Question

You have two beakers. One beaker contains 100 mL of NaOH (a strong base); the other contains 100 mL of aqueous Na3PO4 (a weak base). You test the pH of each solution. Which of the following statements is true ?

Answer 1

Answer:

D. If the pH of NaOH is 12, then that of Na₃PO₄ solution has to be lesser than 12.

Explanation:

In this problem, we are comparing the pH of a strong base to a weak base. A strong base is one that ionizes completely in aqueous solutions where as a weak base ionizes slightly.

The pH scale is good tool for measuring the acidity and alkalinity of various substances. It ranges from 1 - 14;

   

      1                                      7                                               14

                         ←                                       →

      increasing acidity                          increasing alkalinity

                                        neutrality

Strong bases have their pH value close to 14 and weak bases are close to 7.

Since Na₃PO₄ is a weak base, it will have lesser pH value compared to a strong base such as NaOH

Answer 2

The question lack options, that are as follows"

• a. The Na3PO4 has a higher pH because it has more sodium ions than NaOH. NaOH(aq- Na3PO4(aq)
• b. It is possible for the solutions in each beaker to have the same pH
• C. If the pH of the NaOH solution is 12.00, the pH of the Na3PO4 solution has to be greater than 12.00.
• d. If the pH of the NaOH solution is 12.00, the pH of the Na3PO4 solution has to be less than 12.00.

The following statements are true in the given question:

• d. If the pH of the NaOH solution is 12.00, the pH of the Na3PO4 solution has to be less than 12.00.

We know that:

• NaOH is a strong base and Na3PO4 is a weak base.  

• As the strength of OH- in 100ml NaOH and that of OH- in 100ml  Na3PO4 is different. They have different pH values.  
• As we know that pH is inversely proportional to H+ ion concentration.  
• This means the higher the pH value lower is H+ ion concentration.  

Again,

PH +POH =14

From the above equation,

• the higher the PH value of a solution less will be its value of POH vice versa. Hence greater is the OH- ion concentration.  

So,

• the pH of a solution is directly proportional to OH-ion concentration.  

Thus, If pH NaOH = 12.00, NaOH is a strong base and Na3PO4 is a weak base. For the solution, the weak base OH-ion concentration is less. Clearly, the pH of Na3PO4 is less than 12.00.

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