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Amount Of Substance Notes

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Unit 1; 2 Amount of Substance

CALCULATIONS PRECISION Unless specified otherwise;

• Calculations - 3sf

• Relative Ar, Mr, etc - 1dp

• Titration Volumes - 2dp

• Temperatures - 1dp

V. Important Definitions (LEARN) RELATIVE ATOMIC MASS Ar = average mass of 1 atom of an element

1/12th mass of an atom of 12C RELATIVE MOLECULAR MASS, Mr = average mass of a molecule

1/12th mass of an atom of 12C RELATIVE FORMULA MASS, Mr =

average mass of an entity 1/12th mass of an atom of 12C

Moles and the Avogadro's Constant The AVOGADRO CONSTANT, L, is defined as the number of atoms in exactly 12g of

12

C

L = 6.022 x 1023particle mol-1 A MOLE is an amount of substance that contains as many particles (atoms, molecules, ion, electrons) as there are atoms in exactly 12g of 12C Use with solids + gases Amount, in mol =
mass

Molar mass (Mr) Moles; unt mol Mass; units g Mr has no units

Use with solutions No. of moles = concentration (mol/dm3) x volume of solution (in dm3)

n=cxv

Atom Economy The ATOM ECONOMY of a chemical reaction is the proportion of reactants that are converted into useful products rather than waste products.
-Chemical process that have a high atom economy;

> are more efficient

> produce less waste Atom economy = total mass of desired products x 100

total mass of all products CHEMISTRY AS NOTES

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