Concentration, Dilution, Titration & Molarity

Titration

Titration is a way to figure out how strong a liquid is. It is a method used to find the concentration of an unknown solution. You do this by adding a solution with a known concentration until the reaction is complete.

• You have a liquid and you don’t know its concentration.

• You slowly add another liquid that you do know the concentration of.

• When the reaction finishes (usually shown by a color change), you stop.

• The amount you added tells you how strong the unknown liquid was.

You don’t know how strong an acid is. You slowly add a base with a known concentration. When they exactly cancel each other out, you stop. Now you can calculate the acid’s concentration.

EX: you have 25.0 mL of HCl (acid) it’s concentration is unknown. You have 0.100M NaOH (base) its concentration is known. It takes 30.0mL of NaOH to completely react with the acid. Find the concentration of the HCl.

Balanced equation is: HCl + NaOH —> NaCl + H₂O

(Convert your mL to liters (Molarity is based on Liters)).

0.03L NaOH x 0.100mol NaOH/ 1 L NaOH = 0.003 mol NaOH x 1 mol HCl/1 mol NaOH = 0.003 mol HCl / 0.025 L HCl = 0.12M is HCl concentration

Concentration

measures how much solute is present in a given amount of solution. (how much solute is relative to the amount of solution or sometimes solvent). It is always a ratio. EX: 1 spoon of salt in a glass = low concentration. 5 spoons of salt in 1 glass = high concentration

Diluted

less solute, more solvent. Dilution is making something that is highly concentrated less concentrated, and it is done by adding more solvent.

Concentrated

more solute, less solvent. Concentration is making something that is diluted concentrated, it is done by adding more solute.

Concentration =

Molarity. Molarity is moles of solute/ Liters of solution. It is how much solute is present per liter of a solution.

Stock Solution

a concentrated solution that you keep on hand so that you can prepare diluted solutions when needed. THINK: syrup. Syrup is your stock solution (highly concentrated). If you pour some syrup into water, you get a sweet drink (a diluted solution). Stock solution is high in concentration and stored properly so you don’t have to make a fresh solution every time.

Molarity

tells you how concentrated a solution is, because it is the moles of solute/liters of solution. So, Molarity = moles of Solute/ Liters of solution

Dilution Formula

M_H x V_H = M_L x V_L . This is the dilution formula, because you’re going from highly concentrated (M_H, initial molarity) and V_H the volume of the concentrated solution used, to a lower concentration M_L and V_L, the final and total volume after dilution. This formula is ONLY used for dilution problems.

How to use Dilution Formula

1. Identify which is the stock solution (higher concentration) this is your M_H V_H

2. Identify the target solution (diluted) this is M_L V_L

3. Arrange them and solve for your unknown.

EX: You have 3.0M Hydrochloric acid. You take 50 mL of it and dilute it with water until the total volume becomes 300 mL.

3.0 (M_H) x 50mL (V_H) = M_L x 300mL (V_L)

150 = 300M_L (divide both sides by 300) and 0.5 is your M_L