Titration Analysis Chapter 8 – Section 4

Vocabulary Titration – process of carefully measuring and controlling the addition of a solution, called a titrant, from a burette into a fixed volume of another solution, the sample. Equivalence Point – the point at which the exact theoretical amount of titrant has been added to the sample and completely reacted. Endpoint – a sudden observable change in the solution that is permanent

Example: First: Calculate the concentration of the sodium carbonate Next: Write a balanced equation Then: Average the volume of HCl from the 3 best trials SOLVE

Standardizing Titrant Solutions Knowing the concentration of all solutions before a titration begins is key. You must know this in order to proceed with your experiment. Standard Solution – have a high certainty of concentration, like a stock solution Primary Standard – mass and purity of a compound can be measured with high precision, usually obtained from a manufacturing facility, not created in a classroom laboratory setting? WHY? Standardizing – means to find the concentration of a solution after it has been prepared, by reacting it with a solution that has been prepared from a primary standard.

Question???: When adding titrant to a burette, it is critical that the concentration of the solution remain constant. Ideally, the burette should be cleaned and dried just before use to make sure that no impurities change the titrant concentration. It is extremely difficult, however, to quickly dry a burette that has just been cleaned. What technique is used to solve this problem?

Answer: Once the burette has been washed with distilled water, rinse the burette with a small volume of titrant. It will not matter if the inside of the burette is wet, as long as the liquid in it is the same solution that will be used to fill it.

Question???: One purpose of doing multiple trials for an analysis is to immediately identify any mistakes in procedure because these will cause discrepant results. What is the other reason for doing multiple trials?

Answer: Doing multiple trials and averaging the answers, increases the certainty and reliability of the result.

Question???: Acid–base titrations, like Investigation 8.3, typically do not produce any visible product, which presents a problem. There is no direct way of knowing when such a reaction is complete. Explain how this problem is overcome by using another substance that is not part of the reaction, what characteristic of this substance is useful, and what characteristic of the reaction solution is detected by this substance.

Answer: An indicator is used. This is a substance that changes colour in response to changes in pH (hydronium ion concentration) in the reaction solution.

Practice Go to page 332 Complete Question 1 – Showing all of your work!