CHEMISTRY PLEASE HELP!!!!!!! Calculate the concentration of a crystal violet solution prepared by diluting 4.0 mL of 1.0 x 10^-4 M crystal viole...

Question

Calculate the concentration of a crystal violet solution prepared by diluting 4.0 mL of 1.0 x 10^-4 M crystal violet with 2.0 mL of 0.100 M NaOH and 4.0 mL of distilled water. 

 

I am so so so lost and confused. I have no idea where to start solving this problem, and would really love if someone could explain (in terms for a struggling student) how to solve this?! Thank you for your help, I am trying my best but questions like this are making me nervous and stressed out!

Answer 1

Hello Angelica,

 

First, you should recall what concentration (in molarity) means: moles of the solute in liters of the solution. Therefore, if you can calculate the number of moles of your solute, and also the total volume of your solution, you have a simple division to calculate the molarity of the solution.

 

In this problem, you are given a volume of a solution which has a known concentration. The formula for concentration is:

 

concentration (in molar, M) = (moles of solute) / (volume of solution in liters)

 

Algebraic manipulation lets you solve for moles of solute when you are given volume and concentration:

 

moles = (concentration in M) × (volume in L)

 

Since your volume is given in mL, you must convert that to L before you pull out your calculator!

 

moles of crystal violet = (1.0 × 10⁻⁴ M) × (0.0040 L) = 4.0 × 10⁻⁷ mol

 

To get the rest of your needed information, you simply add together the volume of all of the solutions used to make up your final volume:

 

total volume = (volume of starting crystal violet solution) + (volume of NaOH solution) + (volume of water)

 

These add up to

 

total volume = 4.0 mL + 2.0 mL + 4.0 mL = 10.0 mL or 0.0100 L

 

The concentration of the crystal violet in this final solution is

 

concentration = (moles of crystal violet) / (liters of solution) = (4.0 × 10⁻⁷ mol)/(0.0100 L) = 4.0 × 10⁻⁵ M

 

Jim Scripko