Deck 28: Gravimetric and Combustion Analysis

Question 1

Which of the properties below is NOT a property of the ideal solid product for gravimetric analysis?

A)insoluble
B)known composition
C)pure
D)easily filterable
E)high density

Answer 1

high density

Question 2

The iron content of an iron supplement must be determined.The manufacturer states that each tablet contains 1 000.0 mg of bioavailable iron.A tablet with a mass of 4.9283 grams is digested in nitric acid to release Fe³⁺ into solution.After filtration,the iron in solution will be precipitate with sodium bicarbonate.What is the minimum mass sodium bicarbonate must be added to precipitate the iron in solution? Assume no sources of interfering metals are present.

Answer 2

4.2775 g Fe(HCO₃)₃ required to precipitate 1 000.0 mg Fe from iron supplement.

Question 3

Precipitates will often contain impurities and will require treatment to remove impurities.Which of the following precipitation terms is INCORRECTLY defined?

A)gathering - precipitate collects a trace element of the solution
B)masking agent - compound that prevents impurities from reacting with the precipitate
C)inclusion - pocket of impurities trapped within the precipitate
D)digestion - precipitates remains in mother liquor after precipitation to promote slow recrystallization of the product,form larger particles and expel impurities
E)coprecipitation - impurities are precipitated along with the desired product

Answer 3

inclusion - pocket of impurities trapped within the precipitate

Question 4

Which of the following are techniques to promote particle growth?
I Use a large volume of solution so concentration of analyte and precipitant are low.
II Rapidly add the precipitant to precipitate all analyte from solution,then raise the temperature of the solution to promote crystal growth.
III Slowly adding precipitant with vigorous mixing as the precipitant is added to prevent a highly supersaturated condition in solution.
IV Raise the temperature of the solution to increase solubility of precipitate and decrease supersaturation.

A)III and IV
B)II,III,and IV
C)II and IV
D)I,II,and III
E)I,III,and IV

Question 5

____________________ are solid particles with long-range order.

A)Crystalline particles
B)Amorphous particles
C)Rigid particles
D)Regular particles
E)Inelastic particles

Question 6

A 100.0 mL sample of a solution containing copper(II)cation is treated with excess sodium carbonate to precipitate 3.6055 grams of copper(II)carbonate.What is the molarity of the solution?

Question 7

____________________ are solid particles that lack any crystalline order.

A)Crystalline particles
B)Amorphous particles
C)Plastic particles
D)Irregular particles
E)Elastic particles

Question 8

The final precipitation product should have a known,stable chemical composition.One way to obtain a known,stable chemical composition is via____________________ ,which is defined as the strong heating of a precipitate to change the chemical composition of the precipitate to a more stable form.

A)drying
B)ignition
C)charring
D)thermogravimetric analysis
E)annealing

Question 9

Combustion analysis of 0.1938 grams of a hydrocarbon increased the mass of the water trap by 0.2750 grams and the mass of the carbon dioxide trap by 0.5973 grams.What is the percent by mass for C and H?

Question 10

A 100.00 mL solution of copper(II)chloride is reacted with excess silver nitrate to precipitate 8.9260 g silver chloride.Which of the calculations below is NOT required to calculate the molarity of the copper(II)solution?

A)calculate the molar mass of silver chloride
B)calculate the molar mass of copper(II)chloride
C)calculate moles silver chloride from precipitate mass
D)calculate the moles copper(II)chloride with the mole to mole ratios silver chloride : chloride and chloride : copper(II)chloride
E)divide moles copper(II)chloride by volume of the copper(II)chloride solution expressed in liters

Question 11

Modern combustion analysis uses dynamic flash combustion.What is the main reason dynamic flash combustion is employed?

A)to limit the time oxygen flows freely through the analyzer
B)to leave no residue in the ceramic crucible
C)to guarantee the complete oxidation of select reaction products
D)because the GC requires the sample to be injected at once
E)to guarantee the complete reduction of select reaction products

Question 12

Combustion analysis of 0.1938 grams of a hydrocarbon increased the mass of the water trap by 0.2750 grams and the mass of the carbon dioxide trap by 0.5973 grams.What is the empirical formula for the hydrocarbon?

Question 13

Crystallization occurs when precipitant is added to a solution,creating a temporary supersaturated solution.Crystallization occurs in two stages: nucleation and particle growth.Which of the following is NOT true for nucleation and particle growth?
I Nucleation occurs when solutes form clusters of sufficient size which reorganize into a more ordered structure capable of growing into larger particles.
II Particle growth occurs when ions,molecules,or other nuclei condense onto a particle to form a larger crystal.
III Sources of nucleation are solution impurities or small scratches on a glass surface.
IV Particle growth occurs when amorphous particles clump together to create larger amorphous particles.

A)I
B)III and IV
C)IV
D)I,II,and IV
E)II and IV

Question 14

A solution is prepared from an unknown solid containing Ni and Cu by dissolving 5.2832 grams of the solid in nitric acid to release Ni²⁺ and Cu²⁺.The nitric acid is neutralized and the solution diluted to 200.0 mL.Next excess sodium carbonate is added to the solution to form Ni and Cu carbonates with a total mass of 2.5305 grams.The precipitate is then ignited to form NiO and CuO with a total mass of 1.6126 grams.What is the percent by mass Ni and Cu in the solid sample?

Question 15

Combustion analysis of C,H,and S converts each element into nonmetal oxide for analysis.Combustion analysis of O requires a different approach.Which of the steps below is(are)not required or false for combustion analysis for O?
I Sample is thermally heated to decompose the compound in the absence of O₂.
II Gaseous products from pyrolysis are passed through nickelized carbon at 1 075 ^oC to convert oxygen into CO.
III Gaseous products are sent to GC for analysis.
IV Halogens are converted to HX during pyrolysis,dissolved in water and titrated with silver nitrate.
V Gaseous products from pyrolysis are passed through nickelized carbon at 1 075 ^oC to convert oxygen to CO₂.

A)III,IV,and V
B)II and IV
C)IV and V
D)I,II,and III
E)V only

Question 16

Silver cation is precipitated from solution using sodium carbonate.Calculate the gravimetric factor to relate the mass of the product to the analyte.

A)0)782
B)1)278
C)0)391
D)5)112
E)0)196

Question 17

Which of the following is NOT true for traditional combustion analysis of a hydrocarbon?

A)During combustion all carbon is converted to carbon dioxide.
B)During combustion all hydrogen is converted to water.
C)The increase in mass for the trap containing P₄O₁₀ is proportional to the mass H in the compound.
D)The increase in mass for the Ascarite II® trap is proportional to the mass C in the compound.
E)During combustion all carbon is converted to carbon monoxide.

Question 18

Modern combustion analysis uses gas chromatography to measure the amounts of product gas released.Which detector is used with the GC?

A)mass spectrometry
B)thermal conductivity
C)flame ionization
D)electron Ccapture
E)UV-vis

Question 19

Which of the following statements is(are)true for precipitate particle size?
I Particle size must be large enough to not clog or pass through a filter.
II Particle size is controlled by precipitation conditions.
III Thermodynamics favors larger crystals because the surface atoms have higher energy than internal atoms and the fraction of atoms on the surface is smaller for larger crystals than smaller crystals.
IV Ostwald ripening is the process where smaller particles re-dissolve and larger crystals grow.

A)III only
B)I,II,and IV
C)II and IV
D)I,II,III,and IV
E)II,III,and IV

Question 20

Homogeneous precipitation occurs when a precipitant is generated slowly from within an initially homogeneous solution by a chemical reaction.The main benefit from homogeneous precipitation is:

A)nucleation dominates over particle grown when precipitation is slow to give smaller,purer,easily filtered crystals.
B)particle grown dominates over nucleation when precipitation is slow to give smaller,purer,easily filtered crystals.
C)nucleation dominates over particle grown when precipitation is slow to give larger,purer,easily filtered crystals.
D)particle growth dominates over nucleation when precipitation is slow to give larger,purer,easily filtered crystals.
E)None of these answers is correct.