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

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

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

Presenting New Ideas What is RFM? C4 Chemical Calculations

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

Presenting New Ideas What is a mole? C4 Chemical Calculations

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

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

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

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

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

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

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

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

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

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

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