DAT Dest Gen Chem question 256

[Mrhyde]

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NH4Cl gives an acid solution, I get that since Cl would be considered neutral. But How come I cant "Guess-stimate" an acid solution of PH 1.2-2.8 ? How the heck am I supposed to just know this is about 5 to 6 PH ? I would think that because we have a neutral present and we now know this is acidic that our solution would be real Acidic and not a weak acid considering that Cl does not affect it ? How am I supposed to know its 5-6 PH basically..... I chose the wrong answer A ?

 

[ZBehr93]

I would say because they want you to see if you know that NH4Cl is not one of the 7 strong acids. Only the strong acids would give a pH that low, 1.2-2.8. Otherwise, the solution would be only slightly acidic, ~5 or 6

 

[Mrhyde]

I would say because they want you to see if you know that NH4Cl is not one of the 7 strong acids. Only the strong acids would give a pH that low, 1.2-2.8. Otherwise, the solution would be only slightly acidic, ~5 or 6

Thank you

 

[greyworm]

Ok, so this is how i see it. We already know that NH4Cl is a salt that splits as NH4 and Cl-. The Cl- is negligible in terms of considering pH since its a weak base. However NH4 (an acid BUT not a strong one that ionizes 100%) will go on to protonate the H20 in the solution yielding NH4+ H20 -> NH3 + H3O+, thats why you can't assume an extreme pH like 1-2.