.
13.
a. (0.50 mol H2SO4/L dilute
solution)*(1.0 L dilute solution)*(1.0 L conc. solution/18 moles H2SO4)=
0.028 L = 28. mL
Add water
until the solution's volume is 1.0 L
b. (0.50 mol HCl/L dilute solution)*(1.0
L dilute solution)*(1.0 L conc. solution/12 moles HCl)= 0.042 L = 42. mL
Add water
until the solution's volume is 1.0 L
c. (0.50 mol NiCl/L solution)*(1.0 L
solution)*(237.69 g NiCl*6H2O/mole NiCl*6H2O)*(1 mole NiCl*6H2O/1
mole NiCl)=118.84 g NiCl*6H2O.
Add water
until the solution's volume is 1.0 L
d. (0.50 mol HNO3/L dilute
solution)*(1.0 L dilute solution)*(1.0 L conc. solution/16 moles HNO3)=
0.03125 L = 31. mL
Add water
until the solution's volume is 1.0 L
e. (0.50 mol Na2CO3/1 L
solution)*(1.0 L solution)*(105.99 g Na2CO3/mol Na2CO3)=52.995
g = 53 g.
Add water
until the solution's volume is 1.0 L
17.
? mole ethanol/L soln = (1 mole ethanol/46.07 g ethanol)*(0.79 g
ethanol/1 mL ethanol)*(75.0 mL ethanol/250.0 mL solution) = 0.00514 M
[note: 1 mL = 1 cm3 ]
21. molarity is moles sodium ion per liter
solution:
How many moles of sodium?
from sodium carbonate: (3.0 moles Na2CO3/1000
mL solution)*(70.0 mL solution)*(2 mol Na+/mole Na2CO3)
= 0.420 moles Na+
from sodium bicarbonate: (1.0 mol NaHCO3/1000 mL
solution)*(30.0 mL solution)*(1 mol Na+/mole NaHCO3) =
0.0300 mol Na+
total volume = 100.0 mL, concentration = 0.450 moles Na+
/0.100 L = 4.5 M
[note: 1 L = 1000 mL]