2.1.3 - Amount of Substance Flashcards
What does amount of a substance mean?
Moles.
What is the symbol for moles?
mol
What is a mole?
The amount of a substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12 isotope.
What is Avogadro’s constant?
The number of particles per mole of a substance.
What is molar mass?
The mass per mole of a substance.
What is the molar mass equal to?
RFM
What is 1 tonne equal to?
10^6g
What is the molar gas volume?
The volume per mole of gas molecules.
What is the unit for molar mass?
g mol-1
What is the unit for molar gas volume?
dm3 mol-1
What is number of moles equal to in a solid?
Mass / molar mass
How do you work out the number of atoms in a substance?
- Times the number of moles by Avogadro’s constant.
2. Times that number by the number of atoms in one mole (3 in H2S).
What does multiplying moles by Avogadro’s constant give you?
The number of molecules.
Moles of a gas at RTP?
Volume / 24
Moles of a gas at STP?
Volume / 22.4
1dm3 is how many cm3?
1000cm3
1dm3 is how many liters?
1 litre
How many dm3 in 1m3?
1000dm3
How many cm3 in 1m3?
10^6 cm3
What is 0C in Kelvin?
273
How many kPa in 1atm?
101kPa
How many Pascals in 1kPa?
1000Pa
What is temperature and pressure at STP?
0C and 1 atm
What is the ideal gas law?
pV = nRT
What is pressure measured in?
Pa
What is volume measured in?
M3
What is n?
Number of moles.
What is R?
8.314 - gas constant
What is temperature measured in?
K
What is empirical formula?
The simplest whole number ratio of atoms to each element present in a compound.
What is molecular formula?
The number and type of atoms of each element in a molecule.
What does titration allow you to do?
FInd out exactly how much acid is needed to neutralise a quantity of alkali.
What is the titre?
The final reading of the burrette taken from the initial reading.
From where on the meniscus should you take a reading?
The bottom.
Number of moles is equal to what during titrations?
Concentration x volume
Metal + oxygen ->
Metal oxide
Metal + water ->
Metal hydroxide + hydrogen
Acid + metal ->
Metal salt + hydrogen
Acid + base ->
Metal salt + water
Acid + metal carbonate ->
Metal salt + carbon dioxide + water
How do you find g dm-3?
Work out the mass and then divide it by the volume.
What is water of crystallisation?
Number of water molecules chemically combined in a definite molecular proportion, with the salt in its crystal state.
What does hydrated mean?
A solid salt containing water of crystallisation.
What does anhydrous mean?
A salt which doesn’t contain water o crystallisation.
How do you work out the formula for a hydrated salt?
- Work out the number of moles from the water and salt.
- Then divide the moles of water by the moles of the salt.
Percentage yield =
Actual moles of product / theoretical moles of product (x100)
Why don’t we get 100% yield?
- Side reactions may occur, leading to by-products.
- Reactants may not be pure.
- Some of the reactant may have been left behind in the apparatus or used in the experiment.
Percentage atom economy =
Mass (g) of useful product / total mass of product (x100)
In which reactions and why do you get 100% atom economy?
In addition reactions as there is only one product produced.
In a substitution reaction how many products are created?
At least two.
What can low atom economy lead to?
- Waste products which cost money to separate and dispose of safely.
- Less sustainable as raw materials are in limited supply it is better to use them more efficiently to make them last longer.
Why are reactions at lower temperatures sometimes better?
Reactions with high energy demands cost a lot to maintain. Lower temperatures and pressures are cheaper to run and better for the environment.
What sort of materials are better for the environment?
Raw materials which come from renewable sources.
Describe the colour change with methyl orange?
Turns yellow to red when adding acid to alkali.
Describe the colour change in phenolphthalein?
Pink to colourless when adding acid to alkali.
%yield =
Actual moles of product / theoretical moles of product (x100)
Why don’t we get 100% yield?
- Reactions may be at equilibrium and may not go to completion.
- Side reaction may occur, leading to by-products.
- Reactants may not be pure.
What is the difference between atom economy and percentage yield?
Percentage yield is the practical conversion and what is actually converted. Atom economy tells you the proportion of desired products compared with all the products formed. It is theoretical.
%atom economy =
Mass of useful product / total mass (x100)
Describe the economic differences between high and low atom economy?
High atom economy has environmental and economic benefits as it means there are less waste products produced. This is good as it costs money to separate these undesired products. Low atom economy means the reaction is less sustainable.
When is atom economy always 100%
When there is one product.
Why is it good if reactions are sustainable?
Many raw materials are in limited supply so it makes sense to make them last as long as possible.
