Qualitative Analysis Concepts

• The following are answers to long pretest questions

Qualitative Analysis

• In a solution of salt dissolved in water, the salt is the solute.
• A more diluted concentration is represented by 10 ppb.
• Normality refers to the number of equivalents of solute per liter of solution.
• Percent concentration expresses the ratio of solute to the total solution, as a percentage.
• The number of equivalents depends on the reaction in which the solute is involved.
• Molality represents the amount of solute in an amount of solvent (kg).
• In a solution with a volume of 1 liter and a solvent mass of 1 kilogram, molarity is less than molality if the solution's density is 1 g/mL.
• A 10% (w/v) NaCl solution indicates 10 grams of NaCl in 100 mL of solution.
• "Parts per million" (ppm) measures milligrams of solute per liter of solution.
• Parts per million (ppm) is suited for expressing the amount of a solute in a very dilute solution.
• Analytical chemistry studies the separation, identification, and quantification of chemical components in natural and artificial components.
• In the deer case study, the two parts of kidneys were homogenized separately.
• Dissecting the deer and removing the kidneys for analysis illustrates sample preparation in quantitative analysis.
• Assay is the process of determining how much of a given sample is the material indicated by its name.
• Matrix refers to the components of a sample other than the analyte of interest in chemical analysis.
• Establishing physical properties, toxicity, and metabolites of a newly discovered compound is considered bioanalytical chemistry.
• Mass spectrometry, gas chromatography, infrared spectroscopy and UV-Vis spectroscopy are instrumental methods of analysis.
• Ultramicro is a size-based classification of an analytical method.
• The first step in quantitative analysis requires defining the problem, investigating the literature, choosing a method, and method validation.
• A gross sample represents the population not only in chemical composition but also in particle-size distribution.
• For quantifying copper content, sample several portions of the metal by sawing across the place at random intervals and collecting the "saw dust" as the sample.
• A sampling bottle ensures the gross sample is homogeneous
• Sawing, milling, or drilling are used to sample particulate solids.
• A mechanical rile is used in sampling particulate solids
• Most analyses are performed on solution.
• Interference is a substance that prevents direct analyte measurement and must be removed.
• Fluoride acts as a masking agent to prevent iron(III) from interfering in the iodometric determination of copper(II).
• In the deer case study, the analyte concentration was determined using a calibration curve.
• Wet ashing involves oxidizing organic samples with liquid oxidizing reagents like HNO3, H2SO4, or HClO4.
• Flux is an alkali metal salt used to decompose an inorganic material.
• Molarity (M) is the unit of concentration that represents the actual concentration of the solution.
• µg/g=mg/L=nL/ml is equivalent to ppm.
• BaCl2 has a higher osmolarity if the initial concentration is 0.05 M.
• The equivalent weight of Al(OH)3 in the reaction Al(OH)3 + H2SO4 -> Al(HSO4)3 + H2O is FW/3.
• The equivalent weight of sodium carbonate (a salt) is FW/2.
• The unit of the factor in converting N to M in the formula N = M x h is eq/mol.
• The unit of equivalent weight is g/eq.
• Physiologic or isotonic saline, a 0.9% aqueous solution of NaCl, has a specific unit of %w/v.
• The correct statement about 34% sulfuric acid is option D, namely both A and B
• there is 34 g of solute in every 100 g of solution
• there is 0.34 g of solute in every 1 g of solution
• The concentration unit of %w/v is g/L.
• Molality (m) concentration unit is different based on the most general definition of concentration.
• mg/Kg is the unit of T.
• equivalent weight is the same as AW/3 for the reaction Fe(s) + O2(g) -> Fe2O3(g).
• Given the reaction 2KI(aq) + Pb(NO3)2(aq) -> PbI2(s) + 2KNO3(ag), FW/2 expresses equivalent weight of the first reactant.
• 5% (w/v) ethanol and 5% (v/v) ethanol will not give the same Molarity.

Quantitative Analysis

• To make 75.0 mL of 3.50 M HCl, volume of 12.0 M HCl is needed: 21.9 mL.
• The molarity of a 2.0-liter solution containing 58.0 grams of NaCl is 0.496 M.
• Molarity of the solution of HCl gas dissolved in water (20.22% HCl, density 1.10 g/mL) is 6.10 M.
• Normality of the solution of HCl gas dissolved in water (20.22% HCl, density 1.10 g/mL) is 12.2 N.
• Molality of the solution of HCl gas dissolved in water (20.22% HCl, density 1.10 g/mL) is 6.95 m.
• Molarity of commercial vinegar solution (3.78 g acetic acid per 100.0 g, density 1.00 g/mL) is 0.629 M.
• Molality of the solution of solution (3.78 g acetic acid per 100.0 g, density 1.00 g/mL) is 0.606 m.
• The molar concentration of K+ in a solution containing 63.3 ppm of K2Fe(CN)6 is 1.92x10^-4M.
• In the reaction of NaClO with H2SO3, a solution of NaClO containing 10 g of NaClO per liter has a normality of 0.27 N.
• The normality of a HCl solution having a sodium carbonate titer of 5.00 mg/mL is 0.0943 N.
• To prepare 2.50 L of 0.440 N solution for the reaction H2C2O4 + KOH -> K2C2O4 + HOH, 99.0 grams of oxalic acid (H2C2O4) is needed.
• For a 65% solution of HF in water with a density of 1.57 g/mL, the mass of solution containing 44.0 g of HF is 67g.
• The volume (mL) of solution containing 189 mmol of HF in a 65% solution with a density of 1.57 g/mL is 20.7 mL.

Errors

• Inconsistent readings due to temperature fluctuations, is an example of a random error
• Unpredictable variations in measurements characterize random error.
• A bias consistently affecting results in the same direction is classified as systematic error.
• Errors due to human mistakes during experimental procedure (e.g. reading instruments) exemplify gross errors.
• Faulty experimental design or equipment is the primary cause of systematic errors
• Random error is minimized by increasing the number of measurements and then averaging them.
• The following potentially results in a systematic error: instrument drift over time.
• Implementing quality control procedures can identify and correct gross errors.
• Systematic error is typically detected and fixed through careful experimental design and procedure.
• Errors occurring from environmental changes during experimentation get classified as random errors.
• A pipet not repeatably handled during repetitions of a determination exemplifies a random error.
• An analytical balance is miscalibrated represents a systematic error that may occur while weighing a solid on a Balance.
• To reduce the random uncertainty of a measurement in an acid-base titration, replicate the analysis.
• To determine if sunlight exposure makes plastic more brittle, use an F-test followed by a two-sample t-test.
• To compare if the means of parallel tests are different, use t-test statistical test.
• Standard deviation, variance, and coefficient of variance are statistical terms used to describe the precision of a set of replicate data.
• The discovery that a "pure" reagent was actually contaminated but still used in the analyses is an example of systematic error.
• For comparing two mean values, use T-test
• When using the T-test and comparing two mean values use 5 degrees of freedom.
• If the true value for measurements is not within the confidence interval than error is determinate.
• The mass balance equation for 0.10M NaH2PO4: 0.10M = [H2PO4^-] + [HPO4^2-]
• Charge balance equation for a solution (Br, Mg^2+,MgOH) is 2[Mg^2+] + [H3O+] + [MgBr+] + [MgOH+] = [Br-] + [OH-]
• The formula for the charge balance equation of an aqueous solution is: [Na+]+2[Ba^2+]+3[Al^3+]=[ClO4-]+[NO3-]+2[SO4^2-]+[HSO4-]

Methods of Determining Which Statistical Method Is More Precise

• To determine which statistical method is more precise, use the F-test
• Applying the appropriate statistical test returns a number of 7.78
• The best average report is 43.25 when the Q-test for the four measurements at the 90% confidence level is 0.76
• To determine if 5.5 is an outlier, reject 5.5 as an outlier, given Q critical value for that data set is 0.64
• The mean of the data is 3.0
• Machine A is more consistent than Machine B
• If results vary within an acceptable amount, there is no significant difference in variance.