Question

Which of the following pairs of reactants will react together to produce water (H2O) as one of the products?

Answer 1

These are two questions and two answers.

1) Question: Which of the following pairs of reactants will react together to produce water (H2O) as one of the products?

Fe(OH)₃ and CuO
Cu(OH)₂ and H₂S
MgO and Ca(OH)₂
SO₃ and H₂O


Answer:


Cu(OH)₂ and H₂S


Justification:


1) Fe(OH)₃ and CuO: to form water Cu and Fe should react with each other. Being them two metals, they will not do that. So this reaction is not possible.

2) Cu(OH)₂ and H₂S: Being S a non metal and Cu a metal, they can react to form a the salt CuS, and water, as per this equation:


Cu(OH)₂ + H₂S → CuS + 2H₂O


3) MgO and Ca(OH)₂: Being Mg and Ca two metals they will not react with each other, so this reaction is not feasible.


4) SO₃ and H₂O: this is an acid oxide and water reaction which yields to an acid, as per this equation:


SO₃ + H₂O → H₂SO₄


Which is not producing water


2) Question: Based on reactivity, which of the following elements can replace aluminum (Al) in a compound during a single replacement reaction?

B
Ca
Zn
Fe


Answer: Ca.

Justification:

Only an element more reactive than Al will replace it in a compound during a single replacement reaction.

You may predict that being Ca an alkalyne earth element it is more reactive than Al and so Ca will replace Al.

Else,  you have to search a reactivity table, where you will find this order of reactivity among the metals:

Ca more reactive than Al

Al more reactive than Zn

Zn more reactive than Fe.


Being B a metalloid, its matallic character is low and it is less reactive than the other metals on the list.

Answer 2

Answer: 1. Option (b) is the correct answer.

              2. Option (b) is the correct answer.

Explanation:

1. The reaction between the given reactants will be as follows.

(a) $Fe(OH)_{3} + CuO \rightarrow Fe_{2}O_{3} + Cu(OH)_{2}$

(b) $Cu(OH)_{2} + H_{2}S \rightarrow CuS + H_{2}O$

(c) $MgO + Ca(OH)_{2} \rightarrow Mg(OH)_{2} + CaO$

(d) $SO_{3} + H_{2}O \rightarrow H_{2}SO_{4}$

Thus, out of the given options, the reaction $Cu(OH)_{2} + H_{2}S \rightarrow CuS + H_{2}O$ results in the formation of water.

2.  Base on reactivity series, the reactivity of some metals in the decreasing order is as follows.

                  K, Na, Ca, Mg, Al, Zn, Fe

Whereas B is a metalloid so, it will have properties of both metals and non-metals. Thus, boron (B) will also be less reactive than Al.

Therefore, out of the given options, Ca is more reactive than Zn and Fe.