13.2 conservation of atoms and mass in reactions 13.2 preservation of atoms and mass in reaction

13.2 conservation of atoms and mass in reaction (ESADV)

In a chemistry reaction the complete mass of all the building material taking component in the reaction remains the same. Also, the variety of atoms in a reaction continues to be the same. Mass can not be developed or damaged in a chemistry reaction.

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legislation of conservation of fixed

The regulation of preservation of mass states that the complete mass of building materials taking part in a chemical reaction is conserved throughout the reaction.

Table 13.1 illustrates this law for the decomposition the hydrogen peroxide.

The conservation of atom in chemical reactions

We will use the reaction the hydrogen and also oxygen to type water in this activity.


Coloured modelling clay rolled into balls or marbles and prestik to represent atoms. Each colour will represent a various element.


Build your reactants. Use marbles and also prestik or modelling clay to stand for the reactants and put this on one next of your table. Do at the very least ten (( extH_2)) units and at least five (( extO_2)) units.

Place the ( extH_2) and ( extO_2) units on a table. The table represents the “test tube” wherein the reaction is walking to take place.

Let the reaction take place. Every person can now take the ( extH) and also ( extO) unit and also use castle to do water units. Break the ( extH) and ( extO) units apart and build ( extH_2 extO) units v the parts. These are the products. Ar the commodities on the table.

When the “reaction” has finished (i.e. When all the ( extH) and also ( extO) units have actually been used) count the number of atoms (( extH) and ( extO)) and complete the table.

What perform you notification about the number of atoms for the reactants, compared to the products?

Write a balanced equation for this reaction and use your models to develop this equation.


Number the atoms




Number of molecules


You should have noticed that the number of atoms in the reactants is the exact same as the variety of atoms in the product. The variety of atoms is conserved during the reaction. However, girlfriend will additionally see that the variety of molecules in the reactants and also products space not the same. The variety of molecules is not conserved throughout the reaction.

Conservation that matter


To prove the legislation of conservation of matter experimentally.


Reaction 1:

3 beakers; silver nitrate; salt iodide; massive meter

Reaction 2:

hydrochloric acid; bromothymol blue; salt hydroxide solution; mass meter

Reaction 3:

any effervescent tablet (e.g. Cal-C-Vita tablet), balloon; rubber band; fixed meter; check tube; beaker

Always be cautious when managing chemicals (particularly solid acids choose hydrochloric acid) as you deserve to burn yourself badly.


Reaction 1

Solution 1: In one of the beakers dissolve ( ext5) ( extg) of silver- nitrate in ( ext100) ( extmL) the water.

Solution 2: In a 2nd beaker, dissolve ( ext4,5) ( extg) of salt iodide in ( ext100) ( extmL) that water.

Determine the fixed of each of the reactants.

Add systems 1 to equipment 2. What carry out you observe? has a chemical reaction taken place?

Determine the fixed of the products.

What do you notification about the masses?

Write a well balanced equation for this reaction.

Reaction 2:

Solution 1: Dissolve ( ext0,4) ( extg) of sodium hydroxide in ( ext100) ( extmL) the water. Include a few drops that bromothymol blue indicator come the solution.

Solution 2: measure ( ext100) ( extmL) that ( ext0,1) ( extmol·dm$^-3$) hydrochloric acid solution into a 2nd beaker.

Determine the mass of the reactants.

Add little quantities of solution 2 to equipment 1 (you deserve to use a plastic pipette because that this) till a colour adjust has taken place. Has a chemical reaction bring away place?

Determine the mass of hydrochloric mountain added. (You execute this by weighing the remaining solution and subtracting this native the beginning mass)

Compare the mass before the reaction to the complete mass ~ the reaction. What perform you notice?

Write a balanced equation because that this reaction.


Reaction 3

Half to fill a big test tube through water.

Determine the massive of the check tube and also water.

Break one effervescent tablet in 2 or 3 pieces and place lock in a balloon.

Determine the fixed of the balloon and tablet.

Fit the balloon tightly to the check tube, being cautious to no drop the components into the water. You have the right to stand the test tube in a maker to assist you perform this.

Determine the total mass of the test tube and also balloon.

Lift the balloon so the the tablet goes into the water. What perform you observe? has actually a chemical reaction bring away place?

Determine the fixed of the test tube balloon combination.

What carry out you observe about the masses before and also after the reaction?



Fill in the complying with table because that the complete mass of reactants (starting materials) and also products (ending materials).

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Add the masses for the reactants for each reaction. Perform the very same for the products. For each reaction compare the massive of the reactants to the fixed of the products. What carry out you notice? Is the massive conserved?

In the experiment above you need to have discovered that the complete mass at the begin of the reaction is the very same as the mass at the finish of the reaction. Mass walk not show up or disappear in chemical reactions. Fixed is conserved, in various other words, the full mass you begin with is the complete mass you will end with.

Conservation that atoms and mass

Complete the complying with chemical reactions to display that atoms and mass space conserved. For each reaction provide the complete molecular mass of the reactants and the products.