# Acid &Base: Calculate PH of HOCl & Net Ionic Eq.

• APCalculus
In summary, HOCl is a weak acid in water. The Ka expression for HOCl is shown below: [H3O+][OCl-]/ [HOCl]= 3.2 X 10^-8. The equilibrium concentration of HOCl is 0.175-x.
APCalculus
Hypochlorous acid, HOCl, is a weak acid in water. The Ka expression for HOCl is shown below:
[H3O+][OCl-]/ [HOCl]= 3.2 X 10^-8

1) write a chemical equation showing how HOCl behaves as an acid in water.
i got: HOCl + H2O = H3O + OCl

2) calculate the PH of a 0.175 M solution of HOCl.
i got:
HOCl + H2O = H3O + OCl
Initial: 0.175 0 0 0
Change: -x -x +x +x
Equilibrium: 0.175-x -x +x +x

am i doing it right? how do u calculate the PH from x?

3) write the net ionic equation for the reaction between the weak acid HOCl and the strong base NaOH.
I got: HOCl + NaOH = H3O +Na +OH
is it right?

4) In an experiment, 20 mL of 0.175 M of HOCl is placed in a flask and titrated with 6.55 mL of 0.435 M NaOH.
A)Calculate the number of moles of NaOH added.
I did: (6.55/1000) x (0.435 M) = 0.0025

B) Calculate [H3O+] in the flask after the NaOH has been added.
where do i start? i don't get what the question is asking.

C) Calculate [OH-] in the flask after the NaOH has been added.
where do i start? i don't get what the question is asking.

thank you.

bump, anyone?

APCalculus said:
Hypochlorous acid, HOCl, is a weak acid in water. The Ka expression for HOCl is shown below:
[H3O+][OCl-]/ [HOCl]= 3.2 X 10^-8

1) write a chemical equation showing how HOCl behaves as an acid in water.
i got: HOCl + H2O = H3O + OCl
You've forgotten to include the charges on the product ions.

2) calculate the PH of a 0.175 M solution of HOCl.
i got:
HOCl + H2O = H3O + OCl
Initial: 0.175 0 0 0
Change: -x -x +x +x
Equilibrium: 0.175-x -x +x +x
The concentration of water initially is not zero, but that's not important for the calculation - it is assumed there's a sufficient excess of water to not matter.

So you've got [HOCl] = 0.175-x, [H3O+] = x = [OCl-]

Now go back to the question and look at the expression for the Ka of HOCl.

3) write the net ionic equation for the reaction between the weak acid HOCl and the strong base NaOH.
I got: HOCl + NaOH = H3O +Na +OH
is it right?
Well, what are you supposed to get when you neutralize an acid with a base?

4) In an experiment, 20 mL of 0.175 M of HOCl is placed in a flask and titrated with 6.55 mL of 0.435 M NaOH.
A)Calculate the number of moles of NaOH added.
I did: (6.55/1000) x (0.435 M) = 0.0025
Correct.

B) Calculate [H3O+] in the flask after the NaOH has been added.
where do i start? i don't get what the question is asking.

C) Calculate [OH-] in the flask after the NaOH has been added.
where do i start? i don't get what the question is asking.
Once you figure out the correct equation for (3), this will make more sense. See hint for (3).

## 1. What is the difference between an acid and a base?

Acids are substances that release hydrogen ions (H+) in water, while bases are substances that release hydroxide ions (OH-) in water. Acids have a pH less than 7, while bases have a pH greater than 7.

## 2. How do you calculate the pH of a solution?

The pH of a solution can be calculated using the formula pH = -log[H+], where [H+] is the concentration of hydrogen ions in moles per liter (molarity). Alternatively, the pH can also be determined using a pH meter or pH indicator strips.

## 3. What is the pH of HOCl?

The pH of HOCl (hypochlorous acid) can be calculated using the formula pH = -log[H+], where [H+] is the concentration of hydrogen ions in the solution. The concentration of H+ can be determined using the dissociation constant (Ka) of HOCl, which is 2.9 x 10^-8 at 25°C.

## 4. What is a net ionic equation?

A net ionic equation is a chemical equation that shows only the species that are involved in a chemical reaction. It eliminates spectator ions, which are ions that do not participate in the reaction. This type of equation is useful for determining the overall reaction and identifying the products formed.

## 5. How do you balance a net ionic equation?

To balance a net ionic equation, follow these steps:1. Write the unbalanced equation for the reaction.2. Write the ionic equation by separating all the aqueous compounds into their respective ions.3. Cancel out spectator ions on both sides of the equation.4. Balance the remaining ions by adding coefficients as needed.5. Check to make sure the number and type of atoms are balanced on both sides of the equation.

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