Sodium Thiosulfate: Preparation, Risks & Uses

Instructor: Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

Sodium thiosulfate has two unique uses in medicine. To prepare it requires a three-step process. In this lesson, we will discuss how it is prepared, risks surrounding the compound and what is used for.

Uses and Risks

In the rare case that someone is poisoned with cyanide, an antidote is needed quickly. Sodium thiosulfate is that antidote. It is also used in conjunction with the treatment of certain cancers. The chemotherapy drug cisplatin has negative effects on the kidneys and the addition of sodium thiosulfate acts as a neutralizing agent to protect the kidneys. Higher doses of cisplatin can be administered if used in conjunction with sodium thiosulfate. That said, sodium thiosulfate is not totally safe and the risks of using it have to be weighed against the potential outcome of not using it.

When used as a medication, sodium thiosulfate can cause the patient to become nauseous, experience ringing in the ears, blurred vision, pain in the joints along with muscle cramps, and mental irregularities.

Outside of the side effects attributed to sodium thiosulfate use as a medication, there are other risks associated with coming in contact with this chemical. It is a slight irritant when it comes in contact with the skin and eyes. Inhaling or ingesting it is considered hazardous. Now that we know the risks associated with this compound, let's see how it is produced.

Preparation of Sodium Thiosulfate

Sodium thiosulfate is an ionic compound containing two sodium ions (Na+1) and one thiosulfate polyatomic ion (S2 O3-2). The formula for sodium thiosulfate is Na2 S2 O3.

Solid sodium thiosulfate

There is a three-step procedure for the production of sodium thiosulfate involving three separate chemical reactions. The first reaction starts with sodium carbonate, sulfur dioxide, and water.

Step 1:

Na2 CO3 + 2SO2 + H2 O → 2NaHSO3 + CO2

Sodium carbonate reacts with sulfur dioxide and water to produce sodium bisulfite and carbon dioxide. To do this, we dissolve sodium carbonate in water and bubble sulfur dioxide into the solution. Large white bubbles will be seen, which is a result of the carbon dioxide gas escaping the solution.

Step 2:

2NaHSO3 + Na2 CO3 → 2Na2 SO3 + CO2 + H2 O

This reaction might seem strange because we started the three-reaction process with sodium carbonate, and now we are adding sodium carbonate to the product of the first reaction! That is how chemistry works sometimes. This combination is boiled for around 15 minutes and sodium sulfite remains in solution with water while the carbon dioxide escapes.

Step 3:

Na2 SO3 + S → 2Na2 S2 O3

The last step in preparing sodium thiosulfate requires the addition of sulfur that is wetted slightly with ethanol. This solution is boiled in a closed system so that the water that evaporates condenses and drips back into the solution. After the boiling process, the resulting solution is filtered. This separates the remaining solid sulfur from the sodium thiosulfate solution.

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