S1 - Relative formula & molar volumes of gases
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How do you work out the relative formula, Mr?
Just add all the atomic masses of the atoms it contains together
How would you work out the relative formula of MgCl2? Mg atomic mass = 24 Cl atomic mass = 35.5
24 + (2 x 35.5) = 95 So the Mr for MgCl2 = 95
What is the term a “mole” used to represent?
The amount in a substance - convenient way of counting atoms
What does a mole allow chemists to do?
Make predictions about masses of different substances involved in a reaction
What will one mole of atoms have a mass in grams equal to?
The relative formula mass (Ar/Mr) for the substance
What does one mole weigh exactly from the following? Carbon - Ar of 12 Nitrogen gas - Ar of 28 Carbon dioxide - Ar of 44
Carbon - 12b Nitrogen gas - 28g Carbon dioxide - 44g
What is the molar mass of a substance?
The mass of one mole measured in grams
What is one mole?
The Avogadro number of particles (atoms, molecules, ions or electrons) in a substance.
What is the formula for working out the number of moles?
Number of moles = Mass (g)/Mr
What is Avogadro’s law?
One mole of any gas always occupies 24dm3 (24,000cm3) at room temperature and pressure (RTP: 25 degrees and 1 atmosphere)
What is the molar volume?
24dm3
What other two equations can you draw from Avogadro’s law?
Volume (dm3) = moles of gas x 24 Volume (dm3) = mass of gas/ Mr of gas x 24
What does one mole always contains no matter what the element?
6 x 10 23 atoms
What is concentration?
The “amount of stuff” per unit volume.
What are the units for concentration?
1 mole per dm3 (1 mole/dm3)
What is the equation for working out concentration?
Concentration = Number of moles/Volume
What equation can you use to change mol/dm3 - g/dm3?
Mass (g) = Number of moles x Mr