SC14 - Quantitative Analysis ✓ Flashcards Preview

Edexcel GCSE Chemistry (9-1) > SC14 - Quantitative Analysis ✓ > Flashcards

Flashcards in SC14 - Quantitative Analysis ✓ Deck (10)
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1
Q

SC14a - What is the difference between actual and theoretical yield?

A
  • 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
2
Q

SC14a - How do you calculate percentage yield?

A

Percentage yield compares actual yield to theoretical yield

Percentage Yield = Actual Yield / Theoretical Yield

X 100

3
Q

SC14a - What are the 3 reasons that actual yield may be less than theoreticla yield?

A
  1. 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
  2. some of the product is lost - for example, when a liquid is transferred from one container to another
  3. there may be other unwanted side reactions taking place - for example some reacts may react to make a different product
4
Q

SC14a - Why is a higher percentage yield better?

A
  • 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
5
Q

SC14b - How do you work out atom economy and what does it show you?

A
  • 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
6
Q

SC14b - What is one way of improving atom economy?

A

Finding uses for the by-products of the reaction

7
Q

SC14c - How do you convert concentrations from mol/dm³ and g/dm³

A

Using the molar mass forumla

mol/dm³ = (g/dm³) ÷ (Mr or Ar)

8
Q

SC14d CP - Describe the method used to carry out an acid-alkali titration with hydrochloric acid (HCl) and 25cm³ of Sodium Hydroxide solution (NaOH)

A
  • 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
9
Q

SC14e - What is the Molar gas volume at rtp (room temperature and pressure)

A

24dm³

24 000 cm³

10
Q

SC14e - What is the formula for the moles in a gas?

A

Moles = Volume ÷ Molar gas volume (24dm³ at rtp)