Topic 5: Monitoring and Controlling Chemical Reactions - Subtopic 1: Monitoring Chemical Reactions
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What is the equation for concentration in g/dm³ ?
Concentration = Mass of solute (g) / Volume of solution (dm³)
How do you convert from mol/dm³ to g/dm³?
To go from g/dm³ to mol/dm³ : - Divide by the molar mass in grams To go from mol/dm³ to g/dm³ : - Multiply by the molar mass in grams
What must you divide by to go from cm³ to dm³?
Divide by 1000
What is the equation for concentration in mol/dm³?
Concentration = Number of moles of solute (mol) / Volume of solution (dm³)
What is the concentration moles formula triangle?
Moles / Concentration x Volume
What are titrations?
Method of analysing concentration of solutions
What are some examples where titration is used?
• Acid base titration - Determine exact amount of alkali to neutralise quantity of acid • Prepare salts or other precipitates in redox reactions
What are used to show the endpoint in a titration?
Indicators, with phenolphthalein being popular
Why are some indicators not suitable for titration?
Litmus and other indicators are not suitable as they don’t give a sharp enough colour change Universal Indicator also unsuitable as it is a mix of indicators and has too many subtle colour changes
What are the hazards and safety procedure we can take in a titration?
• Dilute HCl can harm eyes or skin • Acids and alkalis are corrosive • Avoid contact with skin and use safety goggles • Pipette with a safety filler to avoid corrosive liquids
Describe a titration of an unknown conc. of sulfuric acid and 0.1 mol/dm³ of NAOH solution
• Use pipette and pipette filler to place exactly 25 cm³ NaOH solution into conical flask • Place flask on white tile so tip of burette is inside • Add few drops of indicator to solution in flask • Perform rough titration by taking burette reading and running in solution in 1-3 cm³ portions, swirling flask vigorously • Close tap when end-point, sharp colour change, is reached • Record volume from meniscus at eye-level • Repeat with fresh NaOH but add one drop at time until colour change when rough end-point volume reached • Swirl and rinse with distilled water and finish at first sign of colour change that persists • Repeat until concordant (within 0.1cm³) results to increase accuracy
What is the volume occupied by one mole of any gas found to be?
24 dm³ or 24,000 cm³ - Molar gas volume at RTP
What is the gas volume triangle?
Volume / Moles x 24 dm³
What is yield?
Describe the amount of product you get from a reaction
Why is it that in practice, you never get 100% yield in a chemical process?
• Some reactants may be left behind in equipment • Reaction may be reversible • Lost during separation and purification • Side reactions • Impurity in substance • Lost during transfer
What is the actual yield?
Recorded amount of product obtained
What is the theoretical yield?
Amount of product that would be obtained under perfect practical and chemical conditions
What is the percentage yield?
• Measures how successful a chemical process is Percentage Yield = Actual Yield / Theoretical Yield X 100
What is atom economy?
• Efficiency of reactions • Studies amount of reactants that get turned into products Atom Economy = Total Mᵣ of reactants / Total Mᵣ of all products
Why are reactions with low atom economies problematic?
They use up many resources, produce substantial waste material requiring expensive disposal, making them unsustainable and economically unattractive.
What makes a reaction economically unattractive?
Raw materials are typically expensive, as is waste disposal (which requires chemicals, equipment, space, and transport).
What factors do companies analyze to improve chemical process efficiency?
Atom economy, percentage yield, rates of reaction, and equilibrium position.
Why are high percentage yields desirable in industrial processes?
They maximize the conversion of reactants to desired products, minimizing waste and improving economic efficiency.
Why are fast reaction rates important in industrial processes?
They allow for greater production volume in less time, improving operational efficiency and reducing costs.