Intro+Chem

** Acids and Bases in General **
Main points you must know:
 * Useful laboratory acids and their formulas: Hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4).
 * All acids contain hydrogen atoms, which can form free hydrogen ions in an acid solution.
 * Strong acids are those that readily form hydrogen ions in a solution.
 * Bases can be metal oxides, metal hydroxides, carbonates, hydrogen carbonates and ammonia.
 * Alkalis are soluble bases, which form hydroxide ions in a solution.
 * A solution, which is neither acidic nor alkaline, is a neutral solution.
 * Indicators such as universal indicator, litmus paper, phenolphthalein and methyl orange can be used to test for acidity or alkalinity.
 * Universal indicator can indicate how acidic or alkaline a solution is
 * The pH of a solution is a number, which indicates how acidic or how alkaline a solution is.
 * A neutral solution has a pH of 7 (green colour in universal indicator). Alkaline solutions have a pH greater than 7 (blue or purple colour) and acidic solutions have a pH less than 7 (yellow, orange or red colour).

** Common Reaction You Must Know **

 * 1) acid + base ---> salt + water
 * 2) acid + metal > salt + hydrogen gas
 * 3) acid + carbonate > salt + water + carbon dioxide gas
 * 4) acid + hydrogen carbonate > salt + water + carbon dioxide gas

** Salts: **
Salts consist of metal ions together with the negative ions from an acid.

A salt is produced when a metal ion takes the place of hydrogen in an acid, for example:

Sodium metal + hydrochloric acid ® sodium chloride + hydrogen gas

Sodium chloride is the salt.

Naming the salt:


 * Hydrochloric acid: metal name plus chloride e.g. potassium chloride
 * Nitric acid: metal name plus nitrate e.g. calcium nitrate
 * Sulfuric acid: metal name plus sulfate e.g. copper II sulfate

Writing Simple Equations
It’s now time to put your formula writing skill to the test and write formula equations from the word equations. At this stage you will not balance the equations, simply review how to write equations. Consider the following reaction:

hydrochloric acid + calcium --> calcium chloride + hydrogen gas This can be written HCl + Ca --> CaCl2 + H2 // Firstly, let’s review some Simple Rules for Writing Equations // : - hydrochloric acid – HCl - nitric acid – HNO3 - sulfuric acid – H2SO4 - water – H2O - carbon dioxide – CO2 - ammonia gas – NH3.
 * When the name of the element only is given, just write the symbol of the element – Ca.
 * When the substance is given as a gas, you will usually write the symbol plus the small 2 - H2.
 * When a compound is given, you will need to write the formula – CaCl2.
 * You will be expected to know the common compounds:

Balancing Chemical Equations

Rules for Balancing Chemical Equations:

Consider the reaction between hydrogen gas and oxygen gas.

Identify the reactants and products where necessary. ||  || __ Reactants __ : hydrogen gas and oxygen gas __ Product __ : water || Write down the word equations ||  || hydrogen gas + oxygen gas à water || Write down the chemical formulas ||  || H2 + O2 à H2O || Count the number of atoms of each element on each side of the arrow. If they are the same on both sides, the equation is balanced and complete. If not, move to rule five. ||  || left hand side right hand side 2 H 2 2 O 1 || Balance the number of atoms of each element on either side of the equation. This may require you to place numbers in front of reactants and/or products. You can’t place a number in any other place in the formula. ||  || Add a 2 in front of the H2O H2 + O2 à 2H2O This balances the oxygen but now the hydrogen needs re-balancing. Add a 2 in front of the H2. 2 H2 + O2 à 2 H2O || Do a final check on the number of atoms on each side to see that they are balanced. ||  || left hand side right hand side 4 H 4 2 O 2 This is now balanced. ||
 * RULE ONE
 * RULE TWO
 * RULE THREE
 * RULE FOUR
 * RULE FIVE
 * RULE SIX

__ Another Example __ :

When magnesium is burnt in air, oxygen gas combines with magnesium to produce magnesium oxide.

Rule 1: __reactants__: oxygen gas and magnesium; __products__: magnesium oxide

Rule 2: magnesium + oxygen gas à magnesium oxide

Rule 3: Mg + O2 à MgO

Rule 4: LHS RHS

1 Mg 1

2 O 1

Rule 5: balance oxygen by placing 2 in front of MgO: Mg + O2 à 2 MgO

re-balance magnesium by placing 2 in front of Mg: 2 Mg + O2 à 2 MgO

Rule 6: LHS RHS

2 Mg 2

2 O 2 The atoms are now balanced on both sides.