2.1- RELATIVE ATOMIC AND MOLECUALR MASSES, THE AVOGADRO CONSTANT, AND THE MOLE Flashcards
What does comparing masses of atoms give?
relative masses
Why are relative masses used instead of actual masses in grams?
actual mass in grams of atoms/ molecules too tiny to find by weighing
How was finding relative masses done in the past?
by defining the relative atomic mass of hydrogen, lightest element as 1
Using the old method of relative mass, what would oxygen’s mass be like?
average mass of atom of oxygen is 16 times heavier, to nearest whole number, so oxygen has relative atomic mass of 16
What do scientists now use for relative masses?
use isotope carbon-12 as baseline for relative atomic masses
Why do scientists now use carbon-12 as the baseline for relative atomic masses? (mass spectrometer)
as mass spectrometer has allowed us to measure masses of individual isotopes extremely accurately
What is the value of one twelfth of the relative atomic mass of carbon-12?
gives value of exactly 1
What is the definition of relative atomic mass?
weighted average mass of an atom of an element, taking into account its naturally occurring isotopes, relative to 1/12 the relative atomic mass of an atom of carbon-12
What is the formula for relative atomic mass?
1/12 mass of one atom 12C
mass of one atom of 12C
What is the definition of relative molecular mass?
mass of that molecule compared to 1/12 the relative atomic mass of an atom of carbon-12
What is the formula for relative molecular mass?
1/12 mass of 1 atom of 12C
mass of 1 atom of 12C
How do you find the relative atomic mass?
add up relative atomic masses of all the atoms present in molecule
What is the term relative formula mass used for?
ionic compounds
Why is the term relative formula mass used for ionic compounds?
they don’t exist as molecules
What is the value of Avogadro’s constant?
6.022* 10^23
What is the definition of Avogadro’s constant?
number of atoms in 12g of carbon-12
What is a mole?
amount of substance that contains 6.022* 10^23 particles
What does the relative atomic mass of an element in grams contain? (moles?)
contains one mole of atoms
What does the relative molecular mass of a substance in grams contain? (mole?)
contains mole of entities
What else can you have a mole of? (2)
ions or electrons
What is the formula for the number of moles?
moles = mass
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Mr
