C3 - Quantitative Chemistry Flashcards
mass = 2
moles X mr
concentration X volume
moles = 3
mass / mr
concentration X volume
volume / 24
relative formula mass = 1
mass / moles
concentration = 1
mass or moles / volume
volume = 2
mass or moles / concentration
moles X 24
24 = 1
volume / moles
percentage mass =
number of atoms of element X Ar / mr X 100%
percentage yield =
actual yield / predicted yield X 100%
atom economy =
mr of desired product / sum of mr of reactants X 100%
How do you get from cm3 to dm3?
divide by 1000
How do you get from dm3 to cm3?
times by 1000
Define relative formula mass (mr)
total mass of all the atoms in the molecule
How do you calculate relative formula mass?
1) Expand any brackets
2) Find the atomic masses for the elements
3) Times the atomic masses by how many times the element appears in the formula
4) Add them together
What does the law of conservation of mass mean?
mass of products = mass of reactants
What does Ar mean?
relative atomic mass
What is the value of 1 mole?
6.022 X 10 to the power of 23 molecules
Why might the mass of a reaction vessel might decrease during a reaction?
gas may be released
Give the 5 steps how to solve a limiting reactants question (calculate the mass of ______ formed when __g of ______ is used)
1) Circle the two substances mentioned in the question
2) Calculate the mr of both
3) Calculate the number of moles of the KNOWN mass (mass/mr)
4) Use the molar ratio (using the big numbers) to calculate how many moles of unknown substance
5) Calculate mass of UNKNOWN mass (moles X mr)
Define excess reagent/reactant
Uses a larger amount than required to ensure a complete reaction
Define limiting reagent/reactant
Limits the amount of product made
Define concentration
Concentration is the number of particles in a given volume
Why is the constant 24dm3 used when calculating volume of gases?
1 mole of any gas will occupy 24dm3
Why is percentage yield not 100%?
-raw materials may not be pure
-some products may be left behind in apparatus
-reaction may not be completely finished
Which is the only equation where you don’t ignore the big number when calculating mr?
Atom economy
Define atom economy
a measure of the amount of starting materials that end up as useful products
