Question

You just prepared 150.0 mL of 0.275M NaOH and then added 75.0mL of 0.552 M NaOH into the flask. What is the concentration of the new solution? The flask containing your new solution is left open for a week and the volume of the solution was reduced to 1000.0 mL, what is the concentration of the solution now?

Answer 1

first calculate the total millimoles

millimoles of NaOH = 150 x 0.275 = 41.25

millimoles of NaOH = 75 x 0.552 = 41.4

total millimoles = 41.25 + 41.4 =82.65

total volume = 150 + 75 = 225 mL

[NaOH] = 82.65 / 225 = 0.367 M

[NaOH] = 0.367 M

after few days you said volume decreased to 1000 mL. but initially 225 mL solution present so how it is possible to reduce volume to 1000 mL

if it is 100 mL

M1V1 = M2V2

M1 = 0.367 M , V1 = 225 mL

M2 = ? , V2 = 100 mL

M2 = (M1V1 /V2)

M2 = (0.367 x 225 / 100)

M2 = 0.826 M