Question

Calculate the concentration of this standard soution.

Pottasium hydroxide(KOH) was prepared by dissolving 20g of KOH in 250ml of distilled water.

Answer 1

Potassium hydroxide molar mass ? can u tell

Answer 2

yes.. 39+16+1=56..

Answer 3

does the distill water change anything?

Answer 4

56 g in 1000ml gives 1M
20 g in 250 ml gives = 1000*20/56*250 =

Answer 5

lol nope distillate wter is just for dilution :P

Answer 6

lol.. im embarrassed for asking this question.. but i freezed sometimes(alot). but thank you for the help

Answer 7

oh and i dont understand why you mutiply 1000 with 20.. is this to convert the unit?

Answer 8

yup :)

Answer 9

ummm.. can you still helpme if i ask another question of the same question?

Answer 10

@ecah1 u r saying KOH was prepared by dissolving KOH in H2O??

Answer 11

yes

Answer 12

mm ok lets see

Answer 13

do u agree with chmvijay? sorry for asking too many question

Answer 14

ok i tried doing it and my answer is 1.428 moldm-3
@ecah1

Answer 15

oh yeah we did it same lol @ecah1

Answer 16

okay.. yeah it the same answer.. :D

Answer 17

his way is right but its a bit confusing
i'll try explaining how i thought

Answer 18

oh.. id aprreciate that

Answer 19

basically saying the question is giving u the mass of KOH= 20g ryt?
formula of concentration is
\[concentration = mole \div dm3\]
now then that means you need mole
when you read the question properly you'll understand that the question itself is giving you the volume ryt? and it is 250ml or 250cm3
reason is because we dissolve KOH in H2O thus volume is 250cm3
do you get it so far?

Answer 20

:D yes

Answer 21

okay cool
so that means we are left with mole
formula of mole is
\[mole = mass \div Mr\]
so in here we need mass and Mr ryt?
mass of KOH is given as 20g and Mr of it is 56 as you calculated
(we ignore water part because its just dilution so has nothing to do with these stuff)
so \[mole = 20 \div 56 = 0.357 \] (rounding off the answer)
so we got mole, we have volume
we can use
\[concentration = mole \div dm3\]
before using this formula we have to make sure the values are in appropriate units ryt?
mole is 0.357 (no need to change anything)
volume is 250cm3 , we need to convert it to dm3
it will be
\[250 \div 1000 = 0.25 dm3\]

Answer 22

now just put the values into the formula
\[concentration = 0.357 \div 0.25 = 1.428 mole/dm3\]
thats it :D

Answer 23

@ecah1 sorry i took this long trying to make it as simple as possible :)

Answer 24

thank you very much somy.. it looks so easy right now. i just need to read it and do it one by one. and it looks short even if it looks like you explain a lot but it simple.. so THANK YOU VERY MUCH.. i have understand this :D

Answer 25

@ecah1 you are welcome :) well thats a good thing then :D happy you understood :3