GC Equilibrium question

[Ryltar]

A saturated solution of MgF2 contains 1.6X10^-3 mol of MgF2 per liter at a certain temperature. What is the Ksp of MgF2 at this temperature?

Correct answer is supposed to be 6.2x10^-9

How I solved:

X= 1.6x10^-3

Ksp = (Mg++)(F-)^2
= (X)(2X)^2
= 4X^3
= 4 (1.6x10^-3)^3
= 1.6x10^-8

Is there something I'm missing here?...

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[Sublimation]

A saturated solution of MgF2 contains 1.6X10^-3 mol of MgF2 per liter at a certain temperature. What is the Ksp of MgF2 at this temperature?

Correct answer is supposed to be 6.2x10^-9

How I solved:

X= 1.6x10^-3

Ksp = (Mg++)(F-)^2
= (X)(2X)^2
= 4X^3
= 4 (1.6x10^-3)^3
= how did u get this.----->1.6x10^-8

Deal with the exponents (-3)*(3) = -9, then just multiply 4 by 1.6 u get appx. 6.2......i dont see wats wrong here.

Is there something I'm missing here?...

Response is in bold

 

[Ryltar]

I must have copied the wrong answer over to the text window. I probably got it wrong because it was a typo, which is common in ACS answers. Thanks for confirming I set up the problem properly.

 

[potbelly]

I must have copied the wrong answer over to the text window. I probably got it wrong because it was a typo, which is common in ACS answers. Thanks for confirming I set up the problem properly.

Hey i don't think you were wrong... I have the same problem...
It is #23 in equilibrium part right?

THe only answer I got is 1.6E-8... I used my calculator but never got 6.2E-9...

I think it is a typo...

 

[potbelly]

Response is in bold

Yes.. I think you made a mistake..
4 (1.6x10^-3)^3

You forgot to calculate 1.6^3 as well... If you use the calculator you will get 1.6E-8...

 

[Sublimation]

Yes.. I think you made a mistake..
4 (1.6x10^-3)^3

You forgot to calculate 1.6^3 as well... If you use the calculator you will get 1.6E-8...

I did it by hand like so. Exponents first. 4[1.6 X 10^(-3)]3 = 4[1.6 X 10^(-9)]= 4[1.6E-9] = 6.4E-9

U might want to put the calculator away and do it by hand and see what you get....i think i followed my order of operations correctly the parenthesis is raised to the third power....so i did exponents first.....hmmmm they might have oversimplified it like i did.....but ya my calc is giving me the same answer u are.....weird....street wolf can prolly solve this for us...

 

[Ryltar]

That's really weird. Do you use a TI-83 too Sublimation?

 

[potbelly]

I did it by hand like so. Exponents first. 4[1.6 X 10^(-3)]3 = 4[1.6 X 10^(-9)]= 4[1.6E-9] = 6.4E-9

U might want to put the calculator away and do it by hand and see what you get....i think i followed my order of operations correctly the parenthesis is raised to the third power....so i did exponents first.....hmmmm they might have oversimplified it like i did.....but ya my calc is giving me the same answer u are.....weird....street wolf can prolly solve this for us...

Okay there is a miscalculation in your answer...

4[1.6 X 10^(-3)]3= 4[ 1.6^3 X 10^(-9)] = 1.6384 E-8

You missed this 1.6^3 = 4.096....
Hope this helps..🙂

 

[Sublimation]

Okay there is a miscalculation in your answer...

4[1.6 X 10^(-3)]3= 4[ 1.6^3 X 10^(-9)] = 1.6384 E-8

You missed this 1.6^3 = 4.096....
Hope this helps..🙂

there we goooo...thanks

 

[chemtopper]

There is no error in the calculation.everything is perfect

= 4 (1.6x10^-3)^3 = 1.6384 X 10^-8
you just rounded it to 1.6 X 10^-8

1.6 ^3= 4.096
4x 1.6 ^3 = 4 x 4.096= 16.384
16.384 X 10^-9 = 1.6384 X 10^-8

no miscalculations at all.Answer is perfect.

 

[sweetcinuhstix]

ACS is correct. Don't forget about pemdas(order of operations) in which exponents come before multiplication! You have to square and then multiply by 4.