Chemistry
GIA 8-2
Unit:
Solutions and Solubility
Reading: Chapter 16
Working
Mode: Pairs. Solve the problems on a separate sheet of notebook paper.
Each pair may submit individual sheets or one sheet for the pair.
Learning
Objective: Interpret dissolving process and precipitation reactions in chemical
equations and apply this understanding to stoichiometry problems which involve
solutions.
Problem
1: NaCl
dissolves in water like this : NaCl(s) à
Na+(aq) + Cl-(aq) 28.3 g of NaCl dissolved in enough water
to make a 350. mL solution. What is the [Na+] and [Cl-]?
Student 1: Determine the moles of NaCl dissolved.
Student 2: Determine the moles of Na+ and Cl-.
Student 1: Determine [Na+].
Student 2: Determine [Cl-].
Problem
2: 48.3 g of
magnesium chloride, MgCl2, dissolves in enough water to make a 225 mL
solution. Determine [Cl-].
Problem
3:
A 500. mL sample of a solution contains an unknown Ca2+
concentration. A student adds 1.00
M Na2CO3 solution until the formation of the white
precipitate, CaCO3 stops forming.
The CaCO3 (s) is filtered, rinsed, dried and weighed.
The dried CaCO3 has a mass of 5.73 g.
Determine the concentration of Ca2+ in the original 500. mL
sample.
Student 1: Write a balanced chemical equation for the reaction involving
only the ions that react.
Student 2: Determine the moles of CaCO3 produced.
Student 1: Determine moles of Ca2+ that were present in the
solution.
Student 2: Determine [Ca2+] in the sample.
Problem
4: A ground
water sample contains the hazardous ion, Pb2+.
A 100. L sample of water is tested for Pb2+.
Na3PO4 (aq) is added until the lead (II) phosphate
precipitate stops forming. After
separation the mass of the pure dry precipitate is 0.313 g.
Determine the original concentration of Pb2+ in the sample.
[Extra
step (Bonus): Assuming the 100. L solution can be approximated to contain 100.
kg of water, how many parts per million (ppm) of Pb2+ does the
solution contain?
(ppm =
mass of component of sol’n
x 106)]
total mass of sol’n
