Molarity is suppose to be an easier topic right?

Full Member
Question is from tbr.

The molarity of potassium is GREATEST in which of the following solutions?

a. 10.0 g KCL in enough water to form 100ml of solution

b. 10 g K2S04 in enough water to form 100ml of solution

C. 10 g K2CO3 in enough water to form 100ml of solution

D. 10 g KNO3 in enough water to form 100ml of solution

Ill post the answer after a few posts. Thanks in advance you guys!

pfaction

Full Member
10+ Year Member
Moles per liter.

So, we can probably knock out D since A has a lower molecular weight and would have more K+ than choice D.

In choice B and C, if I'm doing it right, watch out - you have to double the molarity found since it's K2. So from Wiki, K2SO4 is 175 and K2CO3 is 140. K2CO3 wins here since we're doing grams to grams.

So now between A and C...KCL is 75, so it's 1 x 10/75. K2CO3 is 2 x 10/140. If that's equal to 20/140->10/70, looks like K2CO3 is winner?

Really sorry if my math is not right.

Full Member
Correct and I understand your reasoning better than tbr's. They say "hence, the greatest molarity results from using the compound with the greatest mass percent of potassium, which corresponds to the salt with the lowest molecular mass." Does anyone understand what this is trying to say and how they correlate these two components with each other?

chiddler

Full Member
10+ Year Member
Correct and I understand your reasoning better than tbr's. They say "hence, the greatest molarity results from using the compound with the greatest mass percent of potassium, which corresponds to the salt with the lowest molecular mass." Does anyone understand what this is trying to say and how they correlate these two components with each other?

CO3 vs SO4

which has a larger molar mass?

the latter.

If we attach two K's to both, which would have a larger % mass of potassium? (5+10 vs 10+10. which increased the most percentage?)

the former.

therefore, since K2CO3 has more mass percentage of potassium, it should have the greatest molarity. similarly, if we have two unknowns with mass percent of K in one to be 80% and another with 30%, then the 80% will form a more concentrated K+ solution.

MD
Moderator Emeritus
10+ Year Member
Oh gosh for a minute I wasn't sure if a periodic table would be given and I was like uh...

pfaction

Full Member
10+ Year Member
Oh gosh for a minute I wasn't sure if a periodic table would be given and I was like uh...

I can't do this in my head so I cheated and Wiki'd. But it's okay. I remember CaCO3 is 100, so CO3 is 60. **** SO4 though, that's like...too much. 32 + 4(16)? NO. 6(16) is 96.

milski

1K member
5+ Year Member
Oh gosh for a minute I wasn't sure if a periodic table would be given and I was like uh...

I was in ochem class when I read it - the table was on the wall. It was a toss up what's more boring - listening about yet another enolate or calculating the MWs in my head...

MD
Moderator Emeritus
10+ Year Member
I was in ochem class when I read it - the table was on the wall. It was a toss up what's more boring - listening about yet another enolate or calculating the MWs in my head...
Haha I just try not to attend organic lecture anymore...

pfaction

Full Member
10+ Year Member
Im not cool enough to have an inside conversation on sdn

milski

1K member
5+ Year Member
Im not cool enough to have an inside conversation on sdn

You were supposed to be asleep an hour ago, we don't want to listen to you talking in your sleep.

pfaction

Full Member
10+ Year Member
What, am I on ambien or something?

MD
Moderator Emeritus
10+ Year Member
Got 3.5 hours of sleep last night! Woot.

milski

1K member
5+ Year Member
Woke up at 6:30 am to find out that I don't have to work this morning. 4 extra hours to finish my lab reports - life is good!

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