Reaction between sodium thiosulfate and hydrochloric acid?

Question

I would really appreciate a detailed explanation of the reaction between sodium thiosulfate and hydrochloric acid.

Thanks for the help!😊

Answer 1

Na₂S₂O₃ (aq) + 2HCl (aq) ==> SO₂(aq) + S(s) + H₂O(l) + 2NaCl (aq) ... balanced equation

Not sure how detailed of an explanation you need/want, but you can see from the balanced equation that when sodium thiosulfate (a colorless solution) is combined with aqueous HCl (a colorless solution), one of the products is SOLID sulfur. This causes the reaction mixture to turn cloudy. The other products (SO2 and NaCl) are both soluble in H2O.

If you look at the oxidation number of S in Na2S2O3, you see it is +2.

The oxidation number of S in SO2 is +4.

The oxidation number of S in S(s) is zero.

Thus, this is actually a redox reaction which is called a "disproportionation" reaction.

Is this enough detail?

Answer 2

Both Na₂S₂O₃ and HCl are strong electrolytes, which means they are dissociated in aqueous solutions. In other words, there are no HCl or Na2S2O3 molecules in the HCl/Na₂S₂O₃ mixture. In reality, there are mostly ions: H⁺, Cl^-, Na^-, and S₂O₃^2-

That means, we can forget about Cl^-and Na^- , and focus on H⁺ and S₂O₃^2-

These two ions may associate to form a thiosulfuric acid:

H⁺ -> H₂S₂O₃

If that were sulfuric acid, or any other stable acid, that process could be ignored, for that process is reversible: only a small fraction of the thiosulfate ion (S₂O₃^2-) converts into the acid, and it quickly dissociates again to produce protons and a thiosulfate ion.

However, this case is more unusual, for the thiosulfuric acid (H₂S₂O₃) is unstable. It decomposes quickly onto elementary sulfur, sulfur dioxide and water

H₂S₂O₃ -> H₂O + S + SO₂

Therefore, the whole process can be written as:

2HCl + Na₂S₂O₃ -> H₂O + S + SO₂ + H₂O + 2NaCl

Answer 3

Are you asking to predict the products? If so, let's start with the reactants.

Na₂S₂O₃ and HCl

Start by breaking both compounds into their ions. HCl is made up of H⁺ and Cl^- let's label these A and B. Sodium thiosulfate can be broken apart into the sodium cation (Na⁺) and the polyatomic ion (S₂O₃ ^2-) ... let's label these C and D.

HCl + Na₂S₂O₃

^{A B C D}

This is going to be a double replacement reaction. A double replacement reaction essentially swaps anions (the negative ions, which are written as the second half of the compound,) so the generic reaction will look like this:

AB + CD --> AD + BC

So let's plug in our ions.

H⁺ and S₂O₃ ^2- are going to bond and we want to make sure the charges cancel out. To do so, there must be two H⁺ ions in order to cancel out the 2- charge on the thiosulfate ion. Therefore, the first product is H₂S₂O_3.

The second product will be the compound that forms between the sodium ion (Na⁺) and the chlorine ion (Cl^-) The +1 and -1 charges are equal so they come together as NaCl!

The overall reaction will be Na₂S₂O₃ + HCl --> H₂S₂O₃ + NaCl.

Hope this helps!