Civil Engineering - GATE Exam Questions - Discussion

Discussion Forum : GATE Exam Questions - Section 2 (Q.No. 3)
3.
A wastewater sample contains 10-5.6 mmol/l of OH ions at 25° C. The pH of this sample is
8.6
8.4
5.6
5.4
Answer: Option
Explanation:
No answer description is available. Let's discuss.
Discussion:
19 comments Page 1 of 2.

Swathy said:   2 months ago
How come 3 there, ie; 5.6-3?

Anyone, please explain this step.

Shashank pandit said:   2 years ago
poh = 8.6.

As the mmol will change to mole per lit;
therefore as we know;
pH + pOH = 14.
pH + 8.6 = 14.
pH = 14 - 8.6 = 5.4.
(2)

Manjula said:   4 years ago
H+ * OH- = 10^-14.
H+ *(10^-5.6 *10^-3) = 10^-14.
H+= (10^-14)/(10^-8.6)
= 10^-5.4.
(1)

Suhail said:   4 years ago
Thanks all for explaining it.

Dhanu said:   6 years ago
Thank you all for explaining this.

Ibrahim said:   6 years ago
PH + POH = 14.

Since we are given a concentration of Oh ions we are calculating POH. To get PH we subtract from 14.

Dhanu said:   6 years ago
How come 14 here?

B.S.DALAL said:   6 years ago
Ph -log ^-5.6=-log10^-8.6 = (14-8.6) = 5.4.

Bharath said:   7 years ago
@Sheela :
pH = -log10^-5.6-3 = -log10^-8.6 = 8.6.
then, 14-8.6 = 5.4.

Sheela said:   7 years ago
@ Bhanu:

pH is the negative of the base 10 logarithms of the molar concentration, measured in units of moles per liter, of hydrogen ions. To attain standard unit here mmol/L is converted into mol/L.


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