Question
(Total 11 marks) Q10. This question is about the reaction between sodium thiosulfate solution and hydrochloric acid. The equation for the reaction is: Na_(2)S_(2)O_(3)(aq)+2HCl(aq)arrow 2NaCl(aq)+H_(2)O(l)+SO_(2)(g)+S(s) (a) The mass of the conical flask and contents was greater at the start of the reaction than at the end. Explain why. __
Answer
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(243 Votes)
Rupert
Master · Tutor for 5 years
Answer
This is because sulfur dioxide (SO2) which is a product of the reaction is a gas, and it escapes into the atmosphere resulting in a decrease in the mass of the flask and its contents.
Explanation
This is a typical chemistry question about a specific type of reactive process. To investigate this question, one must interpret and understand the chemical equation successfully. The equation represents the reaction between sodium thiosulfate and hydrochloric acid. According to the question, the mass of the flask and its contents was greater at the start of the reaction than at the end. To answer this seemingly contradictory observation (based on the law of conservation of mass), one must recognize that the gaseous product ─ sulfur dioxide (SO2), comes out and is lost to the atmosphere. In a sealed system, there would be no change in mass. The mass equivalence principle states that the total mass of substances does not change during a chemical reaction. This phenomenon is an exception because it does not respect this principle due to implied open-system circumstances.