These are my class notes on how to tackle solution and gas based equations, as well as avogadro's law. They can be used for both BTEC applied science and forensics, as the unit is identical. Please leave a review!
Solutions and Gases
Standard solution - A solution of known concentration. Used in titration
Concentration - A measure of how much solute is dissolved in a volume of solvent
● Measured in g/dm3 or mol/dm3
moles∨mass
Concentration =
volume
Working with solutions
I have a solution containing 80g of solute in 1 dm3 of solvent, what is the concentration?
●
80 = 80g/mol
1
I have a solution containing 40 g of sodium hydroxide in 2dm3. What is the concentration in
mol/dm3?
● The question wants the answer is mol/dm3 this time. So first we need to find the
number of moles
● Find the Mr of NaOH
● 23 + 1 + 16 = 40
mass
● Number of moles =
Mr
40
● = 1 mol
40
● This can now be put into the concentration equation
1
● = 0.5mol/dm3
2
How many moles of HCl are there in 25cm3 of a 0.1mol/dm3 solution?
● Volume must be measured in dm3
● So 25cm3 becomes 0.025dm3
moles∨mass
● Next we rearrange ‘concentration = ’ so the result is moles
volume
○ Moles = concentration x volume
● Moles = 0.1 x 0.025
● = 0.0025 moles
Avogadro’s law
● At the same pressure and temperature, equal volumes of gases contain equal
molecules
● At room temperature and pressure one mole of gas occupies 24dm3
● Standard conditions are 25°c and 1 atm pressure
● It is easier to measure the volume of gas than to weigh its mass
Molar gas volume = 24dm3
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