C5.1 - Monitoring Chemical Reactions

The yield of a product is the mass of the product made in a chemical process whereas the theoretical yield is the maximum mass it is possible to make from a given mass of reactants.

• The mass of the limiting reactant. • The relative formula masses of reactants and products. • The balanced equation for the reaction.

• Work out the number of moles of the limiting reactant. • Work out the number of moles of the product. • Work out the mass of the product OR Theoretical yield = (mass of limiting reactant/sum of Mr of limiting reactant) x Sum of Mr for the product

• The actual yield is the mass of product you actually make in a chemical reaction. • Percentage yield = (Actual yield / Theoretical yield) x 100

• The reactants may react in a different way than expected. • The reaction may not go into completion - some reactants present may not react - (often in reversible reactions). • Some of the product may be lost when you separate it from the reaction mixture and purify it.

• Atom economy is a measure of the proportion of atoms in the reactants that end up in the desired product. • Atom Economy = (Sum of Mr of desired product / Sum of Mr of all products) x 100

• Yield of the product. • Atom economy of the reaction. • Usefulness or otherwise of by-products. • Rate of the reaction. • Equilibrium position (if it a reversible reaction).

• A by-product is a substance formed in a reaction in addition to the desired product. • Can be sold - Improves the atom economy of the process as the by-product becomes a desirable product.

• Divide by 1000 to convert from cm3 to dm3. - Multiply by 1000 to convert from dm3 to cm3.

concentration in g/dm3 = mass of solute in g / volume of solution in dm3 concentration in mol/dm3 = mass of solute in mol / volume of solution in dm3

Multiply by the molar mass and vice versa if you wanted to convert the other way.

• Known volume and concentration of alkali is added to a conical flask. • Indicator added such as phenolphthalein which is pink in alkaline and colourless in acidic solutions. • Acid added from a burette (a long graduated glass tube with a tap at the bottom). • Acid is stopped being added once the indicator changes colour indicating the end point.

You use a volumetric pipette as it is accurate.

• Swirl the flask during a titration to mix its contents. • Your first titration is usually a rough run, done quickly so that you get an idea of what the titre is. • Later runs you can add acid quickly until you within get a few cm3 of the rough titre then add the acid drop by drop. - Repeat the titration until you obtain at least two - concordant titres (titres that are within 0.10cm3. • You can then calculate a mean with higher precision and repeat without the indicator.

• To 2 decimal places. - Record from the bottom of the meniscus.

n=cV

• One mole of any substance in the gas state occupies the same volume at the same temperature and pressure, this volume is the molar volume. • At room temperature and pressure, the molar volume is 24dm3/mol.

amount in mol = volume in dm3 / (24dm3/mol)