Chemistry C2 3.2 Masses of atoms and moles. 0.0 / 5 ? ChemistryAtoms and compoundsGCSEAQA Created by: Atlanta and JacobCreated on: 08-12-16 18:27 What do we use to compare the masses of atoms? Relative atomic masses. 1 of 18 What is the relative atomic mass of an element? An average value for the isotopes of an element. 2 of 18 How do e work out the relative formula mass of a compound? By adding up the relative atomic masses of the elements in it. 3 of 18 What is one mole of any substance? Its relative formula mass in grams. 4 of 18 Why do we use relative atomic masses (A_r) in calculations? Because atoms are much too small to weigh. 5 of 18 Where are relative atomic masses often shown? In the periodic table. 6 of 18 In the laboratory, what do we usually weigh substances in? Grams (g). 7 of 18 What is the relative atomic mass of an element in grams called? One mole of atoms of the element. 8 of 18 The relative atomic mass of an element (A_r) is an average value that depends on what? The isotopes the element contains, however when rounded to a whole number it is often the same as the mass number of the main isotope of the element. 9 of 18 What do we use an atom of 12 over 6 C for? As a standard atom and compare the masses to of all other atoms with this. 10 of 18 How is the relative formula mass (M_r) of a substance found? By adding up the relative atomic masses of the atoms in its formula. 11 of 18 What is a mole of a substance? The relative formula mass of a substance in grams. 12 of 18 Why is using moles of substances useful? It is useful when we need to work out how much of a substance reacts or how much product we will get. 13 of 18 What is the mass of one mole of sodium atoms? 23g. 14 of 18 Why is the relative atomic mass of chlorine not a whole number? It has (two main) isotopes and the relative atomic mass is an average value. 15 of 18 Calculate the relative formula mass (M_r) of sodium sulfate, Na_2SO_4. (Relative atomic masses: Na=23, S=32, O=16). (23x2)+32+(16x4)=142. 16 of 18 What is the mass of one mole of magnesium carbonate, MgCO_3? (Relative atomic masses: Mg=24, C=12, O=16). 24+12+(16x3)=84g (must have g). 17 of 18 **MAKE SURE THAT YOU CAN CALCULATE THE RELATIVE FORMULA MASS (M) OF A COMPOUND FROM ITS FORMULA** ** 18 of 18
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