C4.1 - Relative masses and moles Flashcards
The mass of a single atom is so tiny that what?
The mass of a single atom is so tiny that it would not be practical to use it in:
1. Experiments
Or,
2. Calculations
The mass of a single atom is so tiny that it would not be practical to use it in experiments or calculations.
So instead of working with the actual masses of atoms, what are used?
Instead of working with the actual masses of atoms, the relative masses of atoms of different elements are used
The mass of a single atom is so tiny that it would not be practical to use it in experiments or calculations.
So instead of working with the actual masses of atoms, the relative masses of atoms of different elements are used.
What are these called?
These are called relative atomic masses, Ar
Relative atomic mass, Ar
Relative atomic mass, Ar, is the average mass of the atoms of an element compared with carbon-12
Why is carbon-12 given a mass of exactly 12 units?
Carbon-12 is given a mass of exactly 12 units, because it has:
- 6 protons
- 6 neutrons
Carbon-12 is given a mass of exactly 12 units, because it has 6 protons and 6 neutrons.
You can then compare the masses of atoms of all the other elements with this standard carbon atom.
Example
For example, hydrogen has a relative atomic mass of 1, because most of its atoms have a mass that is 1/12 of the mass of a carbon atom
Relative atomic mass, Ar, takes into account the proportions of any isotopes of the element found naturally.
So what is it?
So relative atomic mass, Ar, is the mean (average) relative mass of the isotopes of an element compared with the standard carbon atom
Why does chlorine have a relative atomic mass of 35.5, although you could never have half a proton or neutron in an atom?
Chlorine has a relative atomic mass of 35.5, although you could never have half a proton or neutron in an atom, because relative atomic mass, Ar, takes into account the proportions of any isotopes of the element found naturally
Relative formula mass, Mr
Relative formula mass, Mr, is the total of the relative atomic masses, added up in the ratio shown in the chemical formula, of a substance
Mole
Mole is the amount of substance in the: 1. Relative atomic Or, 2. Formula mass of a substance in grams
The abbreviation used for mole
The abbreviation used for mole is mol
The relative atomic mass in grams of carbon (12g of carbon) is how many moles of carbon atoms?
The relative atomic mass in grams of carbon (12g of carbon) is 1 mole of carbon atoms
What is one mole?
One mole is the relative: 1. Atomic mass Or, 2. Formula mass of any substance expressed in grams
What does one mole of any substance always contain?
One mole of any substance always contains the same number of: 1. Atoms 2. Molecules Or, 3. Ions
One mole of any substance always contains the same number of atoms, molecules or ions.
What is this?
This is a huge number and its value is called the Avogadro constant
Avogadro constant
Avogadro constant is the number of: 1. Atoms 2. Molecules Or, 3. Ions in a mole of any substance 6.02 x 10 to the power 23
Number of moles
Number of moles = Mass (g) ÷:
- Ar
- Mr
Mass (g)
Mass (g) = Number of moles x:
- Ar
- Mr
Relative atomic mass, Ar, is the average mass of the atoms of an element compared with carbon-12, which is given a mass of what?
Relative atomic mass, Ar, is the average mass of the atoms of an element compared with carbon-12, which is given a mass of exactly 12
Relative atomic mass, Ar, is the average mass of the atoms of an element compared with carbon-12, which is given a mass of exactly 12.
The average mass must take into account what?
The average mass must take into account the proportions of the naturally occurring isotopes of the element
