# Chemistry doubt

Respected members of Brilliant !

I have a doubt in inorganic chemistry.

What is the pH of the resulting solution when 40 ml of HCl reacts with 16ml of NaOH ? (pH of HCl is 1 and pH of NaOH is 14 )

Note by Manish Dash
5 years, 1 month ago

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Conc. of HCl = 0.1M Conc. of NaOH = 1M No. of moles of HCl= 0.004 No. of moles of NaOH= 0.016 Therefore, 0.004 moles HCl and NaOH will neutralise each other and 0.016-0.004=0.012 moles of NaOH will remain. conc. of NaOH=0.012/0.056=0.2M pOH= -log(0.2)=0.7 ph=13.3

- 5 years, 1 month ago

The given pH of NaOH is 14, hence it's molarity is $1$. Similarly, the molarity of HCl is $10^{-1}$. Now, we have $16$ml NaOH and $40$ml HCl, which means:

Millimoles of NaOH= $16$

Millimoles of HCl= $40*10^{-1}=4$

Now, HCl is in deficit, hence it acts as limiting reagent. $4$ millimoles of HCl will react with $4$ millimoles of NaOH to form $4$ millimoles of neutral compound $NaCl$. Note that $12$ millimoles of NaOH is still in solution.

Now, after adding both solutions, the new volume is $16+40=56\text{ml}$. In this $56$ml, there is $12$ millimoles of NaOH, hence, molarity of this solution is:

$M=\frac {12 \times 10^{-3}} {56} \times 1000 = \frac {12} {56}= \frac {3} {14}=[OH^-]$

Now,

$pOH= -\log {[OH^-]}=-\log{\frac {3} {14}}=0.669$ (approx. . logarithm is in base $10$)

Therefore:

$pH=14-pOH=13.33$

- 5 years, 1 month ago

Thank you very much @Raghav Vaidyanathan

- 5 years, 1 month ago

1, i guess??

- 5 years, 1 month ago

Why do you think so ?

- 5 years, 1 month ago

See, HCl and NaOH being strong acid and base will completely neutralize equal volumes of each other giving us a neutral solution. But Since the volume of HCl solution is more, so we will be left with HCl solution of pH =1. What do you think??

- 5 years, 1 month ago

Is there any thing to do about normality and concentration of solution ?

- 5 years, 1 month ago

- 5 years, 1 month ago

- 5 years, 1 month ago

Equal moles will react and not equal volumes. It depends upon concentration of $HCl$ and $NaOH$

- 5 years, 1 month ago

- 5 years, 1 month ago

Sorry Manish but I have not studied pH & all that stuffs so I cannot help you :(

- 5 years, 1 month ago

- 5 years, 1 month ago

Hi manish, thanks for mentioning me! But I guess U don't know that I am the weakest in Biology and Chemistry! But for your help, I would surely ask my coaching friends!

- 5 years, 1 month ago

Thank you

- 5 years, 1 month ago

Your most welcome ! I hope I could answer you at the earliest.

- 5 years, 1 month ago

Hey manish, could I mention a site for Your help?

- 5 years, 1 month ago

- 5 years, 1 month ago

Stack Exchange Chemistry, post your question here, U would be answered at the earliest!

- 5 years, 1 month ago

Thank you very much

- 5 years, 1 month ago

My pleasure! Feel free to ask me anything or mentioning me!

- 5 years, 1 month ago