Chem 120 Summer 2012 UW Name __________________________________________ Section _____________ WS 6: Solutions 1. Complete and balance the chemical equations for the precipitation reactions, if any, between the following pairs of reactants, and write the net ionic equations. If no reaction occurs, write “NR.” a. Pb(NO3)2(aq) + Na2SO4(aq)  PbSO4(s) + 2NaNO3(aq) Pb2+(aq) + SO42‐(aq)  PbSO4 (s) b. NiCl2(aq) + NH4NO3(aq)  No precipitate will form c. FeCl2(aq) + Na2S(aq)  FeS(s) + 2NaCl(aq) Fe2+(aq) + S2—(aq)  FeS(s) d. 2 K3PO4(aq) + 3 BaCl2(aq)  Ba3(PO4)2(s) + 6 KCl(aq) 2 PO43‐(aq) + 3 Ba2+(aq)  Ba3(PO4)2(s) e. Mg(Cl)2 + 2 AgNO3  2 AgCl(s) + Mg(NO3)2(aq) Ag+(aq) + Cl‐ (aq)  AgCl(s) f. Na3PO4 + MgCl2  No precipitate will form Page1of3
Chem 120 Summer 2012 UW 2. An aqueous solution of potassium carbonate contains 9.65 x 1024 K+ ions in 3 L of solution. What is the molarity of potassium carbonate in this solution? We are looking for molarity, which is moles/L. We have # of ions. 9.65 10
1
1
3
6.02 10
2
Molarity of K2CO3 = 2.67 M 3. How many grams of sodium chloride do you need to weigh out to prepare 250 mL of 0.9% (m/v) saline solution? Looking for grams of NaCl in a 0.9% m/v saline solution. This means that there is 0.9 g of NaCl in 100 mL of solution. 0.9 100% 0.9%
100 If so, we can use 0.9 g / 100 mL as a conversion factor to figure out how many grams in 250mL 250
. 2.25g NaCl Page2of3
Chem 120 Summer 2012 UW 4. Calculate the mass of magnesium carbonate precipitated by mixing 10.0 mL of a 0.200 M sodium carbonate solution with 5.00 mL of 0.500 M magnesium nitrate. First we need the balanced reaction: Mg(NO3)2 (aq) + Na2CO3 (aq)  MgCO3(s) + 2NaNO3(aq) For Mg(NO3)2 (aq): We have 5.00 mL of a 0.500M solution. How many moles of Mg(NO3)2? 1
0.500
5.00
0.00250
1000
1
This means we have 0.00250 moles Mg2+ and 0.00500 moles NO3‐. For Na2CO3(aq): We have 10.0mL of a 0.200 M solution. How many moles of Na2CO3? 0.200
1
0.00200
10.0
1
1000
‐ +
This means we have 0.00400 Na and 0.00200 CO3
This means we have CO3‐ as the limiting reactant with 0.00050 of Mg2+ ions left over. We need the mass of MgCO3 (s) that is formed. 0.00200
.
0.1686 g MgCO3 Page3of3
Chem 120 Summer 2012 UW 5. Two aqueous solutions are separated by a semipermeable membrane. Solution A contains 25 %(m/v) KCl, and solution B contains 75% (m/v) Na2S. Will water flow from compartment A to B or vice versa? How much water would you need to add to 1.00 L of the more concentrated solution to make solutions A and B isotonic? Find the molarity of ions in each side. .
.
= 6.706 M ions = 28.85 M ions Water will flow from A to B. .
.
.
4.302 L Volume 2 must be 4.302 L, so we would need to add 3.3 L of water to B to make it isotonic to A. Page4of3