Ksp problem help

[MoooShuuu]

Advertisement - Members don't see this ad

Can someone tell me how to solve this problem: What is the pH of a saturated aqueous solution of Ca(OH)2? The Ksp of Ca(OH)2 is 8.0X10^-6



Another question: the oxidation state for N in NO3- is 5. Why? N (-2*3)= -6 so I would think it would be 6.

Thank you.

 

[D3ntalDud3]

the NO3 bears a negative charge.. +6 would make it uncharged whereas +5 still leaves a negative charge

 

[IWantSmile]

Can someone tell me how to solve this problem: What is the pH of a saturated aqueous solution of Ca(OH)2? The Ksp of Ca(OH)2 is 8.0X10^-6

Another question: the oxidation state for N in NO3- is 5. Why? N (-2*3)= -6 so I would think it would be 6.

Thank you.

Ca(OH)2 ---> Ca+2 + 2OH-
X 2X
Ksp=(Ca+2) (OH-)^2
= (x) (2X)^2
= 4X^3
Since, we know Ksp = 8x10^-6, we can solve X. I believe X= 4.2X10^-3.
Also, the concentration of OH =2X, therefore (2OH)= 8.4X^-3. pOH=~2.1

pH= 14-pOH= 11.9 ( approximate because my calculation was all rounded.)
I hope someone check my calculation and formula that I used, thanks in advance.

NO3 has overall -1 charged ( NO3=-1) therefore, N + (-2 *3) =-1 ; N=+5

I think

 

[MoooShuuu]

My math is rusty on this part....

8.0 x 10^-6 = 4x^3 ........ solve for x involves taking the cube root of both sides? or is it 64x and divide the other side by 64? Can someone show me how to do this? I'm having issues with this math!!!

 

[chessxwizard]

8 x 10-6 = 4x^3

2 x 10-6 = x^3

1^3=1 and 2^3 is 8, so the cube root of 2 is at the low end, close to one.
The cube root of 10-6 is 10-2.

1.1 x 10-2 = x. [OH-] = 2x = 2.2x10-2.

Therefore pOH is somewhere between 2 and 1, closer to 2. Let's say 1.8.

ph = 14-poh, around 12.2.

 

[IWantSmile]

My math is rusty on this part....

8.0 x 10^-6 = 4x^3 ........ solve for x involves taking the cube root of both sides? or is it 64x and divide the other side by 64? Can someone show me how to do this? I'm having issues with this math!!!

8.0 X 10^-6 = (4) (X^3)
(8.0 x 10^-6) / ( 4) = ( X^3)

then cube root of both sides to solve for X.

 

[IWantSmile]

8 x 10-6 = 4x^3

2 x 10-6 = x^3

1^3=1 and 2^3 is 8, so the cube root of 2 is at the low end, close to one.
The cube root of 10-6 is 10-2.

1.1 x 10-2 = x. [OH-] = 2x = 2.2x10-2.

Therefore pOH is somewhere between 2 and 1, closer to 2. Let's say 1.8.

ph = 14-poh, around 12.2.

Yours are much faster. Thanks!!

 

[keliao]

we can only estimate while calculating pH.
2E-6 = X^3

u know that if is X^2 2E^-6 will be around 1E-3...
.but since its to the ^3 a number less than 3 so 1E-2
pOH of -2 = equals less than 2

so pH= 14 - (less than 2, lets say 1.8) = 12 or 13.

 

[MoooShuuu]

Thanks for the help...you guys are great 🙂

 

[supraman]

Did anyone experience this difficulty of a question on GChem? Although its not bad, I don't like working with decimals ha

 

[keliao]

Did anyone experience this difficulty of a question on GChem? Although its not bad, I don't like working with decimals ha

if you go over Destroyer math, u'll get the hang of it. they work a lot on pH...decimals...and stuff.