por v. para 4

Question

"Lo hago por ti" implies"I do it for your sake, because of you and for you, altogether"."Lo hago para ti"suggests nothing about the true motivation,which may well lay outside the addressee;it only designates ti 'you' as the destination of the "doing". I have found this in:"Delbecque - Towards a cognitive account of the use of the prepositions por and para in Spanish 1996".This, I hope, might explain why "sacrificios por sus hijos"is prefered to"sacrificios para sus hijos".In both cases hijos are the recipients, but the attitude toward the recipients seem to matter.Google search gives 88,500 hits to "sacrificios por sus hijos"and 39 to "sacrificios para sus hijos",suggesting that "para" is a very poor (ungramatical?) choice here.

Answer

Whatever "it" is is the object (or destination).

I do it for you . . . not "because" of you ( por) but "for your benefit/in order to" (para) so, the por/para is an ambiguous choice depending on the intent or actual context of what was said/done before the statement in question.

In most cases por is appropriate if "because of" is a reasonable substitute whereas para is more correct if the recipient benefits . . . if the test phrase is dubious, go with "por".

Answer

Hola Janusz
In this specific sentence "para" would be a poor choice as it is more common to see (as you found in google) the use of por in a sentence using the word "sacrificios" because that's often in a context where you are talking about sacrifying yourself for someone and that "for someone" carries the meaning of "because of someone", hence the use of por. It's difficult to see how the intent of the speaker in this sentence would be making the children the "recipient" of that sacrifice. Although you could also think fo this as in the children will benefit from this sacrifice that is being done, so para could also be used in that case. 
But as Gary said, the use of por and para as in cause and destination sometimes overlaps and is a bit ambiguous so it would be necessary to clarify or to know what the conversation has been about. 
For example you could say:
Trabajo para Antonio. 
Trabajo por Antonio. 
The use of para in the first one would imply that the person who benefits from that work is Antonio, for example, Antonio is his boss.
The use of por in the second one would imply that the speaker is  either working because of Antonio (maybe because Antonio persuaded him to work) or this person is covering for Antonio because he is ill today, so he is working on his behalf. 
Saludos cordiales 
Inma

Answer

Thank you Inma,You write"It's difficult to see how the intent of the speaker in this sentence would be making the children the "recipient" of that sacrifice."For me, it is the other way; I have a hard time realizing that someone might not see the "recipient" here.For me, in "she has made many sacrifices for her children" the primary meaning of "for her children" is "for the benefit of her children";  "because of her children" is the derived secondary meaning (also, "because of" suggests some degree of unwillingness). So, for me, there is a clear recipient, hence "para" seems to be the right choice, unless you know that "por" also indicates recipient, and in a much more "intimate" sense, which together with the "intimacy" of sacrifice gives "por" as the correct choice. To repeat (unless I learn something to the contrary), it seems to me that there is a clear "recipient", "por" is chosen because the "recipient" is "intimate"My problem was learning "para" for "recipients" and not knowing that "por" is used for  "intimate recipients".Janusz