contestada

A student prepared a stock solution by dissolving 20.0 g of NaOH in enough water to make 150. mL of solution. She then took 15.0 mL of the stock solution and diluted it with enough water to make 65.0 mL of a final solution. What is the concentration of NaOH for the final solution?
A) O. 411 M
B) 0.534 M
C) 1.87 M
D) 2.43 M

Respuesta :

boffeemadrid

Answer:

0.7692 M

Explanation:

[tex]m[/tex] = Mass of sample = [tex]20\ \text{g}[/tex]

[tex]V[/tex] = Volume of solution = [tex]150\ \text{mL}[/tex]

[tex]V_1[/tex] = Initial volume taken out of the stock solution = [tex]15\ \text{mL}[/tex]

[tex]Mo[/tex] = Molar mass of NaOH = [tex]39.997\ \text{g/mol}[/tex]

[tex]V_2[/tex] = Final volume of solution = [tex]65\ \text{mL}[/tex]

Molarity of stock solution is given by

[tex]M_1=\dfrac{m}{MoV}\\\Rightarrow M_1=\dfrac{20}{39.997\times 0.15}[/tex]

[tex]M_1V_1=M_2V_2\\\Rightarrow M_2=\dfrac{M_1V_1}{V_2}\\\Rightarrow M_2=\dfrac{\dfrac{20}{39.997\times 0.15}\times 0.015}{0.065}\\\Rightarrow M_2=0.7692M[/tex]

The concentration of NaOH for the final solution is 0.7692 M