Chapter 3 - Amount of substance Flashcards
What is the Avogadro constant?
6.02 x 10^23
The equation for the number of moles
Mass / Mr
What is the molar mass?
The mass of one mole of something
How to work out the number of moles of something?
Multiply the number of moles by the Avogadro constant
What is the molar gas volume?
The space that one mole of a gas occupies at room temperature and pressure
The equation for the number of moles of a gas
Volume (dm3) / 24 dm^3
What is the empirical formula
The smallest whole number of atoms of each element in a compound
What is the molecular formula?
The actual number of atoms of each element in a compound
Formula of nitrate
NO3 -
Formula of carbonate
CO3 2-
Formula of sulfate
SO4 2-
Formula of hydroxide
OH-
Formula of ammonia
NH4 +
Formula of zinc
Zn 2+
Formula of silver
Ag +
What is important to remember about ionic compounds?
The charges always balance
What is produced when acids and bases react?
Water and a salt
What is the water of crystallisation?
The water in an ionic lattice
How to work out the water of crystallisation?
Use COMMA R (see cards)
What is the empirical formula of a compound?
The smallest whole number ratio of atoms in a compound
What is the molecular formula of a compound?
The actual number of atoms of each element in a molecule
How to calculate the empirical and molecular formula?
Use EMMA and COMMA R
What is relative molecular mass?
The mass of a molecule compared to the mass of an atom of carbon 12
What is the relative formula mass?
Compares the mass of a formula unit with the mass of an atom of carbon-12
What is the water of crystallisation?
The water molecules that are part of the crystalline structure of a salt
Assumptions made when using experimental formula (2)
All of the water has been lost
No further decomposition
What is a polyprotic acid?
One which donates more than one proton
What is the ideal gas equation?
Pressure x volume = moles x ideal gas constant x temperature
What is the ideal gas constant?
8.31 Jmol-1K-1
How to go from cm3 to m3?
x10(-6)
How to go from dm3 to m3?
x10(-3)
How to go from Celsius to Kelvin?
+273
How to go from kPa to Pa?
x10(3)
What is stoichiometry?
The ratio of the moles of each reacting substance
Reasons why maximum theoretical yield is rarely reached (3)
The reaction may not have gone to completion
Side reactions may have taken place as well
Purifying the product may result in the loss of some of it
Equation for percentage yield
(Actual yield/theoretical yield) x 100
What is the limiting reagent?
The one that will be used up first and stop the reaction
How to find the limiting reagent?
Work out the moles of each reagent and compare with the equation
What is atom economy?
The proportion of atoms in the reagents that end up as the products
Equation for atom economy
(Mr of desired product / Mr of all products) x100
What is a standard solution?
One with a known concentration
How would you work out the formula of a hydrated salt?
1) Weigh an empty crucible
2) Add the hydrated salt into it and weigh again
3) Heat the crucible and contents strongly for about 3 minutes
4) After leaving to cool, reweigh the crucible and remaining salt
Why aren’t experiments to determine the water of crystallisation always accurate?
They assume that all of the water has been lost and that there is no further decomposition after heating
What is the ideal gas equation?
pV = nRT
