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Questions and Answers

What is the pH of electrically neutral water at 25ºC?

7 (correct)

Which of the following best describes the role of buffers in a solution?

They minimize pH changes when acids or bases are introduced. (correct)

They completely dissociate to maintain pH.

They create a perpetual state of equilibrium.

They only stabilize pH at low concentrations.

According to the Henderson-Hasselbalch equation, what happens when the concentrations of weak acid (HA) and conjugate base (A-) are equal?

The pH will be less than the pKa.

The pH will be greater than the pKa.

The pH will not change.

The pH will equal the pKa. (correct)

What ensures that the pH remains stable in natural biological systems?

The presence of buffers and regulatory molecules. Signup and view all the answers

How does the addition of an acid affect a buffer solution?

It is neutralized by the conjugate base present. Signup and view all the answers

What is the mass of HEPES required to prepare a 50mM solution in 1L of water?

11.915 g Signup and view all the answers

What is the implication of having a higher concentration of the conjugate base than the weak acid in a solution?

The pH will be greater than the pKa. Signup and view all the answers

What does the ion product of water (Kw) represent?

The equilibrium constant for the dissociation of water. Signup and view all the answers

What is the relationship between the wavelength of light and the energy of photons?

Energy is inversely proportional to wavelength. Signup and view all the answers

What is the relationship between buffer concentration and buffering capacity?

Higher concentration increases buffering capacity. Signup and view all the answers

What is the pKa of HEPES?

7.55 Signup and view all the answers

In a Jablonski diagram, what does the S0 level represent?

The lowest energy state of the molecule Signup and view all the answers

In what way must researchers artificially control the pH when studying biometrics in vitro?

Because natural buffering processes are absent. Signup and view all the answers

Which reagent is used to adjust the pH when preparing a buffer?

NaOH Signup and view all the answers

What factor contributes to the different energy levels within a specific S energy level in a molecule?

Vibrational states Signup and view all the answers

What is the required volume of NaOH to achieve the desired conjugate base form of HEPES, given a 1M NaOH concentration?

17.99 mL Signup and view all the answers

What is the total concentration of the buffer components for a 50mM HEPES buffer?

50mM Signup and view all the answers

How much HEPES is needed to prepare 1L of a 50mM buffer?

7.628g Signup and view all the answers

Absorption is primarily described as what type of phenomenon?

A quantum phenomenon Signup and view all the answers

What would be the concentration of A- in the solution to achieve a buffer with a pH of 7.3?

17.99mM Signup and view all the answers

What does the thin horizontal bars within energy levels represent in a Jablonski diagram?

Different vibrational states Signup and view all the answers

The distance between two consecutive peaks of electromagnetic radiation is known as what?

Wavelength Signup and view all the answers

To prepare the HEPES buffer, what mass of HEPES sodium salt do you need?

4.683g Signup and view all the answers

What is the formula for calculating the total moles of solute in a solution?

Molarity x Volume = Moles Signup and view all the answers

What determines whether a photon is absorbed by a molecule?

The energy of the photon matching the energy difference between two energy levels Signup and view all the answers

How quickly does the absorption process take place?

Approximately $10^{-15}$ seconds Signup and view all the answers

What happens when an electron returns to a lower energy state after being excited?

It couples with the loss of heat Signup and view all the answers

What is the primary purpose of a spectrophotometer?

To measure the absorption of light by a substance Signup and view all the answers

Which factor is NOT listed as a consideration for measuring absorption?

The consistency of the solvent Signup and view all the answers

Which type of lamp is commonly used in spectrophotometers for wavelengths of 350-2500nm?

Halogen lamps Signup and view all the answers

What internal processes occur after an electron is excited?

It returns to lower vibrational or rotational levels Signup and view all the answers

What is a significant challenge in measuring absorption in the lab?

Controlling the wavelength and intensity of light Signup and view all the answers

What does the Henderson-Hasselbalch equation indicate about buffers?

Buffers minimize pH changes without entirely preventing them. Signup and view all the answers

What is the typical rule of thumb for selecting a buffer based on pKa?

The pKa should be no more than 1 pH unit from the target pH. Signup and view all the answers

How is buffer capacity defined?

The amount of buffer needed to change the pH of 1L by 1 pH unit. Signup and view all the answers

If the pKa is 8.0 and the pH is also 8.0 with 10 molecules of buffer, what can be concluded after adding 4 molecules of NaOH?

The new pH will substantially change after the addition. Signup and view all the answers

What effect does buffer concentration have on its buffer capacity?

Greater moles of buffer lead to greater buffering capacity. Signup and view all the answers

What happens when a buffer pH is more than 1 unit away from its pKa?

The buffer fails to resist changes in pH significantly. Signup and view all the answers

Why is equal concentration of HA and A important in buffer solutions?

It allows buffering near the pKa. Signup and view all the answers

What is the likely outcome of adding 4 molecules of NaOH to a buffer containing 100 molecules?

The new pH will show little change. Signup and view all the answers

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