Question

Medal and fan
Which cation from the table has the greatest solubility ?
BaSO4 Ksp = 1.1*10^-10
CaCO3 Ksp = 2.8*10^-9
CaF2 Ksp = 5.3*10^-9
CuCl Ksp = 1.2*10^-6

I had answered with CuCl, it marked me wrong. Which one would it be then?

Thanks(:

Answer 1

@sweetburger

Answer 2

where are cations in the table

Answer 3

The Ba, Cu, Ca.

Answer 4

is it BaSO4 Ksp = 1.1*10^-10 ?

Answer 5

How? That just lowers the ksp, which makes it less soluble?

Answer 6

nah
but is it right?

Answer 7

i didn't even think of Ksp

Answer 8

I won't know till the end haha

Answer 9

well i do remember learning that solubility of compounds of group 2 increases down the group

Answer 10

the one that is on the very bottom is Ba from give cations
thus i chose A

Answer 11

But BaSO4 has the smallest ksp..

Answer 12

hmmm don't know really
this is actually what i remember

Answer 13

I just think it has more to do with the points in this lesson rather than previous ones, otherwise they wouldn't give ksp.

Answer 14

ik thats why idk what exactly to think of here

Answer 15

@aaronq

Answer 16

you can solve for the molar solubility for all of them, notice the stoichiometry though, for \(CaF_2\), you have Ksp=\(x^3=5.3*10^{-9}\)

solubility=x=0.0017435 M

check the rest, but this is probably the highest

Answer 17

hmmmmm

Answer 18

i just realized i did that wrong, it's supposed to be \(Ksp=4x^3\)

Answer 19

But wouldn't it be set as (x)(2x)^2? Which means you would have to divide 5.3 by 4 then take the cube root?

Answer 20

Yeahhh haha

Answer 21

haha good eye

Answer 22

It's the same value as CuCl.

Answer 23

And CuCl has less ions.

Answer 24

i think i should go for A levels on my own
i feel so stupid T_T

Answer 25

hmm, it asks for the cation with the highest solubility... I think \(Ca^{2+}\) then?

Try this on paper, choose the same concentration for Cl in CuCl and for F in CaF2.

plug it into the Ksp and solve for the cation concentration

Answer 26

CuCl \(Ksp = 1.2*10^{-6}=[Cu^+][0.1]\)

CaF2 \(Ksp = 5.3*10^{-9}=[Ca^{2+}][0.1]^2\)


see which is higher

Answer 27

0.1 you guys are taking as of anion part?

Answer 28

yeah

Answer 29

interestinggg is it always like that or only when the value for it is not given?>

Answer 30

Wait why .1??

Answer 31

well by choosing an arbitrary concentration for the anion we can compare the values, you could've chosen any number

Answer 32

lol u just realized?

Answer 33

any number?

Answer 34

well any reasonable number

Answer 35

you're not gonna use like \(6.022*10^{23}\)

Answer 36

so that's as long as i take it as constant value everywhere?

Answer 37

for examples like this it works

Answer 38

noted xD thnx
@seehearcreate

Answer 39

u get it?

Answer 40

i just checked it, it still gives Cu^+ as a higher concentration.

Answer 41

so that means it'll form ppt

Answer 42

it means that you can dissolve more Cu^+ than Ca^2+. I'm kinda puzzled, if you say that you chose CuCl and marked it wrong.

Answer 43

im lost

Answer 44

The x for CuCl is actually x=0.0010954
and for CaF2 is x=0.0010983

slightly larger, but larger nonetheless

Answer 45

i guess within sig figs, they're the same though

Answer 46

when i did what u said earlier basically in
BaSO4 Ksp = 1.1*10^-10 Ba=1.1*10^-9
CaCO3 Ksp = 2.8*10^-9 Ca= 2.8*10^-8
CaF2 Ksp = 5.3*10^-9 Ca= 5.3*10^-7
CuCl Ksp = 1.2*10^-6 Cu= 1.2*10^-5

Answer 47

it's more accurate to use the molar solubility, since they vary in stoichiometry.

If you chose CuCl and marked it wrong, then it is definitely \(Ca^{2+}\).

Answer 48

Very sorry! I had to leave to pick up my brother from the bus stop. Yeah, it marked CuCl wrong, I didn't understand it either. I'll try the CaF2.

Answer 49

wops

Answer 50

wait guys i think i got it

Answer 51

this is shown in my book
idk if its the thing we need here or not

Answer 52

OHH. It's a proportion.

Answer 53

even when you find the solubility, you'd be multiplying them by 1 (thats the coefficient). So nothing much is changed

Answer 54

Hold on.

Answer 55

so did that pic help or it was off topic?

Answer 56

its definitely on topic, but it doesnt change anything :S

Answer 57

If anything, that makes the value smaller...

Answer 58

hmmmmmm

Answer 59

I'm about to pound my head against a wall.

Answer 60

me2

Answer 61

when i did like the book said this is what im getting

BaSO4 Ksp = 1.1*10^-10 1.21*10^-20
CaCO3 Ksp = 2.8*10^-9 7.84*10^-18
CaF2 Ksp = 5.3*10^-9 5.62*10^-17
CuCl Ksp = 1.2*10^-6 1.44*10^-12

Answer 62

Yeah, CuCl still has the highest solubility.

Answer 63

why u say that CuCl has highest solubility?

Answer 64

O!!!!!!!!!!!!!!!!!! waaait look at another example
sec i'll take a pic

Answer 65

here

Answer 66

That isn't changing anything, since you square root Ksp in most of them anyway.

Answer 67

ugh

Answer 68

i tried this way and the powers in each increase
but in CaF2 is stays -9 as it was originally

Answer 69

@Loser66

Answer 70

@Kainui save us T_T

Answer 71

BaSO4 Ksp = 1.1*10^-10 Ba+= 1.05*10^-5

CaCO3 Ksp = 2.8*10^-9 Ca+2= 5.29*10^-5

CaF2 Ksp = 5.3*10^-9 Ca+2= 7.49*10^-9

CuCl Ksp = 1.2*10^-6 Cu+= 1.09*10^-3

Answer 72

this is what im getting

Answer 73

I just got feedback, the CaF2 is right. Though how in the heck it is I don't understand. I still want to figure this out.

Answer 74

im trying to find connection

Answer 75

somehow in all of my calculations answers are in similar trend with BaSO4, CaCO3 and CuCl
ONLY CaF2 is totally off trend

Answer 76

Yep. Yet, CaF2 was correct. I'm wondering if the question was faulty. Someone at corporate falling asleep on their calculator.

Answer 77

but
to think of this
all other answers seem way of more then Ksp
only in CaF2 i see only a slight increase

Answer 78

i think it makes sense

Answer 79

O_O

Answer 80

the question is not asking which is 100% soluble right?

Answer 81

noooo haha. Just which one is most soluble. Which in this case, it is CuCl, no matter what.

Answer 82

idk why u think its CuCl but now im kinda sure that its CaF2

Answer 83

I mean remember the precipitation question?

Answer 84

if value is less then K then no ppt
if value more then K then there will be ppt

Answer 85

the more the ppt the less soluble

Answer 86

in all 3 cases the values are very much bigger then K thus we'd expect more ppt which means less soluble
but in CaF2 the value is close to K meaning its even close to being less than K
so that means the amount of ppt formed is way less than in the other 3
thus more soluble than the other 3

Answer 87

idk if im making sense =_=

Answer 88

No, larger values of K produce a higher solubility. When k=1, that means the solution is saturated.

Answer 89

maybe im trying to connect noncollectable stuff

Answer 90

its 1 am night and i can't fall asleep unless this thing is done ~_~

Answer 91

When you find the molar solubilities, \([Cu^+]\)=0.0010954=0.0011 and \([Ca^{2+}]\)=0.0010983=0.0011, you find that they differ a little bit. But not enough within the given significant digits - so the question is flawed in that sense.

Answer 92

i'm off to sleep, mb in the morning i'll get it

Answer 93

I'm pretty sure this is right, but for some reason I'm doubting myself and can't seem to find anywhere that says this on the internet to check myself. At any rate here goes.

All of them only have 2 ions they can dissociate into while CaF2 becomes 3. Even though this might seem insignificant compared to CuCl, it actually ends up being what changes everything.

CaF2 Ksp = 5.3*10^-9
CuCl Ksp = 1.2*10^-6

Let's calculate the concentration of the ions in solution for CaF2 and CuCl. Actually, we don't have to, you've already done it.

[Cu+] = 1.09545*10^-3
[Ca2+]=1.01961*10^-3

Even at this level it appear a close fight, but Copper I ions still win by a marginal amount. But wait a second, what's the total concentration in solution of all the other ions like Chlorine and Fluorine? Looking back at the equilibrium equation, we can see for every 1 copper ion we have 1 chloride. But for every Calcium we have 2 fluoride ions in solution! So let's add them up.

2[Cu+] = 2.19089*10^-3
3[Ca2+] = 3.05884*10^-3

That's your total concentration of dissolved ions in solution. There are more for CaF2 than CuCl. Sorry it took me so long to respond, there was a lot to read through and I am distracted easily lol.

Answer 94

Well slap me and call me sally....thanks so much(:

Answer 95

Thats good stuff @Kainui though the question asked about the concentration of cations only :S

Answer 96

yehhhhh well so much for that lol.