can someone help with this question from kaplans chem

[spoog74]

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if 100 g of an unkown compound is dissolved in 1L of solution, the pH of the resulting solution is measured as 4.56 . Which of the following statements is most likely true of the unkown compound

A. it is a strong base with a formula weight of less than 50 g/ mol
B. It is a weak base with a pkB of less than 5
C. It is a strong acid with a formula weight of less then 50 g/ mol
D. It is a weak acid with a pKa of more than 1.
E. It is a weak acid with a formula weight of less than 10 g/ mol


Can someone weigh in on this? How would one go about doing this the fastest/ easiest way?

Thank s !

 

[JamesBourne]

if 100 g of an unkown compound is dissolved in 1L of solution, the pH of the resulting solution is measured as 4.56 . Which of the following statements is most likely true of the unkown compound

A. it is a strong base with a formula weight of less than 50 g/ mol
B. It is a weak base with a pkB of less than 5
C. It is a strong acid with a formula weight of less then 50 g/ mol
D. It is a weak acid with a pKa of more than 1.
E. It is a weak acid with a formula weight of less than 10 g/ mol


Can someone weigh in on this? How would one go about doing this the fastest/ easiest way?

Thank s !

is answer D?

 

[bharat008]

I think it's D too since that's the only one that makes sense..

 

[spoog74]

I think it's D too since that's the only one that makes sense..

yes answer is D.

Can someone explain?

 

[bharat008]

if 100 g of an unkown compound is dissolved in 1L of solution, the pH of the resulting solution is measured as 4.56 . Which of the following statements is most likely true of the unkown compound

A. it is a strong base with a formula weight of less than 50 g/ mol
B. It is a weak base with a pkB of less than 5
C. It is a strong acid with a formula weight of less then 50 g/ mol
D. It is a weak acid with a pKa of more than 1.
E. It is a weak acid with a formula weight of less than 10 g/ mol

Thank s !

A) Strong Base 50g/mol = 100g/50g = 2mol/1L = 2M : pH would be basic
B) The lower the pKa the stronger the acid; therefore the lower the pKb the stronger the base. pKb is less than 5 so pH would be basic
C) Strong acid 100g/50g = 2mol/1L = 2M pH = -log 2 : really acidic less than 4.56 may be around 2..
D) weak acid with pKa of more than 1; so safe to assume that the lower the pKa the stronger the acid; therefore the pH must be below 7 of the solution.. It says the pH is 4.56 so this could be possible

HOpe that helps..

 

[JamesBourne]

A) Strong Base 50g/mol = 100g/50g = 2mol/1L = 2M : pH would be basic
B) The lower the pKa the stronger the acid; therefore the lower the pKb the stronger the base. pKb is less than 5 so pH would be basic
C) Strong acid 100g/50g = 2mol/1L = 2M pH = -log 2 : really acidic less than 4.56 may be around 2..
D) weak acid with pKa of more than 1; so safe to assume that the lower the pKa the stronger the acid; therefore the pH must be below 7 of the solution.. It says the pH is 4.56 so this could be possible

HOpe that helps..

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