Please Help! Dilution Lab (Introduction to Spectrophotometry) Lab Question

Question

Part 1: Determine the steps required to make 20.0 ml of 25 nanomoles (10^-6) solution of crystal violet from solid crystal violet (molar mass = 408 g)

I'm not really sure what the question is asking for, is it asking for how many nanomoles are required to make 20.0ml of crystal violet or something else?

Answer 1

So for starters, the prefix "nano" refers to 10^-9 and micro refers to 10^-6. For this question, I'm going to assume you mean nanomoles (10^-9).

To make 20mL of a 25nM solution of crystal violet, you need to find the number of moles of crystal violet in the solution, convert that to grams, and make your solution.

0.02 L * (25*10-9 mol / 1L) = 5*10-10 mol of crystal violet

5*10-10mol * (408 g / 1 mol) = 2.04*10-7 g of crystal violet

In a lab setting, you'll want to follow the protocol below.

1) Fill a volumetric flask with ~10 mL of distilled water

2) Add 2.04*10-7 g of crystal violet (this seems like a really low value, so double check you don't mean micromolar and if you do mean micromolar change the exponent in the first expression from -9 to -6)

3) Using distilled water, fill the volumetric flask to 20 mL

Hope this helps! Let me know if you have any additional questions!