Amount of Substance Flashcards
What is relative atomic mass?
Weighted mean mass of an atom relative to 1/12th the mass of one atom of carbon 12
What involves relative formula mass?
Giant ionic
Giant covalent
Giant metallic
What involves relative molecular mass?
Simple molecular
What is the percentage by mass equation?
No.of atoms X relative matomic mass of element
————————————————————————-X100
Mr of compound
What is the equation for atom economy?
Mr of desired product
——————————-X100
Mr of all products
What must you include when doing atom economy?
The big numbers in the equation
What is the equation for percentage yield?
Actual yield
—————–X100
Theoretical yield
How do you calculate percentage yield?
Calc the Mr of reactant not in excess + Mr of product
If doesn’t tell you one in excess calc all
Calc no. of moles
Lowest value = limiting reagent
How do you calculate concentration?
Vol
What is the equation for no. of moles?
Mr
What is the equation for no. of moles in a gas?
24
What is the ideal gas equation?
pv = nRT
What must be the units of volume be in IGE?
M3
What must be the units of pressure be in IGE?
Pa
What must be the units of temperature be in IGE?
K
What must be the units of gas content be in IGE?
J/mol/K
How do you get from cm3 to m3?
X10-6
How do you get from dm3 to m3?
X10-3
How do you get from degrees to K?
+273
How do you get from kPa to Pa?
X10 3
What units must you always give vol if you’re finding it with the ideal gas equation?
Dm3
How do you calculate water of crystallisation?
Find no. of moles of water lost (minus two masses)
Find moles of anhydrous salt
Now work out ration (big/small)
How do you calculate the empirical formula?
Mass/Mr
Both answers divided by smallest value
To find the ratio
What is the equation for no.of atoms?
No.of moles X 6.02 X1O 23
When working out the no. of atoms in an compound, what must you do?
Multiply your answer by the no.of elements
When working out the no. of molecules in an compound, what must you do?
Not multiply your answer by the no. of elements
How do you calculate reacting masses?
Calc moles of compound
Then find moles of mass you want to calc
Moles X Mr = mass
How do you calculate molecular formula from empirical?
Do mass/ Mr of empirical formula
Then multiply every element by your answer
What is empirical formula?
The smallest whole number ration of atoms of each element in a compound
What is molecular formula?
The actual number of atoms of each element in a molecule
What is atom economy?
A measure of the proportion of reactant atoms that become part of the desired product in the balanced chemical equation
What is the theoretical yield?
The mass of the product that should be formed if no chemicals are lost in the process
What should the actual yield always be?
Less than the theoretical
