Concentration

Today, we learned about the wonderful world of.....................concentration!!!!

Solution: A homogeneous mixture
Solute: The component present in the smaller amount
Solvent: The component present in the larger amount
Concentration: Ratio of solute to solvent and can be determined by the following equation:

Amount of Solute
Amount of Solvent

Possible units:
g/mL, g/L, mg/mL, micrograms/mL, m/L, % by mass, % by volume

con'c = concentration

The most useful units for con'c is mol/L which is also known as molarity (M)

molarity=

moles of solute
litres of solution

C = n/v
n = cv
v = n/c

n= number of moles
c= concentration
v= volume

***********THOSE 3 FORMULAS LISTED ABOVE CAN ONLY BE USED FOR LIQUID SOLUTIONS

if a compound formula is in bracket, [like this], it means it is the concentration of the substance.
e.g. [HCl] = 6.0 mol/L


The concentration of HCl (Hydrochloric acid) is 6.0 mol/L



EXAMPLES
What is the molarity of a solution in which 0.45 grams of sodium nitrate are dissolved in 265 mL of solution?

Sodium Nitrate = NaNO₃, molar mass = 84.99 g/mol

0.45 g x 1 mol/84.99 g = 0.005 mol
265 mL x 1L/1000mL = 0.265 L


molarity = 0.005 / 0.265 = 0.01998 mol

the molarity of NaNO_{3 in 265 mL of solution is 0.020}


What will the volume of a 0.50 M solution be if it contains 25 grams of calcium hydroxide?
<sub>calcium hydroxide = Ca(OH)2
molar mass = 74.093 g/mol

25 g x 1 mol/74.093 = 0.3329 mol

v = n/c
= 0.3329 / 0.50 M
= 0.6658 L
=0.67 L</sub>

How many grams of ammonia are present in 5.0 L of a 0.050 M solution?

Ammonia = NH₃
molar mass = 17.031 g/mol

n = cv
= (0.050)(5.0)
=0.25 moles

0.25 moles x 17.031 g/1mol = 4.26 g
= 4.3g

for a worksheet click here