Question

You have a stock solution of HNO3 with a concentration of 4.5x10-4 M. However, you need 275 ml of a 2.50x10-5 M solution. How much of the stock solution will you need?

Answer 1

27.5 mL.

Step-by-step explanation:

We have the rule that the no. of millimoles of the solution before dilution is equal to the no. of millimoles after dilution.

(MV)before dilution = (MV)after dilution,

M before dilution = 4.5 x 10⁻⁴ M, V before dilution = ??? mL,

M after dilution = 2.50 x 10⁻⁵ M, V after dilution = 275.0 mL.

∴ V before dilution = (MV)after dilution / M before dilution = (2.50 x 10⁻⁵ M)(275.0 mL) / (2.50 x 10⁻⁵ M) = 27.5 mL.

Answer 2

You will need 15.27 mL of the stock solution ( concentrated solution)

Step-by-step explanation:

Dilution is the procedure used to prepare a less concentrated solution from a more concentrated solution. It consists of adding solvent to an existing solution. Then the amount of solute does not vary, but the volume of the solvent does: when more solvent is added, the concentration of the solute decreases, as the volume of the solution increases.

There is a simple formula to calculate exactly how much stock solution and water are needed to prepare a given dilution:

Vi*Ci=Vf*Cf

The subscript i indicates initial dissolution, which is the concentrated solution, and the subscript f means final dissolution, which is the least concentrated or diluted.

Then:

• Vi = Volume of the mother solution = Volume of the necessary mother solution.
• Ci = Concentration of the stock solution.
• Vf = Volume to be prepared from the final or diluted solution.
• Cf = Concentration of the final or diluted solution.

So, in this case:

• Vi = ?
• Ci = 4.5x10⁻⁴ M
• Vf = 275 mL
• Cf = 2.50x10⁻⁵ M

Replacing you get:

Vi*4.5x10⁻⁴ M= 275 mL*2.50x10⁻⁵ M

Resolving:

`Vi=(275 mL*2.50*10^(-5)M )/(4.5*10^(-4)M )`

Vi= 15.27 mL

You will need 15.27 mL of the stock solution ( concentrated solution)