Volumetric Analysis: Acid-Base Techniques
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Questions and Answers

What is the primary function of a volumetric flask?

  • To deliver an exact volume of solution
  • To mix different solutions together
  • To measure approximate volumes of liquids
  • To contain a definite volume of solution (correct)

What must be done to a graduated cylinder before use?

  • It should be rinsed with deionised water (correct)
  • It needs to be dried completely
  • It must be calibrated for temperature
  • It should be filled with deionised water

When using a volumetric flask to prepare a solution, how is the last few cm³ of water added?

  • Quickly, to prevent evaporation
  • Carefully, so the meniscus rests on the calibration mark (correct)
  • With a pipette to ensure volume accuracy
  • By pouring directly from a bottle

How is a pipette filled with solution?

<p>By suction, drawing the liquid above the graduation mark (A)</p> Signup and view all the answers

What is the purpose of inverting a stoppered volumetric flask after filling it?

<p>To ensure a homogenous mixture (A)</p> Signup and view all the answers

What is the concentration of the diluted solution obtained from the equation $250 \times M_{dil} = 15 \times 2$?

<p>0.12 M (D)</p> Signup and view all the answers

What is a primary standard?

<p>A substance that can be weighed and dissolved to create a solution of known concentration (D)</p> Signup and view all the answers

Which of the following is NOT a criterion for a substance to be considered a primary standard?

<p>Must be able to undergo incomplete reactions (D)</p> Signup and view all the answers

During the preparation of a standard solution, what is the purpose of rinsing the clock glass with deionised water?

<p>To ensure all solid is dissolved in the solution (B)</p> Signup and view all the answers

What should be done after filling the volumetric flask with the solution almost to the calibration mark?

<p>Add water until the meniscus reaches the mark (B)</p> Signup and view all the answers

Which of the following steps is essential for ensuring a homogeneous solution?

<p>Inverting the flask after stoppering (B)</p> Signup and view all the answers

What is the mass of pure anhydrous sodium carbonate used to prepare the standard solution?

<p>2.65 g (B)</p> Signup and view all the answers

Which of the following actions is NOT part of the mandatory experiment to prepare a standard solution?

<p>Using any available water source (C)</p> Signup and view all the answers

What is the molar mass of anhydrous sodium carbonate, Na2CO3?

<p>106 g/mol (C)</p> Signup and view all the answers

What is the purpose of using a primary standard in a titration?

<p>To create a solution of known concentration (A)</p> Signup and view all the answers

How many moles of anhydrous sodium carbonate are present in 2.65g?

<p>0.0108 moles (A)</p> Signup and view all the answers

What is the final step in preparing the volumetric solution from the sugar supply?

<p>Add deionized water until the bottom of the meniscus is on the mark (D)</p> Signup and view all the answers

What is the color change of methyl orange indicator at the endpoint of the titration?

<p>Orange to red (B)</p> Signup and view all the answers

Which of the following steps is NOT part of the titration process?

<p>Adding water to the burette before starting the titration (D)</p> Signup and view all the answers

Which reaction occurs when hydrochloric acid is titrated with sodium carbonate?

<p>2HCl + Na<del>2</del>CO<del>3</del> → 2NaCl + CO<del>2</del> + H<del>2</del>O (A)</p> Signup and view all the answers

What is the importance of reading the burette at eye level?

<p>To avoid parallax error (C)</p> Signup and view all the answers

What is the purpose of rinsing the pipette with deionised water before use?

<p>To remove any contaminants (A), To ensure it is clean (D)</p> Signup and view all the answers

Which step is crucial to prevent splashing when using a conical flask?

<p>Swirling the flask carefully (D)</p> Signup and view all the answers

What should be done if the level of liquid in the burette is above the zero mark after filling?

<p>Remove the funnel and allow some to flow out (A)</p> Signup and view all the answers

Why is it important to wait a few seconds before removing the pipette from the flask after discharging the solution?

<p>To ensure all the solution is released (B)</p> Signup and view all the answers

Why should the burette not be rinsed with the solution it is going to contain?

<p>It can cause contamination of the solution (C)</p> Signup and view all the answers

What should the pipette be rinsed with after deionised water?

<p>Sodium carbonate solution (C)</p> Signup and view all the answers

What is an essential characteristic of the conical flask design?

<p>Its shape allows for easy swirling and washing down (B)</p> Signup and view all the answers

What is the significance of recording the meniscus level at eye level?

<p>It ensures accurate measurement of volume (D)</p> Signup and view all the answers

What does a 10% w/v NaCl solution indicate?

<p>10 g of sodium chloride is dissolved in every 100 cm^3^ of solution. (D)</p> Signup and view all the answers

How is molarity defined?

<p>The number of moles of solute per litre of solution. (C)</p> Signup and view all the answers

What is the correct meaning of 1 ppm?

<p>1 milligram of solute per litre of solution. (C)</p> Signup and view all the answers

Which of the following statements about a 1 M (molar) solution is true?

<p>It contains 1 mole of solute in 1 liter of solution. (A)</p> Signup and view all the answers

What does the term 'weight per weight' (w/w) mean?

<p>The grams of solute present in 100 g of solution. (B)</p> Signup and view all the answers

Which of the following correctly describes a homogenous mixture?

<p>A mixture where the solute is uniformly distributed throughout the solvent. (C)</p> Signup and view all the answers

What is the purpose of rinsing the burette with diluted vinegar solution before use?

<p>To ensure the burette is clean and free of contaminants (D)</p> Signup and view all the answers

At what point does the phenolphthalein indicator change color during the titration of vinegar with sodium hydroxide?

<p>When the solution turns colorless (A)</p> Signup and view all the answers

When conducting a titration, why is it crucial to perform multiple titrations?

<p>To enhance the accuracy of the results (D)</p> Signup and view all the answers

What is the expected final concentration of sodium carbonate solution after titration with 0.1 M hydrochloric acid?

<p>To be calculated from the volume of acid used (C)</p> Signup and view all the answers

Which indicator is used during the titration of sodium carbonate with hydrochloric acid?

<p>Methyl orange (C)</p> Signup and view all the answers

What is the effect of efflorescence on hydrated sodium carbonate crystals?

<p>They lose water and decrease in mass (C)</p> Signup and view all the answers

What is the main reason for inverting the volumetric flask after mixing the diluted vinegar?

<p>To evenly distribute the solute throughout the solvent (A)</p> Signup and view all the answers

How is the percentage (w/v) of ethanoic acid in the vinegar calculated?

<p>By using the volume of sodium hydroxide consumed (D)</p> Signup and view all the answers

Flashcards

Solution concentration

The amount of solute dissolved in a given volume of solution.

Weight per weight (w/w)

Grams of solute per 100 grams of solution.

Weight per volume (w/v)

Grams of solute per 100 cm³ of solution.

Parts per million (ppm)

1 mg of solute per liter of solution.

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Molarity (M)

Number of moles of solute per litre of solution.

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1 M solution

Contains one mole of solute in one liter of solution.

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0.85% w/v NaCl

0.85 grams of NaCl per 100 cm³ of solution.

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Converting molarity to grams per litre

Calculating the mass of a solute in grams per liter of a given molar concentration solution.

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Titration

A laboratory procedure where a measured volume of one solution is added to a known volume of another solution until the reaction is complete.

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Graduated Cylinder

Used for measuring approximate volumes of liquids. Not very accurate.

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Volumetric Flask

Designed to contain a specific volume of solution. Has a precise calibration mark on its neck.

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Pipette

Used to deliver an exact volume of solution. Filled by suction above the graduation mark.

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Making a solution up to the mark

Adding liquid carefully to a flask until the bottom of the meniscus (curved surface of the liquid) touches the calibration mark.

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Standard Solution

A solution with a precisely known concentration. It's like a reference point for other solutions.

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Primary Standard

A chemical used to prepare a standard solution because it can be weighed accurately, dissolves easily, and is stable over time.

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What are the criteria for a primary standard?

A primary standard must be: highly pure, stable in air, easily dissolve in water, have a high molecular mass, react fully and quickly, and not be hydrated.

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How is a standard solution prepared?

  1. Accurately weigh the primary standard. 2. Dissolve it in a small amount of water. 3. Transfer the solution to a volumetric flask. 4. Add water until the flask is filled to the mark.
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Why is sodium carbonate used to prepare a standard solution?

Sodium carbonate is used as a primary standard because it meets all the criteria; it's readily available, stable, easily dissolves in water, reacts completely, and has a high molecular mass.

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Why is deionized water used?

Deionized water is used to prevent unwanted ions from affecting the concentration of the standard solution.

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Why is the volumetric flask rinsed with water?

Rinsing the volumetric flask ensures that all of the solution from the beaker is transferred to the flask, preserving the accurate concentration.

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Why is the solution inverted after preparation?

Inverting the flask ensures that the solution is thoroughly mixed, resulting in a homogenous solution with a uniform concentration.

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Pipette Filler

A device used to draw liquid into a pipette. It helps avoid using your mouth to suction up the liquid, preventing contamination.

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Meniscus

The curved upper surface of a liquid in a container. When measuring, you read the level at the bottom of the curve.

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Conical Flask

A flask with a conical (cone-like) shape that helps prevent splashing during swirling.

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Deionised Water

Water that has had its ions (like minerals) removed. It's often used to clean glassware and prevent contamination.

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Methyl Orange Indicator

A chemical that changes color depending on the acidity or alkalinity of a solution. It turns red in acidic solutions and yellow in basic solutions.

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Efflorescence

The loss of water of crystallization from a hydrated salt, resulting in a change in its physical appearance and properties. It usually occurs when the salt is exposed to dry air or high temperatures.

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What is a hydrated salt?

A salt that contains water molecules incorporated into its crystal structure.

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What is the purpose of standardizing a solution?

To determine the exact concentration of a solution, typically by reacting it with a known volume of a standard solution.

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What is a primary standard?

A substance with a high purity, known chemical composition, and stable properties that is used to determine the concentration of other solutions.

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What is a secondary standard?

A solution whose concentration is determined by titration against a primary standard.

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What is the purpose of a titration?

A technique to determine the concentration of an unknown solution by reacting it with a known volume and concentration of a standard solution.

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What is the end point of a titration?

The point at which the indicator changes color, signaling the completion of the reaction between the titrant and analyte.

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What is a volumetric flask used for?

A flask designed to accurately hold a specific volume of solution, marked by a calibration line on the neck.

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Preparing a Standard Solution

Involves dissolving a known mass of the primary standard in a known volume of solvent, ensuring the final volume of the solution is precisely measured.

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Endpoint

The point in titration where the reaction is complete, indicated by a distinct color change caused by an indicator.

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Indicator

A substance that changes color at the endpoint of a titration, signaling the completion of the reaction.

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Methyl Orange

An indicator used in titrations, turning from orange to red at the endpoint when the solution becomes acidic.

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Study Notes

Volumetric Analysis: Acid-Base

  • Volumetric analysis is a quantitative method using solutions.
  • A solution is a homogenous mixture of solute and solvent.
  • Solution concentration can be expressed in different ways.

Percentage of Solute

  • Weight per weight (w/w): grams of solute per 100 g of solution (g/100g).
    • Example: 10% NaCl w/w means 10 g NaCl per 100 g solution.
  • Weight per volume (w/v): grams of solute per 100 cm³ of solution (g/100 cm³).
    • Example: 10% w/v NaCl means 10 g NaCl per 100 cm³ solution.
  • Volume per volume (v/v): volume of solute per 100 cm³ of solution (cm³/100 cm³).
    • Example: 10% v/v ethanol has 10 cm³ ethanol per 100 cm³.

Parts per Million (ppm)

  • Used for very dilute solutions.
  • 1 ppm = 1 mg/L

Moles of Solute per Liter of Solution (Molarity)

  • Molarity is the number of moles of solute per litre of solution.
  • 1 M solution contains 1 mole of solute per litre of solution.

Converting Moles per Liter to Grams per Liter

  • To convert moles per liter to grams per liter, multiply by the molar mass.
  • Example: 0.25 M NaCl solution contains 14.625 g/L NaCl.

Converting Grams per Liter to Moles per Liter

  • To convert grams per liter to moles per liter, divide by the molar mass.
  • Exmaple: Solution that contains 3.68 g NaOH per liter of solution is 0.092 M.

Calculating the Number of Moles

  • Number of moles = volume × molarity / 1000
  • Example: 25 cm³ of 0.55M NaOH contains 0.014 moles NaOH.

Dilution of Solutions

  • Moles of solute in diluted solution = Moles of solute in concentrated solution.
  • (Volume of diluted solution)(Molarity of diluted solution)/1000 = (Volume of concentrated solution)(Molarity of concentrated solution)/1000
  • Example: 250 cm³ of 12 M HCl to make 500 cm³ of 3 M HCl requires 100 cm³ of 12M HCl.

Reaction between a Solution and a Solid

  • Example: Mass of magnesium that reacts with 50 cm³ of 0.5 M Hâ‚‚SOâ‚„ is 0.6 g.

Standard Solutions

  • Standard solution: A solution with accurately known concentration.

Primary Standard

  • Primary standard: A pure, stable and soluble solid that can be weighed to accurately prepare a solution.

Mandatory Experiment: Preparing a Standard Solution of Sodium Carbonate

  • Detailed steps for preparing a standard sodium carbonate solution.

Volumetric Analysis: Titration

  • Definition: Measurement of one solution with another.
  • Titration apparatus: Graduated cylinders, Volumetric flasks, Pipettes, Conical Flask.

The Pipette:

  • Exact volume measurement.
  • Using a pipette filler.

Conical Flask:

  • Designed for swirling.
  • Should not be washed directly with solution.

Mandatory Experiment: Standard Solution of Sodium Carbonate to Standardize Hydrochloric Acid Solution

  • Detailed step-by-step procedure of titration experiment

Mandatory Experiment: Determining Ethanoic Acid in Vinegar

  • Detailed steps for calculating concentration of ethanoic acid in vinegar.

Mandatory Experiment: Determining the amount of water of crystallisation in hydrated sodium carbonate

  • Steps for finding the amount of water of crystallisation of sodium carbonate.

Exam Questions (2014)

  • Detailed analysis of exam questions pertaining to washing soda crystals.

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Volumetric Analysis PDF

Description

This quiz covers the fundamentals of volumetric analysis, focusing on acid-base solutions. You'll learn about various ways to express solution concentration, including weight/weight, weight/volume, and molarity. Test your understanding of these concepts and improve your analytical skills.

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