Volumetric Analysis: Acid-Base Concentrations
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Questions and Answers

What is the purpose of a titration in volumetric analysis?

A titration is used to determine the concentration of a solution by adding a measured volume of another solution until the reaction is complete.

What is one key feature of a volumetric flask?

A volumetric flask is designed to contain a definite volume of solution and has an engraved graduation mark on its neck.

Why should a graduated cylinder be rinsed with deionised water before use?

Rinsing a graduated cylinder with deionised water removes contaminants and ensures accurate measurement of liquids.

How does one correctly fill a pipette before use?

<p>A pipette is filled by drawing the solution into it by suction, going above the etched graduation mark and then allowing it to settle.</p> Signup and view all the answers

What steps should be taken to ensure a homogenous mixture in a volumetric flask after preparing a solution?

<p>After filling the volumetric flask to the mark, it should be inverted about 20 times to ensure a well-mixed, homogenous solution.</p> Signup and view all the answers

What is the mass of NaCl in grams in a 0.25 M NaCl solution?

<p>14.625 grams NaCl per litre</p> Signup and view all the answers

What is the molarity of a solution containing 3.68 g of NaOH per litre?

<p>0.092 M NaOH solution</p> Signup and view all the answers

How many moles of NaOH are in 25 cm³ of a 0.55 M NaOH solution?

<p>0.014 moles NaOH</p> Signup and view all the answers

What mass of Magnesium reacts with 50 cm³ of 0.5 M H₂SO₄?

<p>0.6 g magnesium</p> Signup and view all the answers

How do you calculate the number of moles of solute in a diluted solution?

<p>No. of moles = (Volume_dil x M_dil) / 1000.</p> Signup and view all the answers

What volume of 12 M HCl is required to prepare 500 cm³ of a 3 M HCl solution?

<p>125 cm³ of 12 M HCl solution</p> Signup and view all the answers

What is the molecular mass of NaOH?

<p>40 g/mol</p> Signup and view all the answers

What is the relation between moles of Hâ‚‚SOâ‚„ and Mg in the reaction Mg + Hâ‚‚SOâ‚„?

<p>One mole of Hâ‚‚SOâ‚„ reacts with one mole of Mg.</p> Signup and view all the answers

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

<p>To remove any contaminants and ensure that the pipette is clean.</p> Signup and view all the answers

Why is it important to touch the tip of the pipette against the side of the glass beaker after filling?

<p>To remove any drop that may be adhering to the tip, ensuring an accurate measurement.</p> Signup and view all the answers

What is the significance of the meniscus when measuring liquids in a pipette?

<p>The meniscus represents the true level of the liquid and should be at eye level to ensure accuracy.</p> Signup and view all the answers

Describe the proper procedure for filling a burette with hydrochloric acid solution.

<p>Rinse the burette with deionised water, then with the hydrochloric acid solution before filling it above the zero mark.</p> Signup and view all the answers

What should be done if air bubbles are found in the nozzle of the burette?

<p>The tap at the base should be opened to allow the liquid to flow until the air bubble is cleared.</p> Signup and view all the answers

Why should a conical flask not be rinsed with the solution it is to contain?

<p>Rinsing with the solution could lead to dilution and inaccurate results.</p> Signup and view all the answers

What is the purpose of adding methyl orange indicator to the sodium carbonate solution?

<p>Methyl orange indicator helps visualize the endpoint of the titration by changing color.</p> Signup and view all the answers

What is the role of the conical flask when transferring the sodium carbonate solution?

<p>The conical flask is used for mixing the reagents and allows for swirling without spillage.</p> Signup and view all the answers

What is the definition of a solution?

<p>A solution is a completely perfect mixture of a solute and a solvent, where particles of the solute are uniformly distributed throughout the solvent.</p> Signup and view all the answers

How is weight per weight (w/w) concentration expressed?

<p>Weight per weight (w/w) is expressed as grams of solute per 100 grams of solution.</p> Signup and view all the answers

What is the purpose of diluting the vinegar solution before titration?

<p>To ensure that the concentration of acetic acid is within a measurable range for accurate titration results.</p> Signup and view all the answers

What does a 0.85% w/v solution of NaCl indicate regarding mass?

<p>A 0.85% w/v solution of NaCl indicates that there are 0.85 grams of NaCl per 100 cm^3 of solution.</p> Signup and view all the answers

What change occurs to the phenolphthalein indicator at the endpoint of the titration?

<p>It changes from pink to colourless.</p> Signup and view all the answers

What is the significance of parts per million (ppm) in solution concentration?

<p>Parts per million (ppm) is used for very dilute solutions and indicates 1 mg of solute per litre of solution.</p> Signup and view all the answers

Define molarity and its significance in solution concentration.

<p>Molarity is the number of moles of solute per litre of solution.</p> Signup and view all the answers

Why is it important to rinse the burette and pipette with the solutions intended for use before starting the titration?

<p>To prevent contamination that could affect the accuracy of the titration results.</p> Signup and view all the answers

How do you calculate the concentration of ethanoic acid in the diluted vinegar solution?

<p>By using the volume and concentration of sodium hydroxide used to reach the endpoint in the titration.</p> Signup and view all the answers

How do you convert a 0.25 M NaCl solution to grams per litre?

<p>To convert, multiply the molarity (0.25 M) by the molar mass of NaCl (approximately 58.44 g/mol).</p> Signup and view all the answers

What is the final step you must take after preparing the sodium carbonate solution in a volumetric flask?

<p>Invert the flask several times to ensure a homogeneous solution.</p> Signup and view all the answers

What does a 10% v/v ethanol solution mean?

<p>A 10% v/v ethanol solution means it contains 10 cm^3 of ethanol per 100 cm^3 of solution.</p> Signup and view all the answers

What is the formula for calculating the mass of solute needed for a specific volume in w/v?

<p>The formula is: mass = (concentration w/v) x (volume in cm^3)/100.</p> Signup and view all the answers

What does the term 'water of crystallisation' refer to in the context of hydrated sodium carbonate?

<p>It refers to the water molecules that are chemically bound within the crystalline structure of the compound.</p> Signup and view all the answers

What is the significance of obtaining consistent titration readings within 0.1 cm^3?

<p>It ensures the accuracy and reliability of the titration results.</p> Signup and view all the answers

What observation indicates the endpoint in the titration using methyl orange?

<p>The indicator changes from yellow to red/pink.</p> Signup and view all the answers

What does the term 'standardised solution' mean in the context of titrations?

<p>A standardised solution is one whose concentration is exactly known and used as a reference for titration.</p> Signup and view all the answers

Outline the steps to prepare a 250 cm^3 solution from a weighed sample of washing soda crystals.

<p>Dissolve the weighed sample in deionised water, stir until fully dissolved, then transfer to a volumetric flask, rinsing the beaker and bring the solution to the mark.</p> Signup and view all the answers

What precaution should be taken as the end point of the titration approaches, and why is it important?

<p>Add the titrant drop by drop to avoid overshooting the endpoint, ensuring accurate determination of titration end point.</p> Signup and view all the answers

Identify a suitable indicator for the titration of sodium carbonate with hydrochloric acid and describe the colour change observed.

<p>Methyl orange is a suitable indicator, which changes from yellow to pink at the endpoint.</p> Signup and view all the answers

Calculate the concentration of sodium carbonate (Na2CO3) in the original solution in moles per litre based on the titration results.

<p>The concentration of sodium carbonate in the original solution is 0.0432 moles/L.</p> Signup and view all the answers

Using the concentration calculated, what is the concentration of sodium carbonate in grams per litre?

<p>The concentration of sodium carbonate is 4.58 g/L.</p> Signup and view all the answers

Describe how to calculate the percentage water of crystallisation and the value of x in the formula Na2CO3.xH2O.

<p>Calculate the mass of water in the hydrated compound, then divide by the total mass of the hydrate and multiply by 100 for the percentage; x is determined based on the molar ratio between sodium carbonate and water.</p> Signup and view all the answers

Why is it essential to dissolve the samples thoroughly before titration?

<p>Thorough dissolution ensures that all solute particles are in solution for accurate and consistent titration results.</p> Signup and view all the answers

Flashcards

Concentration of a solution

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)

A measure of a very dilute solution: 1 mg of solute per litre of solution.

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Molarity

Moles of solute per liter of solution (mol/L).

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1 Molar (1M) solution

A solution that contains 1 mole of solute per liter of solution.

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0.85% w/v NaCl solution

0.85 grams of NaCl in 100 cm³ of solution.

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Calculating NaCl mass in a solution

Multiply the percentage concentration (w/v) by the volume to find the mass.

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What is titration?

A laboratory technique where a precisely measured solution is added to another solution until the reaction is complete.

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What's a volumetric flask used for?

A volumetric flask is designed to hold a specific volume of solution accurately. It has a mark on the neck to indicate the exact volume.

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Why rinse a volumetric flask with deionized water?

Rinsing a volumetric flask with deionized water ensures that no impurities from previous solutions affect the new solution being prepared.

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Pipette purpose?

A pipette is used to deliver a precise volume of liquid accurately. It's designed for precise transfer.

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How to make a homogenous solution?

After filling a volumetric flask, invert it several times to ensure the solute is evenly distributed throughout the solution.

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Pipette Filler

A device used to draw liquid into a pipette safely and accurately.

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Meniscus

The curved upper surface of a liquid in a tube. It's most pronounced in narrow tubes.

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Conical Flask

A flask with a conical shape that helps prevent liquid splashing and promotes swirling.

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Standard Solution

A precisely known concentration of a substance used to determine the concentration of another solution.

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Titration

A technique where a solution of known concentration is added to a solution of unknown concentration until a reaction is complete.

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Burette

A graduated glass tube with a stopcock at the bottom, used to deliver precise volumes of liquids in titration.

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Methyl Orange Indicator

A chemical indicator that changes color based on the acidity of a solution.

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Why rinse a pipette?

To remove any residual water or previous solution, ensuring accurate measurement of the target solution.

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Standardized solution

A solution whose concentration is accurately known. Its concentration has been precisely determined through a process called standardization, typically using a primary standard.

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Dissolving a sample in a volumetric flask

A chemist carefully dissolves a weighed sample in a volumetric flask. The sample is added to the flask with deionized water, stirred to dissolve, and then made up to the exact volume mark on the flask, ensuring a specific concentration is achieved.

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Precaution for accurate titration

As the titration nears its end point, the chemist adds the titrant drop by drop. This allows for precise control and ensures accurate detection of the end point, improving the titration result.

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Suitable indicator for titration

Methyl orange is a suitable indicator for titrating sodium carbonate with hydrochloric acid. It changes color from yellow to pink at the endpoint, indicating the equivalence point of the reaction.

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Calculating sodium carbonate concentration

Using the balanced equation and titration results, the concentration of sodium carbonate is calculated in moles/liter and grams/liter. The formula involves considering the volumes used, molarity of the acid, and the mole ratios of the reactants.

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Percentage water of crystallization

It represents the mass of water molecules present in 100 grams of the hydrated salt. It's calculated by comparing the mass of water to the total mass of the hydrated salt.

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Value of 'x' in hydrated salt formula

The value of 'x' in the formula Na2CO3·xH2O represents the average number of water molecules associated with each formula unit of sodium carbonate.

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What is the formula to calculate molarity?

Molarity (M) = (moles of solute) / (volume of solution in liters)

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How do you convert grams/liter to molarity?

  1. Find the molecular mass of the solute.
  2. Divide the grams of solute per liter by the molecular mass.
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Calculate moles of solute from volume and molarity

Number of moles = (volume of solution in liters x molarity) / 1000

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How do you dilute a solution?

Add solvent to a concentrated solution to decrease the concentration.

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Dilution equation

Vol(dil) x M(dil) = Vol(conc) x M(conc)

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What is the stoichiometry of a reaction?

The study of the quantitative relationships between reactants and products in chemical reactions.

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How to calculate the mass of a reactant that reacts with a given volume of solution?

  1. Calculate the moles of the reagent using volume and molarity.
  2. Use the stoichiometry of the reaction to find the moles of the reactant.
  3. Convert the moles of the reactant to grams using its molar mass.
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Why is a volumetric flask used?

A volumetric flask is used to prepare solutions to an accurate volume.

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What is a burette used for?

A burette is used to accurately deliver a measured volume of solution.

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How do you ensure a homogenous solution?

After adding the solute to a volumetric flask, you invert it several times to ensure the solute is evenly distributed in the solution.

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What's the purpose of rinsing the burette?

Rinsing the burette with the solution being used ensures that no residual water or other solutions affect the concentration.

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What's the indicator used in the vinegar titration?

Phenolphthalein is used as an indicator in the vinegar titration.

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What's the formula for hydrated sodium carbonate?

Hydrated sodium carbonate is Na₂CO₃·xH₂O, where 'x' represents the number of water molecules.

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What's the indicator used in the sodium carbonate titration?

Methyl orange is used as an indicator in the titration of sodium carbonate with hydrochloric acid.

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What's the purpose of the titration?

Titration is used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.

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Study Notes

Volumetric Analysis: Acid-Base

  • Solution: A perfect mixture of solute and solvent where solute particles are distributed uniformly throughout the solvent (homogeneous).
  • Solution Concentration: The amount of solute dissolved in a given volume of solution. Several ways to express this include percentage (w/w, w/v, v/v), parts per million (ppm) and molarity.
  • 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.
  • Volume per volume (v/v): Volume of solute per 100 cm³ of solution.
  • Parts per million (ppm): A unit for very dilute solutions, used in water analysis. (1 mg per litre = 1 ppm)
  • Molarity: Moles of solute per litre of solution (1M = 1 mole/litre).
  • Conversions: Converting between different concentration units is possible.

Expressing Concentrations of Solutions

  • Example (w/v): A 0.85% w/v salt solution means 0.85 grams of salt per 100 cm³ of solution.
  • Example (0.85 w/v and 250 cm³): To make 250 cm³ of a 0.85% w/v NaCl solution, 2.125 grams of NaCl are needed.

Moles of Solute Per Litre of Solution (Molarity)

  • Example calculation: What is the molarity of a solution containing 3.68 g of NaOH per litre of solution? Rel. Molecular Mass of NaOH = 40. 3.68g/40g/mol = 0.092 M NaOH solution.

Converting Moles per Litre to Grams per Litre

  • Example calculation: How many grams of NaCl per litre are present in a solution marked 0.25 M NaCl? Rel. Molecular Mass of NaCl = 58.5g/mol. 0.25 M x 58.5g/mol = 14.625 g/L

Converting Grams per Litre to Moles per Litre (Molarity)

  • Example Calculation: What is the molarity of a solution containing 3.68 g of NaOH per litre of solution? Rel. Molecular Mass of NaOH = 40. 3.68 g / 40 g/mol = 0.092 M NaOH solution.

Dilution of Solutions

  • Formula: (Volume of dilute solution x Molarity of dilute solution) / 1000 = (Volume of concentrated solution x Molarity of concentrated solution) / 1000
  • Example calculation: What volume of 12 M HCl solution is needed to make 500 cm³ of 3 M HCl solution? (500 x 3) / 1000= ( X x 12) / 1000; X = 125 cm³.

Standard Solutions

  • Definition: A solution whose concentration is accurately known.
  • Primary Standard: A stable, pure, and readily soluble solid substance used to prepare a standard solution.
  • Criteria for primary standards: Available in a pure state, stable in air, dissolve easily in water; high relative molecular mass; complete and rapid reaction; non-hydrated.

Volumetric Analysis: Titrations

  • Definition: A procedure to determine the concentration of an unknown solution by reacting it with a solution of known concentration.

Apparatus

  • Graduated Cylinder: Used for approximate volumes of liquids.
  • Volumetric Flask: Designed to hold a specific volume of solution for accurately measuring solutions.
  • Pipette: Used for the accurate delivery of a precise volume of liquid.
  • Conical Flask: A flask with a wide mouth used in titration experiments.

Reaction between a Solution and a Solid

  • Example calculation: Mg + H2SO4 → MgSO4 + H2. What mass of Magnesium will react with 50cm³ of 0.5 M H2SO4? 0.5 M x 50 cm³ / 1000 = 0.025 Moles. 0.025 moles x 24 g/mol = 0.6 g.

Titrations Methods and Calculations

  • Trial titrations: Are performed before the actual titration to estimate/narrow in on the end point.

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Description

Explore the concepts of volumetric analysis focusing on acid-base solutions. This quiz covers the definitions, calculations, and methods for expressing solution concentrations including molarity and parts per million. Enhance your understanding of solutions in chemistry.

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