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(a) The measured heats of neutralization of acetic acid, formic acid, hydrocyanic acid, and hydrogen sulphide are 13.20, 13.40, 2.90 and 3.80 KCal per g.equiv. respectively. Arrange these acids in a decreasing order of strength. (b) Heat of neutralization of formic acid by NH_(4)OH is 11.9 KCal per g.equiv. What is the heat of ionization of NH_(4)OH? |
| Answer» <html><body><p></p>Solution :`DeltaH_("(<a href="https://interviewquestions.tuteehub.com/tag/neutralization-15018" style="font-weight:bold;" target="_blank" title="Click to know more about NEUTRALIZATION">NEUTRALIZATION</a>)")=DeltaH_("(ionization)")+DeltaH_((H^(+)+OH^(-)))` <br/> `therefore DeltaH_("(ionization)")=DeltaH_("(neutralization)")-DeltaH_((H^(+)+OH^(-)))` <br/> `57.32KJ = 13.2 <a href="https://interviewquestions.tuteehub.com/tag/kcal-531581" style="font-weight:bold;" target="_blank" title="Click to know more about KCAL">KCAL</a>` <br/> `DeltaH_("(neutralization)")" for all acids have a "-ve" sign."` <br/> `=-13.20-(-13.70)` <br/> `=+0.50"Cal/g.equiv"` <br/> `DeltaH` for ionization of formic acid <br/> `=-13.40+13.70` <br/> `=+0.30" Cal/g.equiv."` <br/> `DeltaH` for ionization of hydrocyanic acid <br/> `=-2.90+13.70` <br/> `=+10.80"kCal/g.equiv"` <br/> `DeltaH` for ionisation of hydrogen sulphide <br/> `=-3.80+13.70` <br/> `=+9.90" KCal/g.equiv"`. <br/> The acid with the lowest positive value of heat of ionization will be the strongest acid. Thus formic acid is the strongest and hydrocyanic acid the weakest acid. The trend in decreasing strength of acids is : <br/> Formic acid > acetic acid ? hydrocyanic acid > hydrogen sulphide. <br/> (b) Thermochemical <a href="https://interviewquestions.tuteehub.com/tag/equations-452536" style="font-weight:bold;" target="_blank" title="Click to know more about EQUATIONS">EQUATIONS</a> are : <br/> (<a href="https://interviewquestions.tuteehub.com/tag/1-256655" style="font-weight:bold;" target="_blank" title="Click to know more about 1">1</a>) `HCOOH+NH_(4)OHrarr HCOONH_(4)+H_(2)O""DeltaH_(1)=-11.9KCal` <br/> (2) `HCOOH rarr HCOO^(0)+H^(+)""DeltaH_(2)=+0.30KCal.` <br/> (3) `NH_(4)OH rarr NH_(4)^(+)+OH^(-).""DeltaH_(3)=x. KCal` <br/> (4) `H^(+)+OH^(-)rarr H_(2)O_((l)),""DeltaH_(4)=-13.70KCal` <br/> The sum of reaction (2), (3) and (4) should <a href="https://interviewquestions.tuteehub.com/tag/equal-446400" style="font-weight:bold;" target="_blank" title="Click to know more about EQUAL">EQUAL</a> reaction (1). <br/> `therefore DeltaH_(1)=DeltaH_(2)+DeltaH_(3)+DeltaH_(4)` <br/> `-11.90=0.30+x-13.70` .<br/> `=+1.50"KCal.g.equiv"^(-1)` <br/> `DeltaH` for ionization of <br/> `NH_(4)OH=+1.50" kCal/g.equiv"^(-1)`</body></html> | |