Is it correct to say that sulphur dioxide gas will only turn moist blue litmus paper red but will not bleach it?
I think the answer is yes and no. For a short exposure time AND for small amounts of SO2 generated, moistened litmus paper and SO2 will give the acid test (meaning the litmus paper will turn color); however, with large amounts of SO2 and exposure times long enough,I think enough reaction will occur to bleach the litmus paper.
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Yes, it is correct to say that sulphur dioxide gas will turn moist blue litmus paper red but will not bleach it. This is due to the acidic nature of sulphur dioxide.
To understand why this happens, you need to know the properties of sulphur dioxide gas. Sulphur dioxide (SO2) is a gas that dissolves in water to form sulphurous acid (H2SO3). Sulphurous acid is a weak acid and has acidic properties.
When sulphur dioxide gas comes into contact with moist litmus paper, it reacts with the water present on the paper to form sulphurous acid. This acid turns blue litmus paper red, indicating that the solution is acidic.
On the other hand, bleaching is the process of removing color from a substance. Certain chemicals, such as chlorine gas or sodium hypochlorite, are known as bleaching agents because they are capable of removing color by oxidizing the pigments in the substance.
Sulphur dioxide is not a bleaching agent. It does not possess the ability to oxidize pigments and remove color from a substance. Therefore, it will not bleach litmus paper.
In summary, when sulphur dioxide gas reacts with moisture on litmus paper, it forms sulphurous acid, which is acidic and turns blue litmus paper red. However, sulphur dioxide does not possess bleaching properties and will not remove color from litmus paper.