Value of Kw question

[JohnArthurReyes_1B]

The value of Kw for water at body temperature (37°C) is 2.1 X 10^-14. (a)What is the molarity of H3O+ ions and the pH of neutral water at 37°C? (b) What is the molarity of OH- in neutral water at 37"C?

For part a, I understand that Kw=[H3O] [OH-]
and were given Kw so 2.1 x 10^-14=[H30] [OH-]. I don't know where to go from here with these two pieces of information.

For part b, I understand if I get [H3O] solving for [OH] would entail dividing Kw/[H3O]

[Franca Park 3J]

In water we assume that the concentration of [H3O+] = [OH-]
(such as when Kw = 1.0 x 10^-14, [H3O+] = 1.0 x 10^-7 and [OH-] = 1.0 x 10^-7)
so Kw = 2.1 x 10^-14 = [H3O+][OH-]
but since [H3O+] = [OH-]
Kw = 2.1 x 10^-14 = x^2
so x = square root 2.1 x 10^-14
Then, you get the pH by taking the -log of x.

Part b is simple since you already assumed [H3O+] = [OH-].
[OH-] = x

[Kai_Chiu 1F]

In water we assume that the concentration of [H3O+] = [OH-]
(such as when Kw = 1.0 x 10^-14, [H3O+] = 1.0 x 10^-7 and [OH-] = 1.0 x 10^-7)
so Kw = 2.1 x 10^-14 = [H3O+][OH-]
but since [H3O+] = [OH-]
Kw = 2.1 x 10^-14 = x^2
so x = square root 2.1 x 10^-14
Then, you get the pH by taking the -log of x.

Part b is simple since you already assumed [H3O+] = [OH-].
[OH-] = x

[H3O+] = [OH-] is simply because it is water? Or is it because the question stated neutral water?

[Zoe FC 1C]

This is an old thread but I'm wondering the same thing– how do we know that H30=OH?

[Namita Shyam 3G]

I'm also wondering why they would be equal...any help would be appreciated.

[Lizbeth Garcia 1F]

They would be equal because the problem claims the water is neutral. When water is neutral [H30+]=[OH-].

[Katie Nye 2F]

In water we assume that the concentration of [H3O+] = [OH-]
(such as when Kw = 1.0 x 10^-14, [H3O+] = 1.0 x 10^-7 and [OH-] = 1.0 x 10^-7)
so Kw = 2.1 x 10^-14 = [H3O+][OH-]
but since [H3O+] = [OH-]
Kw = 2.1 x 10^-14 = x^2
so x = square root 2.1 x 10^-14
Then, you get the pH by taking the -log of x.

Part b is simple since you already assumed [H3O+] = [OH-].
[OH-] = x

[H3O+] = [OH-] is simply because it is water? Or is it because the question stated neutral water?

Water is always neutral unless it says otherwise so those would be the same!

[Carla Bruebach 1C]

Since water is neutral its concentration of H3O+ and OH- are equal.

[105764441]

Kw is the ionization constant of water. Ionization means the gain or loss of an electron from a molecule. In the case of water, the molecules that are losing electrons are H3O+ and OH-, and they are losing/gaining an electron in the form of a hydrogen ion. Water is a neutral substance. On the PH scale from 0 which is the most acidic, to 14, which is alkaline or basic, it measures at a 7 and thus is neutral. What does this mean? This means that the hydroxide and hydronium ions are essentially equal in concentration in water. So, if we are given the ionization constant, all we must do is take the square root of the value for the constant, which will tell us the concentration of each molecule! I hope this helps!