Chapter 3 - Amount of substance Flashcards
(19 cards)
What is a mole?
One mole of any substance contains the same number of particles as there are carbon atoms in 12g of carbon 12
What is the formula for working out the amount of a substance
Amount, n (mol) = mass (g) / molar mass (g mol^-1
n = m / Mr
What is Avogadro’s constant?
The number of atoms in carbon 12 which is 6.02 x 10^23
What can you use Avogadros constant (Na) to calculate?
We can use the Avogadro’s constant to find the number of particles in a given amount of a substance. (By multiplying the amount (mol) by 6.02 x 10^23.
What is Avogadro’s law?
Experiments confirmed that at room temperature and pressure, the volume of 1 mole of any gas is 24.0 dm3.
This value is known as the molar has volume and has units of dm3 mol-1
What is the formula for calculating volumes of gases?
Amount of gas, n, (mol) = volume of gas V (dm3) / molar gas volume (dm3 mol-1)
What should you do if the volume of gas is given in cm3
The molar gas volume should be converted to 24,000 cm3
What is the ideal gas equation?
pV=nRT
What is the molecular formulae?
Molecular formulae tell you the number and type of each atom in a simple molecule.
What is empirical formulae?
Empirical formulae show the simplest ratio of atoms of different elements in a compound.
What is concentration?
Concentration is a measure of the amount of solute dissolved per unit of solvent.
What is the calculation for concentration?
Concentration, c, (mol dm-3) = amount, n, (mol) / volume V(dm3)
C=n/V
What is a hydrated salt?
Hydrated salts have water molecules attached to the ions in their crystal structure, called water of crystallisation.
What is the percentage yield?
The calculation to work out the amount of product formed in a reaction.
Assume that all the reactants we converted to products - it would give a yield of 100%
Why is it difficult to get a yield of 100%
The reaction may be reversible
The reactants used may contain impurities
By products may be formed from unexpected reactions
Reactants or products may be left in apparatus during the experiment.
Product may be lost during separation and purification, such as being soaked onto filter paper.
What is the calculation for percentage yield?
Percentage yield = actual amount (mol) of product / theoretical amount (mol) of product
What is atom economy?
Atom economy considers the efficiency of a reaction by looking at the proportion of the products formed that are actually useful
Why are reactions with a high atom economy increasingly important?
They make better use of finite resources
They reduce the need to process and safely dispose of waste products
What is the calculation for atom economy?
Atom economy = molecular mass of desired product / sum of molecular masses of all products
