Question 1

Plants convert nitrogen into ammonia. This biological nitrogen fixation is effected by enzymes called nitrogenases. The enzymes assist in the transfer of electrons. The unbalanced reaction equation is N₂(g) + H⁺(aq) + e^-$\rarr$ H₂(g) + NH₃(aq) What is the stoichiometric coefficient for the electrons in the balanced reaction equation?

Accepted Answer

To balance the reaction, each nitrogen atom in N2 needs three electrons to form NH3. Since there are two nitrogen atoms, a total of 6 electrons are needed for nitrogen. Additionally, 2 electrons are needed to form H2 from H+. Therefore, the total stoichiometric coefficient for electrons is 8.

Question 2

How much energy must be expended by a cell to transport 1 mole of sodium ions across a membrane with an electrochemical potential of 62 mV in order to maintain this potential?

Accepted Answer

The energy required can be calculated using the formula ΔG = zFΔψ, where ΔG is the change in free energy, z is the charge on the ion (for Na+, z = +1), F is Faraday's constant (approximately 96,485 C/mol), and Δψ is the electrochemical potential difference across the membrane (62 mV or 0.062 V). Thus, ΔG = (1)(96,485 C/mol)(0.062 V) = 5,982 J/mol, which is approximately 6.0 kJ/mol.

Question 3

Different concentrations of ions on either side of a cell membrane constitute a concentration cell, which is described by the Nernst equation given below. A cell must expend energy to maintain this concentration gradient by moving ions from one side of the membrane to the other. How much energy must be expended to transport 1 mole of sodium ions across a membrane when the sodium ion concentration is 0.10 M on one side of the membrane and 0.010 M on the other side, and the temperature is 37°C (body temperature)? (Given: Na⁺ + e^- $\rarr$Na, $E _ { \mathrm { red } } ^ { 0 }$ = -2.71 V; F = 96,485 C; 1 J = 1 C V; R = 8.315 J / (mol K)) $E = E { } ^ { \circ } - \frac { R T } { n F } \ln Q$

Accepted Answer

The answer of Different concentrations of ions on either side...

Question 4

Calcium carbonate is used to form exoskeletons. It has a solubility-product constant of 5.0 * 10^-⁹. What is the molar concentration of calcium ions in a saturated solution of calcium carbonate?

Accepted Answer

The solubility-product constant (Ksp) of calcium carbonate is given as:

Ksp = [Ca2+][CO32-]

Since calcium carbonate is a sparingly soluble salt, the concentration of calcium ions in a saturated solution is expected to be low.

Let x be the molar concentration of calcium ions in a saturated solution of calcium carbonate. Then, the concentration of carbonate ions is also x because the salt dissolves in a 1:1 ratio.

Substituting these values in the expression for Ksp, we get:

Ksp = x^2

5.0 x 10^-9 = x^2

x = 7.1 x 10^-5 M

Therefore, the molar concentration of calcium ions in a saturated solution of calcium carbonate is 7.1 x 10^-5 M, which is closest to option B.

Question 5

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the change in oxidation number of nitrogen in this reaction? NO₃^-(aq) + H₂O(l) + e^- $\rarr$0 NO₂^-(aq) + OH^-(aq)

Accepted Answer

The answer of Enzymes in plants convert nitrate into ammonia....

Question 6

What is the dominant role played by iodine in the body?

Accepted Answer

Iodine is primarily involved in the function of the thyroid gland, as it is a key component of thyroid hormones. These hormones play a critical role in regulating metabolism and growth throughout the body. While iodine may also have other important functions in the body, such as acting as an antioxidant or helping to maintain fluid balance, its role in supporting thyroid function is generally considered to be its most critical job.

Question 7

Calcium carbonate is used to form exoskeletons. It has a solubility-product constant of 5.0 *10^-⁹. What is the mass of calcium ions dissolved in 1.0 L of a saturated solution of calcium carbonate?

Accepted Answer

The answer of Calcium carbonate is used to form exoskeletons....

Question 8

Tooth enamel is composed of the mineral hydroxyapatite. It is essentially insoluble in water with K_sp = 2.3* 10^-⁵⁹, but it reacts with weak acids in the mouth as described by one of the reaction equations below. You can determine the equilibrium constant, K, for this reaction from K_sp and K_w (the equilibrium constant for water autoionization). How do you do this? Ca₅(PO₄)₃(OH)(s) $\rightleftarrows$ Ca₅(PO₄)₃⁺(aq) + OH^-(aq) Ca₅(PO₄)₃(OH)(s) + H⁺(aq) $\rightleftarrows$ Ca₅(PO₄)₃⁺(aq) + H₂O(l)

Accepted Answer

The equilibrium constant, K, for the reaction is equal to the product of the concentrations of the products raised to their stoichiometric coefficients divided by the product of the concentrations of the reactants raised to their stoichiometric coefficients. For the given reaction, the equilibrium constant expression is: K = [Ca5(PO4)3OH][H+][OH-] / [Ca5(PO4)3OH]. The concentration of water is not included in the expression since it is in excess and its concentration remains constant. The equilibrium constant for water autoionization, Kw, is given by the equation: Kw = [H+][OH-]. Dividing the reaction equilibrium constant by the water ionization constant: K / Kw = [Ca5(PO4)3OH] / [H+][OH-] or K = [Ca5(PO4)3OH] / [H+][OH-] * Kw. Thus, K = K_sp/K_w.

Question 9

Plants convert nitrate into ammonia by using enzymes called ________

Accepted Answer

Plants convert nitrate into ammonia using enzymes called reductases.

Question 10

Tooth enamel is composed of the mineral hydroxyapatite. It is essentially insoluble in water with K_sp = 2.3 *10^-⁵⁹, but it reacts with weak acids in the mouth as described by one of the reaction equations below. You can determine the equilibrium constant, K, for this reaction from K_sp and K_w (the equilibrium constant for water autoionization, K_w = 1.0 *10^-¹⁴). What is the value of K? Ca₅(PO₄)₃(OH)(s) $\rightleftarrows$ Ca₅(PO₄)₃⁺(aq) + OH^-(aq) Ca₅(PO₄)₃(OH)(s) + H⁺(aq) $\rightleftarrows$Ca₅(PO₄)₃⁺(aq) + H₂O(l)

Accepted Answer

The equilibrium constant for the reaction is K = [Ca(PO4)(OH)(s)][H+] / [Ca(PO4)2-][H2O]. Since pure water has an equilibrium constant of 1, the K value can be simplified to [Ca(PO4)(OH)(s)][H+]/[Ca(PO4)2-]. Using the given solubility product constant for hydroxyapatite, K_sp = 2.3 F1F1F1S1F1F1F10 10^-^{^45}, we can write K = 2.3 F1F1F1S1F1F1F10 10^-^{^45} / [Ca(PO4)2-]. However, [Ca(PO4)2-] is equal to [Ca(PO4)(OH)(s)], which is given to be a constant, so K is also equal to 2.3 F1F1F1S1F1F1F10 10^-^{^45}, which corresponds to answer choice C.

Question 11

Plants convert nitrogen into ammonia. This biological nitrogen fixation is effected by enzymes called nitrogenases. The enzymes assist in the transfer of electrons. The unbalanced reaction equation is N₂(g) + H⁺(aq) + e^-$\rarr$ H₂(g) + NH₃(aq) What is the change in the oxidation number of nitrogen in this reaction?

Accepted Answer

In this reaction, the nitrogen in N₂(g) has an oxidation number of 0. In the product NH₃(aq), the oxidation number of nitrogen is -3. Therefore, the change in oxidation number of nitrogen is -3 - 0 = -3. Therefore, the answer is B, -3.

Question 12

The average concentration of calcium in the human body is 15 mg/g of body mass. What is the mass of calcium in the body of a person weighing 150 lb? (1 lb = 454 g)

Accepted Answer

The answer of The average concentration of calcium in the...

Question 13

The average person has 15 mg of calcium per gram of body mass. How many pounds of calcium does a person weighing 175 lb contain? (1 lb = 454 g)

Accepted Answer

To solve this problem, first convert the weight of the person from pounds to grams:
175 lb x 454 g/lb = 79,450 g

Next, calculate the total amount of calcium:
79,450 g x 15 mg/g = 1,191,750 mg

To convert the result to pounds, divide by the number of milligrams per pound:
1,191,750 mg / 453,592 mg/lb = 2.63 lb

Therefore, the answer is C, 2.63 lb.

Question 14

The concentration of sodium in the human body is approximately 1.5 mg/g of body mass. What is this concentration in ppm (parts per million)?

Accepted Answer

1.5 mg/g is equivalent to 1,500 mg/kg, which is 1,500 ppm since 1 ppm is 1 mg/kg.

Question 15

Urea is a waste product produced when the body metabolizes protein. What is the oxidation number of nitrogen in urea, (NH₂)₂CO?

Accepted Answer

In urea, carbon has an oxidation number of +2 because it is bonded to two electronegative oxygen atoms. The total oxidation number of the two oxygen atoms is -4, so the nitrogen atoms must have oxidation numbers that sum to +4 in order to balance out the oxidation number of carbon. Since there are two nitrogen atoms in urea, each nitrogen atom must have an oxidation number of -3. Therefore, the answer is B.

Question 16

Different concentrations of ions on either side of a cell membrane constitute a concentration cell, which is described by the Nernst equation given below. What is the electrochemical potential across a membrane when the sodium ion concentration is 0.10 M on one side of the membrane and 0.010 M on the other side, and the temperature is 37°C (body temperature)? (Given: Na⁺ + e^- $\rarr$Na, $E _ { \mathrm { red } } ^ { 0 }$= -2.71 V; F = 96,485 C; 1 J = 1 C V; R = 8.315 J / (mol K)) $E = E { } ^ { \circ } - \frac { R T } { n F } \ln Q$

Accepted Answer

The electrochemical potential across a membrane can be calculated using the Nernst equation:$E = E { } ^ { \circ } - \frac { R T } { n F } \ln Q$where:$E$ is the electrochemical potential in volts$E { } ^ { \circ }$ is the standard reduction potential in volts$R$ is the ideal gas constant in J/(mol K)$T$ is the temperature in Kelvin$n$ is the number of electrons transferred in the reaction$F$ is the Faraday constant in C/mol$Q$ is the reaction quotientIn this case, the reaction is:$Na { } ^ { + } + e { } ^ { - } \rightarrow Na$and the standard reduction potential is -2.71 V. The temperature is 37°C, which is 310 K. The number of electrons transferred is 1. The Faraday constant is 96,485 C/mol. The reaction quotient is:$Q = \frac { [Na { } ^ { + } ] } { [Na] }$where:$[Na { } ^ { + } ]$ is the concentration of sodium ions on the side of the membrane with the higher concentration$[Na]$ is the concentration of sodium ions on the side of the membrane with the lower concentrationIn this case, $[Na { } ^ { + } ]$ is 0.10 M and $[Na]$ is 0.010 M. Therefore, the reaction quotient is:$Q = \frac { 0.10 M } { 0.010 M } = 10$Substituting these values into the Nernst equation, we get:$E = -2.71 V - \frac { 8.315 J / (mol K) \times 310 K } { 1 \times 96,485 C/mol } \ln 10$$E = -2.71 V - 0.0615 V \ln 10$$E = -2.71 V - 0.0615 V \times 2.303$$E = -2.71 V - 0.141 V$$E = -2.85 V$Therefore, the electrochemical potential across the membrane is -2.85 V.

Question 17

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the stoichiometric coefficient of the electrons, e^-, in the balanced reaction equation? NO₃^-(aq) + H₂O(l) + e^- $\rarr$NO₂^-(aq) + OH^-(aq)

Accepted Answer

In order to balance the nitrogen atoms, we need to have 2 nitrogen atoms on both the reactant and product side. This means we need a 2 as the stoichiometric coefficient for the nitrate. Since the nitrate is gaining electrons, we must balance this by having 2 electrons on the reactant side. Therefore, the stoichiometric coefficient of the electrons is 2.

Question 18

Plants react urea with water to produce ammonia and carbon dioxide. This reaction is an example of a ________ reaction.

Accepted Answer

The reaction between urea and water involves the breaking of a chemical bond through the addition of water. This is known as hydrolysis, making choice C the correct answer. Redox reactions involve the transfer of electrons, metathesis reactions involve the swapping of ions, combustion reactions involve the reaction of a fuel with oxygen, and precipitation reactions involve the formation of a solid from a solution. None of these reactions accurately describe the urea and water reaction.

Question 19

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the stoichiometric coefficient of the hydroxide in the balanced reaction equation? NO₃^-(aq) + H₂O(l) + e^- $\rarr$NO₂^-(aq) + OH^-(aq)

Accepted Answer

The answer of Enzymes in plants convert nitrate into ammonia....

Question 20

Plants convert nitrogen into ammonia. This biological nitrogen fixation is effected by enzymes called nitrogenases. The enzymes assist in the transfer of electrons. The unbalanced reaction equation is N₂(g) + H⁺(aq) + e^-$\rarr$ H₂(g) + NH₃(aq) What is the stoichiometric coefficient for ammonia in the balanced reaction equation?

Accepted Answer

The balanced reaction equation is 8 N₂(g) + 16 H⁺(aq) + 8 e^-F1F1F1S1F1F1F10 NH₃(aq) + 10 NH3(g). Therefore, the stoichiometric coefficient for ammonia is 10, which corresponds to option B.

Quiz 22: Life and the Periodic Table

How much energy must be expended by a cell to transport 1 mole of sodium ions across a membrane with an electrochemical potential of 62 mV in order to maintain this potential?

Calcium carbonate is used to form exoskeletons. It has a solubility-product constant of 5.0 * 10^-⁹. What is the molar concentration of calcium ions in a saturated solution of calcium carbonate?

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the change in oxidation number of nitrogen in this reaction? NO₃^-(aq) + H₂O(l) + e^- $\rarr$ 0 NO₂^-(aq) + OH^-(aq)

What is the dominant role played by iodine in the body?

Calcium carbonate is used to form exoskeletons. It has a solubility-product constant of 5.0 *10^-⁹. What is the mass of calcium ions dissolved in 1.0 L of a saturated solution of calcium carbonate?

Plants convert nitrate into ammonia by using enzymes called ________

The average concentration of calcium in the human body is 15 mg/g of body mass. What is the mass of calcium in the body of a person weighing 150 lb? (1 lb = 454 g)

The average person has 15 mg of calcium per gram of body mass. How many pounds of calcium does a person weighing 175 lb contain? (1 lb = 454 g)

The concentration of sodium in the human body is approximately 1.5 mg/g of body mass. What is this concentration in ppm (parts per million) ?

Urea is a waste product produced when the body metabolizes protein. What is the oxidation number of nitrogen in urea, (NH₂) ₂CO?

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the stoichiometric coefficient of the electrons, e^-, in the balanced reaction equation? NO₃^-(aq) + H₂O(l) + e^- $\rarr$ NO₂^-(aq) + OH^-(aq)

Plants react urea with water to produce ammonia and carbon dioxide. This reaction is an example of a ________ reaction.

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the stoichiometric coefficient of the hydroxide in the balanced reaction equation? NO₃^-(aq) + H₂O(l) + e^- $\rarr$ NO₂^-(aq) + OH^-(aq)

Quiz 22: Life and the Periodic Table

How much energy must be expended by a cell to transport 1 mole of sodium ions across a membrane with an electrochemical potential of 62 mV in order to maintain this potential?

Calcium carbonate is used to form exoskeletons. It has a solubility-product constant of 5.0 * 10-9. What is the molar concentration of calcium ions in a saturated solution of calcium carbonate?

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the change in oxidation number of nitrogen in this reaction? NO3-(aq) + H2O(l) + e- →\rarr→ 0 NO2-(aq) + OH-(aq)

What is the dominant role played by iodine in the body?

Calcium carbonate is used to form exoskeletons. It has a solubility-product constant of 5.0 *10-9. What is the mass of calcium ions dissolved in 1.0 L of a saturated solution of calcium carbonate?

Plants convert nitrate into ammonia by using enzymes called ________

The average concentration of calcium in the human body is 15 mg/g of body mass. What is the mass of calcium in the body of a person weighing 150 lb? (1 lb = 454 g)

The average person has 15 mg of calcium per gram of body mass. How many pounds of calcium does a person weighing 175 lb contain? (1 lb = 454 g)

The concentration of sodium in the human body is approximately 1.5 mg/g of body mass. What is this concentration in ppm (parts per million) ?

Urea is a waste product produced when the body metabolizes protein. What is the oxidation number of nitrogen in urea, (NH2) 2CO?

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the stoichiometric coefficient of the electrons, e-, in the balanced reaction equation? NO3-(aq) + H2O(l) + e- →\rarr→ NO2-(aq) + OH-(aq)

Plants react urea with water to produce ammonia and carbon dioxide. This reaction is an example of a ________ reaction.

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the stoichiometric coefficient of the hydroxide in the balanced reaction equation? NO3-(aq) + H2O(l) + e- →\rarr→ NO2-(aq) + OH-(aq)

Calcium carbonate is used to form exoskeletons. It has a solubility-product constant of 5.0 * 10^-⁹. What is the molar concentration of calcium ions in a saturated solution of calcium carbonate?

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the change in oxidation number of nitrogen in this reaction? NO₃^-(aq) + H₂O(l) + e^- $\rarr$ 0 NO₂^-(aq) + OH^-(aq)

Calcium carbonate is used to form exoskeletons. It has a solubility-product constant of 5.0 *10^-⁹. What is the mass of calcium ions dissolved in 1.0 L of a saturated solution of calcium carbonate?

Urea is a waste product produced when the body metabolizes protein. What is the oxidation number of nitrogen in urea, (NH₂) ₂CO?

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the stoichiometric coefficient of the electrons, e^-, in the balanced reaction equation? NO₃^-(aq) + H₂O(l) + e^- $\rarr$ NO₂^-(aq) + OH^-(aq)

Enzymes in plants convert nitrate into ammonia. The unbalanced half-reaction equation is given below. What is the stoichiometric coefficient of the hydroxide in the balanced reaction equation? NO₃^-(aq) + H₂O(l) + e^- $\rarr$ NO₂^-(aq) + OH^-(aq)