AISS 2024 Mole Notes

Chemistry 6092 1 Ahmad Ibrahim Secondary School Name:___________________________________ ( ) Class:________ Date:__________ Chapter 9 : The Mole A Relative Atomic Mass (Ar) Definition: The relative atomic mass (Ar) of an atom is the average mass of one atom of that element compared to 𝟏 𝟏𝟐 of the mass of one carbon-12 atom. For example: Chlorine consists of 2 isotopes  Cl-35 (75%) and Cl-37 (25%) Ar of each chlorine atom = (75 𝑥 35)+(25 𝑥 37) 100 = 35.5 Check Point 1 Calculate the Ar of the following elements, with the given isotopic abundances. Element Isotopes Relative Abundance Ar of Element (a) Carbon C-12 98.89% (98.9 𝑥 12)+(1.11 𝑥 13) 100 = 12.0111 = 12.0 C-13 1.11% (b) Neon Ne-20 90.5% (90.5 𝑥 20)+(0.3 𝑥 21)+(9.2 𝑥 22) 100 = 20.187 = 20.2 Ne-21 0.3% Ne-22 9.2% (c) Potassium K-39 93.38% (93.38 𝑥 39)+( 0.01 𝑥 40)+( 6.61 𝑥 41) 100 = 39.1323 = 39.1 K-40 0.01% K-41 6.61% At the end of this section, you should be able to:  Define relative atomic mass, Ar. Formula, Stoichiometry, Mole Concept  Relative Atomic Mass  Relative Molecular/ Formula Mass  Percentage Composition of an Element in a Compound  Mass of an Element in a given mass of a Compound

Chemistry 6092 2 From the Periodic Table, Check Point 2 Write down the relative atomic mass for the following elements: (a) Sodium, Na 23 (b) Calcium, Ca 40 (c) Oxygen, O 16 (d) Copper, Cu 64 B Relative Molecular/ Formula Mass (Mr) Definition: The relative molecular / formula mass of a compound is the average mass of one molecule of that element of compound compared to 𝟏 𝟏𝟐 of the mass of one carbon-12 atom. C12 6 Atomic (mass) number = Relative atomic mass Proton number At the end of this section, you should be able to:-  Define relative molecular mass, Mr  Calculate relative molecular mass (and relative formula mass) as the sum of relative atomic masses

Chemistry 6092 3 For example: Mr = (2 x 14) + (8 x 1) + (1 x 12) + (3 x 16) = 96.0 What is the relative molecular mass, Mr, of this compound? 2 8 1 3 How many atoms of each of these elements does it contain? Ammonium Carbonate (NH4)2CO3 Name the different elements present in this compound, and write down the relative atomic mass, Ar, of each element Element: N Ar: 14 Element:H Ar: 1 Element: C Ar: 12 Element: O Ar: 16

Chemistry 6092 4 Check Point 3 1 Find the relative molecular mass of each of the following compounds: (a) Carbon dioxide, CO2 (b) Ammonium chloride, NH4Cl (c) Ammonium phosphate, (NH4)3PO4 (d) MgSO4.7H2O 2 Calculate the value of x in CuSO4.xH2O, given the Mr of CuSO4.xH2O is 250. C Percentage Composition of an Element in a Compound To calculate the percentage composition of an element in a compound: