Acidic soils

I would have thought that acetic acid was not the correct kind for calciphobic plants (lime hating). The normal thing to add is sulphur.
Actually changing the acidity of a soil is rather difficult, it is determined by the underlying geology of the area. You can increase acidiy slightly by the addition of compost, pine needles, leaf mould from trees from an acidic source, peat (if you must), but if the surrounding soil has lime in it, it will eventually seep back in.
One point is that Rhodo's will tolerate a neutral soil if they are heavily mulched with chopped rhodoendron leaves! It is thought that in alakaline soils manganese is not available and it is found in the leaves.
You can also water them with chelated iron (Sequestrene) if they become chlorotic.( yellow leaves).

Thank you for your quick reply. All of it you've mentioned, I have tried. It works just fine. Also, the chelated iron, I use 1 cup of chelated iron in 2 lt water. Is it OK?
And one question more, what is the best way for sterizilize soil and sand?

It rather depends on the quantity of soil you wish to sterilise. If just a small amount then the best way is to pop it in a microwave oven (check there are no metal bits in the soil). Not sure of the times, you need to experiment.
I have sterilised soil by spreading it out thinly on concrete and going over it with a flame gun. You need to be careful though, I set fire to the fence!
There are chemical sterilising agenst available, but never used them so no advice there.

The general thought really is to work with the soil you've got rather than trying to change it (ie alkaline to acid). If you really must have a rhodo, my advice would be to grow it in a container of ericaceous compost and water it with rain water. Shallow rooted plants such as rhodos could also be tried in a raised bed as long as that contained an acidic growing medium. 'Inkarho' rootstock, developed in Germany, allows grafted rhodos to be grown in soils with a pH as high as 7; good Garden Centres may be able to supply common varieties grafted on to this rootstock

I agree with Andrewr. Ericaceous compost in a seperate container is the best way to go. Alan Titchmarsh said if your soil's limey and you want to grow Rhododendrons - move house!