Question

Part A: When 40.0mL of 2M sodium chloride (NaCl) is diluted to 100 mL, what is the new concentration? Note: FW of NaCL = 58.

Part B: If absorbance of a 0.34M sol'n of a chemical x is 0.18 at a certain wavelength, what is the concentration of a solution with chemical x that has an absorbance at 0.023 measured at that same wavelength?

Please, show equations and work.

Answer 1

Part A :

Since the solution is diluted, the solute remains constant

M₁V₁ =M₂V₂

M₁: molarity before dilution

M₂: molarity after dilution

V₁: intial volume

V₂: Final volume

Substituting we get

40*2= M₂ * 100

M₂= 0.8 M

So final concentration of NaCl solution would be 0.8 M

- PART B :

When wavelength is kept constant the absorbance is directly proportional to concentration for a same substance

. A₁C₂=A₂C₁

Given data A₁=0.18

. C₁=0.34 M

. A₂=0.023

Now substituting we get

. 0.18*C₂= 0.023*0.34

C₂=0.0434 MM

So concentration of chemical when absorbance is 0.023 is 0.0434 M