SQA Higher Chemistry Mass calculations
This page covers the following topics:
1. Percentage mass
2. Theoretical mass
3. Atom economy
Percentage mass is a way of representing the percentage of an element in a compound. Mass percentage is calculated by the mass of the element divided by the total mass of the compound.
Due to incomplete reactions, when experiments are carried out there is not a 100% yield of products. The theoretical yield is the amount of product you could produce theoretically. The percentage yield is a measure of the amountthe actual yield you get from an experiment.
Atoms are not gained or lost in a chemical reaction, some atoms from the reactants end up in the product, and some in by-products. The atom economy of a reaction expresses how efficiently a reaction makes use of reactant atoms, i.e. how much product is creating in comparasion to by-product. Atom economy is a percentage, thus the highest it can possibly be is 100%.
The production of ethanol via glucose fermentation has relatively low atom economy. How could the atom economy of this reaction be improved?
Element Z has a percentage mass of 65.3% in the compound H₂SZ₄ (molecular mass = 98). What is element Z?
3 g of C₃H₇OH has reacted with an excess of CH₃COOH (Ar = 60 g/mol) to give 1.8 g of C₃H₇OOCCH₃ (Ar = 102 g/mol) and some water, what is the actual yield of this reaction?
What is the atom economy for the production of Nickel in the reaction NiO + C → Ni + CO ?
30.0 g of KClO₃ is heated until it completely decomposes into KCl + O₂ via the following reaction: 2KClO₃ → 2KCl + 3O₂. What is the theoretical yield of oxygen gas in this experiment?
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