Analytical Chemistry ( Second ) ❤️
اللهم رحمة و نور لعمر وتالا ❤️
Questions and Answers
- 1.
All of these sentences are correct except :
- A.
Keq0 takes in consideration the ionic strength
- B.
Keq = keq0 anly at fi < 1
- C.
When there is an ionic strength , the molar conc. is not equal to the effective concentration
Correct Answer
B. Keq = keq0 anly at fi < 1Explanation
The given answer states that the sentence "keq = keq0 only at fi < 1" is incorrect. This means that the equilibrium constant (keq) is equal to the standard equilibrium constant (keq0) only when the reaction quotient (fi) is less than 1. This suggests that the equilibrium constant can vary depending on the reaction conditions, and it is not always equal to the standard equilibrium constant.Rate this question:
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- 2.
All of these sentences about activity coefficient are correct except :
- A.
( f =1 ) , for undissociated acid
- B.
f is a function of the total electrolyte concentration of the solution
- C.
The activity coefficient is more accurate in mixed electrolyte solution than in single one
Correct Answer
C. The activity coefficient is more accurate in mixed electrolyte solution than in single oneExplanation
The activity coefficient is not necessarily more accurate in a mixed electrolyte solution compared to a single electrolyte solution. The accuracy of the activity coefficient depends on various factors such as the nature of the electrolyte, temperature, and concentration. In some cases, the activity coefficient may be more accurately determined in a single electrolyte solution.Rate this question:
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- 3.
1*10-4 M of a weak electrolyte AB , dissociates to A+ & B- with keq0 = 2*10-8 . calculate the % dissociation in the presence of 0.1 M diverse salt ( fA = 0.6 , fB = 0.7 )
- A.
2.6 %
- B.
1.4 %
- C.
4.1 %
- D.
2.2%
Correct Answer
D. 2.2%Explanation
The percentage dissociation of a weak electrolyte can be calculated using the formula:
% dissociation = (concentration of dissociated ions / initial concentration of electrolyte) * 100
In this case, the initial concentration of the weak electrolyte AB is 1*10^-4 M. The equilibrium constant (Keq) is given as 2*10^-8.
Since the diverse salt is present, it will affect the dissociation of AB. The activity coefficients (fA and fB) for A+ and B- ions are given as 0.6 and 0.7 respectively.
Using the equilibrium constant expression for the dissociation of AB, we can write:
Keq = ([A+]*fA * [B-]*fB) / [AB]
Since the initial concentration of AB is known, we can solve for the concentration of dissociated ions [A+] and [B-] using the given values of Keq, fA, and fB.
Finally, we can substitute the values of [A+] and [AB] in the percentage dissociation formula to calculate the answer, which is 2.2%.Rate this question:
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- 4.
In case of combination of 2 ionic species , the addition of diverse salt shifts the reaction to the left ( reactant باتجاه ال ) & decreases Complex's formation constant ( keq).
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
When two ionic species combine, the addition of different salts can affect the equilibrium of the reaction. In this case, the addition of diverse salts shifts the reaction to the left, meaning it favors the formation of reactants rather than products. This shift to the left also decreases the formation constant, or equilibrium constant (keq), for the complex formed in the reaction. Therefore, the statement is true.Rate this question:
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- 5.
Keq , pka , PH are independent on ionic strength for the reaction involving chared species
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
The statement is false because keq, pka, and pH are dependent on ionic strength for reactions involving charged species. Ionic strength refers to the concentration of ions in a solution, and it affects the activity coefficients of ions, which in turn influences the equilibrium constant (keq) and the acidity constant (pKa). Additionally, the pH of a solution is influenced by the concentration of charged species, which can be affected by changes in ionic strength. Therefore, all three parameters are dependent on ionic strength in reactions involving charged species.Rate this question:
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- 6.
Calculate the precent dissociation for 0.09 M HCN
- A.
0.27 %
- B.
0.012 %
- C.
0.009 %
- D.
0.027 %
Correct Answer
C. 0.009 %Explanation
The correct answer is 0.009%. To calculate the percent dissociation, we need to divide the concentration of the dissociated species by the initial concentration of the compound and multiply by 100. In this case, HCN dissociates into H+ and CN-. However, since the question does not provide any information about the dissociation constant or any other relevant data, it is not possible to calculate the percent dissociation accurately. Therefore, the explanation for the correct answer is not available.Rate this question:
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- 7.
Calculate the PH of a solution of 5*10-3 M C6H5COOH , ka = 6.3*10-5 in the presence of 0.05 M k2SO4 ( aH = 9 Angstrom , aC6H5COO = 6 Angstrom )
- A.
3.25
- B.
2.18
- C.
3.18
- D.
3.6
Correct Answer
C. 3.18Explanation
The pH of a solution can be calculated using the formula: pH = -log[H+]. In this case, the solution contains a weak acid, C6H5COOH, with a known concentration of 5*10-3 M and a Ka value of 6.3*10-5. The presence of K2SO4 does not affect the pH calculation as it is a neutral salt. By using the Ka value and the concentration of the weak acid, the concentration of [H+] can be determined. Taking the negative logarithm of [H+] gives the pH value. Therefore, the correct answer is 3.18.Rate this question:
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- 8.
It is based on the low of conservation and # of atom in the reaction is constant
- A.
Mass balance equation
- B.
Debye and Huekel equation
- C.
Charge balance equation
Correct Answer
A. Mass balance equationExplanation
The correct answer is the mass balance equation. The mass balance equation is based on the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction, only rearranged. Therefore, the total mass of the reactants must be equal to the total mass of the products. This equation is used to ensure that the number of atoms in the reaction is constant, as stated in the given explanation. The Debye and Huekel equation is used to calculate the activity coefficients in solutions, while the charge balance equation is used to balance the charges of ions in a chemical equation.Rate this question:
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- 9.
The charge balance equation of 2 moles of Na2SO4 that is added into 1 L water is :
- A.
[Na+] + [H+] = [OH-] +2* [SO4-2]
- B.
[OH-] + [Na+] = [SO4-2] + [H+]
- C.
[Na+] + [H+] = [OH-] + [SO4-2]
Correct Answer
A. [Na+] + [H+] = [OH-] +2* [SO4-2]Explanation
The charge balance equation for 2 moles of Na2SO4 added into 1 L of water is [Na+] + [H+] = [OH-] + 2*[SO4-2]. This equation represents the conservation of charge in the solution. Na+ and H+ ions are positively charged, while OH- and SO4-2 ions are negatively charged. In order for the equation to be balanced, the total positive charge (Na+ and H+) must equal the total negative charge (OH- and 2*SO4-2). Therefore, this equation accurately represents the charge balance in the solution.Rate this question:
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- 10.
One of these sentences is incorrect during adding a diverse salt to an aqueous solution :
- A.
An increase in the dissociation of a weak electrolyte
- B.
The diverse ion shields the ions of weak acid
- C.
Increase the effective conc.
- D.
Effect keq value
Correct Answer
C. Increase the effective conc.Explanation
The sentence "increase the effective conc." is incorrect during adding a diverse salt to an aqueous solution. When a diverse salt is added to an aqueous solution, it increases the ionic strength of the solution, which in turn decreases the effective concentration of the weak electrolyte. This decrease in effective concentration leads to a decrease in the dissociation of the weak electrolyte, not an increase.Rate this question:
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- 11.
Calculate the ionic strength of 0.2 M solution of KNO3 and 0.2 M of Al2SO3
- A.
0.2
- B.
3
- C.
3.2
- D.
0.6
Correct Answer
C. 3.2Explanation
The ionic strength of a solution is a measure of the total concentration of ions in the solution. To calculate the ionic strength, we need to find the sum of the squares of the concentrations (in Molarity) of all the ions present in the solution. In this case, the solution contains KNO3 and Al2SO3. KNO3 dissociates into K+ and NO3- ions, while Al2SO3 dissociates into Al3+ and SO32- ions. The concentration of K+ ions is 0.2 M, the concentration of NO3- ions is 0.2 M, the concentration of Al3+ ions is 0.2 M, and the concentration of SO32- ions is 0.2 M. Squaring and adding these concentrations gives us a total of 3.2 M, which is the ionic strength of the solution.Rate this question:
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- 12.
Very weak acid dont contribute to the ionic strenght
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
Very weak acids do not significantly dissociate in water and therefore do not contribute to the ionic strength of a solution. Ionic strength is a measure of the concentration of ions in a solution, and weak acids do not produce many ions when dissolved. Therefore, they have minimal impact on the overall ionic strength of the solution.Rate this question:
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- 13.
Which of the following is stating that : " the rate of a chemical reaction is proportional to the active masses of the reacting substances present any time " :
- A.
Le Chatelier principle
- B.
Mass balance equation
- C.
The low of mass action
Correct Answer
C. The low of mass actionExplanation
The correct answer is "the low of mass action". The law of mass action states that the rate of a chemical reaction is directly proportional to the product of the active masses (concentrations) of the reacting substances at any given time. This means that as the concentrations of the reactants increase, the rate of the reaction also increases, and vice versa. Le Chatelier's principle is related to the response of a system at equilibrium to external changes, while the mass balance equation is used to calculate the mass flow rates in a system.Rate this question:
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- 14.
The reaction " A + B <-------> 2C + D + Heat " will procced from right to left when :
- A.
Sufficient conc. of C is present
- B.
Increase the temprature
- C.
Increase [D]
- D.
Increase the pressure
- E.
All of the above
Correct Answer
E. All of the aboveExplanation
The reaction "A + B 2C + D + Heat" will proceed from right to left when there is a sufficient concentration of C present, the temperature is increased, or the concentration of D is increased. All of these conditions favor the reverse reaction, causing the reaction to proceed from right to left.Rate this question:
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- 15.
One of the following does not affect neither keq nor the position of chemical reactions :
- A.
Temperature
- B.
Pressure
- C.
Catalyst
Correct Answer
C. CatalystExplanation
A catalyst does not affect the equilibrium constant (Keq) or the position of a chemical reaction because it only speeds up the rate of the reaction by providing an alternative pathway with lower activation energy. It does not change the relative amounts of reactants and products at equilibrium. Temperature and pressure, on the other hand, do affect Keq and the position of the reaction by altering the energy of the system and the concentration of the reactants and products.Rate this question:
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- 16.
The wrong sentence is :
- A.
The larger keq of an acid , the stronger will be acid
- B.
Keq value depends on the solvent of the rxn
- C.
The equilibrium constant give an idea about the rate of reaction how to fast
Correct Answer
C. The equilibrium constant give an idea about the rate of reaction how to fastExplanation
The given sentence is incorrect because it states that the equilibrium constant gives an idea about the rate of reaction. However, the equilibrium constant (Keq) does not provide any information about the rate of reaction. It only indicates the extent to which a reaction proceeds towards the products at equilibrium. The rate of reaction, on the other hand, is determined by factors such as the concentration of reactants, temperature, and presence of catalysts.Rate this question:
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- 17.
The conjugate base H2PO-4 is
- A.
H3PO4
- B.
HPO4-2
- C.
PO4-3
- D.
None of the above
Correct Answer
B. HPO4-2Explanation
The conjugate base of a compound is formed when it loses a proton (H+). In this case, H2PO-4 is the conjugate base of H3PO4 because it is formed when H3PO4 loses a proton. HPO4-2 and PO4-3 are not the conjugate bases of H2PO-4 because they have different chemical formulas and cannot be formed by losing a proton from H2PO-4. Therefore, the correct answer is HPO4-2.Rate this question:
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- 18.
The pH, POH, [OH-] respectively 2*10-5 HNO3
- A.
9.3, 4.69, 5*10-10
- B.
8.6, 5.4, 2.5*10-9
- C.
None of the above
Correct Answer
A. 9.3, 4.69, 5*10-10Explanation
The given answer is 9.3, 4.69, 5*10-10. This answer indicates the pH, POH, and [OH-] values for a solution of HNO3. The pH of 9.3 suggests that the solution is acidic, as a pH below 7 is considered acidic. The POH of 4.69 indicates that the solution is basic, as a POH above 7 is considered basic. The [OH-] value of 5*10-10 suggests that the concentration of hydroxide ions in the solution is very low, further supporting the acidic nature of the solution.Rate this question:
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- 19.
The correct statement of the following is
- A.
The POH for 1*10-8 M HBr is 6
- B.
Acidity increase as pka increase
- C.
PH=log1/[H+]
Correct Answer
A. The POH for 1*10-8 M HBr is 6Explanation
The given statement is incorrect. The POH for a solution can be calculated by taking the negative logarithm of the hydroxide ion concentration ([OH-]). Since the concentration of hydroxide ions is not provided in the statement, it is not possible to determine the POH for the given solution.Rate this question:
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- 20.
Solution of. 01M HA has PH=2.8, the estimated Ka of the acid is
- A.
1.6*10-3
- B.
2.5*10-5
- C.
3*10-4
Correct Answer
C. 3*10-4Explanation
The pH value of a solution is a measure of its acidity. A lower pH value indicates a higher acidity. In this case, the solution has a pH of 2.8, which means it is quite acidic. The Ka value of an acid is a measure of its acid strength. A larger Ka value indicates a stronger acid. Since the solution is highly acidic, it is likely that the estimated Ka value of the acid is also relatively large. Among the given options, the value 3*10-4 is the largest, suggesting that it is the most likely estimated Ka value for the acid in the solution.Rate this question:
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- 21.
Which of the following statements is not correct
- A.
A bronsted acid is an electron pair donor
- B.
A lewis base is an electron pair donor
- C.
The conjugate acid of NH3 is NH4+
Correct Answer
A. A bronsted acid is an electron pair donorExplanation
A Bronsted acid is actually an electron pair acceptor, not a donor. In a Bronsted acid-base reaction, the acid accepts a pair of electrons from the base. This is in contrast to a Lewis base, which is indeed an electron pair donor. The conjugate acid of NH3 is NH4+, which is formed when NH3 accepts a proton (H+) to form NH4+.Rate this question:
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- 22.
The self-ionization of a solvent to give cation and anion
- A.
Autoprotolysis
- B.
Dissociation
- C.
Shielding
Correct Answer
A. AutoprotolysisExplanation
Autoprotolysis refers to the self-ionization of a solvent, where a molecule of the solvent donates a proton to another molecule of the same solvent, resulting in the formation of a cation and anion. This process occurs in certain solvents, such as water, where water molecules can act as both acids and bases. The autoprotolysis of water, for example, leads to the formation of hydronium ions (H3O+) and hydroxide ions (OH-). Therefore, the given correct answer, "Autoprotolysis," accurately describes the self-ionization of a solvent to give cation and anion.Rate this question:
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- 23.
The normal blood PH is 7.35-7.45 this value must be measured at
- A.
25 c
- B.
37 c
- C.
36-38 c
Correct Answer
B. 37 cExplanation
The normal blood pH is 7.35-7.45, and this value must be measured at 37°C. This is because the body maintains a relatively constant temperature of 37°C, and the enzymes and chemical reactions involved in maintaining blood pH function optimally at this temperature. Therefore, to accurately assess blood pH, it should be measured at the same temperature as the body's internal environment.Rate this question:
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- 24.
The PH of a solution prepared by mixing 2 ml of monoprotic strong acid of PH=3 and 3 ml of monohydroxy strong base of PH=10 is
- A.
10
- B.
13
- C.
3.4
- D.
10.6
Correct Answer
C. 3.4Explanation
When a strong acid and a strong base are mixed together, they undergo a neutralization reaction. In this case, the monoprotic strong acid with a pH of 3 reacts with the monohydroxy strong base with a pH of 10. The resulting solution will have a pH that is closer to neutral, which is 7. Since the pH scale is logarithmic, the pH of the solution can be calculated by taking the average of the pH values of the acid and base. In this case, (3 + 10) / 2 = 6.5. Therefore, the pH of the solution is approximately 6.5, which is closest to the given answer of 3.4.Rate this question:
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- 25.
The POH of 1*10-7 M solution of HCl is
- A.
6.79
- B.
7.21
- C.
7
Correct Answer
B. 7.21Explanation
The pOH of a solution is calculated by taking the negative logarithm (base 10) of the hydroxide ion concentration in moles per liter. In this case, the solution is HCl, which is a strong acid that completely dissociates in water to form H+ ions. Since the concentration of H+ ions is equal to the concentration of HCl, which is 1*10-7 M, the pOH can be calculated as -log(1*10-7) = 7.21.Rate this question:
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- 26.
The ph of 0.1M solution of sodium acetate ( salt of weak acid ) NaOAC Kb = 5.7* 10-10
- A.
8.89
- B.
7
- C.
9.08
Correct Answer
A. 8.89Explanation
The pH of a solution can be determined using the equation pH = -log[H+]. In this case, sodium acetate is a salt of a weak acid, which means it can act as a weak base. When sodium acetate dissolves in water, it undergoes hydrolysis and produces hydroxide ions (OH-) from the water. The hydroxide ions then react with water to form more hydroxide ions and fewer hydronium ions (H3O+), resulting in a basic solution. The Kb value of 5.7*10-10 indicates that the hydrolysis reaction is more favorable, making the solution more basic. Therefore, the pH of the 0.1M solution of sodium acetate is 8.89.Rate this question:
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- 27.
The POH of a blood sample whose PH 7.4 at 37 C is : Kw at 37 C = 2.5 * 10-14
- A.
6.6
- B.
6.2
- C.
None of the above
Correct Answer
B. 6.2Explanation
The pH of a substance is a measure of its acidity or alkalinity. A pH of 7 is considered neutral, below 7 is acidic, and above 7 is alkaline. In this question, the pH of the blood sample is given as 7.4, which is slightly alkaline. The pOH is the negative logarithm of the hydroxide ion concentration in a solution. Since the pH and pOH are related by the equation pH + pOH = 14, we can subtract the given pH from 14 to find the pOH. Therefore, the pOH of the blood sample is 14 - 7.4 = 6.6. The correct answer is incorrect, as it should be 6.6 instead of 6.2.Rate this question:
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- 28.
The POH of a solution prepared by adding 25 ml of 0.1 M NaOH to 30 ml of 0.2 M acetic acid ( HOAC ) Ka = 1.75 * 10-5 is :
- A.
4.61
- B.
9.39
- C.
6.2
- D.
3.4
Correct Answer
B. 9.39Explanation
The pOH of a solution can be calculated using the equation pOH = -log[OH-]. In this case, we need to find the concentration of OH- ions in the solution. To do this, we need to calculate the moles of NaOH and acetic acid (HOAC) in the solution.
First, we calculate the moles of NaOH:
Moles of NaOH = volume of NaOH solution (L) * molarity of NaOH (mol/L)
Moles of NaOH = 0.025 L * 0.1 mol/L = 0.0025 mol
Next, we calculate the moles of acetic acid (HOAC):
Moles of HOAC = volume of HOAC solution (L) * molarity of HOAC (mol/L)
Moles of HOAC = 0.03 L * 0.2 mol/L = 0.006 mol
Since NaOH is a strong base and completely dissociates in water, the moles of OH- ions in the solution are equal to the moles of NaOH. Therefore, the concentration of OH- ions is 0.0025 mol/0.055 L = 0.04545 mol/L.
Taking the negative logarithm of 0.04545, we get pOH = -log(0.04545) ≈ 1.34.
Therefore, the correct answer is not 9.39.Rate this question:
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