Which one is correct? (Maybe both are correct.)
He passed away on the morning of March 5.
Or
He passed away in the morning of March 5.
Which one is correct? (Maybe both are correct.)
He passed away on the morning of March 5.
Or
He passed away in the morning of March 5.
In your sentences, on is the correct preposition and in is the incorrect one. This is a bit tricky.
"He passed away on March 5" is correct. "He passed away in the morning" is also correct. However, in your sentence, "the morning" is a characteristic possessed by March 5, "March 5's morning," as it were. (Note that we would never say "March 5's morning"; I'm just using it to help illustrate that we're using a form of the possessive here). So, "He passed away on the morning of March 5" is correct.
If we turn things around a bit it may help to make things a bit more clear: since "he passed away on March 5 in the morning" is correct, it follows that "he passed away in the morning on March 5" is also correct.
A couple of additional observations:
He passed away some time in the three hours prior to Joe's arrival.
He passed away at 10 am on March 5.
You say "in the morning/in the afternoon/in the evening". These indications of time stand alone and the concept is in + period of time.
It is another thing for "on the morning of the first of May". Here the concept of date/on this day prevails and has become the accepted expression.
Well, it seems none of the answers explain why is it like that, what are the rules, what's the usage, and no-one provided references. I will elaborate and will post my investigation, as I did here at ELU.
Just to cut the long story short, for this specific case: "on" is the correct preposition and "in" is the incorrect one.
"The morning of" functions as an adjectival phrase clarifying the specific time and date "on March 5". "On" is used because it belongs to the date here, specific part of the day.
The normal language constructions would be:
But, when we talk about a specific morning, afternoon, or when we describe the part of the day it should be used with on:
You can't say "I will see you on the morning" - it's incorrect.
here's the reference for more examples: http://dictionary.cambridge.org/grammar/british-grammar/at-on-and-in-time
In or on?
We use in with morning, afternoon, evening and night, but we use on when we talk about a specific morning, afternoon, etc., or when we describe the part of the day.
He passed away in the morning on March 5 - is correct.
We use in for mornings, months and years, and on for dates. We use on for the days (Monday, Tuesday...etc). We use at for time (At 7 o'clock in the morning on Sunday in March...for example).
Further reading here.
On + "noun which is a time label stands for a long time( usually one day / one month )"
on Saturday : Are you free on Saturday to come for a dinner?
on Monday
In + "the" +"noun which is a time label stands for a short time( usually some point of the day)"
in the morning: he is the type who would wake up in the morning.
Why do you see "On the morning"?
this is mostly comes from " on Monday morning ". but "On the morning" is incorrect.
These both sound weird to me. I would reword to:
He passed away in the morning on March 5
or
He passed away during the morning of March 5
In the second, minute, hour, morning, afternoon, evening, night, day, week, month, year, decade, century and millenium using "in" means within or during. On the second, minute, hour, morning, afternoon, evening, night, day and week using "on" means a specific moment in time. For a specific month, year, decade, century or millennium, on is dropped and only the definite article is needed. THE month, year, decade, century or millennium is indicated as a specific time period and on becomes redundant.