SPM Form 4 Terminology and Concepts Chemical Formulae and Equations

7/31/2019 SPM Form 4 Terminology and Concepts Chemical Formulae and Equations

1/7

SPM Form 4Terminology and Concepts: Chemical Formulae and EquationsPart 1

1. Relative atomic mass, Ar is the atomic mass of an atom when compared to a standard atom

2. Standard atom:

Hydrogen scale: hydrogen is the lightest atom of all and the mass of one hydrogen atom wasassigned 1 unit.

Weakness of Hydrogen scale:

not too many elements can react readily with hydrogen, the reactive masses of some elements were not accurate, hydrogen exists as a gas at room temperature and has a number of isotopes with different masses.

Helium scale: the second lightest atom of all and the mass of one helium atom was assigned 1unit.

Weakness of Helium scale:

Mass of 1 helium atom = 4 times the mass of a hydrogen atom So, mass of 1 helium atom = 4 times 1/12 mass of a carbon atom helium exists as a gas at room temperature and helium is an inert gas.

Oxygen scale: chose as the standard atom to compare the masses of atoms

Weakness of Oxygen scale:

the existence of three isotopes of oxygen were discovered, natural oxygen (containing all the three isotopes) as the standard (Chemist) and used the isotopes oxygen-16 as the standard (Physicists).

Carbon scale: standard atom of comparison internationally.

a carbon-12 atom is 12 times heavier than an atom of hydrogen, used as the reference standard in mass spectrometers,

exists as a solid at room temperature, most abundant carbon isotope, happening about 98.89% and carbon-12 is close to the agreement based on oxygen.

3. Relative molecular mass, Mr of a substances is the average mass of a molecule (two or more

atoms) of the substances when compared 1/12 with of the mass of a carbon-12 atom.


2/7

4. Relative formula mass, Fr is for ionic compound which is calculated by adding up the

relative atomic masses of all the atoms.

5. Example:

Relative atomic mass, Ar of helium = 4

Relative molecular mass, Mr of CO2 = 12 + 2(16) = 44 Relative formula mass, Fr of NaCl = 23 + 35.5 = 58.5 Relative formula mass, Na2CO310H2O = 2(23) + 12 + 3(16) + 10 [2(1) + 16] = 286

SPM Form 4Terminology and Concepts: Chemical Formulae and Equations (Part 2)

1. Avogadro constant / Avogadros number is 6.02 x 1023

2. Atomic substances

Elementsall the particles are atoms. Example: zinc (Zn), sodium (Na), aluminium (Al) and all noble gases, argon (Ar), helium

(He) and neon (Ne).

RAM (Relative Atomic Mass) of Na = 233. Molecular substances

Covalent compoundsthe particles are molecules. Example: carbon dioxide (CO2), water (H2O) and non-metal elements, iodine (I2),

nitrogen (N2) and oxygen (O2). RMM (Relative Molecular Mass) of I2 = 127 + 127 = 254

4. Ionic substances

Ionic compoundsthe particles are ions. Example: sodium chloride (NaCl), hydrochloric acid (HCl) and potassium iodide (KI). RFM (Relative Formula Mass) of HCl = 1 + 35.5 = 36.5

5. Avogadros Law /Gas Law states that equal volumes of all gases contain the same number

of molecules under the same temperature and pressure.

Example: equal volumes of molecular hydrogen and nitrogen would contain the samenumber of molecules under the same temperature and pressure.

6. Volume of gas (dm3) = Number of moles of gas x Molar volume

7. Room temperature and pressure (r.t.p.) = 24 dm3 mol-1 (25C and 1 atm)


3/7

Example: What is the volume of 5.0 mol helium gas at s.t.p.? Volume of gas = Number of moles x Molar gas volume

= 5.0 mol x 24 dm3 mol-1

= 120 dm3

8. Standard temperature and pressure (s.t.p.) = 22.4 dm

3

mol

-1

(0C and 1 atm)

Example: What is the volume of 5.0 mol helium gas at s.t.p.? Volume of gas = Number of moles x Molar gas volume

= 5.0 mol x 22.4 dm3

mol-1

= 112 dm3

9. Mass (g) = Number of moles x Molar mass

10. Number of particles = Number of moles x Avogadro constant

11. Volume (dm

3

) = Number of moles x Molar volume

SPM Form 4Terminology and Concepts: Chemical Formulae and Equations (Part 3)

Empirical and Molecular Formulae

1. Empirical (simplest ratio of atoms of each element that present in the compound) and

molecular formulae (actual number of atoms of each element that are present in one molecule of

the compound) indicate:

the types of the elements the symbols of the elements and the ratio of atoms or moles of atoms of each element in a compound.

2. Molecular formula = (empirical formula)n

n is a positive number

Compound Molecular formula n Empirical formula

Carbon dioxide CO2 1 (CO2) = CO2

Ethane CH3 2 (CH3)2 = C2H6Propene CH2 3 (CH2)3 = C3H6

Glucose CH2O 6 (CH2O)6 = C6H12O6

Quinine C10H12NO 2 C20H24N2O2

3. Chemical formulae for covalent compounds.


4/7

Name Chemicalformula

Number of each element

Nitrogen gas N2 2 nitrogen atoms

Oxygen gas O2 2 oxygen atoms

Ammonia NH3 1 nitrogen atom and 3

hydrogen atomsWater H2O 2 hydrogen atoms and 1

oxygen atom

4. Cations are positively-charged ions.

Charge Cations Formula

+1 Ammonium ion NH4+

+1 * Copper(I) ion Cu+

+1 Hydrogen ion H+

+1 Lithium ion Li+

+1 * Nickel(I) ion Ni

+

+1 Potassium ion K+

+1 Silver ion Ag+

+1 Sodium ion Na+

+2 Barium ion Ba2+

+2 Calcium ion Ca2+

+2 * Copper(II) ion Cu2+

+2 * Iron(II) ion Fe2+

+2 * Lead(II) ion Pb2+

+2 Magnesium ion Mg2+

+2 * Manganese(II) ion Mn2+

+2 Nickel(II) ion Ni2+

+2 * Tin(II) ion Sn2+

+2 Zinc ion Zn2+

+3 Aluminium ion Al3+

+3 * Chromium(III) ion Cr3+

+3 * Iron(III) ion Fe3+

+4 * Lead(IV) ion Pb4+

+4 * Tin(IV) ion Sn4+

* refer to the Roman numerals

5. Anions are negatively-charged ions.

Charge Anions Formula

-1 Bromide ion Br-

-1 Chloride ion Cl-


5/7

-1 Chlorate(V) ion ClO3-

-1 Ethanoate ion CH3COO-

-1 Fluoride ion F-

-1 Hydride ion H-

-1 Hydroxide ion OH-

-1 Iodide ion I-

-1 Manganate(VII) ion MnO4-

-1 Nitrate ion NO3-

-1 Nitrite ion NO2-

-2 Oxide ion O2-

-2 Carbonate ion CO32-

-2 Chromate(VI) ion CrO42-

-2 Dichromate(VI) ion Cr2O72-

-2 Sulphide ion S2-

-2 Sulphate ion SO42-

-2 Sulphite ion SO32-

-2 Thiosulphate ion S2O32-

-3 Nitride ion N3-

-3 Phosphate ion PO43-

-3 Phosphite ion PO33-

6. Chemical formulae for ionic compounds

Name Chemical formula Number of

cation

Number of

anion

Zinc chloride ZnCl2 1 Zn2+ 2 Cl-Copper(II) sulphate CuSO4 2 Cu

2+ 2 SO42-

Aluminium sulphate Al2(SO4)3 2 Al3+

3 SO42-

7. Meaning of prefixes

Prefix Meaning

Mono- 1

Di- 2

Tri- 3

Tetra- 4Penta- 5

Hexa- 6

Hepta- 7

Octa- 8

Nona- 9

Deca- 10


6/7

8. Naming of chemical (non-metal) compounds with Greek numerical prefixes.

Non-metal compound Chemical formula

Carbon monoxide CO

Carbon dioxide CO2

Sulphur dioxide SO2Sulphur trioxide SO3

Carbon tetrachloride

(tetrachloromethane)

CCl4

Form 4Terminology and Concepts: Chemical Formulae and Equations (Part 4)

Chemical Equation

1. Importance of chemical equation:

The types of reactants; the physical conditions; the quantity of reactants and products and stated

in moles.nA + nB> pC + pD

2. Reactants are written in the left side of the reaction and products are written in the right side ofthe reaction.

Example 1:Word equation: Sodium hydroxide + sulphuric acid > sodium sulphate + water

Chemical equation: NaOH + H2SO4> Na2SO4 + H2O

Balancing equation: 2NaOH + H2SO4

> Na2SO4 + 2H2OComplete chemical equation: 2NaOH + H2SO4> Na2SO4 + 2H2O

Example 2:Word equation: Aluminium + copper(II) oxide > aluminium(III) oxide + copperChemical equation: Al + CuO > Al2O3 + Cu

Balancing equation: 2Al + 3CuO> Al2O3 + 3Cu

Complete chemical equation: 2Al + 3CuO> Al2O3 + 3Cu

Example 3:Word equation: Nitrogen + hydrogen ammonia

Chemical equation: N2 + H2 NH3

Balancing equation: N2 + 3H2 2NH3

Complete chemical equation: N2 + 3H2 2NH3

3. Information obtainable from chemical equations.

i) mass of reactants ii) volume of reacting gas iii) mass of products formed iv) volume of gas produced


7/7

Example:2 cm

3of lead (II) nitrate solution is added to excess of potassium iodide solution.

How many molecules of potassium nitrate will be formed?

[Relative atomic mass: N, 14; O, 16; K, 39; I, 127; Pb, 207; Avogadro's constant: 6.02 x

1023

mol-1

]

Step 1: Write a complete chemical equation.

Pb(NO3)2(aq) + 2KI(aq) > PbI2(s) + 2KNO3(aq) From the equation, 1 mole of Pb(NO3)2 reacts with 2 moles of KI formed 1 mole PbI2 of

and 2 moles of KNO3.

Step 2: Convert to moles.

No. of moles of Pb(NO3)2= Mass of Pb(NO3)2/ Relative molecular mass

= 2 / [207 + 2(14 + 3 x 16)]= 6.04 x 10-3 mol

Step 3: Ratio of moles.

Number of moles of KNO3/ Number of moles of Pb(NO3)2= 2/1

Number of moles of KNO3= (2 x 6.04 x 10

-3) / 1

= 12.08 x 10-3

mol

Step 4: Convert to the number of molecules of potassium nitrate.

Number of molecules of KNO3= 12.08 x 10

-3x 6.02 x 10

23

= 7.27 x 1021

SPM Form 4 Terminology and Concepts Chemical Formulae and Equations

Documents

Transcript of SPM Form 4 Terminology and Concepts Chemical Formulae and Equations