Thats one thing Ive really never looked into, why we should use specific acids for specific wines. I always use the blend but I do know that certain acids raise or do not raise the ph as much so that is something to take into account.
This is spoiling the fun from one of my future web-log entries I have planned but do the tests yourself:
Take 1 liter water and add 10 gram tartaric, measure acidity.
Now take 1 liter water and add 10 gram malic, measure acidity.
Again a fresh liter and add citric acid. Measure again......