Please enable JavaScript.
Coggle requires JavaScript to display documents.
mole concept and stoichiometry chemistry chapter 7 - Coggle Diagram
mole concept and stoichiometry chemistry chapter 7
Relative atomic mass
Atoms are very small.It is incovenient to describe their masses using units like grams and kilograms.Instead we compare the mass of atoms.this gives us their relative masses
Carbon-12 is taken as the standard atom.All the other atoms are compared with this standard atom
the relative atomic mass(A) of an element is the average mass of 1 atom of that element relative to 1/12 of an atom of carbon-12
Carbon-12 has a relative atomic mass of 12.Magnesium has a relative atomic mass of 24.This means that a magnesium atom is 24 times as heavy as 1/12 of an atom of carbon-12
Calculating relative atomic mass of elements with isotopes
Some elements are found in nature as a mixture of isotopes with different atomic masses.Thus, the relative atomic mass is determined by the average atomic mass of the isotopes
The relative atomic mass of chlorine is given in decimal form.This is because there are only 2 stable isotopes of chlorine- chlorine-35 and chlorine-37
A sample of chlorine usually contains 75% of chlorine-35 and 25% of chlorine-37.We can calculate the relative atomic mass of chlorine.Relative atomic mass of chlorine=(75/100 x 35)+(25/100 x 37)=35.5
Relative molecular mass of a molecular substances is the average mass of 1 molecule of that substance relative to 1/12 the mass of an atom of carbon-12
H2O=2H 1O
relative atomic mass of 2H = 2x1=2
relative atomic mass of 1O=1x16=16
Relative atomic mass=2+16=18
Relative formula mass
Ionic compounds do no exist as molecules. We use term relative formula mass to refer to the relative mass of an ionic compound
The relative formula mass of an ionic compound is the average mass of 1 unit of that compound relative to 1/12 the mass of an atom of carbon-12
Calculating percentage mass
Percentage mass=number of atoms of the element in the formula x relative atomic mass/molecular mass of compound
The percentage mass of an element in a compound can be calculated using the above formula
What is the mole
Defining mole in terms of the Avogadro constant
The word "mole" is used to count the number of particles.1 mole represents 6.02x10 to the power of 23 particles, that is too many particles to count.This number is called the Avogrado constant as this constant does not change
The particles that is being referred in Avogrado constant can be atoms, molecules, ions and sub-atomic particles such as electrons
The symbol for the mole is mol. The number of moles from the number of particles are found through this formula
Number of moles=number of particles divided by 6.02x10 to the power of 23
Moles and molar mass
One mole of any substance has a mass equal to its relative atomic mass, relative molecular mass or relative formula in grams.This mass is the molar mass of the substance
The unit for molar mass is g/mol
Eg of relative atomic or molecular mass of some substances are iron as its molecular mass and atomic mass are 56 but its molar mass is 56 g/mol
Number of moles of a substance=mass of substances in g divided by molar mass of the substance in g/mol
Moles and gaseous volumes
1 mole of any gas occupies a volume of 24dm cube at room temperature and pressure
Number of moles of gas=volume of the gas in dm cube divided by 24dm cube
Concentration of a solution is the amount of a solute dissolved in a unit volume of the solvent
Concentration in g/dm cube
concentration in g/dm cube=mass of solute in g divided by volume of solvent in dm cube
Concentration in mol/dm cube=concentration in g/dm cube divided by molar mass of solute in g/mol