C/P NextStep PT #4

What is the pH of a 0.010 M perchloric acid solution? A. 2 B. 4 C. 7 D. 12

A is correct. Perchloric acid is a strong acid that completely dissociates in aqueous solution, so the hydrogen ion concentration is 1.0 x 10-2 M. pH = -log[H+] = -log[10-2] = 2.

At what angle relative to the velocity of a red blood cell should the transducer be held during Doppler ultrasound to most accurately determine blood velocity? A. 0º B. 30º C. 45º D. 90°

A is correct. Cosine θ is applied as a correction for the angle between the ultrasound beam and the direction of blood flow. Cos θ = 1 if the beam is parallel to the direction of blood flow, which allows for maximum velocity to be measured. Cos θ = 0 if the beam is perpendicular to the direction of blood flow and zero velocity is measured.

Which specific class of enzymes is primarily responsible for the release of free glycerol from stored triglycerides? A. Lipases B. Carboxylases C. Phosphorylases D. Kinases

A is correct. Lipases are the enzymes that digest lipids (fats). Most dietary fats originally exist in the form of triglycerides.

In 250 mL of the MH solution with the most favorable solubility profile, how many moles of nicotinamide (MW = 122 g/mol) are present? Table 1 shows that there are 40 mg/mL of total hydrotrope in each MH solution. A. 3.1 x 10-2 B. 3.1 x 10-1 C. 1.6 x 10-2 D. 1.6 x 10-1

A is correct. The solution with the most favorable solubility is that with an N:B:C ratio of 15:20:5. In this solution, the concentration of nicotinamide (N) is 15 mg/ml. Since the question states there are 250 mL of solution, the amount of nicotinamide must be 250 x 15 mg, or 3750 mg. We can estimate this value as 4000 mg, which is equal to 4 g. 4 g nicotinamide x (1 mol nicotinamide / 122 g) = approximately 3.33 x 10-2

Which of the following boundaries would give the lowest-quality image to a physician? A. Fat/muscle B. Muscle/bone C. Muscle/blood D. Water/fat

B is correct. The passage states that if the ΔZ is very large, all of the ultrasound will be totally reflected at the boundary. The imaging will be poor because too much sound was reflected back, and there was not enough left to be able to penetrate further and continue imaging. If ΔZ is small, a small amount of sound will be reflected back, which would allow enough sound left to continue through for further imaging. Muscle and bone have the largest difference in impedance (7.8 - 1.7 = 6.1) of all the combinations given.

Three students in physics lab are given four capacitors, each with a capacitance of 4 μF, and are told to construct a circuit with the maximum possible total capacitance. Student 1 attaches all four capacitors in series. Student 2 attaches all four capacitors in parallel. Student 3 only inserts a single capacitor in his circuit. Which of the following is true? A. Student 1 and Student 3 will create circuits that have the same total capacitance. B. Student 2 will create the circuit with the highest capacitance. C. Student 2 and Student 3 will create circuits that have the same total capacitance. D. Student 3 will create the circuit with the highest capacitance.

B is correct. The total capacitance of capacitors in parallel is simply the sum of their individual capacitances, so student 2 would create a circuit with 16 μF and the highest capacitance. Student 3, by only using a single capacitor, would create a circuit with 4 μF capacitance. When capacitors are connected in series, the reciprocal of the total capacitance is found by adding the reciprocals (like resistors in parallel), so student 1 would only create a circuit with 1 μF capacitance.

Which of the following is most likely the net charge on a valine molecule in the human body? A. -1 B. 0 C. +5 D. +1

B is correct. This question is asking us to remember what factors contribute to the net charge on a valine molecule. Being an amino acid, valine has an acidic carboxy group that will be deprotonated at physiological pH. It also has a basic amine group that will be protonated at physiological pH, as well as a neutral side chain.

The Arrhenius equation, k = Ae-Ea/(RT), expresses the relationship between the rate constant, k, and the temperature of a reaction. According to this equation, which of the following will increase the rate of a reaction? A. Decreasing the pre-exponential factor, A B. Increasing the temperature, T C. Increasing the activation energy, Ea D. Decreasing the temperature, T

B is correct. While this question introduces the Arrhenius equation, you can answer it simply by remembering the principle in general chemistry that increasing temperature increases the rate of reaction.

Which of the following correctly represent the units of the Boltzmann constant? A. kg/s B. N/K C. J/K D. K/J•s

C is correct. According to the last paragraph, k = 1.38 x 10-23 (m2•kg)/(s2•K). We can use the units given to derive another equivalent unit for the Boltzmann constant. (m2•kg)/(s2•K) = m•(m/s2)•kg/K = [(unit of distance)(unit of acceleration)(unit of mass)] / unit of temperature Mass multiplied by acceleration is force. (m2•kg)/(s2•K) = [(unit of distance)(unit of force)] / unit of temperature Force multiplied by distance is work. (m2•kg)/(s2•K) = (unit of work) / unit of temperature Therefore, another unit for the Boltzmann constant is J/K.

Which of the following situations would present Participant 3 with the greatest risk for TBI? A. A linear acceleration of 10 m/s2 for 2 ms in a car crash B. A single punch to the head causing acceleration of 100 m/s2 for 3 ms C. Riding a roller coaster of 9 m/s2 sustained for 40 s D. Total body acceleration of 15 m/s2 for 1 ms

C is correct. According to the second paragraph of the passage, G-forces alone do not predict TBI. Besides the force, the time duration over which the force is applied is important in determining the severity of a brain injury. The second paragraph also states that the body can endure a large G-force if it occurs over a very short time period. Using Equation 1 from the passage, we can calculate the value of P for each of these activities. The acceleration values are given for all the choices. To incorporate acceleration, we rewrite the equation into P = m*a*t, where "m" represents the mass of the brain (which, since the subject is the same, can be assumed to be equal for all cases). Therefore, the impulse will be:

Aspartame (N-L-alpha-aspartyl-L-phenylalanine 1-methyl ester) is a very well-known artificial sweetener found in the large majority of non-sugar containing food products. This compound is classified as a(n): A. ketone. B. phenol. C. dipeptide. D. amino acid.

C is correct. Aspartame contains two amino acids as mentioned above in the formula; thus, it is a dipeptide. Aspartame (shown below) is the methyl ester of the dipeptide containing aspartic acid and phenylalanine. Of course, you do not need to have any outside knowledge about the structure of aspartame, but you should be able to recognize the structure below as a dipeptide.

What is the normality of a 0.015 M solution of phosphoric acid? A. 0.015 N B. 0.030 N C. 0.045 N D. 0.060 N

C is correct. The chemical formula of phosphoric acid is H3PO4. Normality, in the context of acids, refers to the number of moles of protons per liter of solution (in other words, to the "molarity of protons"). Normality can be calculated by multiplying the molarity of the solution by the number of protons per molecule of acid (here, 3). (0.015 M solution) x (3 protons per molecule) = 0.045 N

A certain metabolic process in the liver produces NADH as a part of the process. If this process is up-regulated, which of the following effects associated with gluconeogenesis is most likely to follow? A. Intracellular levels of oxaloacetate will increase. B. Plasma glucose concentrations will increase significantly. C. The rate of gluconeogenesis in the liver will decrease. D. Plasma glucose concentrations will decrease significantly.

C is correct. The key to this question is that we do not know which process the question stem refers to; we only know that it produces NADH. We are given no reason to assume that this process is the same as that described in the question stem, in which "the conversion of lactate to pyruvate is coupled with the reduction of NAD+ to NADH." Since we cannot assume that this is the process being discussed, the only information available fo

An object made of silicon (specific heat = 698 J/kg°C) absorbs 3500 J of heat while increasing its temperature from 43°C to 53°C. What is the approximate mass of the object? A. 350 g B. 400 g C. 500 g D. 2050 g

C is correct. The most efficient way to find this answer is by using dimensional analysis and the equation Q (the heat in or out of a system) = mcΔT. Plugging in numbers, we get: 3500 J = m x 698 J/kg°C x (53°C - 43°C) We can rearrange to get: m = 3500 J / [698 J / kg°C] *10°C ≈ 3500/7000 kg = 0.5 kg = 500 g

Which of the following compounds is amphiprotic? A. Acetic acid, HC2H3O2 B. Sodium acetate, NaC2H3O2 C. Sodium bicarbonate, NaHCO3 D. Sodium carbonate, Na2CO3

C is correct. The prefix "amphi-" means "both." Therefore, an amphiprotic species is one that can act as both an acid or a base. Sodium bicarbonate (choice C) dissolves in aqueous solution to produce sodium ions and bicarbonate ions. The former ion is neither acidic nor basic, but the bicarbonate ion, HCO3-, can act as a Bronsted-Lowry acid by loss of a hydrogen ion and can act as a B-L base by accepting a hydrogen ion to form carbonic acid, H2CO3.

The frequency used in U/S imaging must be greater than: A. 1 kHz. B. 10 kHz. C. 20 kHz. D. 40 MHz.

C is correct. Ultrasound is defined as sound with a frequency above the human range of hearing ("ultra" = "above"). To answer this question, then, we need to know what the human range of hearing is. This range is 20 Hz to 20 kHz, so anything greater than 20 kHz qualifies as ultrasound.

A large steel water storage tank with a diameter of 20 m is filled with water and is open to the atmosphere (1 atm = 101 kPa) at the top of the tank. If a small hole rusts through the side of the tank, 5.0 m below the surface of the water and 20.0 m above the ground, assuming wind resistance and friction between the water and steel are not significant factors, how far from the base of the tank will the water hit the ground? A. 5.0 m B. 10.0 m C. 20.0 m D. 30.0 m

C is correct. We first need to determine the velocity of the water that comes out of the hole, using Bernoulli's equation. P1 + ρgy1 + 1/2 ρv12 = P2 + ρgy2 + 1/2 ρv22 The atmospheric pressure exerted on the surface of the water at the top of the tank and at the hole are essentially the same. Additionally, since the opening at the top of the tank is so large compared to the hole on the side, the velocity of water at the top of the tank will be essentially zero. We can also set y1 as zero, simplifying the equation to: 0 = ρgy2 + 1/2 ρv22 -gy2 = 1/2 v22 Inserting the value for gravitational acceleration (g = -10 m/s2), and the level of the hole below the surface (y2 = 5.0 m) into the equation, we get: (10 m/s2)(5.0 m) = 1/2 v2 50 = 0.5 v2 102 = v2 10 m/s = v This velocity will be in the horizontal direction, and we will assume that the water acts like a projectile. Now, we need to determine the time that it will take the water to fall to the ground. We can assume that the initial vertical velocity of the water is zero and the displacement of the water is -20 m, because the hole is 20.0 m above the ground. The kinematic equation is: d = vit + 1/2 gt2 -20 = 0 + 1/2 (-10) t2 -20 = -5 t2 4 = t2 2 s = t Finally, we can determine the range, or displacement in the horizontal direction. Since the acceleration in the horizontal direction is zero, the equation becomes d = vit d = (10 m/s)(2 s) d = 20 m

Conversion of pyruvate into glucose requires enzymes present in: A. the interstitial fluid only. B. the mitochondria only. C. the cytosol only. D. both the mitochondria and the cytosol.

D is correct. Conversion of pyruvate to glucose requires its initial conversion into oxaloacetate, in a reaction catalyzed by pyruvate carboxylase in the mitochondria. Oxaloacetate (OAA) is then decarboxylated and phosphorylated by cytosolic or mitochondrial forms of phosophoenolpyruvate carboxykinase (PEPCK). After transport of either OAA in the form of malate or PEP directly from the mitochondria, the remainder of gluconeogenesis takes place in the cytosol.

How many grams of hydrogen gas are required to completely react with 32 g of oxygen to form hydrogen peroxide? A. 0.5 g B. 1.0 g C. 1.5 g D. 2.0 g

D is correct. The formation reaction for hydrogen peroxide is: H2 (g) + O2 (g) → H2O2 (l) 32 g O2 x (1 mol/32 g) x (1 H2/1 O2) x 2 g/mol = 2 g H2

The piezoelectric effect, when generating ultrasound waves, involves the conversion of: A. chemical energy to mechanical energy. B. electrical energy to potential energy. C. kinetic energy to electrical energy. D. electrical energy to mechanical energy.

D is correct. The piezoelectric effect begins with voltage generating a current through the crystal (electrical energy) and culminates in the crystal vibrating (mechanical energy). Mechanical energy is made up of kinetic and potential energy, as it is associated with the motion and position of an object.

All of the following phenomena serve to attenuate the ultrasound signal as it passes through the body EXCEPT: A. absorption. B. refraction. C. scattering. D. amplification.

D is correct. The question stem asks about attenuation, which is a weakening of the U/S signal. Sound energy is attenuated as it passes through the body because parts of the signal are reflected, scattered, absorbed, refracted or diffracted. Amplification does the opposite of attenuation; it makes the signal stronger. Since this is an "EXCEPT" question, amplification is our answer.

In addition to a drug's solubility in hydrophilic media, which of the following is likely to be an important factor in determining its oral bioavailability? A. pKa B. pKb C. Solubility enhancement ratio D. Membrane permeability

D is correct. This question asks us to infer which factor is most likely to affect bioavailability, or the ability of a drug to be absorbed by the body and take effect. The passage tells us that hydrophilic solubility is important, most likely because the vast majority of biological solvents are hydrophilic. In addition, an orally-administered drug must be absorbed across the membranes of the gums, stomach, or small intestine to be effective. Therefore, membrane permeability must be important because if it is low, the drug will not cross these membranes into the bloodstream.

A scientist wished to prepare a buffer for an experiment to be conducted at pH 9.7. Which of the following organic acids would be the best choice for this experiment? A. Acetic acid (pKa = 4.76) B. Carbonic acid (pKa = 6.35) C. Tricine (pKa = 8.05) D. Taurine (pKa = 9.06)

D is correct. To construct the best possible buffer, we should choose the organic acid with the pKa closest to the pH at which the experiment will take place (9.7). This gives us answer choice D. Note that an ideal buffer should have a pKa within 1 pH unit of the expected experimental conditions.

Tollens' test typically involves exposure of a carbohydrate to a solution of CuO in ammonia (NH3). Glucose yields a positive Tollens' test, but sucrose does not. Which of the following best explains this fact? A. Sucrose contains a hemiacetal group, while glucose does not; this classifies sucrose as a reducing sugar. B. Sucrose contains a hemiacetal group, while glucose does not; this classifies glucose as a reducing sugar. C. Glucose contains a hemiacetal group, while sucrose does not; this classifies sucrose as a reducing sugar. D. Glucose contains a hemiacetal group, while sucrose does not; this classifies glucose as a reducing sugar.

D is correct. Tollens' test is intended to identify "reducing sugars," or sugars with the capacity to serve as reducing agents. Specifically, sugars with hemiacetal groups can undergo mutarotation, allowing them to be oxidized by CuO. The process of mutarotation requires ring opening, which occurs at a hemiacetal group. Thus, sugars with hemiacetal groups can be oxidized and can thus function as reducing sugars. We do not need to have the structures of glucose and sucrose memorized to answer this question. Instead, simply note that the question stem tells us that glucose yields a positive Tollens' test. Glucose must therefore contain a hemiacetal group, whereas sucrose (which gives a negative test result) must not. The hemiacetal group on glucose, shown below, marks it as a classic reducing sugar. Remember, a hemiacetal consists of a carbon atom directly attached to one -OR and one -OH group. The same carbon atom is also attached to a hydrogen atom and an R group.

What is the pH of a 0.010 M sodium hydroxide solution at 25°C? A. 1 B. 2 C. 7 D. 12

D is correct. You should immediately notice that choice D is the only option that is basic. To answer this question using math, however, first note that sodium hydroxide is a strong base that completely dissociates in aqueous solution. Therefore, the hydroxide ion concentration of this solution is also 0.010 M, or (in scientific notation) 1 x 10-2 M. Taking the negative logarithm of the hydroxide concentration gives a pOH of 2. Since pH + pOH = 14 (at 25ºC), we can calculate the pH by subtracting the pOH from 14, which yields pH = 14 - 2 = 12.

Britton-Robinson buffer solution? I. A polyprotic, weak acid II. Na2HPO4 III. NH3

I and II only For RN I, a polyprotic, weak acid fits the criteria for an acidic buffer solution. Therefore, RN I is correct. RN II is a salt formed from a weak acid (phosphoric acid), so it is also correct.