Molarity Written Response

Question

Angelica made 100mL of a 3.5M salt solution. She wanted to dilute this solution to make 100mL of a 2.1M solution. She calculated that she needed 60mL of her stock solution. She added the 60mL to the volumetric flask, and then filled up the flask with water. After careful evaluation, Angelica noticed that the meniscus was above the line marked on the flask. Not wanting to start over, she simply used a pipette to suck out some of the water to get it to the correct level. Although Angelica corrected the volume, explain why she has now ruined the molarity of the solution. Identify if the molarity is now too high or too low than she wanted.

Answer 1

No matter how careful Angelica is, she's already diluted the solution and the concentration will be lower than she wanted.  Hence, she must start from scratch.