C5.1 Flashcards
What is yield of product?
Mass of the product made in a chemical process
What is the theoretical yield?
Maximum mass possible to make from a given mass of reactants
How do you calculate the theoretical yield?
1) calculate the Mr of the limiting reactant and the products
2) calculate the sum of the limiting reactant Mr with the stoichiometry and products Mr
3) theoretical yield = (mass of the limiting reactant (given)/sum of Mr of limiting reactant) x sum of Mr of products
N2 + 3H2 > 2NH3, theoretical yield of ammonia when 12g of hydrogen reacts with excess nitrogen
12/6 x 34 = 68g
What is the actual yield?
Mass of product you actually make in a chemical reaction
Usually less than the theoretical yield
How do you calculate percentage yield?
Percentage yield = actual yield/ theoretical yield x 100
What factors affect the percentage yield?
- reactants may react in different ways, side products form, than expected so percentage will be lower
- reaction may not go to completion, mainly in reversible reactions
- transfer losses
- impure reactants
What is atom economy?
Measure of how many atoms in the reactants form a desired product
What is the equation for atom economy?
Atom economy = sum of Mr of the desired product / sum of Mr of all products x 100
What are the factors to consider when doing a reaction?
Yield of product
Atom economy of the reaction
Rate of reaction
Usefulness of by products
Equilibrium position
Reversible or not
What is a by-product?
Substance formed in a reaction in addition to the desired product
Sometimes can be useful and so can be sold
Therefore atom exonomybinceeases as the byproduct becomes a desired products
How to calculate cm^3 to dm^3?
/ 1000 for cm^3 to dm^3
x 1000 for dm^3 to cm^3
How do you calculate concentration?
Concentration in mol/dm^3 = moles / volume dm^3 (May have to convert from cm^3)
What is a titration?
A method to determine the concentration of a solution
How do you prepare for a titration?
- use either a measuring cyclinde or volumetric pipette (more accurate) to measure 25cm^3 of the alkali solution for the conical flask
- clamp a brunette vertically and fill it with acid
- add a few drops of indicator to the alkali in a conical flask
How do you carry out a titration?
1) add a know volume of acid to a conical flask and add a few drops of an indicator (phenolphthalein)
2) then add acid to a burette
3) slowly add the acid from the tap of the burette into the conical flask until it changes colour (the endpoint)
4) take an intital and final reading from the burette
5) the difference between the two readings is the TITRE VALUE (volume of acid added to the alkali)
6) record the tires to 2d.p, the reading must be from the bottom of the meniscus
7) first titration is normally a rough run after add the acid
within a few cm^3 of the rough titer value then slowly add a few drops
8) calculate a mean Tigre value
