Question

1-

A student weighs out a 11.8 g sample of copper(II) acetate, transfers it to a 300 mL volumetric flask, adds enough water to dissolve it and then adds water to the 300 mL tic mark. What is the molarity of Cu(CH3COO)2 in the resulting solution?

2-

How many moles of potassium hydroxide, KOH, are there in 257 mL of a 0.158 M solution?

3-

A student wants to prepare a solution of zinc acetate with a known molarity.

How many grams of Zn(CH₃COO)₂ must be weighed out to prepare 250. mL of a 0.137 M aqueous solution of the salt?

Answer 1

1)

Cu(CH3COO)2 mass = 11.8 g

Cu(CH3COO)2 molar mass = 181.63 g

volume = 300 mL = 0.3 L

moles of Cu(CH3COO)2 = 11.8 /181.63 = 0.0650

volume = 0.3 L

molarity = moles / volume

molarity = 0.0650 / 0.3

= 0.217 M

2)

molarity = 0.158 M

volume = 257 mL = 0.257 L

moles = molarity x volume

= 0.158 x 0.257

=0.0406

moles = 0.0406

3) moles = molarity x volume = 0.137 x 250 / 1000 = 0.0342

molar mass of Zn(CH3COO)2 = 183.47 g/mol

mass = moles x molar mass

= 0.0342 x 183 .47

= 6.28 g