SC14 - Quantitative Analysis ✓
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SC14a - What is the difference between actual and theoretical yield?
• Theoretical yield: The maximum mass of product that can be formed from the reactant • Actual yield: The yield you get once the experiment has been conducted
SC14a - How do you calculate percentage yield?
Percentage yield compares actual yield to theoretical yield Percentage Yield = Actual Yield / Theoretical Yield X 100
SC14a - What are the 3 reasons that actual yield may be less than theoreticla yield?
• the reaction may be incomplete, so not all of the reactants are used up - possibly because the reaction has not been left for long enough or the reaction may reach equilibrium • some of the product is lost - for example, when a liquid is transferred from one container to another • there may be other unwanted side reactions taking place - for example some reacts may react to make a different product
SC14a - Why is a higher percentage yield better?
• A high yield means that fewer raw materials are used to make the same amount of product, so there is less waste and more profit can be made
SC14b - How do you work out atom economy and what does it show you?
• It shows you the perentage of atoms that have gone into making useful products and how many atoms you are wasting • Allows you to compare and work out the most efficient way fo making a product • Atom economy = (Mr of useful product(s) ÷ Sum of Mr of reactants) x 100 • Mr can also be Ar
SC14b - What is one way of improving atom economy?
Finding uses for the by-products of the reaction
SC14c - How do you convert concentrations from mol/dm³ and g/dm³
Using the molar mass forumla mol/dm³ = (g/dm³) ÷ (Mr or Ar)
SC14d CP - Describe the method used to carry out an acid-alkali titration with hydrochloric acid (HCl) and 25cm³ of Sodium Hydroxide solution (NaOH)
• Use a pipette to measure out 25cm³ of sodium hydroxide and empty this solution into a conical flask • Place the conical flask on a white tile (So you can see the colour change later on) • Wash out a burette with hydrochloric acid and fill it up to top with this. • Record the inital reading on the burette (from the bottom on the meniscus) • Add a few drops of indicator (methyl orange or phenolphthalein) to the conical flask and move this and the white tile under the burette • Open the tap of the buretted letting the acid flow through. Constantly swirl the flask • When you first see a colour change, slow down the tap • For phenolphthalein this will be pink to colourless; For methyl orange this will be yellow to red • Once the colour has changed and won’t change back, stop the tap and read the value on the burette (from the bottom of the meniscus) • Work out how much acid has been used • Repeat multiple times and take an average of the concordant results
SC14e - What is the Molar gas volume at rtp (room temperature and pressure)
24dm³ 24 000 cm³
SC14e - What is the formula for the moles in a gas?
Moles = Volume ÷ Molar gas volume (24dm³ at rtp)