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OCR A-level Chemistry Mass calculations

Mass calculations

This page covers the following topics:

The principle of mass conservation states that for any system closed to any tranfer of matter or energy, the mass of they system must remain constant, meaning no quantity of atoms can be added or taken away. This means there must be equal atoms of each element on either side of an equation. This is true only in an enclosed system.

Conservation of mass

The relative formula mass of a compound is written Ar. To calculate the relative formula mass of a compound, add together the realtive atomic masses of each element within the compound.

Relative formula mass

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.

Percentage mass

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.

Theoretical mass

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%.

Atom economy

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What is the percentage mass of hydrogen in CH₃COOH?

OCR A-level Chemistry Mass calculations What is the percentage mass of hydrogen in CH₃COOH?
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Element Y has a percentage mass of 1.19% in the compound NaYCO₃ (RFM = 84). What is element Y?

OCR A-level Chemistry Mass calculations Element Y has a percentage mass of 1.19% in the compound NaYCO₃ (RFM = 84). What is element Y?
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What is the theoretical yield?

OCR A-level Chemistry Mass calculations What is the theoretical yield?
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9.6 g CH₃OOCCH₃ is produced when 5g CH₃OH reacts with excess CH₃COOH. The theoretical yield of this reaction is 11.56 g. What is the percentage yield of this reaction?

OCR A-level Chemistry Mass calculations 9.6 g CH₃OOCCH₃ is produced when 5g CH₃OH reacts with excess CH₃COOH. The theoretical yield of this reaction is 11.56 g. What is the percentage yield of this reaction?
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The theoretical yield of the production of Cu in this reaction from 6.5g Zn is 75%: Zn + CuSOβ‚„ β†’ ZnSOβ‚„ + Cu. What mass of Copper is produced?

OCR A-level Chemistry Mass calculations The theoretical yield of the production of Cu in this reaction from 6.5g Zn is 75%: Zn + CuSOβ‚„ β†’ ZnSOβ‚„ + Cu. What mass of Copper is produced?
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Ethanol can be made by the fermentation of glucose by the following reaction: C₆H₁₂O₆ β†’ 2COβ‚‚ + 2Cβ‚‚Hβ‚…OH. What is the atom economy of this process?

OCR A-level Chemistry Mass calculations Ethanol can be made by the fermentation of glucose by the following reaction: C₆H₁₂O₆ β†’ 2COβ‚‚ + 2Cβ‚‚Hβ‚…OH. What is the atom economy of this process?
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7

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What is the definition of atom economy?

OCR A-level Chemistry Mass calculations What is the definition of atom economy?
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What is the atom economy for the production of Nickel in the reaction NiO + C β†’ Ni + CO ?

OCR A-level Chemistry Mass calculations What is the atom economy for the production of Nickel in the reaction NiO + C β†’ Ni + CO ?
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