Chapter 6 - Balancing Equations

Law of Conservation of Mass

The Law of Conservation of Mass states that the total mass of the products of a chemical reaction is the same as the total mass of the reactants.​

The Law of Conservation of Matter

The Law of Conservation of Matter states that in any chemical reaction, matter is neither created nor destroyed but merely changes from one form into another.

How to balance equations

1. Work with the element before the equals sign and then refer to the other side

3. To find how many of what is needed divide out the element that is lacking

2. The subscript belongs to one element not 2 but the whole number refers to the entire line

What do with a fraction in a chemical equation

1. Multiply the line by 2

2. Only multiply the big number not the subscript

What do you do when there's an odd and even subscript

Multiply by the lowest common multiple

Anion

A negatively charged ion

Detect the presence of chloride in an aqueous solution (key steps)

Key Steps:

1. Chloride salt is dissolved in deionised qater

2. A clear solution is obtained

3. A few drops of silver nitrate solution are added to the chloride salt solution

Detect the presence of chloride in an aqueous solution (Observation)

Observation

1. The solution turns cloudy

2. A white material settles out of solution

- The name given to this is the preicipitate

Detect the presence of chloride in an aqueous solution (Explanation)

- In this experiement the precipitate formed is called silver chloride. It is formed when the silver ionds from the silver nitrate combines with the chloride ions from the chloride salt that are dissolved in the water

- The cloudiness observed is formed because silver nitrate does not dissolve in in water

Detect the presence of chloride in an aqueous solution (Confirmatory Test)

To confirm the white precipitate is silver chloride, dilute ammonia solution is added to the cloudy solution

Detect the presence of chloride in an aqueous solution (confirmatory test - Observation)

The cloudiness disappears because silver chloride is dilute in ammonia solution

Detect the presence pf sulfate and sulfite ions in an aqueous solution - Key steps

- A sulfite and a sulfate are dissolved in deionised water in separate test tubes

- A clear solution is obtained in each test tube

- A few drops of barium chloride are added to each solution

Detect the presence pf sulfate and sulfite ions in an aqueous solution (Observation)

The clear solution in each solution turns cloudy

- White solid material settles out of the solution

Detect the presence pf sulfate and sulfite ions in an aqueous solution (explanation)

The insoluble material formed is either barium sulfate or barium sulfite. These compounds are formed when the barium ions from the barium chloride solution combine with the sulfate ions and the sulfate ions dissolve in the water

Distinguish between sulfate and sulfite ions

- Dilute hydrochloric acid is added to each of the above test tubes containing white precipitate

- The cloudy precipitate remains in the test tube that contained the sulfate ions

- The clouidness disappears in the tube that contained the sulfite ions

Distinguish between sulfate and sulfite ions (Explanation)

Barium sulfate is insoluble in dilute HCL

Where as barium sulfite dissolves or more correctly reacts with the dilute hydrichloric acid

To detect the presence of carbonate ions and hydrogencarbonate ions in the aqueous solution (Key steps)

- Carbonate salt is placed in a boiling tube

- A one hold rubber stopper is inserted into the boiling tube

- The apparatus is set up

- The one holed rubber stop is removed and dilute hydrochloric acid is added to the carbonate salt in the boiling tube

- The one hold rubber stopper is replaced

To detect the presence of carbonate ions and hydrogencarbonate ions in the aqueous solution (Observation)

- A brisk effervescence (fizzing is observed as the acid comes into contact with the carbonate

_ The gas given off is seen bubbling through the limewater

- The limewater turns a milky colour

Explanation

1. The fizzing is caused by the carbonate ions reacting with the acid to give off gas

2. The fact that the limewater turns milky shows that the gas is carbon dioxide. Carbon dioxide reacts with limewater to form chalk (limestone)> The chemical name for chalk is calcium carbonate

Distinguishing between carbonate and hydrogencarbonate ions

- Magnesium sulfate solution is added to the solutions of the carbonate and the hydrogencarbonates salt in seperate test tubes

- A white precipitate is formed in the solution containing carbonate whilst no precipitate is formed in the solution containing hydrogencarbonate

Distinguishing between carbonate and hydrogencarbonate ions (Explanation)

- In solution of carbonate an insoluble predcipitate of magnesium carbonate is formed

- In the solution of the hydrogencarbonate no white precipitate is formed which means the magnesium hydrogencarbonate is soluble in water

To detect the presence of nitrate ions in an aqueous solution

The brown ring test

To detect the presence of nitrate ions in an aqueous solution (Procedure)

- A nitrate salt is dissolved in deionised water in a test tube

- Freshly prepared ion sulfate solution is added to the solution in the test tube

- Using a dropper concentrated sulfiric acid is added down the inside of the test tube. The test tube is slanted and since the sulfuric acid is so dense it settles at the bottom at the bottom of the test tube of the mixture

To detect the presence of nitrate ions in an aqueous solution (Observation)

- A brown ring is formed at the juction of the 2 layers

To detect the presence of nitrate ions in an aqueous solution (Explanation)

The brown ring is formed a result of nitrate ions being present and hence is the confirmation for the presence of the nitrate ion

- The brown colour is as a result of the formation of the substance FeSo4 No

To detect the presence of of phosphate ions in aqueous solution (Key steps)

- Phosphate salt is dissolved in deionised water in a test tube

- Amonium molydbate solution is added

- With the aid of a dropper a few drops of concentrated nitric acid is added to the tesgt tube

- Test tube is placed in warm water

To detect the presence of of phosphate ions in aqueous solution (Obsevations)

A yellow Precipiatet is formed

To detect the presence of of phosphate ions in aqueous solution (Explanation)

The yellow substance formed is called ammonium phosphommolydbate