১.
What is the conjugate base of the dihydrogen phosphate ion, H2PO4−?
৪৯তম বিসিএস ⎯ প্রাণ রসায়ন [৬০১]
মোট প্রশ্ন২৯
সিলেবাস
Exam 4
Biophysical Chemistry — Acids and Bases; Spectrometry
[Source: Class–2 and relevant books]
৪৯তম বিসিএস ⎯ প্রাণ রসায়ন [৬০১]
৪৯তম বিসিএস ⎯ প্রাণ রসায়ন [৬০১] · তারিখ অনির্ধারিত · ২৯ প্রশ্ন
২.
In the reaction HCl + H2O ⇌ H3O++ Cl−, which species acts as a Brønsted-Lowry base?
ব্যাখ্যা
According to the Brønsted-Lowry definition, a base is a substance that accepts a proton. In this reaction, water (H2O) accepts a proton from hydrochloric acid (HCl) to form the hydronium ion (H3O+).
৩.
According to the Lewis acid-base concept, a base is a substance that can:
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The Lewis theory provides a broader definition where a base is an electron-pair donor and an acid is an electron-pair acceptor.
৪.
What is the pH of a 0.01 M solution of potassium hydroxide (KOH)?
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৫.
An indicator, HIn, has a Ka of 1×10−6. The protonated form, HIn, is red, and its conjugate base, In−, is blue. What color will the indicator be in a solution of pH 8?
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৬.
The primary physiological buffer system in human blood is the:
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The bicarbonate buffer system, composed of carbonic acid (H2CO3) and the bicarbonate ion (HCO3−), is the most important buffer in the blood, maintaining its pH within the narrow range of 7.35 to 7.45.
৭.
You need to prepare a buffer solution with a pH of 7.0. Which of the following weak acids would be the best choice?
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A buffer has its maximum buffering capacity when the pH is equal to the pKa of the weak acid. To create an effective buffer, you should choose a weak acid with a pKa as close as possible to the desired pH. The pKa of 7.21 is closest to the target pH of 7.0.
৮.
What is the pH of a buffer solution containing 0.2 M acetic acid (CH3COOH) and 0.2 M sodium acetate (CH3COONa)? (Given: pKaof acetic acid = 4.76)
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৯.
The buffering capacity of a buffer is at its maximum when:
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Buffering capacity refers to the ability of a buffer to resist pH change. This ability is greatest when the concentrations of the weak acid and its conjugate base are equal, which is the point where the pH of the solution is equal to the pKa of the acid.
১০.
A complete neutralization reaction between a strong acid and a strong base produces:
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The reaction between a strong acid (like HCl) and a strong base (like NaOH) proceeds to completion, forming a neutral salt (NaCl) and water (H2O).
১১.
The ion product of water, Kw, at 25°C is 1.0×10−14. What is the concentration of OH−ions in pure water at this temperature?
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১২.
If 100 mL of 0.2 M HCl is mixed with 100 mL of 0.2 M NaOH, the pH of the final solution will be:
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You are mixing equal volumes of a strong acid and a strong base at the same concentration. This means the number of moles of acid is equal to the number of moles of base. They will completely neutralize each other, leaving only salt and water, resulting in a neutral solution with a pH of 7.
১৩.
Which of the following species is amphiprotic (can act as both a Brønsted-Lowry acid and base)?
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Water is the classic example of an amphiprotic substance. It can donate a proton to form OH−(acting as an acid) or accept a proton to form H3O+(acting as a base).
১৪.
The autoionization of water is an endothermic process. If the temperature of pure water is raised from 25°C to 60°C:
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১৫.
When a small amount of strong acid is added to an acetate buffer, the pH remains relatively constant because the added H+ions are consumed by:
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Explanation: The function of a buffer is to neutralize added acid or base. The conjugate base component of the buffer, the acetate ion (CH3COO-), reacts with and neutralizes the added hydrogen ions (H+) by forming weak acetic acid (CH3COOH).
১৬.
Beer's Law states that absorbance is directly proportional to the:
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The Beer-Lambert law is given by the equation A=ϵbc, where A is absorbance, ϵ is the molar absorptivity, b is the path length, and c is the concentration. This equation shows a direct, linear relationship between absorbance and concentration.
১৭.
Optical Density (OD) is mathematically defined as:
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১৮.
If a solution has a transmittance of 10%, its absorbance is:
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১৯.
For constructing a standard curve to determine the concentration of an unknown protein sample, you should plot:
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Explanation: This is the standard convention. A series of solutions with known concentrations (the standards) are prepared, their absorbances are measured, and a graph is plotted. The concentration of an unknown can then be found by measuring its absorbance and interpolating from this curve.
২০.
A solution of substance X has an absorbance of 0.5 in a cuvette with a 1 cm path length. According to the Beer-Lambert law, what would be the absorbance if the path length were increased to 2 cm?
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According to the Beer-Lambert law (A=ϵbc), absorbance is directly proportional to the path length (b). If you double the path length while keeping everything else constant, the absorbance will also double.
২১.
The purpose of using a "blank" in spectrophotometry is to:
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Explanation: The "blank" contains the solvent and any other reagents in the sample except for the substance being measured. By zeroing the spectrophotometer with the blank, you ensure that the measured absorbance is solely due to the substance of interest and not from the container or the solvent.
২২.
To determine the concentration of a purified DNA sample, you should measure its absorbance at:
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Explanation: The nitrogenous bases in nucleic acids (adenine, guanine, cytosine, thymine, uracil) have a characteristic maximum light absorbance at a wavelength of 260 nm. This property is used to quantify DNA and RNA
২৩.
The unit of molar absorptivity (ϵ) is:
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Explanation: By rearranging the Beer-Lambert law, ϵ=A/(bc). Since absorbance (A) is unitless, concentration (c) is in M (moles/liter), and path length (b) is in cm, the units for ϵ must be M-1cm-1 to make the equation dimensionally consistent.
২৪.
The concentration of a substance is doubled, and the path length of the cuvette used for measurement is also doubled. The new absorbance value will be:
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২৫.
You are monitoring an enzyme that converts a colored substrate to a colorless product. To measure the rate of this reaction spectrophotometrically, you would:
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Explanation: The colored substrate absorbs light. As the enzyme converts it to a colorless product, the concentration of the substrate decreases. According to Beer's Law, this decrease in concentration will lead to a proportional decrease in absorbance. The rate at which the absorbance decreases reflects the rate of the enzymatic reaction.
২৬.
Which statement accurately distinguishes between the Brønsted-Lowry and Lewis acid-base definitions?
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Explanation: A proton (H+) is essentially a nucleus with no electrons, making it an excellent electron pair acceptor. Therefore, any substance that can donate a proton is, by extension, a Lewis acid. The Lewis definition is more general and includes substances without protons that can still accept electron pairs.
২৭.
A buffer solution is prepared with 0.1 M weak acid (HA) and 0.1 M of its conjugate base (A−). If the pKa of the acid is 5.0, what is the effective buffering range of this solution?
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Explanation: A buffer is generally considered effective within a pH range of ±1 unit from the pKa of the weak acid. For a pKa of 5.0, this range is from pH 4.0 to pH 6.0.
২৮.
A solution contains a compound with a molar absorptivity of 5000 M-1cm-1. What concentration is required to produce an absorbance of 0.4 in a 1 cm cuvette?
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২৯.
The Henderson-Hasselbalch equation is most useful for: