Mastering mole calculations is absolutely essential for A-level chemistry success....
Chemistry208 views·Updated 9 Jul 2026·2 pagesMastering Mole Calculations in AS Chemistry
Isabelle @isabelle_study
1
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Mole Calculations and Chemical Efficiency
Atom economy tells you how efficient a reaction is by comparing the mass of your desired product to all the reactants you started with. The formula is straightforward: divide the total Mr of desired products by the total Mr of reactants, then multiply by 100%. Higher percentages mean less waste, which is brilliant for both your wallet and the environment.
When finding empirical formulas, you're basically working backwards from percentage composition to find the simplest ratio of atoms. Start with the percentages, divide each by the atomic mass, then find the smallest whole number ratio. If the molecular mass is given, you can scale up the empirical formula to get the actual molecular formula.
Percentage yield compares what you actually got in the lab to what the equation predicted you should get. Real reactions never give 100% yield due to side reactions, incomplete reactions, or simply losing some product during handling. This calculation helps you evaluate how well your experiment went.
Top Tip: Always check your mole ratios from the balanced equation - they're the key to converting between different substances in your calculations.
2
of 2
Concentrations and Gas Calculations
Concentration calculations use the simple relationship: moles = concentration × volume. Remember to convert cm³ to dm³ by dividing by 1000, and always use the mole ratios from your balanced equation to work out how much of each substance you're dealing with. These calculations are particularly useful in titrations where you know the volume and concentration of one solution.
The ideal gas equation PV = nRT connects pressure, volume, temperature, and the number of moles of any gas. This equation is incredibly powerful because it works for any gas under normal conditions. Make sure you use the right units: pressure in Pa, volume in m³, temperature in Kelvin (add 273 to Celsius), and R = 8.31.
Converting between units is crucial for gas calculations. Pressure often needs converting from kPa to Pa (multiply by 1000), and volume frequently needs converting between m³ and cm³ (multiply by 1,000,000 to go from m³ to cm³). Getting the units wrong will completely mess up your answer.
Key Point: Always double-check your unit conversions - they're the most common source of errors in gas calculations, and the numbers can look very wrong if you've mixed up m³ and cm³.
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Chemistry208 views·Updated 9 Jul 2026·2 pagesMastering Mole Calculations in AS Chemistry
Isabelle @isabelle_study
Mastering mole calculations is absolutely essential for A-level chemistry success. These calculations connect atoms, molecules, and real-world masses, helping you predict how much product you'll get from reactions and work with gas volumes and concentrations.
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Mole Calculations and Chemical Efficiency
Atom economy tells you how efficient a reaction is by comparing the mass of your desired product to all the reactants you started with. The formula is straightforward: divide the total Mr of desired products by the total Mr of reactants, then multiply by 100%. Higher percentages mean less waste, which is brilliant for both your wallet and the environment.
When finding empirical formulas, you're basically working backwards from percentage composition to find the simplest ratio of atoms. Start with the percentages, divide each by the atomic mass, then find the smallest whole number ratio. If the molecular mass is given, you can scale up the empirical formula to get the actual molecular formula.
Percentage yield compares what you actually got in the lab to what the equation predicted you should get. Real reactions never give 100% yield due to side reactions, incomplete reactions, or simply losing some product during handling. This calculation helps you evaluate how well your experiment went.
Top Tip: Always check your mole ratios from the balanced equation - they're the key to converting between different substances in your calculations.
2
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Concentrations and Gas Calculations
Concentration calculations use the simple relationship: moles = concentration × volume. Remember to convert cm³ to dm³ by dividing by 1000, and always use the mole ratios from your balanced equation to work out how much of each substance you're dealing with. These calculations are particularly useful in titrations where you know the volume and concentration of one solution.
The ideal gas equation PV = nRT connects pressure, volume, temperature, and the number of moles of any gas. This equation is incredibly powerful because it works for any gas under normal conditions. Make sure you use the right units: pressure in Pa, volume in m³, temperature in Kelvin (add 273 to Celsius), and R = 8.31.
Converting between units is crucial for gas calculations. Pressure often needs converting from kPa to Pa (multiply by 1000), and volume frequently needs converting between m³ and cm³ (multiply by 1,000,000 to go from m³ to cm³). Getting the units wrong will completely mess up your answer.
Key Point: Always double-check your unit conversions - they're the most common source of errors in gas calculations, and the numbers can look very wrong if you've mixed up m³ and cm³.
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