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Die molkonsep

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Cobus de Beer

on 29 August 2013

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Transcript of Die molkonsep

Quantitative aspects of chemical change
Molar mass is the mass of 1 mole of any substance.
Molêre massa is die massa van 1 mol van 'n stof.
The molar mass is the relative atomic mass, molecular mass or formula mass of a substance given in grams.
Die molêre massa is die relatiewe attommassa, molekulêre massa of formule massa van 'n spesifieke stof in gram.
Symbol : M; Unit: g/mole
1 mole of carbon-12 atoms = 12 g carbon = 6.02 x 10^23 carbon atoms
Examples:
M(Na) = 23 g/mole
M(H2O) = 2 + 16 = 18 g/mole
M(NaCl) = 23 + 35.5 = 58.5 g/mole
M(CaCO3) = 40 + 12 + 3(16) = 100 g/mole
M(HCl) = 1 + 35.5 = 36.5 g/mole
Atomic, molecular and formula masses
1 mole of water contains 6,02 x 10^23 H2O molecules
1 mole of Mg contains 6,02 x 10^23 magnesium atoms
1 mole NaCl contains 6,02 x 10^23 NaCl formula units
1 mole NaCl contains 6,02 x 10^23 sodium ions (Na+) and 6,02 x 10^23 chloride ions (Cl- )
1 mole H2O contains 2 mole (2 x 6,02 x 10^23 ) of H atoms and 1 mole (6,02 x 10^23 ) of O atoms

The Mole Concept
The mole
Examples
Units of amounts in everyday life:
1 pair = 2 eggs
1 dozen = 12 eggs
1 gross = 144 eggs
1 million = 1 000 000 eggs
1 mole = 602 000 000 000 000 000 000 000 eggs

A number scientists use to indicate a specific amount of a substance.
Getal wat wetenskaplikes gebruik om 'n sekere hoeveelheid van 'n stof aan te dui.
SI unit for amount of substance.
SI eenheid vir hoeveelheid van 'n stof.
Chemists measure the number of atoms/molecules in moles.
Avogadro's number: 6.02 x 10^23.
1 mole contains 6.02 x 10^23 particles (atoms or molecules).



How many particles in a mole?
Hoeveel deeltjies in 'n mol?
Relative atomic mass (Ar) - mass of one atom of that element.
Relatiewe atoommassa (Ar) - massa van een atoom van 'n element.
The mass of one hydrogen atom is 1.66 x 10^-24 g.
The values are to small, therefore we rather use a relative scale.
Measured in atomic mass units (amu) or u.
Gemeet in atoomassa eenheide (amu) of u.
We use the C-12 isotope as the standard mass and all other masses are relative to the mass of a C-12 isotope.

Relative molecular mass (Mr) - mass of one molecular element or compound.
Relatiewe molekulêre massa (Mr) - massa van een molekule.
(Sum of atomic masses of all the atoms in a molecule or formula.)
(Som van die atoommassa van al die atome in die molekule of formule.)

Relative atomic mass of Na: Ar (Na) = 23 u
Relative molecular mass of water: Mr (H2O) = 18 u
Relative formula mass of NaCl: Mr(NaCl) = 58,5 u

Calculate the relative formula mass of the following chemical substances:
CH4
Al2(SO4)3
CuSO4.5H2O

Molar Mass
The mole is the amount of substance that contains the same number of elementary units (atoms molecules or other particles) as there are atoms in exactly 12 grams of carbon-12.

Die mol is die hoeveelheid van 'n stof wat dieselfde aantal elementêre eenhede (atome, molekules of ander deeltjies) bevat as wat daar atome is in presies 12 gram van koolstof-12.
Calculations using mole
The equation that links the mass of a substance to the number of moles present is:

number of moles (n) = mass (m) / molar mass (M)

Example 1:
How many moles of NaOH are there in 60g of sodium hydroxide?
Example 2:
Calculate the mass of 0.5 mole of ammonium nitrate.
Example 3:
What is the mass of 0,5 mol H2O?

Percentage composition
Table of information on products - composition of product - how many grams of fat, protein in each 100 grams.

Use same principle to calculate percentage composition of a compound.

% Element = (atomic mass) / (molar mass) x 100

Example: Carbon dioxide
Empirical formula
Empirical formula:
Simplest whole number ratio of the elements making up the compound.

Empirical formula calculations:
Percentage composition - assume 100g of a product.
g/100g
n=m/M
simplest ratio

Example:
Determine the empirical formula of a compound containing 56.5% K, 8.7% C and 34.8% O.

Molecular formula
Molecular formula:
Total number of atoms of each element present in a molecule of a compound.
Can differ from the empirical formula.
The actual molecular formula could be a multiple of the empirical formula
Can be determined if the empirical formula and the molar mass is known.

Example:
Calculate the molecular formula of a compound with molar mass 88.0 g/mole and percentage composition of 53.35% C, 9.09% H and 36.36% O.


Hydrates
Hydrated salts:
The crystals of some salts have a specific number of water molecules attached to them - water of crystallization.

Anhydrous salt:
Salt without water, water released after heating

Can calculate the number of moles of water of crystallization in a hydrated salt if we know the percentage composition.

Example:
Calculate the number of moles of water of crystallization in hydrated aluminium chloride (AlCl3.nH2O) if 44.72% of the mass is water.
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