1. What is the molarity of a solution containing 0.525 mol of sucrose in 855 mL

Question

1. What is the molarity of a solution containing 0.525 mol of sucrose in 855 mL of solution? (give correct units and sig figs)

2, Isotonic solution is a 0.15 M aqueous solution of NaCl the simulates the total concentration of ions found in many cellular fluids. Therefore, common saline IV fluids given in the hospitlal are 0.15 M NaCl solutions. How would you prepare 800 ml of 0.15 M NaCl from a 6.0 M stock solution?  (give correct units and sig figs)

3. Using the balanced chemical equation, What volume of 0.250 M Na2S203(aq) is needed to completely react with 12.44 ml of 0.125 M KI(aq)?  (give correct units and sig figs)

Explanation / Answer

Solution:

1. Molarity = moles / volume

                = 0.525 / 0.855

                = 0.614 M

2. for 0.15 M --> (c*V) of 1 = (c*V) of 2

    0.8 * 0.15 = 6 * V in L

    V = (0.8 * 0.15)/6 = 0.02 L = 20 mL

    20 mL of 6.0 M stock is required to prepare 0.15 M of NaOH

3. balanced equation,

    2S2O32- (aq) +I3- (aq) ----> S4O62- (aq) + 3 I- (aq)

moles KI3 --> 0.01244 L of 0.125 mol/Litre KI3 =0.001555 moles KI3

moles K2S2O3 --> 0.001555 moles KI3 requires twice as much K2S2O3 = 0.00311 moles

Volume of K2S2O3 --> 0.00311 moles @ 0.250 mol/Litre K2S2O3 = 0.01244 litres

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