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Acid & Base titrations: MCQ 4
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Acid & Base titrations: MCQ 4

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Questions and Answers

What is the purpose of swirling the conical flask during a titration experiment?

  • To wash down any solution adhering to the sides of the flask (correct)
  • To mix the acid and base solutions thoroughly
  • To speed up the colour change
  • To prevent the solution from overflowing
  • What is the reason for standardising acid solutions?

  • Because acid solutions are always volatile
  • Because acid solutions are not reactive
  • Because acid solutions are highly concentrated
  • Because acid solutions are unstable and can vary in concentration (correct)
  • What is the purpose of the indicator Methyl Orange in a titration experiment?

  • To neutralise the acid solution
  • To catalyse the reaction between acid and base
  • To indicate the equivalence point of the reaction (correct)
  • To increase the concentration of the acid solution
  • What is the formula used to calculate the concentration of the unknown acid solution in a titration experiment?

    <p>Concentration = moles / volume</p> Signup and view all the answers

    Why is it necessary to use a base to standardise an acid solution?

    <p>Because acids are unstable and can vary in concentration</p> Signup and view all the answers

    What is the purpose of diluting the vinegar in the titration experiment?

    <p>To prevent a colour change after adding a small volume of acid</p> Signup and view all the answers

    What is the role of phenolphthalein in the titration experiment?

    <p>As an indicator to detect the endpoint</p> Signup and view all the answers

    What is the purpose of using a pipette to transfer 25 cm³ of vinegar into a volumetric flask?

    <p>To accurately measure the volume of vinegar</p> Signup and view all the answers

    What is the purpose of inverting the volumetric flask 10 times after adding deionised water?

    <p>To mix the solution thoroughly</p> Signup and view all the answers

    What is the purpose of titrating hydrated sodium carbonate against a standardised acid?

    <p>To determine the percentage of water of crystallisation</p> Signup and view all the answers

    What is the percentage of water in the hydrated compound?

    <p>57.84%</p> Signup and view all the answers

    What is the mole ratio of Na₂CO₃ to Na₂CO₃×H₂O?

    <p>1:1</p> Signup and view all the answers

    Study Notes

    Titration

    • Acid from the burette is dropped into the conical flask, and the flask is constantly swirled as the acid is added.
    • Any solution adhering to the sides of the conical flask can be washed down with DI water from a wash bottle.
    • Acid is added until a colour change occurs, and this is known as the 1ˢᵗ titration.
    • 2 accurate titrations are then carried out to determine the value of the unknown concentration of the acid.

    Titration Calculations

    • Write out titration conclusion
    • Use ratio from chemical equation to work out moles of unknown solution
    • Find concentration of unknown using moles & volume
    • Work out number of moles of known solution

    Standardizing Acids

    • Acids are generally unstable solutions, and their concentrations can vary due to HCl being volatile, HNO₃ being volatile, and Hâ‚‚SOâ‚„ being hygroscopic.
    • These acids must be standardized with a base.

    Acid & Base Titrations

    • Indicator used: Methyl Orange
    • Colour change: Yellow → Peach/Pink
    • Experiment 1: Standardisation of HCl

    Vinegar Titrations

    • Vinegar contains ethanoic acid
    • Experiment 2: Vinegar vs. NaOH
    • Indicator used: Phenolphthalein
    • Colour change: Pink → Colourless
    • Steps in solving vinegar titration questions:
      • Work out the concentration of titrated vinegar
      • Take account of the dilution factor
      • Convert g/L into % w/v
      • Calculate the concentration of ethanoic acid in the original vinegar

    Experiment 3: Water of Crystallisation

    • Some substances involved in neutralisation reactions contain water in their crystalline structure
    • Sodium carbonate can either be anhydrous or hydrated
    • Hydrated sodium carbonate is represented as Naâ‚‚CO₃.xHâ‚‚O
    • By titrating this base against a standardised acid, we can work out both the value of x and the % water of crystallisation in the structure

    Solving Water of Crystallisation Q’s

    • Solve for the concentration of the base
    • Convert M → g/L…….× Mr
    • Use actual volume to get mass of anhydrous base
    • Find the % water of crystallisation

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    Description

    Learn about the step-by-step process of titration, including the addition of acid, swirling, and washing of the conical flask, as well as calculations and conclusions. Test your understanding of this fundamental chemistry concept.

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