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### Course: AP®︎/College Chemistry>Unit 4

Lesson 7: Introduction to titration

# Worked example: Determining solute concentration by acid–base titration

The concentration of an acid solution can be determined by titration with a strong base. First, calculate the number of moles of strong base required to reach the equivalence point of the titration. Then, using the mole ratio from the balanced neutralization equation, convert from moles of strong base to moles of acid. Finally, divide the number of moles of acid by the given volume of the acid solution to find the concentration. Created by Jay.

## Want to join the conversation?

• When using the shortcut MV = MV for the acid and the base, shouldn't the unit of the volume be in litres (the same way that molarity uses litres)?
• When you divide both sides by 20 mL, the units cancel out so it does not matter what you choose. All that matters is that the unit you choose is the same throughout the equation. Dividing 27.4mL by 20mL is the same as dividing 0.0274L by 0.02L. You will get the same number and there will be no units! So, we can say that mL were used simply because the information was given in mL and it would have been unecessary to change.
• why are we not dividing the molarity by total volume for both parts when solving? Or in general, why are we not adding both volumes to make one value for a total volume when solving for this question?
• You have a base reacting with an acid. The question asks how much acid you need to react with base so that they neutralize each other (and form a salt with water, but no floating acids or bases). So, when are MV(basic)=MV(acidic). The greater volume that is made will not influence the equilibrium point because water is at pH 7 (neutral) so the ratio to total volume is irrelevant.
• what is the molar solution?
• Molar solution is actually a concentration term. This means when a given solution contains one mole of atoms , ions, molecules, or any chemcial compound in its one litre solution, that solution is called molar solution
• how did you predict the product of the acid-base reaction at ? I never learned that
• Acids (using the Arrhenius definition) are chemicals which produce H+ ions, while bases are chemicals which produce OH- ions. So when barium hydroxide (Ba(OH)2) and hydrochloric acid (HCl) enter a water solution they will dissociate, or split up. The barium hydroxide will split into one barium ion, Ba^(2+), and two hydroxide ions, OH-. And the hydrochloric acid will split into one hydrogen ion, H+, and one chloride ion, Cl-.

At this point the reaction becomes a double replacement reaction essentially where the hydroxide and hydrogen ions combine to form water, OH- + H+ = H2O. And the barium and chloride ions form barium chloride, BaCl2. For the barium chloride we need that 1:2 ratio of barium to chloride ions because it is an ionic compound and the charges must combine and cancel each other to make a neutral compound.

Hope that helps.
• at how did we know we had Ba2+ and cl-?
• We work with ions. The barium ion has a charge of 2+ and chlorine ion has a cahrge of 1-.
• what does titration and finding the equilibrium help us with
• That simply tells you how much acid (or base) you need to add to a solution to neutralize it. This becomes particularly important when you do research in a lab because neutralization will become very important.
• What was the pH indicator used for this titration?
Would this influence the final result?
***
• The ph indicator used here is phenolphthalein. these indicators are used not more than 1 to 2 drops, so they influence very less. To know more how the structure of Hph (phenolphthalein) changes after reacting with a base. hope it helps.
• Is it necessary to include all the zeros after the number ? ( 0.02*00*)