percentage yield Flashcards
What is percentage yield?
It gives us a measure of the effectiveness of a synthetic procedure :
%yield = (actual yield/theoretical yield ) x 100
What is the importance of percentage yield?
- indicates the successful ness of the reaction
- tells us what % of our reactants have been converted into useful products
What can percentage yield also indicate?
- unwanted by products may be produced as a result of side reactions occurring. Meaning that some product may be lost and the reaction may not proceed to completion as it is in equilibrium
What are limiting reagents/factors?
A reactant in a reaction is not in excess thus dictates the amount of product that is produced.
When nitrogen and hydrogen react according to the following equation to form ammonia : N2+3H2-> 2NH3
0.5g of nitrogen and 0.6g of hydrogen are reacted together. Which is the limiting reagent?
Moles=mass/mr N: 0.5/28 (n is diatomic) = 0.017 H: 0.6/2 =0.3 0.017<0.3 so hydrogen is the limiting reagent.
Ethane is a hydrocarbon it can be combusted in oxygen according to the equation given below:
2C2H6(g)+O2(g) -> 4CO2(g) +6H2O(g)
16g of ethane is combusted to produce 22g of CO2. What is the percentage yield of this reaction?
(A/t)x100 Molar mass of e= 12x2 +6 =30 16/30 =0.533mol 1:2 ratio of reactants .. 1.066 moles of CO2 Mass of CO2 = 1.066 x (12 +16x2) = 46.904
22/46.904 x 100
=46.9%
NH3, ammonia can be produced by the reaction given: N2+3H2->2NH3
10 mol of H2 is reacted with excess N2 to produce 20.25 g of NH3 what is the % yield of this reaction?
10 mol of H2->3:2 Moles of NH3= 6.667mols Mass= 6.667xmr =6.667x 17 =113.33g
(20.25/113.33)x100
= 17.87%
Water can be formed through the combination of hydrogen and oxygen as shown in the reaction: 2H2+O2->2H2O
If 30g of O2 and 3.5g of H2 are combined to form 29g of H2O what is the %yield of this reaction?
Actual yield: 29g H2: 3.5g/2 =1.75mols O2: 30g/32 =0.9375mols 0.9375<1.75 so O2 is the limiting reagent. 1:2 0.9375 x 2 = 1.875mols of H2O Mass = 1.875x18 ->33.75 29/33.75 x 100 =85.93%
Aspirin is formed in a multi-step process from a substance called sodium phenoxide there is a 1:1 ratio of sodium phenoxide reacted to aspirin produced. The molar mass of aspirin is 180gmol^-1 and the mr of sodium phenoxide is 116gmol^-1. The process consists of 3 steps. The overall yield of the first step is 90%the second step is 80% and the third step is 98%. Calculate the mass in tonnes of aspirin that would be formed from 1 tonne of sodium phenoxide.
Yield: (0.8x0.9x0.98)x100 =70.6% Moles of Na phenoxide 1000000/116 =8621mol Moles of aspirin. 1:1 =8621 x 0.706 =6086 moles formed 6086 x 180 = 1095517g -> 1.096 tonnes
Note: some may be wrong because I looked at the comments section and there is something about it being hydrogen as the limiting reagent as there is less of it I don’t remember which question.
https://www.youtube.com/watch?v=–3gzdOpz9I&list=PLkocNW0BSuEFvnpnhj8fKN-KFUOlnKiT0&index=6
