3.3 Moles and Volumes

Question 1

How to convert cm^3 into dm^3

Answer 1

Divide by 1000

Question 2

What do you need to work out the amount in moles of a measured volume

Answer 2

The concentration in mol dm^-3

Question 3

A 1 mol dm^-3 solution contains…

Answer 3

…1 mol of solute dissolved in each 1 dm^-3 of solution

Question 4

Equation which links amount in moles, volume and concentration

Answer 4

n=c*V
In which:
n - amount in moles
V - volume in dm^3
c - concentration in mol dm^-3

Question 5

What is a standard solution

Answer 5

A solution of known concentration

Question 6

How are standard solutions prepared

Answer 6

By dissolving an exact mass of the solute in a solvent and making up the solution to an exact volume

ie.

1. Solid weighed accurately
2. Solid dissolved in beaker using less distilled water than needed to fill volumetric flask to max
3. This solution transferred to volumetric flask. Traces of solution rinsed into with distilled water.
4. Flask filled to graduation line by adding distilled water a drop at a time until bottom of meniscus lines up with mark
5. Volumetric flask slowly inverted several times to mix, ensure that results are concordant

Question 7

How to convert between moles and grams

Answer 7

n=m/M
In which:
n - number of mole
m - mass in grams
M - relative molecular mass

Question 8

At the same temperature and pressure, equal volumes of different gases contain…

Answer 8

…the same number of molecules

Therefore, when you measure a gas volume you are indirectly counting the number of gas molecules

Question 9

What is the molar gas volume

Answer 9

Vm

Volume per mole of gas molecules at a stated temperature and pressure

Question 10

What is RTP

Answer 10

Room Temperature and Pressure
20 Degrees C
101kPa

Question 11

What is the molar gas volume at RTP

Answer 11

24dm^3mol^-1

Question 12

Equation to convert between amount in moles and gas volume

Answer 12

n=V/Vm
In which:
n - amount in moles
V - Volume
Vm - Molar gas volume

At RTP, Vm = 24dm^3mol^-1

Question 13

Assumptions for the molecules of an ideal gas

Answer 13

Random motion
Elastic collisions
Negligible size
No intermolecular forces

Question 14

Ideal gas equation

Answer 14

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

Question 15

How to convert degrees celcius to Kelvin

Answer 15

Add 273

Question 16

How to convert cm^-3 to m^-3

Answer 16

*10^-6

Question 17

Convert dm^3 to m^3

Answer 17

*10^-3

Question 18

kPa to Pa

Answer 18

*10^3

Question 19

Finding relative molecular mass of a volatile liquid using the ideal gas equation and an experiment

Answer 19

1. Add a sample of the volatile liquid to a small syringe via a needle
2. Inject the sample into a gas syringe through the selg-sealing rubber cap
3. Reweigh the small syringe to find the mass of the volatile liquid added to the gas syringe
4. Place the gas syringe in a boiling water bath at 100 degrees C. The liquid vaporises producing a gas, the pressure is recorded
5. Use the ideal gas equation to calculate the relative atomic mass

Question 20

The ideal gas equation relies on two key assumptions which are:

Answer 20

Forces between molecules are negligible

Gas molecules have negligible size compared to the size of their container

Question 21

Why were improvements made to the ideal gas equation

Answer 21

As certain conditions cause the ideal gas equation to break down
Such as high pressure

Question 22

What is the real gas equation

Answer 22

(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