Question 1

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

Accepted Answer

High density is not a property of the ideal solid product for gravimetric analysis. The ideal solid product should be insoluble, have a known composition, be pure, and be easily filterable. High density is not necessarily a requirement for gravimetric analysis.

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.

Accepted Answer

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?

Accepted Answer

C

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.

Accepted Answer

Techniques to promote particle growth include using a large volume of solution to keep concentrations low (I), slowly adding precipitant with vigorous mixing to prevent supersaturation (III), and raising the temperature to increase solubility and decrease supersaturation (IV). These methods help in achieving larger, more uniform particles by controlling the rate of nucleation and growth. Rapid addition of precipitant (II) typically leads to smaller particles due to rapid nucleation, which is not conducive to particle growth.

Question 5

____________________ are solid particles with long-range order.

Accepted Answer

Crystalline particles have a regular and repeating arrangement of atoms or molecules, known as long-range order. This long-range order gives them their characteristic properties, such as a specific melting point, hardness, and cleavage planes. In contrast, amorphous particles lack long-range order and have a disordered atomic arrangement.

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?

Accepted Answer

The answer of A 100.0 mL sample of a solution...

Question 7

____________________ are solid particles that lack any crystalline order.

Accepted Answer

Amorphous particles lack a defined structure or arrangement, unlike crystalline particles which have a repeating pattern. The other options (plastic, irregular, and elastic) don't accurately describe the lack of order in amorphous 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.

Accepted Answer

Ignition involves strong heating of a precipitate to change its chemical composition to a more stable form. This process ensures a known and stable chemical composition of the final precipitation product. Drying involves only the removal of water or solvent and does not alter the chemical composition of the precipitate. Charring is the partial burning or carbonization of organic substances and is not a suitable method for obtaining a known, stable chemical composition. Thermogravimetric analysis is a method of measuring the change in weight of a substance as it is heated, and annealing is the process of heating a material to a specific temperature and then cooling it slowly to make it less brittle or more ductile.

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?

Accepted Answer

The answer of Combustion analysis of 0.1938 grams of a...

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?

Accepted Answer

To calculate the molarity of the copper(II) chloride solution, you don't need the molar mass of copper(II) chloride itself. You need the molar mass of silver chloride to find the moles of silver chloride precipitated, which can then be used to find the moles of copper(II) chloride through stoichiometry, and finally, the molarity of the copper(II) chloride solution by dividing by the volume of the solution.

Question 11

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

Accepted Answer

The answer of Modern combustion analysis uses dynamic flash combustion.What...

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?

Accepted Answer

The answer of Combustion analysis of 0.1938 grams of a...

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.

Accepted Answer

The statement "Particle growth occurs when amorphous particles clump together to create larger amorphous particles" is not true. Particle growth occurs when ions, molecules, or nuclei condense onto a particle to form a larger crystal with a more ordered structure. Therefore, only statement III is true for nucleation and statement IV is false for particle growth.

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?

Accepted Answer

The answer of A solution is prepared from an unknown...

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.

Accepted Answer

Combustion analysis of oxygen does not require step II where gaseous products are passed through nickelized carbon to convert oxygen into CO. Combustion analysis of oxygen requires a different method where the sample is exposed to an oxygen-rich environment and the combustion products are analyzed using infrared spectroscopy. Therefore, options D and E are also incorrect as they include step II. Option A is incorrect as it includes step III which is required for all combustion analyses. Option B is incorrect as it includes step IV which is required for halogens, not oxygen. Option C is the best choice as it correctly identifies the steps that are not required for combustion analysis of oxygen.

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.

Accepted Answer

The gravimetric factor is the ratio of the molar mass of the analyte to the molar mass of the product. In this case, the analyte is silver cation (Ag+) and the product is silver carbonate (Ag2CO3). The molar mass of Ag+ is 107.87 g/mol and the molar mass of Ag2CO3 is 275.79 g/mol. Therefore, the gravimetric factor is:GF = (molar mass of Ag+) / (molar mass of Ag2CO3)GF = 107.87 g/mol / 275.79 g/molGF = 0.391

Question 17

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

Accepted Answer

During combustion, all carbon is converted to carbon dioxide, not 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?

Accepted Answer

Thermal conductivity detectors are commonly used in gas chromatography for combustion analysis because they can detect a wide range of gases, including those produced in combustion processes.

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.

Accepted Answer

All statements are true regarding precipitate particle size. Statement I is practical in nature, ensuring that particles are of a size that can be effectively filtered. Statement II highlights the influence of precipitation conditions (like concentration, temperature, and presence of additives) on particle size. Statement III explains the thermodynamic preference for larger crystals due to lower surface energy per atom. Statement IV describes Ostwald ripening, a process that leads to the growth of larger particles at the expense of smaller ones, further influencing the size distribution of precipitates.

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:

Accepted Answer

In homogeneous precipitation, slow precipitation allows particle growth to dominate over nucleation, resulting in larger, purer, and easily filtered crystals.

Quiz 28: Gravimetric and Combustion Analysis