4.5 Quantitative Chemical Analysis

4.5 Quantitative Chemical Analysis

  • By the end of this section, you will be able to describe the fundamental aspects of titrations.
  • The calculations are done using typical titration and gravimetric data.
  • The strength of the samples was determined by the amount of K2CO3 that had to be added a little at a time.
    • The bigger the amount of carbonate added to reach the point where the bubbling ended, the more concentrated it was.
  • The effervescence that occurred during this process was caused by the reaction with acetic acid, CH3CO2H.

  • The concentration of acetic acid was determined from the amount of reactant that combined with the solute present in a known volume of the solution.
  • Measurement of the amount of product that results is used to determine the amount of substance present in a sample.
  • If a change in the appearance of the sample solution accompanies the completion of the reaction, the equivalence point of a titration can be seen.
    • Equivalence points can be detected by measuring solution property that changes in a predictable way during the titration.
    • The difference between the equivalence and end points is negligible when properly designed titration methods are used.
  • Though any type of chemical reaction may serve as the basis for a titration analysis, the three described in this chapter are most common.
    • The chapter on acid-base equilibria provides additional details about titration analysis.
  • The end point was reached by adding 35.23 mL of 0.250 M NaOH to the sample.
  • The balanced chemical equation shows the relation between the amounts of the chemical species of interest.
    • The approach outlined in previous modules of this chapter is followed with additional considerations since the amounts of reactants provided and requested are expressed as solution concentrations.

  • The calculation of the analyte concentration can be done with the mass measurement of the sample, the isolated analyte, or some other component of the analysis system.
    • The first techniques used for quantitative chemical analysis are still important tools in the modern chemistry laboratory.
  • Various physical and chemical processes can be used to achieve the required change of state.
  • The mass of a sample before and after it is subjected to a controlled heating process that evaporates the water is used to determine the water content.
    • The techniques in which the analyte is subjected to a precipitation reaction are common.
  • The reaction mixture is usually isolated from the precipitate by drying and weighing it.
    • The mass of the precipitate can be used to calculate analyte concentration.
  • Precipitate can be removed from a reaction mixture.
  • The precipitation of 0.6168 g of BaSO4 was caused by a 0.4550-g solid mixture dissolved in water and treated with an excess of Ba(NO3)2.
  • The central step of the calculation is the connection between the moles of BaSO4 and MgSO4.
    • The sample mixture's mass may be used along with the mass of MgSO4 to calculate the percentage concentration.
  • In a combustion analysis, a weighed sample of the compound is heated to a high temperature under a stream of oxygen gas, resulting in its complete combustion to yield gaseous products of known identities.
    • Carbon dioxide and water will be the only products from the complete combustion of hydrocarbons.
    • The mass increase of each device corresponds to the mass of the absorbed product and may be used in an appropriate calculation to derive the mass of the relevant element.
  • The schematic diagram shows the basic components of a combustion analysis device.
  • Food-storage bags and many other flexible plastic items are produced with the help of polyethylene.

  • The amount of carbon and hydrogen in the sample should be calculated using the mass of carbon dioxide and water.
    • The empirical formula for the compound can be written with these amounts.
  • The empirical formula for the compound is derived from the smallest whole-number multiples.
    • The H-to-C ratio is mol H mol C, which is 1.79 x 10-4 mol H, and 2 mol H 89.95 x 10-5 mol C.
  • A sample of polystyrene, made from carbon and hydrogen, produced over 700 grams of CO2 and over 150 grams of H2O in a combustion analysis.

  • Chemical equations represent chemical and physical changes.
    • Formulas for the substances undergoing the change and substances generated by the change are separated by an arrow and preceded by coefficients.
    • Balanced equations result in equal numbers of atoms for each element in the reactants and products.
    • Chemical reactions in a solution that involve ionic reactants may be represented by complete ionic equations and net ionic equations.
  • Chemical reactions are classified according to their behavior.
    • There are three categories of important reactions: precipitation, acid-base, and oxidation-reduction.
    • Precipitation reactions involve the formation of insoluble products.
    • The transfer of hydrogen ion between reactants is an acid-base reaction.
    • Redox reactions involve a change in oxidation number.
    • The half-reaction method is used to simplify the writing of balanced equations for some redox reactions.
  • A balanced chemical equation can be used to describe a reaction.
    • Coefficients from the equation can be used to derive factors that can be used for computations.
  • The amount of product generated will be determined by the limit of the reactant.
    • The amount of product generated by a chemical reaction is the actual yield.
  • The amount of product predicted by the balanced chemical equation represents the reaction's theoretical yield.
    • The percent yield is the extent to which a reaction creates a theoretical amount of product.
  • Quantitative chemical analysis methods may be based on the analysis of chemical reactions.
    • Titrations involve measuring the volume of a sample solution.
    • This volume is used to calculate the concentration of analyte in the sample.
  • The method for determining the mass and concentration of analyte is called gilmetrics.
  • A gravimetric method is used to determine the composition of a compound by collecting and weighing the gaseous products of its combustion.
  • Consider the ionic equations.
  • Write a balanced equation for each reaction.
  • Write a balanced equation for each reaction.
  • The OpenStax book is free and can be found at http://cnx.org/content/col11760/1.9.
  • Aqueous hydrogen fluoride is used to etch glass and to analyze minerals.
    • Hydrogen fluoride will react with sand.
  • A solution of calcium chloride and sodium fluoride can be used to make solid calcium fluoride.
  • A novel process for getting magnesium from the sea.
    • Each step of the process should have a balanced chemical equation written on it.

  • Determine the oxidation states of the elements.
    • There are no superoxides or peroxides in the oxygen-filled compounds.

  • The highest possible oxidation state is given by the following oxidation-reduction reactions.

  • The highest possible oxidation state is given by the following oxidation-reduction reactions.
  • Balance the equations for the neutralization reactions.
    • Write the reactants and products as ionized water.
    • Depending on the amount of reactants used, there may be more than one correct answer.
  • Diamonds, which are pure carbon, are oxidation by atmospheric oxygen.
  • The military has been experimenting with lasers that produce intense light.
  • The Great Lakes Chemical Company produces bromine from bromide salts in Arkansas brine.
    • Write a balanced equation for a reaction.
  • In the general chemistry laboratory, magnesium metal is heated in the air to produce magnesium oxide.
    • In these experiments, magnesium looks gray due to small amounts of Mg3N2, a compound formed as some of the magnesium reacts with nitrogen.
    • For each reaction, write a balanced equation.
  • It is possible to absorb carbon dioxide in enclosed environments.
    • The reaction involves 2mol of LiOH per 1mol of CO2.
  • It is possible to add calcium propionate to bread.
    • This compound can be prepared by the reaction of CaCO3 with propionic acid, C2H5CO2H, which has similar properties to acetic acid.
  • Solid copper(II) oxide and gaseous sulfur trioxide can be produced by oxidation of copper(II) sulfide.
    • Liquid hydrogen sulfate is the only product after the gaseous product reacts with liquid water.
  • Write the equations that represent the reactions.
  • Write balanced chemical equations for the reactions used to prepare the following compounds.
    • Additional reactants may be required in some cases.
  • Calcium cyclamate Ca(C6H11NHSO3)2 is an artificial sweetener that is banned in the United States.
    • It can be converted to barium salt through the reaction of the acid C6H11NHSO3H with barium carbonate, and then neutralized with calcium hydroxide.

Write the balanced equation, then outline the steps needed to determine the information requested in each of the following:

  • SiC is a very hard material used as an abrasive in a variety of applications.
    • It is made by the reaction of pure sand with carbon.
    • The other product of this reaction is carbon monoxide.
    • To calculate how much SiO2 is required to produce SiC, you need to write the balanced equation.
  • When a sample of NaN3 is rapidly decomposing, automotive air bags inflate.
  • The urea, CO(NH2)2, is used to make urea-formaldehyde plastics and as afertilizer.
  • There was a spilled solution of nitric acid.
    • Two kilograms of Na2CO3 was quickly spread and CO2 was released.
  • A small car can get up to 37 miles per gallon on the highway.
    • The mass of carbon dioxide produced during a 500-mile trip is determined by the density of the gasoline.

  • A mordant is a substance that combines with a dye to produce a stable color.
    • A mordant is made of calcium acetate.
    • The reaction of acetic acid with calcium hydroxide is what prepared it.
  • rutile, TiO2, has replaced the toxic white lead in white paints.
  • The following quantities are placed in a container: 1.5 x 1000 atoms of hydrogen, 1.0 mol of sulfur, and 88.0 g of diatomic oxygen.
  • A sample of carbon dioxide was obtained by heating calcium carbonate.
  • The preparation from CCl4 is called freon-12, CCl2F2.
    • The other product of this reaction is HCl.
  • Determine the percent yield of a reaction that produces 12.5 g of CCl2F2 from 32.9 g of CCl4.
    • The use of freon-12 as a refrigerant has been banned because it has a very long lifetime in the atmosphere.
    • Determine the percent yield.
  • Toluene, C6H5CH3 is oxidized by air under carefully controlled conditions to C6H5CO2H, which is used to prepare the food preservative C6H5CO2Na.
  • The reaction of 3.0 mol of H2 with 2.0 mol of I2 produced 1.0 mol of HI.
    • The percent yield for this reaction is determined by the theoretical yield in grams.
  • Do the calculations after outlining the steps needed to solve the problem.
    • The original use of ether as an anesthetic has been replaced by safer and more effective medications.
  • When 30.0 g of propane, C3H8, is burned with 75.0 g of oxygen, there are steps needed to determine the limiting reactant.
  • Determine the reactant.
  • The steps needed to determine the limiting reactant are outlined in the following chemical equation.
  • If you dissolved it as UO2(NO3)2, then separated it as UO2(C2O4), it can be isolated from its ores.
    • 3H2O.
  • Determine the limit and percent yield of the reaction.
  • phosphoric acid is made by burning phosphorus in oxygen.
  • If 10.0 g of P4O10 is isolated from the reaction, the percent yield is calculated.
  • To reach the end point.
  • Hg(NO3)2 is used in a medical laboratory to determine the concentration of free chloride ion in blood.

  • Potatoes can be peeled commercially by soaking them in a 3-M to 6-M solution of sodium hydroxide and spraying them with water.
  • A sample of gallium bromide, GaBr2, weighing 0.165 g was dissolved in water and treated with silver nitrate, AgNO3.
    • The data can be used to calculate the % Ga by mass.
  • Naphthalene is a compound with a mass of about 130 amu and contains only carbon and hydrogen.
    • A sample of naphthalene burns to give CO2.
    • Determine its empirical andmolecular formulas.
  • A 0.025-g sample of a compound composed of boron and hydrogen, with a molecular mass of 28 amu, burns spontaneously when exposed to air, producing 0.063 g of B2O3.
  • If you want to purify NaHCO3 you need to dissolving it in hot water (60 degreesC), cooling it to 0 degreesC, and then removing the insoluble impurities from the solution.
    • Any NaHCO3 that is still in solution is not recovered.
    • The NaHCO3 can be found in hot water of 60 degrees.
    • 69 g/L is how much cold water it issoluble in.

  • A sample of Ca(OH)2 is allowed to stand in water until a saturated solution is formed.
  • To reach the end point, the acid needs 36.6 liters.
  • Many laboratories, including general chemistry laboratories, use KHP to standardize solutions of base.
    • KHP is one of the few stable acids that can be dried.
  • Black crystals of a compound containing only tungsten and chlorine can be seen from the reaction of WCl6 with Al.
    • When reduced with hydrogen, a sample of this compound gives 0.2232 g of tungsten metal and hydrogen chloride, which is absorbed in water.
    • To reach the end point.