OCR A-Level Chemistry: Chapter 3 - Amount of Substance
This deck covers key concepts from Chapter 3 of OCR A-Level Chemistry, focusing on the amount of substance, including definitions, formulas, and principles related to moles, molecular and empirical formulas, and stoichiometry.
What is Avogadro’s Constant?
Key Terms
The amount of any substance containing as many particles as there are particles in 12g of the carbon-12 isotope.
What is the equation for the number of moles of a substance?
n=m/Mr
n - number of moles (mol)
m - mass (g)
Mr - molar mass (g/mol)
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| Term | Definition |
|---|---|
What is Avogadro’s Constant? | The number of atoms per mole of the carbon-12 isotope. |
What is a mole? | The amount of any substance containing as many particles as there are particles in 12g of the carbon-12 isotope. |
What is the equation for the number of moles of a substance? | n=m/Mr |
What is relative formula mass? | The weighted mean mass of the formula unit of a compound compared with 1/12th of an atom of carbon-12 |
What is the molecular formula? | The number of atoms of each element in a molecule. |
What is the empirical formula? | The simplest whole-number ratio of atoms of each element in a compound. |
How is the empirical formula found? | |
How is the molecular formula found? | Find empirical formula. |
What is relative molecular mass? | The mass of a molecule compared with the mass of an atom of carbon-12. |
In hydrated salts, what is the name given to water molecules? | Waters of crystallisation |
What is the concentration of a solute? | The amount of solute (in moles) dissolved in each 1dm^3 of solution |
What is the equation for finding a solution’s concentration? | c=n/v |
What is molar volume? | The volume per mole of a gas. Measured in dm^3/mol |
What is the value of molar volume at room temperature and pressure? | 24 dm^3/mol |
What is the equation for molar volume? | mgv=V/n |
What are the assumptions made about an ideal gas? | Random motion |
What is the equation for the ideal gas law? | pV=nRT p - pressure (Pa) V - volume (m^3) n - number of moles (mol) R - ideal gas constant (J/mol/K) T - temperature (K) |
What are the standard conditions? | 298K or 25C 101kPa or 1 atm of pressure |
What is stoichiometry? | The balancing numbers giving the ratio of the amount, in moles, of each substance in a balanced equation. |
What are the balanced equations used to find? | The quantities of reactants required to prepare a required quantity of a product. |
What is the percentage yield? | The actual yield divided by the theoretical yield expressed as a percentage. |
Why is the theoretical yield so hard to achieve? | The reaction is incomplete. |
What is the limiting reagent? | The reactant that is not in excess. |
What is atom economy? | The molar mass of desired products divided by the sum of the molar masses of all products expressed as a percentage. |
What are the benefits of a high atom economy? | Produce a larger proportion of desired products and few waste products.
Important for sustainability, the best use of natural resources. |