Anachem: Expe 6

• Acid


  Compound that produces H+ ions upon dissolution
• Base


  Compound that produces OH- ions when dissolved in water
• Neutralization reaction


  Acid + Base → Salt + Water
• In an aqueous solution, virtually all of the OH- ions present will react with all of the H+ ions which are present</b>
• When a solution of hydrochloric acid, HCl, is exactly neutralized with a solution of sodium hydroxide, NaOH


  The number of moles of NaOH used will equal the number of moles of HCl originally present
• Acid-base indicator


  Changes color in a certain pH range to indicate the endpoint of a titration
• Phenolphthalein indicator changes color in the range pH 8.3 to 10.0 and can be used to determine when the correct amount of base has been added to an acidic solution to exactly neutralize it
• Calcium carbonate (CaCO3)


  Comprises more than 4% of the earth's crust, found in chalk, limestone and marble, gives hardness and strength to things such as seashells, rocks and eggshells
• A good quality eggshell will contain, on average, 2.2 grams of calcium in the form of calcium carbonate
• Approximately 94% of a dry eggshell is calcium carbonate and has a typical mass of 5.5 grams although these values can differ depending on sources
• Determining the percentage of calcium carbonate in an eggshell

  1. Reacting the eggshell by back titration with a standardized HCl solution

  2. Excess acid is reacted with the calcium carbonate in eggshells

  3. Remaining acid is titrated with standardized NaOH solution to determine the amount of acid that did not react with the eggshell
• HCl + CaCO3


  CaCl2 + H2O + CO2
• HCl + NaOH


  H2O + NaCl
• Gravimetric analysis


  Separation of a specific substance from other material of a sample in such manner that the separated substance can be isolated in a pure form
• Gravimetric analysis

  1. Precipitation

  2. Filtration

  3. Washing

  4. Ignition

  5. Weighing
• Precipitation


  A reagent is usually added that will affect this precipitation. Choice of a precipitating agent is closely related to the nature of precipitate desired.
• Filtration


  The filtering media used depend upon the nature of the precipitate and on the treatment needed to convert the precipitate in a form suitable for weighing.
• Washing

  In order to reduce solubility losses, the qualities of wash liquid should be as small as possible.
• Ignition


  The conversion of the precipitate into a form suitable for weighing.
• Weighing

  Ignited precipitates should be weighed in covered crucibles to prevent contact of the precipitate with moist air.
• Carbonate determination

  1. Addition of acid to the sample

  2. Removal of carbon dioxide by boiling

  3. Titration of the excess acid
• Calcium carbonate determination by titration

  1. Dissolution of carbonate on excess of 1M HCI

  2. Back titration of the remaining acid using NaOH
• The main ingredient in eggshell is calcium carbonate
• The shell itself is about 95% CaCO3
• The remaining 5% includes calcium phosphate and magnesium carbonate and soluble and insoluble proteins
• About 94% of the dry eggshell is calcium carbonate weighing 5.5 grams
• The average eggshell contains about 3% phosphorus and 3% magnesium and traces of sodium, potassium, zinc, manganese, iron and copper
• There was an average mass percent of 72% CaCO3 in the eggshell, compared to the reported value of 94% calcium carbonate, an error of 24%
• Reaction of CaCO3 with Hydrochloric acid

  CaCO3 + 2HCI →CaCl2 + CO2 + H2O
• Solubility-Product Constant, Ksp


  The constant Ksp is called the solubility product constant or simply solubility product for the equilibrium expression
• Solubility-Product Constant, Ksp


  • It is the equilibrium constant for the equilibrium that exists between a solid ionic solute and its ions in a saturated aqueous solution