PH problem weak acid and weak base

In summary, the conversation was about finding the pH of a soft drink using the Henderson-Hasselbach Equation. The major buffer ingredients were 6.90g of NaH2PO4 and 5.70g of Na2HPO4 per 355mL of solution. The person asked for help and the expert explained the procedure, including finding the molarity of each compound and the pKa of phosphoric acid. The person thanked the expert for their answer.
  • #1
hsgnfgkid
4
0
Hi

I have been trying several days to solve this problem. But i can't find the procedure to solve this weak acid and weak base problem. I will really appreciate some help.

What is the pH of a soft drink in which the major buffer ingredients are 6.90 g of NaH2PO4 and 5.70 g of Na2HPO4 per 355 mL of solution?

Thanks:smile:
 
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  • #2
To find the pH of a buffer solution, you use the Henderson-Hasselbach Equation:

pH = pKa + log ([[tex]A^{-}[/tex]] / [HA])

[[tex]A^{-}[/tex]] is the molarity of your conjugate base
[HA] is the molarity of your acid

So you want to find the concentration of acid and base in your buffer solution. Keep in mind that NaH2PO4 is your acid and Na2HPO4 is your base.

Also, you need the Ka (acidity constant) of phosphoric acid (I don't know this off the top of my head).

Before anything else, I would find the molarity of each solution. I'm sure you know how to do this, but if not, find the molar mass of each compound and plug into the following equations:

# moles = grams / molar mass (in g/mol) and Molarity = Moles / Liters

Once you have the molarity of each compound and the Ka of phosphoric acid, find the pKa of phosphoric acid by doing:

pKa = -log(ka)

So, plug these values into the Henderson-Hasselbach equation and you'll be all set.
 
  • #3
Hi Staf9

I would really want to thank you for th answer. Youre the best, really i appreciate your work. THANKS ONCE AGAIN
 

1. What is the definition of a weak acid and a weak base?

A weak acid is an acid that only partially dissociates in water, meaning it does not completely break apart into its ions. Similarly, a weak base is a base that only partially dissociates in water.

2. How does a weak acid and a weak base affect the pH of a solution?

A weak acid will lower the pH of a solution, making it more acidic. On the other hand, a weak base will raise the pH of a solution, making it more basic.

3. What is the relationship between the concentration of a weak acid or base and its pH?

The concentration of a weak acid or base affects its pH in a logarithmic manner. This means that a small change in concentration can result in a large change in pH.

4. How do you calculate the pH of a solution containing a weak acid or base?

The pH of a solution containing a weak acid or base can be calculated using the Henderson-Hasselbalch equation, which takes into account the concentration of the weak acid or base and its dissociation constant.

5. What are some examples of weak acids and bases?

Some examples of weak acids include acetic acid, formic acid, and citric acid. Weak bases include ammonia, pyridine, and diethylamine.

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