Anahid nos muestra una excelente sesión de estadística, donde trataron el tema del error estándar.…
Problema de Ácidos y Bases (sin Ka)
Comentarios del tutor: Algunas veces los estudiantes se conectan preguntando si un ácido o base es débil o fuerte sin tener conocimiento de la constante de disociación. Sin embargo su familiaridad experimental con los ácidos y/o algún conocimiento general les permite resolver estos problemas. Veamos la sesión:
Student: which is a stronger base? H2PO4-? or HSO4-?
Tutor: Hello. Welcome Do you have any idea how you might solve this problem?
Student: hey thanks. Ummm i have sort of one
Tutor: tell me what do you think?
Student: the one with the the less H?
Tutor: that’s an interesting idea but there exists a better criterion. The stronger base comes of the weaker conjugate acid. Let’s see where comes the HSO4-
Student: it would come from SO4 -2. Sorry meant to put the h IN THERE
Tutor: you were almost right but we are considering the reaction starting from an acid. We can set up something similar for the other ion
Student: ohh ok my bad i understand
Tutor: it’s ok. Would you like to set up the same for the H2PO4-? Well done! Have you used the dissociation constants?
Student: I dont think so
Tutor: ok, now the problem is to find the stronger acid. We can do it by two means: using the acid dissociation constant Ka or using our experience working with acids. Maybe you have worked in the lab with sulfuric and phosporic acids, do you know which is stronger?
Student: no i am not aware yet
Tutor: ok, I will teach you, basically the strongest acids are: – sulfuric acid – nitric acid
Student: I know the seven strongest
Tutor: oh, great. Is there both, sulfuric and phosphoric?
Student: sulfuric is one of them but phosphoric no
Tutor: yes, you are right
Student: so it would be H2PO4-? Because it has a weaker acid?
Student: and the next question asks which is a weaker base Cl- or NO2- and it would be Cl- right? because HCl is a strong acid
Tutor: right, well done!
Student: alright thanks!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!
Tutor: you are welcome, thanks for using our service. Have a nice night
Student: you too
Colaborador: Diego Tapias, Tutor Colombiano de Química