Question

Which of the following does NOT show the law of conservation of mass?

Answer 1

The correct option is $\boxed{\mathbf{B}}$  

Further explanation:

The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. For example, when wood burns, the mass of the ashes, and gases, equals the original mass of the charcoal and the oxygen on reaction. In this the mass of the product equals the mass of the reactant.  

When two or more elements chemically interact to make a new substance are called reactant and the new substance that is formed as the result of a chemical reaction is called product. Mass and matter may not be created or destroyed, but it can change forms to other substances like liquids, gasses, solids.

According to law of conservation of mass, the mass of product is equal to the mass of reactant.

${\text{Mass of product}} = {\text{Mass of reactant}}$

 

A)

In this the reactant Mg and oxygen reacts to form product MgO. ${\text{Mass of MgO}} = {\text{mass of Mg}} + {\text{mass of oxygen}}$…… (1)

Mass of Mg is 24g.

Mass of oxygen is 32g.

Mass of product (MgO) is 56 g.

Substitute these values in equation (1)

$\begin{aligned}{\text{56 g}}&= {\text{24 g}} + {\text{32 g}}\\{\text{56 g}}&= {\text{56 g}}\\\end{aligned}$  

Hence, it follows law of conservation of mass. Therefore, option a is incorrect.

B)

In this 24 mL of Mg burn in 32 mL of oxygen and produces 56 mL of MgO. Volumes cannot be added as there is variation in volume when different substances are added. So, the reactant is not equal to the product.It does not show the law of conservation of mass. Hence, option b is correct.

C)

In this 2 atoms of Mg reacts with 1 oxygen atom to form 2 unit of MgO.

The chemical reaction that shows production of MgO is as follows:

${\text{2Mg}} + {{\text{O}}_{\text{2}}} \to {\text{2 MgO}}$

Number of Mg atom is 2

Number of Oxygen atom is 2.

Number of MgO atom is 2.

The above reaction is balanced as number of atom in reactant is equal to number of atom in product. It follows law of conservation of mass. Hence, option c is incorrect.

D)

In this 1 atom of Mg react with 1 atom of O to produce 1 unit MgO.The number of atom of reactants and product are equals as MgO contains two atoms.It follows law of conservation of mass. Hence, option d is incorrect.

Learn more:

1. Balanced chemical equation: brainly.com/question/1405182

2. Number of covalent bonds does nitrogen formed with its unpaired: brainly.com/question/5974553

Answer details:

Grade: High School

Subject: Chemistry

Chapter: Chemical reaction and equation

Keywords: Law of conservation of mass, reactant, product, burn, mL,volume, g, Mg, O, MgO, oxygen.

Answer 2

I think the correct answer from the choices listed above is option B.  24 mL of Mg burn in 32 mL O2 to produce 56 mL of MgO does not show the law of conservation of mass. Volumes cannot be added because there are volume effects when you add different substances. So, the reactants is not equal to the product.