Question #8935

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?

Expert's answer

a) Pb(NO_{3})_{2}(s) ----> Pb^{2+}(aq) + 2NO_{3}^{-}(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

b)

n = m/M

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

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