Download AR Chemistry Notes: Solutions

AR Chemistry Notes: Solutions
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Most chemical reactions release too much energy when pure samples are mixed together (explosions). To
control chemical reactions, most chemicals are dissolved in water to reduce the explosiveness of the reaction.
Solutions: two or more materials that are evenly mixed at the molecular level (homogeneous)
Solute:
the material being dissolved, such as salt in water, oxygen in air
Solvent: the material doing the dissolving, such as water in salt water, nitrogen in air
(when 2 gases or 2 liquids are mixed together, the one with the highest percentage is known as
the solvent).
Equality: 1.00 L = 1000 mL ******
A. Concentration (determined by the amount of solute dissolved in the total solution.
1. ******* Molarity (M) *********
Examples:
moles dissolved
M = ------------------------Liters solution
=
mol
---------L
a. What is the molarity if 2.5 moles are dissolved in 0.50 L?
mol
M = ----------L
b. **How many Liters are needed to deliver 1.4 moles from a 6.0 M solution?
mol
M = ----------L
c. How many moles are needed to make 2.0 Liters of a 3.0 M solution?
mol
M = ----------L
AND of course, we can ALWAYS start or end at GRAMS!!!! (1 mol = MM g)
2. Percentage Mass (% Mass)
grams solute
% Mass = ----------------------- x 100
total grams
(g solute + g solvent)
***Actually an easy one step conversion if you think you always have 100 grams to start
Ex: 3% H2O2 in water
3 g H2O2 = _____ g H2O = ______ g Total Solution
3 g H2O2 = 97 g H2O = 100 g Total
a. How many grams of water are needed to dissolve 40.0 grams of H2O2 to make a 3% solution?
b. How many grams of H2O2 are needed to be added to 270. grams of water to make a 3% solution?
c. You are told that you have 82 grams of H2O2 in a 3% solution. What is the total mass of the solution?
3. Grams per Liter (pretty much like % mass but EASIER)
Ex: A 50.0 gram/Liter solution of CaCl2
The equality: _______ g CaCl2 = _______ Liters
a. How many grams CaCl2 are in 0.250 L of solution?
b. How many Liters are required to deliver 75 grams of CaCl2?
4. Parts Per Million (PPM) (actually Mass, NOT number of particles)
Used for very small concentrations, such as radioactive particles, toxins, pollutants.
grams solute
PPM = ---------------------------- x 1,000,000
total grams solution
ex: What is the ppm if 10 grams of solute is in 500,000 Liters of water (1 g = 1 mL water)
Problem Set to Follow