# Hydronium Concentration Calculation

#### HopefulOncoDoc

10+ Year Member
5+ Year Member
What is the hydronium concentration in a gastric solution where the pH is 2.3?

A. 5x10^-2 M
B. 2x10^-2 M
C. 5x10^-3 M
D. 2x10^-3 M

Alright so I got it all the way down to [H3O+] = 10^-2.3 but my math is pretty bad from there. Could someone please explain the mathematics involved after this? Thanks a lot! The answer is C by the way.

Last edited:

#### capn jazz

10+ Year Member
7+ Year Member
Um, your choices A/C and B/D are the same...

#### G1SG2

10+ Year Member
5+ Year Member
What is the hydronium concentration in a gastric solution where the pH is 2.3?

A. 5x10^-3 M
B. 2x10^-3 M
C. 5x10^-3 M
D. 2x10^-3 M

Alright so I got it all the way down to [H3O+] = 10^-2.3 but my math is pretty bad from there. Could someone please explain the mathematics involved after this? Thanks a lot! The answer is C by the way.
[H3O+] = 10^-2.3==> 10^1/2 x 10^-2.8 ==> sqrt10 x 10^-2.8 ==> 3.2 x 10^-2.8, which is equal to 5 x 10^-3.

#### HopefulOncoDoc

10+ Year Member
5+ Year Member
[H3O+] = 10^-2.3==> 10^1/2 x 10^-2.8 ==> sqrt10 x 10^-2.8 ==> 3.2 x 10^-2.8, which is equal to 5 x 10^-3.
Got it. Thanks a lot pookiez. Sorry about some of the answers being the same I typed it up in a hurry but its fixed.

Laura S.

#### amine2086

10+ Year Member
7+ Year Member

Laura S.
You know the equation, pH = -log[H+]. We are given pH of 2.3

2.3 = -log[H+]
-2.3 = log [H+]
[H+] = 10^-2.3

From this we know that the hydronium ion concentration must be smaller than 10^-2 and greater than 10^-3. Only answer that fits that criteria is C.

I solved it in my head without using any math. I used the ph/Ka trick. You know the one with if the number is greater than 3. Use the search tool to find out how to solve this with the trick. I can't remember exactly what thread its in. 