GENERAL CHEMISTRY-I (1411)
S.I. # 19
1. How many grams of solute are present in 50.0 mL of 0.360 M K2Cr2O7?
M=(mol/L) mol = (MxL) (0.360 mol/1L)(0.05L)(294.2 g / mol) = 5.30 g K2Cr2O7
2. If 4.28 g of (NH4)2SO4 is dissolved in enough water to form 300 mL of solution,
what is the molarity of the solution?
(4.28 g)(1mol/132.2g) = 0.0324 mol / 0.3 L = 0.108 M (NH4)2SO4
3. How many milliliters of 0.240M CuSO4 contain 2.25 g of solute?
(2.25 g) (1 mol / 159.6 g) (1L / 0.240 mol)(1000 mL / 1L) = 58.7 mL solution
4. Which will have the highest concentration of potassium ion: 0.20 M KCl, 0.15 M
K2CrO4, or 0.080 M K3PO4?
KCl K+ + Cl- ; 0.20 M KCl = 0.20 M K+
K2CrO4 2 K+ + CrO42- ; 0.15 M K2CrO4 = 0.30 M K+
K3PO4 3 K+ + PO43- ; 0.080 M K3PO4 = 0.24 M K+
0.15 M K2CrO4 has the highest K+ concentration.
5. Which will contain the greater number of moles of potassium ion: 30.0 mL of
0.15M K2CrO4 or 25 mL of 0.080M K3PO4?
K2CrO4: (0.30 M K+) (0.030 L) = 0.009 mol K+ greater
K3PO4: (0.24 M K+) (0.025 L) = 0.006 mol K+
6. Indicate the concentration of each ion or molecule present in the following
a. 0.22 M NaOH
0.22 M Na+ and 0.22 M OH-
b. 0.16 M CaBr2
0.16 M Ca2+ and 0.32 M Br-
c. 0.15 M CH3OH
0.15 M CH3OH is a molecular solute
d. a mixture of 40.0 mL of 0.15M KClO3 and 35.0 mL of 0.22M Na2SO4.
M2 = M1V1/V2 where V2 is the total solution volume.
K : (0.15 M x 0.040 L) / (0.075 L) = 0.080 M
ClO3- : concentration ClO3- = K+ = 0.080 M
SO42-: (0.22 M x 0.0350L) / (0.075 L) = 0.1027 M SO42-
Na+ : concentration of Na+ = 2xSO42- = 0.21 M Na+
7. What mass of NaOH is needed to precipitate the Cd2+ ions from 25.0 mL of
0.500M Cd(NO3)2 solution?
Cd(NO3)2(aq) + 2NaOH(aq) Cd(OH)2(s) + 2NaNO3(aq)
(0.025 L) (0.50mol Cd(NO3)2 / 1L) ( 2 mol NaOH / 1mol Cd(NO3)2)(40gNaOH/1mol) = 1g NaOH.
8. How many milliliters of 0.120M HCl are needed to completely neutralize 50.0 mL
of 0.101 M Ba(OH)2 solution?
2HCl(aq) + Ba(OH)2 (aq) BaCl2(aq) + 2H2O (l)
[(0.101 mol Ba(OH)2 /1 L] (0.05 L Ba(OH)2 ) (2 mol HCl / 1 mol Ba(OH)2) x
(1L HCl / 0.120mol HCl) = 0.0842 L HCl soln.
9. How many milliliters of 0.125 M H2SO4 are needed to neutralize 0.200 g of
H2SO4 (aq) + 2NaOH (aq) Na2SO4 (aq) + 2H2O (l)
(0.200 g NaOH) (1mol NaOH / 40.0 g ) (1mol H2SO4 / 2 mol NaOH) x
(1L H2SO4/0.125 mol H2SO4) = 0.0200 L or 20 mL H2SO4 soln.
10. If 55.8 mL of BaCl2 solution is needed to precipitate all of the sulfate ion in a
752-mg sample of Na2SO4, what is the molarity of the solution?
BaCl2 (aq) + Na2SO4 (aq) BaSO4 (s) + 2NaCl (aq)
752 mg = 0.752 g Na2SO4
(0.752 g Na2SO4) (1 mol Na2SO4 / 142.1 g )(1mol BaCl2 / 1 mol Na2SO4) (1 / 0.0558L) =
0.0948 M BaCl2