1. 25cm3 of NaOH is neutralised by 12.7cm3 of 2mol/dm3 HCl.
What is the concentration of the alkali?
NaOH + HCl
C4 Chemical Calculations

2. Equations and Calculations Concentration of Solutions
Conservation of Mass
Topic C4: Chemical Calculations
Lesson Title: Volumes of Gases
Relative Formula Mass
Moles
Equations and Calculations
Yield and Atom Economy
Concentration of Solutions
Volumes of Gases
Titrations

3. Calculate the volume of gas at room temperature and pressure.
Lesson
Volume of Gases
4-6
Identify the volume of a mole of gas at 20°C and 1 atmosphere pressure and rearrange equations.
7-9
Calculate the volume of gas at room temperature and pressure.
C4 Chemical Calculations

4. Presenting New Ideas
What is RFM?
C4 Chemical Calculations

5. This means that water has a relative formula mass of 18.
Presenting New Ideas
Earlier in the topic we learned that relative formula mass (RFM) is the total of the atomic masses of the different atoms in a compound.
For example water has the formula H₂O. This means it contains 2 hydrogen atoms and 1 oxygen atom.
This means that water has a relative formula mass of 18. 1 H 1 H 16 O 8

6. Presenting New Ideas
What is a mole?
C4 Chemical Calculations

7. H H O Presenting New Ideas
We also learned that a mole is the relative atomic mass or relative formula mass of a substance in grams. The abbreviation used for mole is mol.
Water has a relative formula mass of 18 and so therefore one mole of water has a mass of 18g. 1 H 1 H 16 O 8
C4 Chemical Calculations

8. Presenting New Ideas
In this topic we have used this knowledge to calculate the mass of reactants and products, however, sometimes some of the reactants and products are gases and we can also use knowledge about relative formula mass and moles to calculate the volume of a gas.
C4 Chemical Calculations

9. Presenting New Ideas
1 mole of a gas always takes up the same volume under the same temperature and atmospheric conditions. When it is 20°C and 1 atmospheric pressure 1 mole of gas is 24dm³ which is 24,000cm³.
To calculate the number of moles in a gas you use the formula below:
No. of moles in a gas = volume of gas (dm³) / 24dm³ OR
No. of moles in a gas = volume of gas (cm³) / 24000cm³
C4 Chemical Calculations

10. Constructing Ideas
Calculate the number of moles of the following gases at 20°C and 1 atmospheric pressure:
5dm³ of N2
10dm3 of O2
8.2dm3 of CO2
46000cm3 of CH4
250cm3 of H2
650cm3 of Cl2
C4 Chemical Calculations

11. Presenting New Ideas
Sometimes though you may be asked to calculate the volume of gas instead and this means you will need to rearrange the formula:
From this…
No. of moles in a gas = volume of gas (dm³) / 24dm³
To this….
Volume of gas = no. of moles in a gas x 24dm3
C4 Chemical Calculations

12. Constructing Ideas
Calculate the volume of the following gases at 20°C and 1 atmospheric pressure:
7 moles of N2
2 moles of O2
8.2 moles of CO2
10.5 moles of CH4
2.8 moles of H2
6.25 moles of Cl2
C4 Chemical Calculations

13. Presenting New Ideas
However, sometimes you may be asked to calculate the volume of gas but you are given the mass of gas rather than the number of moles and this means you will need to do some calculations before you can use the formula below:
Volume of gas = no. of moles in a gas x 24dm3
First, you will need to find the number of moles which we have done before using the formula below:
No. of moles = mass / RFM (in g)
C4 Chemical Calculations

14. Sodium hydrogen carbonate, NaHCO3, undergoes thermal decomposition on heating to produce sodium carbonate, Na2CO3, water and carbon dioxide. The equation for the reaction is:
2NaHCO3  Na2CO3 + H2O + CO2
Calculate the minimum mass of sodium hydrogen carbonate that must be heated to produce 0.25 dm3 of carbon dioxide.
Relative atomic masses, Ar, values: Na = 23, H = 1, C = 12, O = 16

16. Constructing Ideas
Calculate the volume of the following gases at 20°C and 1 atmospheric pressure:
7g moles of N2
2g moles of O2
8.2g moles of CO2
10.5g moles of CH4
2.8g moles of H2
6.25g moles of Cl2
C4 Chemical Calculations

17. Demonstrating Ideas
When sodium nitrate is heated it decomposes to make sodium nitrite and oxygen. What mass of sodium nitrate is needed to make 10dm3 of oxygen?
C4 Chemical Calculations

18. Wednesday, 02 January 2019
Title: Volumes of Gases
Create a checklist that someone should use when calculating volumes of gases.
C4 Chemical Calculations