# Amount of substance

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• Created by: r98
• Created on: 04-04-16 15:26
What's the definition of relative atomic mass, Ar?
The weighted average mass of an atom of an element, taking into account its naturally occuring isotopes, relative to 1/12th the relative mass of an atom of carbon-12.
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What's the equation for the relative atomic mass, Ar?
Ar = (average mass of one atom of an element x 12) / (mass of an atom of carbon-12)
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What's the definition of relative molecular mass, Mr?
The mass of that molecule compared to 1/12th the relative atomic mass of an atom of carbon-12.
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What's the equation for the relative molecular mass, Mr?
Mr = (average mass of one molecule x 12) / (mass of an atom of carbon-12)
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What is the term relative fo4mula mass, Mr, used for?
Used for ionic compounds because they don't exist as molecules.
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What's the definition of the Avogadro constant?
The number of atoms in 12g of carbon-12.
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What's a mole?
The amount of substance that contains 6.022 x 10^(23) particles.
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How many moles of atoms does the relative atomic mass of any element, in grams, contain?
One mole of atoms.
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What does the relative molecular mass, or relative formula mass, of a substance in grams contain?
One mole of entities.
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What is the molar mass?
The mass per mole of substance.
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What are the units of molar mass?
kg mol^(-1) or g mol^(-1).
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The molar mass in g mol^(-1) is the same as what?
Numerically it's the same as Mr.
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What is the equation involving number of moles and mass?
Number of moles = (mass in g) / (mass of 1 mole in g)
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Is the volume of a gas fixed?
No, it changes with pressure and temperature.
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What's the ideal gas equation?
pV = nRT
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In the ideal gas equation, what are the units of P, pressure?
Pa.
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In the ideal gas equation, what are the units of V, volume?
m^(3).
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In the ideal gas equation, what are the units of T, temperature?
K.
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In the ideal gas equation, what are the units of R?
J K^(-1) mol^(-1).
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How do you convert celcius to kelvin?
Add 273 to celcius value.
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What is the empirical formula?
The formula that represents the simplest ratio of the atoms of each element present in a compound.
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What's the first step to find an empirical formula?
Find the masses of each of the elements presont in a compound.
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What's the second stage to find an empirical formula?
Work out the number of moles of atoms of each element.
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What's the third stage to find an empirical formula?
Convert the number of moles of each element into a whhole number ratio.
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How would you find the simplest whole ratio of elements, when the ratios are not easy to convert to whole numbers?
Divide each number by the smallest number you will end up with whole numbers.
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What information does the molecular formula give?
It gives the actual number of atoms of each element in one molecule of the compound.
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What does the molecular formula only apply to?
Substances that exist as molecules.
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Is the empirical formula always the same as the molecular formula?
No, there may be several units of the empirical formula in the molecular formula.
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How do you find the number of units of the empirical formula in the molecular formula?
Divide the relative molecular mass, Mr, by the relative mass of the empirical formula.
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What are organic compounds based on?
Carbon & hydrogen.
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What is combustion analysis?
The basic method of finding the empirical formulae of new compounds.
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What does combustion analysis involve?
Burning the unknown compound in excess oxygen and measuring the amounts of water, carbon dioxide and other oxides that are produced.
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What does a solution consist of?
A solvent with a solute dissolved in it.
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What does the concentration of a solution tell us?
How much solute is present in a known volume of solution.
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If the concentration of a solution is 1 mol dm^(-3), how many moles of solute are there?
1 mole of solute per cubic decimetre of solution.
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What is the equation for finding concentration?
Concentration = (number of moles) / (volume in dm3)
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What's the definition of stoichiometry?
The simple whole number ratios in which chemical species react.
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What state symbols are there?
(s) means solid; (l) means liquid; (g) means gas; (aq) means aqueous solution, dissolved in water.
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What is a good way of checking whether the equation is balanced?
The total mass should be the same on both sides of the equation.
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What is the name given to ions that do not take part in the reaction?
Spectator ions.
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During a titration, what does it show about the solution in the conical flask when the colour just changes, due to the addition of acid?
The solution in the conical flask is now neutral.
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What is the equation for calculating percentage atom economy?
% atom economy = (mass of desired product) / (total mass of reactants) x 100
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What does the atom economy tell us?
It tells us in theory how many atoms must be wasted in a reaction.
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What does the yield tell us?
It tells us about the practical efficiency of the process, how much is lost by; the practical process of obtaining a product, and as a result of reactions that do not go to completion.
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What is the equation for calculating the yield of a reaction?
Yield of chemical reaction = (the number of moles of a specified product) / (theoretical maximum number of moles of the product) x 100%
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What other equation can define the yield of a reaction?
Yield of chemical reaction = (the number of grams of a specified product obtained in a reaction) / (theoretical maximum number of grams of the product) x 100%
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## Other cards in this set

### Card 2

#### Front

What's the equation for the relative atomic mass, Ar?

#### Back

Ar = (average mass of one atom of an element x 12) / (mass of an atom of carbon-12)

### Card 3

#### Front

What's the definition of relative molecular mass, Mr?

### Card 4

#### Front

What's the equation for the relative molecular mass, Mr?

### Card 5

#### Front

What is the term relative fo4mula mass, Mr, used for?