1.2.2 molar mass

Mole

definition

the amount of any substance, which contains the same number of particles ⚠(atoms, ions, molecules, formulae or electrons) as there are carbon atoms in exactly 12 g of the carbon -12 isotope.

⭐ the Avogadro constant Screen Shot 2020-04-23 at 2.51.21 PM

The number of atoms per mole of carbon-12 isotopes: 6.02e23 mol^-1

1 mole of chlorine atoms =6.02e23 atoms

Molar mass

1 mole of chlorine molecules=6.02e23 molecules
=1.204e24atoms

the mass per mole of a substance,[g/mol]

Moles to Mass

FORMULAR: Mass= Moles x Molar Mass

m(g)=n(mol) x Mr(g/mol)

EXAMPLE

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Masses to Moles

FORMULAR: Moles= Mass/Molar Mass

n(mol)=m(g)/Mr(g/mol)

EXAMPLE

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Moles to Molar Mass

FORMULAR: Molar Mass= mass/ moles

Mr(g/mol)=m(g)/n(mol)

Significant figures

Scientific notation

only pays attention to the mantissa and ignore the 10^n part

multiplication and division Screen Shot 2020-04-23 at 3.51.51 PM

Addition and subtraction Screen Shot 2020-04-23 at 3.53.22 PM

multiplication and division

EXAMPLEScreen Shot 2020-04-23 at 3.55.13 PM

STEP 1: Find the number has the least significant numbers

STEP 2: The result must have the same number of significant figures as that number.

The use of scientific notation: when the significant figure is hard to achieve since they are a whole number/ large number Screen Shot 2020-04-28 at 11.07.39 AM Screen Shot 2020-04-28 at 11.07.58 AM

eg:7.100 x 10^23 has 4sf (zeros counts since they are at the right hand of the constant )

Zeros:

If it is at the left of a non-zero number: does not count.

If it is at the right of a non-zero number, only counts when there is a decimal place.

When it has decimal places: 0.498=4.98x10^-1

If it is measured by top ban balance, such as 560g, the zero counts. So it has 3 significant figures.

Apply molar mass calculation in chemical equations

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