1.25: Write Word Equations and Balanced Chemical equations (Including State Symbols): For Reactions Studied in this Specification, For Unfamiliar Reactions Where Suitable Information is Provided

WRITING BALANCED CHEMICAL EQUATIONS:

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When balancing equations, there needs to be the same number of Atoms of each Element on either side of the equation:

• Work across the equation from left to right, checking one Element after another
• If there is a Group of Atoms (such as Nitrate group, NO3), which has not changed from one side to the other, then count the whole Groups, rather than counting the individual Atoms

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USING STATE SYMBOLS:

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State symbols are written after formulae in chemical equations to show which physical state each substance is in:

SOLID	LIQUID	GAS	AQUEOUS
(s)	(l)	(g)	(aq)

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Example 1:

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Aluminium (s)  +   Copper (II) Oxide (s)  →   Aluminium Oxide (s)  +   Copper (s)   UNBALANCED SYMBOL EQUATION:    Al     +     CuO     →     Al2O3     +     Cu ALUMINIUM: There is 1 Aluminium Atom on the left and 2 on the right so if you end up with 2, you must start with 2. To achieve this, it must be 2Al           2Al     +     CuO     →     Al2O3     +     Cu OXYGEN: There is 1 Oxygen Atom on the left and 3 on the right so if you end up with 3, you must start with 3. To achieve this, it must be 3CuO           2Al     +     3CuO     →     Al2O3     +     Cu COPPER: There is 3 Copper Atoms on the left and 1 on the right. The only way of achieving 3 on the right is to have 3Cu           2Al     +     3CuO     →     Al2O3     +     3Cu          The Equation is Now Balanced

Example 2:
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Magnesium Oxide (s)  +  Nitric Acid (aq)  →   Magnesium Nitrate (aq)  +   Water (l)   UNBALANCED SYMBOL EQUATION:  MgO   +   HNO3   →   Mg(NO3)2   +   H2O MAGNESIUM: There is 1 Magnesium Atom on the left and 1 on the right so there are equal number of Magnesium Atoms on both sides so is kept the Same           MgO   +   HNO3   →   Mg(NO3)2   +   H2O OXYGEN: There is 1 Oxygen Atom on the left and 1 on the right so there are equal number of Oxygen Atoms on both sides so is kept the same (remember that you are counting the Nitrate Group as separate Group, so do not count the Oxygen Atoms in this Group)           MgO   +   HNO3   →   Mg(NO3)2   +   H2O HYDROGEN: There is 1 Hydrogen Atoms on the left and 2 on the right. Therefore you must change HNO3 to 2HNO3           MgO   +   2HNO3   →   Mg(NO3)2   +   H2O          The Equation is Now Balanced

1.26: Calculate Relative Formula Masses (Including Relative Molecular Masses) (Mr) from Relative Atomic Masses (Ar)

RELATIVE ATOMIC MASS: Given by the symbol Ar

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• Calculated from the Mass Number and Relative Abundances of All the Isotopes of a particular Element

   

Example for Isotopes:
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The Table Shows Information about the Isotopes in a sample of Rubidium ISOTOPE NUMBER OF PROTONS NUMBER OF NEUTRONS PERCENTAGE OF ISOTOPE IN SAMPLE 1 37 48 72 2 37 50 28       Use Information from the Table to Calculate the Relative Atomic Mass of        this Sample of Rubidium. Give your Answer to One Decimal Place     (   72   x   85   )   +   (   28   x   87   )     ____________________________     =   85.6                              100     Relative Atomic Mass = 85.6

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RELATIVE FORMULA MASS: Given by the Symbol Mr

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• To calculate the Mr of a substance, you have to add up the Relative Atomic Masses of all the Atoms present in the formula

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Example:

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SUBSTANCE	ATOMS PRESENT	Mr
HYDROGEN ( H2 )	2 x H	( 2 x 1 ) = 2
WATER ( H2O )	( 2 x H ) + ( 1 x O )	( 2 x 1 ) + 16 = 18
POTASSIUM CARBONATE ( K2CO3 )	( 2 x K ) + ( 1 x C ) + ( 3 x O )	( 2 x 39 ) + 12 + ( 3 x 16 ) = 138
CALCIUM HYDROXIDE (  Ca(OH)2  )	( 1 x Ca ) + ( 2 x O ) + ( 2 x H )	40 + ( 2 x 16 ) + ( 2 x 1 ) = 74
AMMONIUM SULFATE ( (NH4)2SO4  )	( 2 x N ) + ( 8 x H ) + ( 1 x S ) + ( 4 x O )	( 2 x 14 ) + ( 8 x 1 ) + 32 + ( 4 x 16 ) = 132

1.27: Know that the Mole (Mol) is the Unit for the Amount of a Substance

MOLE: Measure of the amount of a substance

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• One Mole (1 Mol) is the amount of a substance that contains 6 x 1023 particles (Atoms, molecules or formulae) of the substance (6 x 1023 is known as the Avogadro Number

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Example:

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1 Mol of Sodium (Na) contains  6 x 1023  Atoms of Sodium

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1 Mol of Hydrogen (H2) contains  6 x 1023  Molecules of Hydrogen

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1 Mol of Sodium Chloride (NaCl) contains  6 x 1023  Formulae of Sodium Chloride

1.28: Understand How to Carry Out Calculations Involving Amount of Substance, Relative Atomic Mass (Ar) and Relative Formula Mass (Mr)

MOLE CALCULATIONS

          

1. CALCULATING MOLES

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EQUATION:

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Amount in Moles     =     Mass of Substance in Grams    ÷      Mr

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Example:

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SUBSTANCE	MASS	Mr	AMOUNT
NaOH	80 g	40	( 80 ÷ 40 ) = 2 Mol
CaCO3	25 g	100	( 25 ÷ 100 ) = 0.25 Mol
H2SO4	4.9 g	98	( 4.9 ÷ 98 ) = 0.05 Mol
H2O	108 g	18	( 108 ÷ 18 ) = 6 Mol
CuSO4.5H2O	75 g	250	( 75 ÷ 250 ) = 0.3 Mol

2. CALCULATING MASS

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EQUATION:

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Mass of Substance (Grams)     =     Moles    x      Mr

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Example:

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SUBSTANCE	AMOUNT	Mr	MASS
H2O	0.5 Mol	18	( 0.5 x 18 ) = 9 g
NaCl	3 Mol	58.5	( 3 x 58.5 ) = 175.5 g
K2CO3	0.2 Mol	138	( 0.2 x 138 ) = 27.6 g
(NH4)2SO4	2.5 Mol	132	( 2.5 x 132 ) = 330 g
MgSO4.7H2O	0.25 Mol	246	( 0.25 x 246 ) = 61.5 g

3. CALCULATING RELATIVE FORMULA MASS

EQUATION:

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Mr     =     Mass of Substance in Grams     ÷     Moles

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Example:

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10 Mol of Carbon Dioxide has a Mass of 440 g. What is the Relative Formula Mass of Carbon Dioxide?

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Relative Formula Mass = Mass ÷ Number of Moles Relative Formula Mass = 440 ÷ 10 =44                                                        Relative Formula Mass of Carbon Dioxide = 44