3.3 Moles and Volumes Flashcards
How to convert cm^3 into dm^3
Divide by 1000
What do you need to work out the amount in moles of a measured volume
The concentration in mol dm^-3
A 1 mol dm^-3 solution contains…
…1 mol of solute dissolved in each 1 dm^-3 of solution
Equation which links amount in moles, volume and concentration
n=c*V In which: n - amount in moles V - volume in dm^3 c - concentration in mol dm^-3
What is a standard solution
A solution of known concentration
How are standard solutions prepared
By dissolving an exact mass of the solute in a solvent and making up the solution to an exact volume
ie.
- Solid weighed accurately
- Solid dissolved in beaker using less distilled water than needed to fill volumetric flask to max
- This solution transferred to volumetric flask. Traces of solution rinsed into with distilled water.
- Flask filled to graduation line by adding distilled water a drop at a time until bottom of meniscus lines up with mark
- Volumetric flask slowly inverted several times to mix, ensure that results are concordant
How to convert between moles and grams
n=m/M In which: n - number of mole m - mass in grams M - relative molecular mass
At the same temperature and pressure, equal volumes of different gases contain…
…the same number of molecules
Therefore, when you measure a gas volume you are indirectly counting the number of gas molecules
What is the molar gas volume
Vm
Volume per mole of gas molecules at a stated temperature and pressure
What is RTP
Room Temperature and Pressure
20 Degrees C
101kPa
What is the molar gas volume at RTP
24dm^3mol^-1
Equation to convert between amount in moles and gas volume
n=V/Vm In which: n - amount in moles V - Volume Vm - Molar gas volume
At RTP, Vm = 24dm^3mol^-1
Assumptions for the molecules of an ideal gas
Random motion
Elastic collisions
Negligible size
No intermolecular forces
Ideal gas equation
pV=nRT In which: p - pressure V - volume in m^3 n - amount in moles R - Ideal gas constant (8.31Jmol^-1K-1) T - Temperature in Kelvin
How to convert degrees celcius to Kelvin
Add 273
How to convert cm^-3 to m^-3
*10^-6
Convert dm^3 to m^3
*10^-3
kPa to Pa
*10^3
Finding relative molecular mass of a volatile liquid using the ideal gas equation and an experiment
- Add a sample of the volatile liquid to a small syringe via a needle
- Inject the sample into a gas syringe through the selg-sealing rubber cap
- Reweigh the small syringe to find the mass of the volatile liquid added to the gas syringe
- Place the gas syringe in a boiling water bath at 100 degrees C. The liquid vaporises producing a gas, the pressure is recorded
- Use the ideal gas equation to calculate the relative atomic mass
The ideal gas equation relies on two key assumptions which are:
Forces between molecules are negligible
Gas molecules have negligible size compared to the size of their container
Why were improvements made to the ideal gas equation
As certain conditions cause the ideal gas equation to break down
Such as high pressure
What is the real gas equation
(p+(n^2a)/v^2)(V-nb)=nRT
In which:
(n^2a)/V^2 accounts for intermolecular forces
nb accounts for volume of gas molecules
