have you ever tried counting the number of rice particles in your bowl?
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Have you ever tried counting the number of rice particles in your bowl?. Relative Masses of Atoms and Molecules. Masses of Particles in Chemistry. the mass of a hydrogen atom is 0.000 000 000 000 000 000 000 0014g very small values and very inconvenient to write - PowerPoint PPT PresentationTRANSCRIPT
Have you ever tried counting the number of rice particles in your bowl?
Relative Masses of Atoms and Molecules
Masses of Particles in Chemistrythe mass of a hydrogen atom is
0.000 000 000 000 000 000 000 0014g
very small values and very inconvenient to write
so, scientists do not use these actual masses in their calculation
Relative Massesscientists overcome this by
comparing the masses of atoms with the mass of a carbon-12 atom
it is a ratio and has no unit
Relative Atomic Mass
The relative atomic mass (Ar) of an element is
the average mass of one atom of the element when compared with of the mass of an atom of carbon-12.
112
NO UNITS!
Relative Molecular Massmany elements and compounds
exist as molecules
the mass of a molecule is found by
adding the relative atomic masses of all atoms in the molecule
this mass is known as the relative molecular mass (Mr)
Relative Molecular Mass
The relative molecular mass (Mr) of a molecule is
the average mass of one molecule of the substance when compared with of the mass of an atom of carbon-12.
112
NO UNITS!
Relative Formula Massionic compounds consist of ions, not molecules
instead of relative molecular mass, we use the term relative formula mass
the relative formula mass of an ionic compound is found by
adding the relative atomic masses of all the atoms in the formula
Let’s try! TB P137 Q2
Calculate the relative molecular/formula masses of the following substances.
a. H2O
b. NH3
c. O2
d. CaCO3
e. H2SO4
f. Cu(NO3)2
g. (NH4)2SO4
h. CuSO4.5H2O
Percentage Compositionthe percentage composition of an element in a
compound can be calculated from:the formula, and the relative atomic masses of its elements
percentage of an element in a compound =number of atoms of the element in the formula
x Ar of the element
Mr of the compoundx 100%
Calculating the mass of an element in a compound
mass of an element in a compound =number of atoms of the element in the formula
x Ar of the element
Mr of the compoundx mass of the sample
Calculating the mass of water in a compound
hydrated compounds are compounds that contain water (“water of crystallisation”)
crystals are dry because water is part of the crystal structure
mass of water in a compound =number of water
molecules in the formulax Mr of H2O
Mr of the compoundx mass of the sample
Let’s try! TB P140 Q2
Calculate
a. the percentage of calcium and oxygen in calcium carbonate, CaCO3, and
b. the percentage of oxygen in CuSO4.5H2O
Let’s try! TB P140 Q3
Calculate the mass of
a. calcium in 25 g of calcium carbonate, CaCO3, and
b. chlorine in 27 g of copper(II) chloride, CuCl2