Question

When a piece of magnesium ribbon is placed in a beaker of copper sulfate solution, which one of the following is most likely to happen?
A. A vigorous reaction immediately takes place, with the release of a lot of heat.
B. The blue color of the copper sulfate solution gets darker.
C. The blue color of the copper sulfate solution gets lighter.
D. The magnesium catches fire.

Answer 1

Hint: Actually the given question is based on a practical experiment as we need to draw out conclusions like color produced, type of reaction happened etc: by doing it experimentally. But these are exactly some common reactions of magnesium so that we must be able to remember it any time rather than doing it experimentally. We need to first analyze the chemical reaction happening here along with mentioning the products formed as well as we should know about the nature of reaction to happen. This is the only method to proceed with this question. Here the reaction will be based on reactivity series and the reaction which takes place is termed as displacement reaction.

Complete step-by-step answer:At first, let us write down the chemical reaction involved here with mentioning the products formed as when a piece of magnesium ribbon is placed in a beaker of copper sulfate solution. The chemical reaction involved is shown below,
 \[Mg + CuS{O_4} \to MgS{O_4} + Cu\]
From the above equation, we can see that when we add magnesium to \[CuS{O_4}\] , the \[CuS{O_4}\] solution turns to \[MgS{O_4}\]. This is the particular chemical reaction involved here.
Let us examine what exactly happens here because then only we can reach near to the answer. Actually we can see the place occupied by \[Cu\] in \[CuS{O_4}\] solution is now occupied by \[Mg\] which turns out to be \[MgS{O_4}\]. In general we can say \[Mg\] displaces \[Cu\] and such reactions are called displacement reactions. Here we have to know that no metal can simply displace another metal during a chemical reaction. It strictly happens only when one metal is more reactive than the other which means a more reactive metal can displace a less reactive metal. Such reactions are called displacement reactions which we mentioned above as it is the same one that happened in the chemical reaction given.
Here, \[Mg\] is more reactive than \[Cu\] so that it displaces the place of \[Cu\] . One important point we have to note here is we cannot simply determine the reactivity of certain metals while doing these type problems as reactivity range is important for us to decide whether which particular metal is more reactive or less reactive which in turn helps to figure out the displacement reaction by displacing metals based on reactivity.
We have to know that metals are arranged in increasing or decreasing order based on reactivity on a particular series called Reactivity series. When we take the case of a given reaction, we can see \[Mg\] is above in place of \[Cu\] in the reactivity series. Due to this, \[Mg\] can displace \[Cu\] in \[CuS{O_4}\] solution and also we have to note that the content of \[CuS{O_4}\] also decreases.
We know the nature of the color of \[CuS{O_4}\] solution which is blue in color. We already mentioned that the content of \[CuS{O_4}\] will be decreased which means the blue color can fade out. This is because colorless magnesium sulfate solution is formed which actually results in a decrease of blue colored \[CuS{O_4}\] solution.
Hence the blue color of copper sulfate solution gets lighter.
During this reaction, no vigorous reaction takes place immediately releasing heat and the magnesium will not catch fire at any moment. Since the blue color of the\[CuS{O_4}\] solution gets lighter during the reaction, there is no chance of the blue color of the copper sulfate solution to get a dark color.

Hence option C is the correct answer.

Note:We should know that the reaction takes place here is the displacement reaction in which a more reactive metal displaces a less reactive metal. The main point we have to keep in mind is if we do the reverse of the reaction which means if we put copper into magnesium sulfate solution, no reaction can be recognized since copper is not at all reactive to displace magnesium from magnesium sulfate solution. We have to know that all this happened based on the displacement reaction according to the reactivity series. So, we must be aware of the arrangement of metals based on reactivity in the reactivity series so that we can attempt any question related to the same question given. The brown copper formed in the product side as a result of reaction will coat on the surface of magnesium.