Q: In the developing solution, sodium sulfite is:
sodium sulfite dental hygiene exam prep

Q: In the developing solution, sodium sulfite is:

sodium sulfite dental hygiene exam prep

Q: In the developing solution, sodium sulfite is:

(A). A retarder
(B). A restrainer
(C). A preservative
(D). An accelerator

One of the components found in the developing solution for dental x-ray processing is the preservative sodium sulfite, which prevents rapid oxidation of the developing agents. This is very important to know for the dental hygiene boards! This chemical is often confused with sodium sulfate – note that one letter (“A” instead of” “I) makes a difference.

Sodium sulfate: Sodium sulfate, also known as sulfate of soda, is the inorganic compound with formula Na₂SO₄ as well as several related hydrates. Sodium sulfate is mainly used for the manufacture of detergents and in the Kraft process of paper pulping.

Answer: (C). A preservative

Learn more for the dental hygiene boards

Let’s look at the other chemicals in the film processors.


  • Reducing agent: hydroquinone or elon – reduces exposed silver halide crystals into black metallic silver. Dark areas appear.
  • Alkalizer: sodium carbonate – softens film emulsion and speeds up action.
  • Restrainer: potassium bromide – inhibits the development of unexposed silver halide crystals.
  • Preservative: sodium sulfite – prevents oxidation.


  • Fixing agent: sodium thiosulfate – clears unexposed silver halide crystals. White areas appear.
  • Hardener: potassium alum – shrinks and hardens emulsion.
  • Acidifier: acetic acid – keeps medium acidic and stops additional development.
  • Preservative: sodium sulfite – prevents oxidation.
Wake Up Memory Technique (WMT) by StudentRDH

Now we have to think about how we are going to memorize those chemicals. Because when you are stressed during your exam, it will be even harder to remember.

  • Sodium sulfite: see the word “fight” in “sulFITE.” This chemical fights oxidation. (Please know that this word is often confused with sulfate – completely different)
  • Hydroquinone: see the word “quinoa” in “hydroQUINOne.” Then think about roasting (baking) some healthy quinoa grains with your green beans for dinner. But cooked them too much and they are DARK. -> Hydroquinone creates DARK areas on a radiograph.
  • Elon: add an “M” in front of the word; make it a “melon.” Now when you cut this melon, you see that is was completely rotten inside. The fruit is DARK, unlike its nice green outside. Yuck, can’t eat that. -> Elon creates DARK areas on a radiograph.
  • Sodium carbonate: see the word “carb” in “CARBonate.” A nice bread roll is a carb, it is SOFT. -> Sodium carbonate makes the crystals on a radiograph SOFT.
  • Potassium bromide: see the word “bro” in “BROmide” (I know it is a stretch)? You use the broom on your patio once a while to prevent the floor from becoming too DARK and dirty. -> potassium bromide prevents
  • Sodium thiosulfate: focus on the word “ATE” at the end. You ate everything on your plate, your plate is clean -> sodium thiosulfate “clears” unexposed ­silver halide crystals -> when your plate is clean, it is “white” (assuming that the plate was originally white).

Radiology is NOT an easy chapter, there are lots of information you need to know. StudentRDH has become the best prep course for the dental hygiene boards, and we have a fantastic radiology chapter. All the information is extremely concise and straight to the point. Your time is precious!

Related post in Radiology: Which radiographic error caused this “flat” smile?

(Disclaimer: StudentRDH is NOT affiliated with the NBDHE, NDHCE, CSCE, CDCA, WREB.)

Written by
Claire Jeong, RDH, MS

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