Are citric acid and ascorbic acid the same thing?

Citric acid and ascorbic acid are not the same thing. Indeed, ascorbic acid is the more versatile and essential of the two acids.

Ascorbic acid, or vitamin C, has a chemical make-up of C₆H₈O₆. While it is found in citrus fruits, billygoat plums, rose hips, blackcurrants, guavas, kiwi fruits, broccoli, and Brussels sprouts are much better sources. Most animals can also produce it themselves, although most fish, some birds, all guinea pigs, and some primates — and man — cannot, and so must get it from other sources.

In cooking, besides keeping cut fruits and vegetables from turning brown, ascorbic acid promotes the growth of yeast, and so is also often added as an enhancer to bread dough. In commercial food processing it is used as an antioxidant preservative.

Citric acid has one more oxygen atom than ascorbic acid; its formula is C₆H₈O₇. It occurs naturally in citrus fruits and some other fruits and vegetables. It can also be synthetically produced from sugar.

Citric acid is used commercially to enhance the tartness in fruit-flavored candy and in soft drinks. It is also added to some ice creams to keep fat globules from coagulating. Some bakers use it in sourdough bread to produce an especially assertive tang.