sc14, quantative analysis (paper 1) Flashcards
what is the yield
the mass of a product made in a chemical process
what are the two main rules in any chemical reaction
- no atoms are gained or lost
- the total mass stays the same
what is the theoretical yield
for a given mass for a limiting reactant, you can make only a maximum mass of a product
what is the actual yield
the mass of the product that you really get at the end of a chemical process
true or false: the actual yield is always less than the theoretical yield
true
true or false: the actual yield is always more than the theoretical yield
false
how do you calculate the percentage yield
(actual yield / theoretical yield) x 100
true or false: a higher percentage yield means more mass is made
true
true or false: a lower percentage yield means less mass is made
true
true or false: a higher percentage yield means less mass is made
false
true or false: a lower percentage yield means more mass is made
false
what are the three main reasons for now obtaining the theoretical yield
- incomplete reactions
- side reactions
- practical losses
what does a complete reaction mean in terms of not obtaining the theoretical yield
reaction hasn’t finished or reached equilibrium
what does a side reaction mean in terms of not obtaining the theoretical yield
competing/unwanted reactions can cause by-products to be mae
what does a practical loss mean in terms of not obtaining the theoretical yield
losses during purification (e.g filtration) or transfers (e.g liquid left behind in containers)
what is meant by the atom economy
a way of measuring the number of atoms wasted when making a substance
how do you calculate atom economy
(total Mr of desired products/total Mr of all products) x 100
what does a 100% atom economy mean
all atoms in the reactants can be converted to the desired products
what are the only two circumstances in which a 100% atom economy can happen in
- there is only one product (e.g manufacturing ammonia)
- all by-products are used (e.g as feedstock (reactants) for other products)
how do you work out the titre
end reading - start reading
what are concordant titres
titres identical or very close together (within 0.1cm3)
what does the volume occupied by a gas depend on
- the number of particles present
- the tempurature of the gas
- the pressure of the gas
what is the molar volume
the volume occupied by one mol of any gas at room tempurature and atmospheric pressure
how do you work out the volume of gas
volume of gas (dm3 or cm3) = molar volume (dm3/mol or cm3/mol) x amount (mol)
what is 1 dm3/mol in cm3/mol
1000
what is 1 cm3/mol in dm3/mol
0.001
