Question

Calculate the concentration of sodium ions made by diluting 45.0 mL of a 0.748 M solution of sodium sulfide (Na2S) to a total volume of 250.0 mL

Answer 1

Use M1V1 = M2V2

M = molarity
V = volume

Answer 2

I can't see, to get the correct answer using that formula. The right answer is 0.2693 M and I keep getting 1.346

Answer 3

@Somy Can you help me figure out what I'm doing wrong?

Answer 4

Step 1
M1V1 = M2V2
M = molarity
V= make sure your unit is in dm3

Answer 5

I'm not sure what dm3 means

Answer 6

ml / 1000 = dm3
its a unit

Answer 7

im trying to work it out

Answer 8

That didn't come out right either. Hmmmm

Answer 9

i know
there is more to it
im thinking

Answer 10

If you can't figure it out I can always email my teacher. Thanks for trying :)

Answer 11

well look
after that you will get the molarity of Na2S
but u need molarity of Na alone
so you have the final molarity as 0.13464 M
so this is total molarity
now you have final molarity and volume
so use it & find final mole of the solution
so Molarity = mole/ dm3
mole = molarity x dm3
so molarity is 0.13464 M
dm3 is 250/1000
and now u get whole mole

Answer 12

That doesn't come up to .2693 M either

Answer 13

after that you need mole of Na only
which is why you do a some cross math stuff
Na2S = molecular mass is (23*2) + 32 = get it
now molecular mass of Na in there will be 23*2 = get it, because there are 2 of Na in this compound
so
mole of Na2S - molecular mass of Na2S
mole of Na - molecular mass of Na atoms which is 46
now
mole of Na = (mole of Na2S x 46) / molecular mass of Na2S
and you got mole of Na

now concentration of Na will be
molarity = mole/ dm3
btw molarity & concentration are same thing
so
you have mole of Na
and you have final dm3 = 250/1000
now use both values and get molarity of Na+ ions

Answer 14

yeah, though the working is like this
i cant seem to get the answer you say is the correct one

Answer 15

Okay. Glad it's not just me. I'll email my teacher. Thank you!

Answer 16

no problem :)

Answer 17

nah, i checked it using your correct answer 0.2693M
i did backward working and it brings me to a ridiculous number
so i did this :
molarity = mole/dm3
mole = 0.2693 x (250/1000)
= 0.067325 mole of Na
now i want to find mole of Na2S
0.067325 = 23
X = 78
X= 0.067325 x 78 /23 = 0.228 mole of Na2S
so from here i'll get total conc of Na2S
molarity = mole / dm3
molarity = 0.228 / (250/1000)
= 0.912M = M2
woah

thats like triple of the answer using
M1V1 = M2V2
0.748 x (45/1000) = M2 x (250/1000)
M2 = 0.13464

its a mistake, in your correct answer, i dont know where you got it from but its wrong
how can u dilute something and get higher concentration instead?
look
initial concentration of solution is 0.748M and final you see it here as 0.912M
it increased
that cant be because the q states 'diluted'
final answer of dilution of solution HAS to be less in concentration

lol i guess now you can prove that the 'correct' answer is wrong
backward working helps to figure it out :D

Answer 18

i mean more than triple lol

Answer 19

So @Somy I figured out how to get to the correct answer. You work it out like this
0.748M x 45.0 mL = C2 x 250 mL
33.66/250= C2 x 250/ 250
.13464= C2
.13464 x2 = C2
C2=.2693 M
You multiple the answer by 2 because there is 2 sodium ions is each mole of sodium sulfide

Answer 20

yeah but the faulty part here is
the concentration that you are getting up there as .13464M is the concentration of diluted Na2S
but the q is asking for Na+ concentration IN that diluted solution
so you can't really multiply that by 2
well ask your teacher, i curious too of whats wrong here

Answer 21

im*

Answer 22

I did ask her. That's what she said needed to be done to it