Answer to Question #8935 in Chemistry for Chemist

Question

2. A solution is prepared by dissolving 1.50 g of Pb(NO3)2 in a small amount of water and diluting to a total volume of 250.00 mL.
a. Write a chemical equation (with phase symbols) to show what happens to a formula unit of Pb(NO3)2 when it is dissolved in water.
b. What is the molarity of this solution?
c. If a 25.00 mL sample of this solution were removed and diluted to a total volume of 100.00 mL, what would be the molarity of the diluted solution?

Answer 1

a) Pb(NO₃)₂(s) ----> Pb²⁺(aq) + 2NO₃^-(aq)

b)
n = m/M_r = 1.50/331 = 0.0045 mol
0.0045 mol in 250 ml
x mol in 1000 ml
x = 0.018 mol/1000 ml = 0.018 M

c)
in 1000 ml is 0.018 mol
in 25 ml is x
x = 0.00045 mol
0.00045 mol in 100 ml
x mol in 1000 ml
x = 0.0045 M