Organic Lab 💚
Midterm
Questions and Answers
- 1.
How does the presence of an impurity affect the melting point of a compound?
- A.
Decreases
- B.
Increases sharply
- C.
Slightly increases
- D.
No change
Correct Answer
A. DecreasesExplanation
The presence of an impurity in a compound disrupts the regular arrangement of its molecules, making it more difficult for them to pack closely together. This disruption weakens the intermolecular forces between the molecules, which are responsible for holding the compound in its solid state. As a result, less energy is required to break these weaker forces and convert the compound from a solid to a liquid, causing the melting point to decrease.Rate this question:
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- 2.
The purity of the compound is confirmed by :
- A.
Its melting point and boiling point
- B.
Chromatographic technique
- C.
Spectroscopy
- D.
All of the mentioned
Correct Answer
D. All of the mentionedExplanation
The purity of a compound can be confirmed by various methods including its melting point and boiling point, chromatographic technique, and spectroscopy. Melting point and boiling point are physical properties that can be used to determine the purity of a compound. If the observed melting and boiling points match the expected values for the pure compound, it indicates that the compound is pure. Chromatographic techniques, such as thin-layer chromatography or high-performance liquid chromatography, can separate and identify the different components present in a mixture, allowing for the determination of purity. Spectroscopy techniques, such as UV-Vis spectroscopy or NMR spectroscopy, can provide information about the molecular structure and composition of a compound, helping to confirm its purity. Therefore, all of these methods can be used to confirm the purity of a compound.Rate this question:
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- 3.
Select the correct statement from the following options.
- A.
The transformation of solid to liquid is called melting and the reverse process is called freezing
- B.
The transformation of solid to liquid is called freezing and the reverse process is called melting
- C.
The transformation of liquid to solid is called melting and the reverse process is called freezing
- D.
None of the mentioned
Correct Answer
A. The transformation of solid to liquid is called melting and the reverse process is called freezingExplanation
The correct statement is that the transformation of solid to liquid is called melting and the reverse process is called freezing. This is because when a solid substance is heated, it gains enough energy to break its intermolecular bonds and become a liquid. This process is called melting. On the other hand, when a liquid substance is cooled, it loses energy and its particles slow down, forming intermolecular bonds and becoming a solid again. This process is called freezing.Rate this question:
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- 4.
The melting point determination of a substance helps us to (a)know the mass of the substance
- A.
Know the functional group present in a compound
- B.
Know the purity of a compound
- C.
Know the mass of the substance
- D.
Know the volume of the substance
Correct Answer
B. Know the purity of a compoundExplanation
The melting point determination of a substance helps us to know the purity of a compound. The melting point of a pure substance is a characteristic property, meaning it remains constant regardless of the amount of the substance present. If impurities are present in the compound, they can cause the melting point to decrease or have a broadened range. Therefore, by comparing the observed melting point of a sample to the known melting point of the pure compound, we can assess its purity.Rate this question:
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- 5.
Different solids have different melting points. Why?
- A.
Difference in the method of determination of melting point
- B.
Difference in the bond length between atoms
- C.
Difference in the surface area of the substances.
- D.
Intermolecular forces of different strength.
Correct Answer
D. Intermolecular forces of different strength.Explanation
Different solids have different melting points because they have different intermolecular forces of different strength. The strength of intermolecular forces determines the amount of energy required to break the bonds between the molecules and convert the solid into a liquid. Solids with stronger intermolecular forces will have higher melting points because more energy is needed to overcome these forces and break the bonds. On the other hand, solids with weaker intermolecular forces will have lower melting points as less energy is required to break the bonds and convert the solid into a liquid.Rate this question:
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- 6.
The melting point of a pure compound is a unique property of that compound, independent of its source. Is this statement:
- A.
True
- B.
Fase
Correct Answer
A. TrueExplanation
The statement is true because the melting point of a pure compound remains the same regardless of its source. This is because the melting point is determined by the specific arrangement and strength of the intermolecular forces within the compound. As long as the compound is pure and its chemical structure remains the same, the melting point will be consistent. Different sources or samples of the compound may have slight variations in impurities or crystal structures, but the melting point will remain unchanged as long as the compound itself is pure.Rate this question:
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- 7.
No two pure compounds can have the same melting point. Is this statement:
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
This statement is false. It is possible for two pure compounds to have the same melting point. The melting point of a compound is determined by its chemical structure and intermolecular forces. If two compounds have similar structures and intermolecular forces, they can exhibit the same melting point. Additionally, impurities or mixtures can also affect the melting point of a compound, causing it to change or become similar to another compound. Therefore, it is not true that no two pure compounds can have the same melting point.Rate this question:
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- 8.
Melting does not occur instantaneously, because molecules must absorb the energy and then physically break the binding forces Is this statement :
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
The statement is true because melting is a process that requires energy for molecules to overcome the forces holding them together in a solid state. The energy is absorbed by the molecules, causing them to vibrate and eventually break the binding forces. This process takes time and does not happen instantaneously.Rate this question:
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- 9.
The crystal is dried in the oven Is this statement :
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The statement "The crystal is dried in the oven" is false. The given statement implies that the crystal is dried using an oven, which may not be the correct method. Drying crystals usually involves techniques like air drying, desiccation, or using a desiccator. The use of an oven may damage or alter the crystal structure. Therefore, the statement is false.Rate this question:
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- 10.
If the crystal does not from what should you do?
- A.
Scratching the inside surface of the flask by glass rod
- B.
Seeding crystal
- C.
Ice water bath
- D.
All the above
Correct Answer
D. All the aboveExplanation
If the crystal does not form, it means that the crystallization process is not occurring properly. Scratching the inside surface of the flask with a glass rod can provide rough surfaces for crystal growth to start. Seeding crystal involves adding a small crystal of the desired substance to the solution, which can act as a template for the growth of larger crystals. An ice water bath can provide a controlled environment with lower temperatures, which can promote crystallization. Therefore, using all the above techniques can help improve the chances of crystal formation.Rate this question:
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- 11.
The right crystal size is?
- A.
Small crystal
- B.
Moderate crystal
- C.
Large crystal
Correct Answer
B. Moderate crystalExplanation
The term "right" in the question suggests that there is an optimal or ideal crystal size. Large crystals may have their advantages, such as being visually appealing, but they can also be prone to imperfections or structural issues. On the other hand, small crystals may lack the desired impact or presence. Therefore, a moderate crystal size seems to strike a balance between the two extremes, offering a satisfactory combination of visual appeal and structural integrity.Rate this question:
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- 12.
Crystallization is performed in Erlenmeyer flask not in beaker .Why?
- A.
It increase the amount of evaporated solvent because its sloping side will act as a condense
- B.
Bumping
- C.
Covered
- D.
B+c
Correct Answer
D. B+cExplanation
The correct answer is b+c. Crystallization is performed in an Erlenmeyer flask instead of a beaker because the sloping sides of the flask help to prevent the loss of solvent due to evaporation. The condensation that occurs on the sides of the flask helps to keep the solvent from escaping, allowing for a higher yield of crystals. Additionally, the flask can be covered to further prevent evaporation and contamination.Rate this question:
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- 13.
Why does the size of the crystal becomes large?
- A.
Dilute solution
- B.
Saturated solution
- C.
Slow cooling
- D.
Bubbles
Correct Answer
A. Dilute solutionExplanation
When a solution is dilute, it means that there is a small amount of solute dissolved in a large amount of solvent. In this case, the solute particles are more spread out and have more space to move around. When the solution is left to cool slowly, the solute particles have more time to come together and form crystals. Since there are fewer solute particles in a dilute solution, the crystals that form are larger in size.Rate this question:
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- 14.
If the temperature increases, the amount of solute that can be dissolved in a solvent decrease. Is this statement :
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The given statement is false. According to the principle of solubility, as the temperature increases, the amount of solute that can be dissolved in a solvent generally increases. This is because higher temperatures provide more energy to the solvent molecules, allowing them to break the intermolecular forces and accommodate a greater amount of solute particles.Rate this question:
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- 15.
Why added Na2CO3 in extraction?
- A.
To remove the tannins compound .
- B.
Remove excess of H2O
- C.
To remove trace of basic compound in organic solution.
- D.
Change the distribution coefficient between organic solvent and aqueous solvent,
Correct Answer
A. To remove the tannins compound .Explanation
Na2CO3 is added in extraction to remove the tannins compound. Tannins are a class of compounds that can interfere with the extraction process and affect the purity of the desired compound. Na2CO3, also known as sodium carbonate, is a basic compound that can react with tannins and form insoluble complexes, which can then be easily separated from the organic solution. This helps in obtaining a cleaner and purer extract.Rate this question:
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- 16.
Why added NaHCO3 in extraction?
- A.
To remove excess of acidic compound in organic solution
- B.
Remove excess of H2O
- C.
To remove trace of basic compound in organic solution.
- D.
Change the distribution coefficient between organic solvent and aqueous solvent,
Correct Answer
A. To remove excess of acidic compound in organic solutionExplanation
NaHCO3 is added in extraction to remove excess of acidic compound in the organic solution. This is because NaHCO3 is a basic compound and can react with acidic compounds to form water-soluble salts. By adding NaHCO3, the acidic compound will be converted into a salt that can be easily separated from the organic solution. This helps to purify the organic solution by removing any excess acidic compound present.Rate this question:
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- 17.
Mixing the layers for remove gases in extraction ?
- A.
False
- B.
True
Correct Answer
B. TrueExplanation
Mixing the layers is an effective method for removing gases in extraction. When different layers are mixed, it increases the surface area of contact between the gases and the liquid, facilitating the transfer of gases from the liquid phase to the gas phase. This process is commonly used in various extraction techniques, such as liquid-liquid extraction or gas absorption, where the goal is to separate components from a mixture. Therefore, the statement "Mixing the layers for remove gases in extraction" is true.Rate this question:
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- 18.
Why Added few drop of ethanol in extraction?
- A.
Remove excess of H2O
- B.
To remove excess of acidic compound in organic solution
- C.
To remove trace of basic compound in organic solution.
- D.
Anti foaming agent
Correct Answer
D. Anti foaming agentExplanation
The correct answer is "anti foaming agent." Adding a few drops of ethanol in extraction acts as an anti foaming agent. Foaming can occur during extraction due to the presence of impurities or surfactants in the solution. Ethanol helps to reduce the formation of foam by breaking down the surface tension of the solution. This allows for a more efficient extraction process by preventing excessive foaming and ensuring accurate results.Rate this question:
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- 19.
We added lightly grease on key of sep-funnel To seal ground glass joints.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
Applying a light grease on the key of a sep-funnel helps to create a tight seal when connecting the ground glass joints. This is important because a secure seal prevents any leakage or loss of the substances being separated in the sep-funnel. The grease acts as a lubricant and helps to ensure a smooth and secure connection between the glass joints, enhancing the effectiveness of the separation process. Therefore, the statement is true.Rate this question:
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- 20.
How can Selection of suitable solvent for extraction?
- A.
Immiscible with the first solvent
- B.
The extraction solvent should be sufficiently volatile
- C.
To solvent should have a density different from that of water to from two distinguishable layers
- D.
Dissolve the compound to be extracted and don’t react
- E.
All the above
Correct Answer
E. All the aboveExplanation
The selection of a suitable solvent for extraction involves several factors. The solvent should be immiscible with the first solvent to ensure proper separation. It should also be sufficiently volatile, allowing for easy evaporation. Additionally, the solvent should have a density different from that of water to form two distinguishable layers, aiding in the separation process. Lastly, the solvent should be able to dissolve the compound to be extracted without reacting with it. Therefore, all of the above factors are important in the selection of a suitable solvent for extraction.Rate this question:
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- 21.
Fractional Distillation less Efficient than Simple Distillation.Because Fractional Distillation depend along a column
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The given statement is false. Fractional distillation is actually more efficient than simple distillation. In fractional distillation, a fractionating column is used which allows for multiple distillations to occur within the column. This column contains several trays or packing material which provides a larger surface area for vaporization and condensation to take place. This allows for the separation of liquids with closer boiling points. Simple distillation, on the other hand, only involves a single distillation process and is used for separating liquids with larger differences in boiling points.Rate this question:
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- 22.
Thermometer an instrument for measuring atmospheric pressure.
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The given statement is incorrect. A thermometer is not used for measuring atmospheric pressure. Instead, it is used for measuring temperature. Therefore, the correct answer is False.Rate this question:
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- 23.
Boiling point is?
- A.
The temperature at which its vapor pressure equals atmosphere pressure.
- B.
is the temperature at which the first crystal just starts to melt
- C.
A+c
- D.
None of the above
Correct Answer
A. The temperature at which its vapor pressure equals atmosphere pressure.Explanation
The boiling point of a substance is the temperature at which its vapor pressure is equal to the atmospheric pressure. At this temperature, the liquid begins to rapidly vaporize and turn into a gas. The vapor pressure of a substance increases with temperature until it reaches the boiling point, at which point the vapor pressure matches the atmospheric pressure, allowing the substance to boil.Rate this question:
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- 24.
When to use Steam distillation
- A.
Used specially to purify liquids that are not Very Volatile and are Immiscible with Water
- B.
When the boiling point of the compound(or the solvent)is too high
- C.
Used effectively to separate liquids that less than 70 degrees difference in their boiling points
- D.
Used effectively to separate liquids that have at least 70 degrees difference in their boiling points
Correct Answer
A. Used specially to purify liquids that are not Very Volatile and are Immiscible with WaterExplanation
Steam distillation is used specifically to purify liquids that are not very volatile and are immiscible with water. This method is suitable when the boiling point of the compound or solvent is too high for regular distillation. It is also effective in separating liquids that have a difference in boiling points of less than 70 degrees. However, it may not be as effective when the difference in boiling points is greater than 70 degrees.Rate this question:
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- 25.
Simple distillation is useful in the for removal of _____ components that are dissolved in ____
- A.
Volatile, liquid
- B.
Non-volatile, liquid
- C.
Non-volatile, solid
- D.
Volatile, solid
Correct Answer
B. Non-volatile, liquidExplanation
Simple distillation is a technique used to separate components based on their boiling points. In this case, the correct answer is "non-volatile, liquid." Non-volatile components do not easily vaporize at low temperatures, so they remain in the liquid phase during distillation. On the other hand, volatile components have lower boiling points and readily vaporize, allowing them to be collected as a separate fraction. Therefore, simple distillation is effective for removing non-volatile components that are dissolved in a liquid.Rate this question:
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- 26.
Compounds with stronger attractive forces or higher molecular weights have lower boiling points?
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
Compounds with stronger attractive forces or higher molecular weights have higher boiling points. This is because stronger intermolecular forces require more energy to break, resulting in a higher boiling point. Similarly, compounds with higher molecular weights have more atoms or particles, leading to stronger intermolecular forces and therefore higher boiling points.Rate this question:
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- 27.
Purpose of distillation Separation of a liquid/liquid or liquid/solid mixture based on the diff volatilities/VP pressures of the compound.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
The purpose of distillation is to separate a mixture of liquids or a liquid and solid based on the different volatilities or vapor pressure pressures of the compounds. Distillation takes advantage of the fact that different compounds have different boiling points, allowing them to be separated by heating the mixture and collecting the vapor that is produced. This process is commonly used in industries such as oil refining and chemical manufacturing to purify substances and obtain desired products. Therefore, the statement "Purpose of distillation: Separation of a liquid/liquid or liquid/solid mixture based on the diff volatilities/VP pressures of the compound" is true.Rate this question:
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- 28.
Chromatograph is the separation of two or more compounds or ions by the distribution between two phases, one which is moving (stationary) and the other one is mobile phase
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The explanation for the answer "False" is that chromatography is not the separation of two or more compounds or ions by the distribution between two phases. Instead, chromatography is a technique used to separate and analyze mixtures based on their different interactions with a stationary phase and a mobile phase. It involves the movement of the mobile phase through the stationary phase, leading to the separation of the components of the mixture.Rate this question:
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- 29.
The phase that is fixed in place in chromatography column or plate -could be solid or liquid
- A.
Mobile phase
- B.
Stationary
Correct Answer
B. StationaryExplanation
In chromatography, the stationary phase refers to the phase that remains fixed in place, either in a column or on a plate. This phase can be either solid or liquid. It acts as a medium for the separation of the components of a mixture based on their different affinities for the stationary and mobile phases. The mobile phase, on the other hand, is the phase that moves through the stationary phase, carrying the sample along with it. Therefore, the correct answer is "stationary."Rate this question:
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- 30.
The phase that carries the analyte mixture through the stationary phase -could be gas or liquid
- A.
Mobile phase
- B.
Stationary
Correct Answer
A. Mobile phaseExplanation
The mobile phase refers to the phase that carries the analyte mixture through the stationary phase. It can be either a gas or a liquid. In chromatography, the mobile phase is responsible for transporting the sample components over the stationary phase. It interacts differently with the analytes, causing them to separate based on their affinity for the stationary phase. The mobile phase plays a crucial role in the separation process and is essential for the analysis of the analyte mixture.Rate this question:
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- 31.
When using column chromatography with samples that have very different Rf values what size of column is appropriate?
- A.
Short
- B.
Tall
- C.
A+c
Correct Answer
A. ShortExplanation
A short column is appropriate when using column chromatography with samples that have very different Rf values. This is because a short column allows for better separation of the compounds, as the compounds with higher Rf values will move faster through the column compared to those with lower Rf values. A shorter column also reduces the time required for the chromatographic process, making it more efficient.Rate this question:
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- 32.
What are two types of adsorbents used in column chromatography?
- A.
H2O
- B.
Organic solvent
- C.
Alumina, or silica gel
- D.
He or H2
Correct Answer
C. Alumina, or silica gelExplanation
Alumina and silica gel are two types of adsorbents commonly used in column chromatography. These adsorbents have high surface areas and can interact with different compounds in the sample mixture. Alumina is often used for separating polar compounds, while silica gel is suitable for non-polar compounds. These adsorbents work by adsorbing the target compounds onto their surfaces, allowing for separation based on their different affinities for the adsorbent.Rate this question:
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- 33.
What are the major steps for TLC?
- A.
The Stationary phas
- B.
The Mobile Phase:
- C.
Spotting the Plate
- D.
A+c
Correct Answer
C. Spotting the PlateExplanation
The major steps for TLC include preparing the stationary phase, preparing the mobile phase, and spotting the plate. Spotting the plate refers to the process of applying the sample onto the stationary phase of the TLC plate. This step is crucial as it allows the separation of the components of the sample to occur when the plate is developed. By spotting the plate, the sample is evenly distributed on the stationary phase, ensuring accurate separation and analysis.Rate this question:
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- 34.
In TLC, the sample is applied to the plate before the solvent
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
In thin-layer chromatography (TLC), the sample is indeed applied to the plate before the solvent. This is because TLC involves the separation of different components in a mixture based on their different affinities to the stationary phase (the TLC plate) and the mobile phase (the solvent). By applying the sample first, it allows the components to interact with the stationary phase and become immobilized before the solvent is added. This ensures that the components are properly separated and can be visualized as distinct spots on the TLC plate after the solvent has moved up the plate.Rate this question:
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- 35.
In TLC the separation in is based on the many equilibrations the solutes experience between the moving and the stationary phases
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
In thin-layer chromatography (TLC), the separation of solutes is achieved by their equilibration between the mobile phase (moving phase) and the stationary phase. The stationary phase is a thin layer of adsorbent material coated on a plate, and the mobile phase is a solvent that moves up the plate by capillary action. As the solutes migrate through the plate, they repeatedly interact with the stationary phase, leading to equilibration between the two phases. This equilibration process allows for the separation of different components in the mixture based on their different affinities for the stationary phase. Therefore, the given statement is true.Rate this question:
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- 36.
Uncolored spot can be show by :
- A.
Iodine chamber
- B.
Vanillin
- C.
KMnO4
- D.
All the above
Correct Answer
D. All the aboveExplanation
The uncolored spot can be shown by all of the above options, including the iodine chamber, vanillin, and KMnO4. These substances have the ability to react with certain compounds or substances, causing a visible color change. Therefore, when any of these options are used, they can help in identifying the presence of uncolored spots or compounds by producing a color change reaction.Rate this question:
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- 37.
Column chromatography is a technique based on both adsorptivity and solubility. It is a solid–liquid phase-partitioning technique
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
Column chromatography is indeed a technique that relies on both adsorptivity and solubility. It involves the separation of components in a mixture based on their differing affinities for the stationary phase (solid) and mobile phase (liquid). The stationary phase adsorbs certain components more strongly, causing them to move more slowly through the column, while the less adsorptive components move more quickly. This separation is possible due to the varying solubilities of the components in the mobile phase. Thus, the statement "Column chromatography is a technique based on both adsorptivity and solubility" is true.Rate this question:
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