Question

What is the new concentration of a solution if you take 25 ml of 5 M NaCl and dilute by adding 75 ml of distilled water?

Answer 1

Calculate the number of moles of NaCl you have in the 5M solution.

Answer 2

36 ml and 75 ml?

Answer 3

Then divide that by the total volume of the diluted solution. Make sure you use L since molarity os mol/L.

Answer 4

so divide 36/5m?

Answer 5

Where is 36 coming from?

Answer 6

i mean 25 or 75 divide to the 5 m

Answer 7

I don't understand what you mean.

Answer 8

how you divide it. sorry

Answer 9

To find the moles of the undiluted solution, take the molarity (which is in mol/L and multiply it by your current volume in L.

Answer 10

25 mL = 0.025 L

Answer 11

sp thats the volume

Answer 12

This cancels out liters and leaves moles.

Answer 13

the molarity is 5?

Answer 14

5M NaCl means the molarity is. 5.

Answer 15

so mulitply 5 and 0.025 which is 0.125

Answer 16

Good. That gives you the moles of NaCl.

Answer 17

thanks

Answer 18

When you add 75 mL of water, what is your new volume?

Answer 19

75.125

Answer 20

?

Answer 21

how you add the 75 ml to the new volume?

Answer 22

The initial volume was 25 mL.

Answer 23

Add 75 mL, you get 100 mL diluted volume.

Answer 24

right 75 plus 25 is 100

Answer 25

But the number of moles is the same as undiluted.

Answer 26

Right, good.

Answer 27

So, the new concentration is the number of moles of NaCl /diluted volume in L.

Answer 28

100/ 0.025?

Answer 29

which is 4,000?

Answer 30

Not quite. We found number of moles to be .125 moles and 100 mL = .1 L

Answer 31

So, it should be .125/.1

Answer 32

ahh so divide that instead

Answer 33

Yup :)

Answer 34

8,000

Answer 35

?

Answer 36

I get 1.25

Answer 37

oh sorry its 1.25

Answer 38

my mistake.

Answer 39

No worries

Answer 40

thank you for explaining

Answer 41

You 're welcome. I hope you understand it better now.

Answer 42

And that is 1.25M