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 )

Please post the answer and solution.

Thanking you in advance

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## Comments

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TopNewestConc. 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

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@Manish Dash

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:

\(pH=14-pOH=13.33\)

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Thank you very much @Raghav Vaidyanathan

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Comment deleted Apr 15, 2015

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Why do you think its a buffer solution? A mixture of strong acid \((HCl)\) and a salt of strong acid and strong base \((NaCl)\) is not a buffer solution.

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I apologise.

My approach would be to calculate the number of moles of the acid or the base that still remains and then work on it's pH

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Any method to support your statement?

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

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Yes please !!!

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

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Comment deleted Apr 15, 2015

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Comment deleted Apr 15, 2015

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Hi Manish, I am sorry to have deleted what I posted. I found that there was a big mistake. The answer to your question is : it is 1 m because it is by the definition of Ph. By definition of PH , PH of 0.1 M HCL is 1 and 1M NaOH is 1.

Edit : (I shall read up a bit on the dissociation values and try the problem again, I guess I messed up there)

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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!

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Thank you

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

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

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No problem. Thanks for replying

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1, i guess??

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Why do you think so ?

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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??

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