Quantitative chemistry

The mole – amount of chemical substance The mole (mol) is a unit of measurement used to measure the amount of a chemical substance. A mole of a substance has the same number of particles as 12.00g of 12C The number of particles (atoms, ions or molecules) in a mole is equal to Avogadro’s constant (L) which is: 6.02 x 1023 602000000000000000000000 1 mole of any substance has 6.02 x1023 particles

Examples

Moles, mass, and molar mass n = amount (mol) m = mass (g) M = molar mass (gmol-1)

Molar mass (M) Molar mass is the mass in grams of one mole of substance (gmol-1) It is calculated by adding up the masses of each atom in a compound. Example: H2O Hydrogen (H) = 1.01, oxygen (O) = 16.00 M (H2O) = (2x1.01) + 16.00 = 18.02 gmol-1

Molar volume of a gas 1 atm = 101.3 kPa At STP (101.3 kPa and 273K), one mole of any gas occupies a volume of 22.4 dm3 Examples: What volume does 32.00g of O2 occupy at STP? Molar mass of O2 = 32.00 gmol-1 (16.00 x 2) Therefore 32.00g of O2 occupy 22.4 dm3 at STP. What volume does 22.005 g of CO2 occupy at STP? Molar mass CO2 = 44.01 gmol-1 22.005/44.01 = 0.5000 moles of CO2 Therefore 0.5000 moles of CO2 occupies 22.4/2 = 11.2 dm3 at STP.

Relative atomic mass and relative molecular mass Relative atomic mass (Ar) is defined as the average mass of an atom compared to 1/12 the mass of one atom of carbon-12. Relative molecular mass (Mr) is defined as the average mass of a molecule compared to 1/12 the mass of one atom of carbon-12. Both are relative scales and therefore have no units.

Empirical and molecular formula Empirical formula is defined as the lowest whole number ratio of atoms in a compound. Molecular formula is the actual number of atoms in a compound. Example: Butane has the molecular formula C4H10 The empirical formula is C2H5

Molar mass Molar mass is the mass of one mole of a substance in grams. The unit is gmol-1 Examples: The molar mass of NaCl is (22.99 + 35.45) = 58.44 gmol-1 The molar mass of butane (C4H10) (4x12.01) + (10x1.01) = 58.14 gmol-1

Avogadro’s law Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain the same number of particles. What volume of CO2 is produced when 10 dm3 of CO reacts with 10 dm3 of O2? 2 volumes of CO react with 1 volume of O2 to make 2 volumes of CO2 Ratio of CO to O2 is 2:1 – 10 dm3 of CO reacts with 5dm3 of O2 There is excess O2 (CO is limiting reactant) so 10 dm3 of CO2 is produced.

Avogadro’s law What volume of CO2 is produced when100 cm3 of C2H4 is reacted with 400 cm3 of O2? What volume of O2 remains? 1 volume of C2H4 reacts with 3 volumes of O2 to produce 2 volumes of CO2 and H2O Ratio of C2H4 to O2 is 1:3 – 100 cm3 of C2H4 reacts with 300 cm3 of O2 O2 is excess (C2H4 is limiting reactant) Ratio of C2H4 to CO2 is 1:2, therefore (2 x 100) 200cm3 of CO2 is produced Volume of O2 remaining (400-300) = 100cm3

Gas laws Pressure and volume (Boyle’s law) Temperature and volume (Charles’ law) Temperature and pressure (Gay Lussac’s law) The combined gas law Ideal gas law

Pressure and volume Pressure is inversely proportional to volume at constant temperature. If the volume of a fixed mass of an ideal gas is doubled, the pressure decreases by half. Example: What is the new volume of 6 dm3 of gas if the pressure is halved at constant temperature? Halve the pressure, the volume is doubled. New volume = 12 dm3

Pressure and volume Linear graph Non - linear graph

Temperature and pressure Pressure is proportional to absolute temperature (K) at constant volume. If the pressure of a fixed mass of an ideal gas is doubled at constant volume, the temperature also doubles.

Temperature and volume The volume of a gas is proportional to the absolute temperature (K) at constant pressure. If the temperature of a fixed mass of an ideal gas is doubled, the volume also doubles (at constant pressure). What is the new volume of 10dm3 of an ideal gas if the temperature is increased from 200K to 400K at constant pressure? Double the temperature, the volume also doubles = 20dm3

What happens to a fixed mass of an ideal gas when the pressure and temperature are both doubled? Pressure is doubled, volume is halved. Temperature is doubled, volume is doubled. Therefore the volume does not change. The volume of an ideal gas at 27.0 °C is increased from 3.00 dm3 to 6.00 dm3. At what temperature, in °C, will the gas have the original pressure? Volume is doubled, pressure is halved To get back to the original pressure the temperature can be doubled (convert 27oC to K = 300K) Double 300K = 600K, then convert back to oC (600-273) = 327oC

Ideal gas equation

Ideal gas equation

Converting to m3 cm3 to m3 divide by 1x106 dm3 to m3 divide by 1x103

Converting to m3 Convert the following into m3 78.4 cm3 456 cm3 38.6 dm3 198.78 dm3

Converting oC to K Convert the following to K 5oC 23oC 100oC 0oC = 273K Convert the following to K 5oC 23oC 100oC

Converting atm to Pa 1 atm = 1.01x105 Pa Convert the following to Pa

Concentration of solutions

Solute, solvent and solution Solute – the substance that dissolves in the solvent. Solvent – the liquid that the solute dissolves in. Solution – solute + solvent together. When Copper sulfate is dissolved in water, a blue solution is formed. State the solute and the solvent. Copper sulfate is the solute and water is the solvent.

Calculating concentration 𝑪𝒐𝒏𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏= 𝒎𝒐𝒍𝒆𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝒗𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒔𝒐𝒍𝒗𝒆𝒏𝒕 𝑪= 𝒏 𝑽 number of moles moldm-3 volume of solvent (dm3) volume must be in dm3 (divide cm3 by 1000 to get dm3)

Example 1 Find the concentration of a solution containing 20.0g of sodium hydroxide (NaOH) in 200.0 cm3 of solution.

Example 2 Find the concentration of a solution containing 0.830g of potassium iodide (KI) in 25.0 cm3 of solution.

Example 3 What mass of sodium chloride (NaCl) is required to make 500.0 cm3 of 0.500 mol dm-3 solution?

Limiting reactant The limiting reactant (reagent) is the reactant that is completely used up during a chemical reaction. The reactant that is in excess is the reactant that is not completely used up during the chemical reaction - there is some of this reactant left over at the end of the reaction. Wheels are the limiting reactant, car bodies are in excess.