Azúcar

Question

Wouldn't we always use "el azúcar" for phonetic reasons?Thanks!Marcos

Accepted Answer

Hola Marcos
That would make sense because of the double "a": la azúcar, and this is why you will normally hear this word used in masculine "el azúcar"(far more common than in feminine), but the R.A.E accepts both. 
Saludos
Inma

Answer

Hola A
 
The gender applied to calor is masculine by RAE, but there is also an extra note saying that it's also used in feminine in Andalucía and some parts of Latin America. 
I am from Andalucía and use it very often in feminine. Although there are also comments about considering "la calor" as something vulgar, I can tell you this is not the effect it has in Southern Spain, although this may be the case in other regions that prefer  "el calor". as the only option.
Have a look at what Fundeu says about this.
Saludos
Inma

Answer

The RAE dictionary that I have lists Calor as being masculine only.

Answer

Marcos, what I have learned is that we use el rather than la for feminine nouns that begin with an accented A sound. Thus we have el agua, but la abuela. In azúcar, as you can see, the A is not accented, so if we consider it feminine we would use la azúcar.