Chemical Equations PDF

Chemical Equations: Tests for Anions When elements combine together to form a compound, it is said that a chemical reaction has taken place. A new substance is always formed when a chemical reaction takes place. Chemical Equations When a chemical reaction takes place, the substances that react toge...

Chemical Equations: Tests for Anions When elements combine together to form a compound, it is said that a chemical reaction has taken place. A new substance is always formed when a chemical reaction takes place. Chemical Equations When a chemical reaction takes place, the substances that react together are changed into new substances. The starting substances are called the reactants, the substances formed are called the products. For example: carbon + oxygen → carbon dioxide or; C + O → CO2 Balancing Chemical Equations **Definition: 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.** This tells us that all of the atoms that go into a reaction must come back out at the end. Atoms don’t just appear and disappear. Another way to say this is: **Definition: The Law of Conservation of Matter states that in any chemical reaction, matter is neither created nor destroyed but merely changes from one form to another.** If a certain number of atoms of an element go into a reaction, the exact same number of atoms of the element must be present at the end of the reaction. This is the reason for insisting a chemical equation must be balanced. Balance the equation CH4 + O2 → CO2 + H2O Left – hand side Right – hand side 1 C atom 1 C atom 4 H atoms 2 H atoms 2 O atoms 3 O atoms To get four H atoms on the right-hand side of the equation, put a ‘2’ before the H2O. CH4 + O2 → CO2 + 2H2O Left – hand side Right – hand side 1 C atom 1 C atom 4 H atoms 4 H atoms 2 O atoms 4 O atoms Oxygen atoms are not balanced. To get four oxygen atoms on the left-hand side, put a 2 before the O2. 1 CH4 + 2O2 → CO2 + 2H2O Left – hand side Right – hand side 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms The equation is now balanced. Tests for Anions in Aqueous Solutions To detect the presence of Chloride ions in aqueous solution 1. Add 2 cm3 of sodium chloride solution to a clean test tube. Using a dropping pipette add a few drops of silver nitrate solution. Record your observations in the table below. Write equations for any reaction occurring. 2. Add 2 cm3 of dilute ammonia solution to the contents of the test tubes at the end of the step 3. Record your observations in the table below. Chloride Observations upon addition of White precipitate forms AgNO3 solution Equation for reaction between the Ag+ + Cl- → AgCl↓ salt and AgNO3 Observation upon addition of NH3 Precipitate dissolves solution 2 To detect the presence of sulfate ions (SO42-) and sulfite ions (SO32-) in aqueous solution 1. Add 2 cm3 of sodium sulfate solution to a clean test tube labelled A and 2 cm3 of sodium sulfite solution to a clean test tube labelled B. Using a dropping pipette add 1 cm3 of barium chloride solution to each. Record your observations in the table below. Write equations for any reactions occurring. 2. Add 2 cm3 of dilute hydrochloric acid to the contents of the test tubes labelled A and B at the end of Step 1. Record your observations in the table below. Write equations for any reactions occurring. Sulfate Sulfite Observation upon White precipitate forms White precipitate forms addition of BaCl2 solution Equation for reaction Ba2+ + SO4 2- → BaSO4↓ Ba2+ + SO3 2- → BaSO3↓ between the salt and BaCl2 Observation upon White precipitate White precipitate addition of HCl solution remains disappears Equation for reaction BaSO4 + HCl → no BaSO3 + 2HCl → BaCl2 upon addition of HCl reaction + SO2 + H2O 3 To detect the presence of carbonate ions (CO32-) and hydrogencarbonate (HCO3-) in aqueous solution 1. Add 2 cm3 of sodium carbonate solution to a clean test tube labelled A, and 2 cm3 of sodium hydrogencarbonate solution to a clean test tube labelled B. 2. Using a dropping pipette add 2 cm3 of dilute hydrochloric acid to each test tube. Record your observations in the table below 3. Repeat steps 1 and 2 using the arrangement shown in the diagram. Record your observations in the table below. Write equations for the reactions occurring in the table below. 4. Add 2 cm3 of sodium carbonate solution to a clean test tube labelled C, and 2 cm3 of sodium hydrogencarbonate solution to a clean test tube labelled D. Using a dropping pipette add 2 cm3 of magnesium sulfate solution to each. Record your observations in the table below. Write equations for any reactions occurring. 5. Carefully heat the contents of test tubes labelled C and D at the end of the step 4. Record your observations in the table below. Write equations for any reactions occurring Carbonate Hydrogencarbonate Observations upon Fizzing/ effervescence Fizzing/ effervescence addition of HCl solution Observations and Carbonate ions Hydrogencarbonate conclusion from reacting with acid to ions react with HCl to limewater test give off a gas give off a gas Equation for reaction Co32- +2H+ → CO2 + H2O Ca(OH)2 + CO2 → between the salt and CaCO3 ↓ + H2O HCl 4  Observation upon White precipitate forms No precipitate forms addition of MgSO4 solution Equation for reaction Mg2+ + CO22- → MgCO3↓ Mg2+ + 2HCO3- → between the salt and Mg(HCO3)2 MgSO4 To detect the presence of nitrate ions (NO3-) in aqueous solution 1. Add 2 cm3 of potassium nitrate solution to a clean test tube. Using a dropping pipette, add 3 cm3 of cold saturated iron(II) sulfate solution. Using a dropping pipette, carefully add 2 cm3 of concentrated sulfuric acid slowly down the wall of the test tube. Do not mix the contents of the test tube. 2. Allow the mixture to stand undisturbed for a few minutes. Record your observations in the table below. Nitrate Observation upon addition of A brown ring is formed at the junction concentrated H2SO4 of the two layers 5 To detect the presence of phosphate ions in aqueous solution 1.Add 2 cm3 of disodium hydrogenphosphate(V) solution to a clean test tube. 2.Using a dropping pipette add approximately 6 cm3 of the clear ammonium molybdate reagent to the test tube. 3.Warm gently by placing in a beaker of water at a temperature not exceeding 40 C. Record any observations in the table below. 4.Add an equal volume of ammonia solution to the contents of the test tube at the end of step 2. Record your observations in the table below. Phosphate Observations upon addition of A yellow precipitate is formed ammonia solution 6