Answer:
The burette is contaminated with an acid solution- The concentration is too high
The burette contains a large air bubble in the tip, which disappears during the titration- The concentration of the acid is too low.
A small volume of the acid is spilled when you transfer it into the Erlenmeyer flask- The concentration of the acid is too low.
Explanation:
The molality of a solution is the number of moles of solute per liter of solution. The concentration of an unknown solution is obtained by titration against a standard solution of acid or base whose concentration is known. It is a volumetric method of analysis.
If the burette is contaminated with the acid, then the concentration of the base that reacts with the acid is less than the stated amount and consequently the concentration of the acid calculated is higher than it should be.
If the tip of the burette contains air bubbles, the volume of the acid reported is less than the volume of acid actually delivered during the titration hence the calculated concentration of the acid is too low.
If some volume of acid is spilled when you transfer the acid into the Erlenmeyer flask, the volume of the acid reacted is decreased and consequently the calculated concentration of the acid is too low.
