Stoichiometry - 2009
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- Mole
concept & Avogadro's constant |
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1.1.1 Describe the mole concept and apply it to
substances.
The mole concept applies to all kinds of particles: atoms, molecules,
ions, formula units etc. The amount of substance is measured in units
of moles. The approximate value of Avogadro's constant (L), 6.02 x
1023 mol-1, should be known.
1.1.2 Calculate the number of particles and the amount of substance
(in moles).
Convert between the amount of substance (in moles) and the number
of atoms, molecules or formula units. |
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Formulae |
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1.2.1 Define the term molar mass (M) and calculate
the mass of one mole of a species.
1.2.2 Distinguish between atomic mass, molecular mass and formula
mass.
The term molar mass (in g mol-1) can be used for all of
these.
1.2.3 Define the terms relative molecular mass (Mr) and relative atomic
mass (Ar).
The terms have no units.
1.2.4 State the relationship between the amount of substance (in moles)
and mass, and carry out calculations involving amount of substance,
mass and molar mass.
1.2.5 Define the terms empirical formula and molecular formula.
The molecular formula is a multiple of the empirical formula.
1.2.6 Determine the empirical formula and/or the molecular formula
of a given compound.
Determine the:
empirical formula from the percentage composition or from other suitable
experimental data
percentage composition from the formula of a compound
molecular formula when given both the empirical formula and the molar
mass |
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Chemical Equations |
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1.3.1 Balance chemical equations when all reactants
and products are given. Distinguish between coefficients and subscripts.
1.3.2 Identify the mole ratios of any two species in a balanced chemical
equation. Use balanced chemical equations to obtain information about
the amounts of reactants and products.
1.3.3 Apply the state symbols (s), (l), (g) and (aq). Encourage the
use of state symbols in chemical equations. |
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Mass and gaseous volume relationships in chemical reactions |
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1.4.1 Calculate stoichiometric quantities and use these to determine
experimental and theoretical yields. Mass is conserved in all chemical
reactions. Given a chemical equation and the mass or amount (in moles)
of one species, calculate the mass or amount of another species.
1.4.2 Determine the limiting reactant and the reactant in excess when
quantities of reacting substances are given. Given a chemical equation
and the initial amounts of two or more reactants:
identify the limiting reactant
calculate the theoretical yield of a product
calculate the amount(s) of the reactant(s) in excess remaining after
the reaction is complete.
1.4.3 Apply Avogadro's law to calculate reacting volumes of gases.
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- Solutions |
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1.5.1 Define the terms solute, solvent, solution
and concentration (g dm-3 and mol dm-3).
Concentration in mol dm-3 is often represented by square
brackets around the substance under consideration, eg [CH3COOH].
1.5.2 Carry out calculations involving concentration, amount of solute
and volume of solution.
1.5.3 Solve solution stoichiometry problems.
Given the quantity of one species in a chemical reaction in solution
(in grams, moles or in terms of concentration), determine the quantity
of another species. |
1.1 Mole concept & Avogadro's constant
1 Mole is equivalent to 6.023 x 1023 (Avogadro's number) units
of any substance.
| Mass of 1 mole of atoms (monatomic) |
Relative atomic mass in grams |
Symbol used: RAM |
| Mass of 1 mole of a compound |
Relative molecular mass in grams |
Symbol used: Mr |
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| Number of moles = |
mass |
| mass per mole |
1.2 Formulae
Chemical formula is the number of each type of atom in the smallest viable
unit of the substance.
Empirical formula is the simplest possible ratio of elements in a substance.
By definition the molecular formula will be an integral number of empirical
formulae (x1, x2 etc)
Examples:
| Compound |
Sulphuric acid
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Ethane
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hydrogen peroxide
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propane
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Ethene
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| formula |
H2SO4
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C2H6
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H2O2
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C3H8
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C2H4
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| empirical formula |
H2SO4
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CH3
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HO
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C3H8
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CH2
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1.3 Chemical Equations
The simplest ratio of the number of moles of reactants and products in
a chemical reaction. The balancing numbers are known as the coefficients
of the reaction. Use of balancing number is essential to fulfill the law
of conservation of matter. The overall set of balancing coefficients of
a chemical reaction is known as the reaction stoichiometry
State symbols: (s)-Solid , (l)-liquid, (g)-gas, (aq)-aqueous solution...ie
something dissolved in water. These should be included in all chemical
reactions.
1.4 Mass relationships in chemical reactions
The ratio of two reacting masses will be always maintained for a specific
chemical reaction. These mass ratios can be found from the stoichiometry
(balancing numbers) of the equation and the molar masses of the reactants
and products
Limiting reagent is a term used to describe the product which will completely
react leaving other reactants unused.
The reactant left behind unused at the end of a reaction is said to be
in excess
1.5 Solutions
Solvent - the dissolving medium (usually water)
Solute - the substance that is dissolved.
Solution - the above components when mixed together intimately so that
the solid phase becomes indistinguishable from the liquid phase.
Concentration - the amount of solute per amount of solvent (units mols
per dm3 (litre) or grams per litre)
Concentration = grams or moles/volume (also called Molarity)
Resources
Pop up calculator
Useful links
http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/stoichiometry/stoic_select_both.html
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