A multiple choice question that has me stumped... (1 Viewer)

[Jaserius]

Hey guys,

1020 mL of water is added to 240 mL of a 0.12 mol L-1 potassium bromide solution, and the mixture is thoroughly stirred. The concentration of the potassium bromide is now closest to:-

A. 0.020 mol L-1
B. 0.024 mol L-1
C. 0.12 mol L-1
D. 0.0288 mol L-1

I keep getting D for my answer, but the correct answer is B.

Good luck.

 

[lfc_reds2003]

lol i know what ur doing wrong

u haven't added the volume of potassium bromide (240 mL) to the 1020 mL of water for the new volume


NOTE: i am presuming u used C1V1=C2V2

so 0.012 times 0.24 = unknown times (1.02 + .24)

....

 

[Jaserius]

Yeah, I did that... its 0.12 by the way, and that still doesnt work.

 

[KFunk]

1020 mL of water is added to 240 mL of a 0.12 mol L^-1

no. moles present = 0.12 x 0.24 = 0.0288 mol

number of litres in new solution = 1.02 + 0.24 = 1.26L

so mol L^-1= 0.0288/1.26 = 0.022857142.... mol L^-1

rounded to 3 d.p. its 0.023 mol L^-1 which is closest to B