Final answer:
Normally, sodium hydroxide would turn litmus paper blue, indicating its basic nature. If no effect is observed, it may suggest an error with the litmus paper or observation. In typical experiments with sodium hydroxide, indicators such as bromothymol blue will usually show a color change to blue, and reactions like dissolving sodium carbonate in an acid will result in visible reactions like bubbling.
Step-by-step explanation:
If a student prepared a 20% sodium hydroxide solution and noted that it has no effect on litmus paper, this observation would be unexpected, as sodium hydroxide is a well-known strong base. Typically, sodium hydroxide solutions turn red litmus paper blue, indicating its basicity. However, if no effect is observed, it could indicate that the litmus paper is faulty or that an incorrect observation was made. Normally, when bromothymol blue is added to a sodium hydroxide solution, the indicator should turn blue, reflecting the high pH of the solution.
During experiments like dissolving sodium carbonate in hydrochloric acid or adding hydrochloric acid to sodium hydroxide, one would expect to see bubbling or color changes due to chemical reactions occurring. These reactions typically produce salts and water, and in the case of sodium carbonate and hydrochloric acid, carbon dioxide gas is also released. When adding zinc metal to copper sulfate, a displacement reaction occurs, and one would observe zinc sulfate formation and copper precipitating out.