Question

A student combined two colorless aqueous solutions. One of the solutions contained Na2CO3 as the solute and the other contained HCl. The chemical reaction that took place is represented by the equation above. What experimental result would be evidence that a chemical reaction took place when the solutions were combined?

Answer 1

Answer: The formation of effervescence is an evidence to a chemical reaction.

Explanation:

Sodium carbonate is a salt and hydrochloric acid is an acid.

When a carbonate reacts with an acid, it releases carbon dioxide gas

The chemical equation for the reaction of sodium carbonate and hydrochloric acid follows:

$Na_2CO_3+2HCl\rightarrow 2NaCl+H_2O+CO_2$

By Stoichiometry of the reaction:

1 mole of sodium carbonate reacts with 2 moles of hydrochloric acid to produce 2 moles of sodium chloride, 1 mole of water and 1 mole of carbon dioxide gas

When the two solutions are mixed, effervescence is produced due to the release of carbon dioxide gas

Hence, the formation of effervescence is an evidence to a chemical reaction.

Answer 2

So the evidence that a chemical reaction took place: the formation of bubbles

Further explanation

In the matter of a substance, there is a process of change.

2 changes occur in the mater: physical changes and chemical changes

Classification uses the principle of the initial and final state of the substance.

Physical changes are changes in the matter which in the process do not cause new substances. So the properties of the particles remain the same.

Generally, the physical changes that occur are changes in shape / size and changes due to heating, or changes in volume

Example: melting, freezing, boiling

Chemical changes are changes in the process that produce new substances that are different from the initial / forming substances. Chemical changes are usually known as chemical reactions. So there are products / reactions and reactants and there is a change in the molecule / particle

Chemical reactions can be known from the results of the reaction after the two solutions / compounds are mixed.

This chemical change can be :

• 1. Change the color of the solution

New colors emerge from mixing 2 solutions

• 2. Formation of a precipitate

We use the Solubility Rules to determine whether a precipitation reaction will occur or not

• 3. Release heat

Occurs in the exothermic or endothermic process

• 4. release gas (bubbles)

bubbles occur because the gas in the solution that comes out

The reaction between Na₂CO₃ and HCl:

2HCl + Na₂CO₃ -> 2NaCl + CO₂ + H₂O

From the reaction results obtained NaCl and CO₂

NaCl itself is a soluble compound salt that may not be visible after mixing occurs, while CO₂ is a gas that can be seen from the formation of bubbles in the solution

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