# Chemical Equations and Tests for anions. Chemical Reactions Whenever two elements combine to form a compound a chemical reaction has taken place In a.

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Chemical Equations and Tests for anions

Chemical Reactions Whenever two elements combine to form a compound a chemical reaction has taken place In a chemical reaction the starting substances are called the Reactants and the substances formed are called the Products

Word Equations We generally wrote chemical reactions in words as word equations Carbon + Oxygen Carbon Dioxide Can you identify the reactants and products above?

Chemical Equations We can also use the chemical symbols of the substances to describe the chemical reaction that has taken place C + O 2 CO 2 The reactants are written on the left of the arrow and the products on the right this is generally always the case The arrow sign means “react to give” the + sign means “and”

Balancing Chemical Equations French Chemist Antoine Lavoisier found that the total mass of products is always equal to the total mass of reactants

Law of Conservation of Mass The total mass of the products of a chemical reaction is the same as the total mass of the reactants For example if 12 grams of Carbon dioxide react with 32 grams of oxygen 44 grams of carbon dioxide will be formed

Law of Conservation of Matter In any chemical reaction matter is neither created nor destroyed but merely changes from one form to another If there is a particular number of atoms at the start of a reaction then there must be the same number of atoms at the end of the reaction

Is the equation balanced? C + O 2 CO 2 How many C atoms are there on the left? How many are on the Right? How many O atoms are on the Left? How many are on the right?

Remember when balancing Equations You may adjust the number in front of the atoms/molecules, but you may not change the formula by changing the small number after an atom This method of balancing equations is known as balancing by inspection practice with question 6.1 (a) to (n) on p77

Tests for Anions in Aqueous Solutions Negative ions are also known as anions You learned off some common anions in chapter 5 The ions we will test for are : 1.Chloride ion (Cl - ) 2.Sulfate ion (SO 4 2- ) 3.Sulfite ion (SO 3 2- ) 4.Carbonate ion (CO 3 2- ) 5.Hydrogencarbonate ion (HCO 3 - ) 6.Nitrate ion (NO 3 - ) 7.Phosphate ion (PO 4 3- )

Because we are only testing to see if these anions are present and not to see how much of them is present this is known as Qualitative analysis Testing to see how much of a substance is present is known as Quantitative analysis

The various tests for anions are summarised in this table

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