AS - Amount Of Substance Flashcards
Define relative atomic mass.
The average mass of an atom or element on a scale where an atom of carbon-12 is 12.
Define relative molecular mass.
The Ava rage mass of a molecule on a scale where an atom of carbon-12 is 12.
When is relative formula mass used?
For ionic compounds.
What is the Avogadro constant?
The number of particles in a mole.
What’s the formula for the number of particles?
Number of moles x Avogadro’s constant
What is the equation relating number of moles, mass and Mr?
Number of moles equals mass of substance divided by Mr.
What is the equation relating moles, concentration and volume? What are the units for concentration and volume?
Number of moles equals concentration (mol dm-3) x volume (dm3).
How many cm3 are in 1 dm3?
1000 cm3. So to convert from cm3 to dm3, divide by 1000.
What is the ideal gas equation? What does each letter stand for?
pV=nRT
p = pressure (Pa) V = volume (m3) n = number of moles R = gas constant (J K-1 mol-1) T = temperature (K)
What is the empirical formula?
The simplest whole number ratio of atoms of each element in a compound.
What is the molecular formula?
The actual number of atoms of each element in a compound.
What is the theoretical yield? What does it assume?
The mass of product that should be formed in a chemical reaction. It assumed that no chemicals are lost in the process.
Why is the actual yield always less than the theoretical yield?
For many reasons. For example, not all the reactants fully react. Some chemicals are lost. Some solution is left on filter paper. Some is lost in transfer between containers.
What is the formula for percentage yield?
Actual yield divided by theoretical yield x 100
Why doesn’t percentage yield actually tell you how wasteful a reaction is?
It tells you how wasteful a process is based on how much product is lost during the process. However a reaction with 100% yield could still be wasteful if the reactants end up as by-products as opposed to desired products.
