Medical Chemistry: Class Test 2

1.

What is the pH of a solution with [H⁺] = 1 x 10^-6 M.

Correct Answer
6
6.00

Explanation
pH is calculated by the formula

pH = - log [H+]

Substitute [H+] with the concentration in the question.

pH = - log (1 x 10-6)
pH = -(-6)
pH = 6

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2.

What is the pH of a 0.025 M solution of Hydrobromic Acid?

Correct Answer
1.602
1.6

Explanation
Hydrobromic Acid or HBr, is a strong acid and will dissociate completely in water to H+ and Br-. For every mole of HBr, there will be 1 mole of H+, so the concentration of H+ will be the same as the concentration of HBr. Therefore, [H+] = 0.025 M.

pH is calculated by the formula

pH = - log [H+]

Enter the concentration found before

pH = - log (0.025)
pH = -(-1.602)
pH = 1.602

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3.

What is the pH of a 0.05 M solution of Potassium Hydroxide?

Correct Answer
12.7

Explanation
Potassium Hydroxide or KOH, is a strong base and will dissociate completely in water to K+ and OH-. For every mole of KOH, there will be 1 mole of OH-, so the concentration of OH- will be the same as the concentration of KOH. Therefore, [OH-] = 0.05 M.

Since the concentration of OH- is known, the pOH value is more useful. pOH is calculated by the formula

pOH = - log [OH-]

Enter the concentration found before

pOH = - log (0.05)
pOH = -(-1.3)
pOH = 1.3

The value for pH is needed and the relationship between pH and pOH is given by

pH + pOH = 14

pH = 14 - pOH
pH = 14 - 1.3
pH = 12.7

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4.

How many electrons does phosphorus have to gain in order to achieve a noble-gas electron configuration?
- A.
  
  2
- B.
  
  3
- C.
  
  5
- D.
  
  4
Correct Answer
B. 3

Explanation
b – It has five valence electrons, and wants eight like argon.

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5.

What is the effect of a surfactant on surface tension?
- A.
  
  It increases it
- B.
  
  It decreases it
Correct Answer
B. It decreases it
6.

Why is hydrogen bonding only possible with hydrogen?
- A.
  
  Hydrogen is the least electronegative element known.
- B.
  
  The size of a hydrogen atom is similar to that of oxygen, nitrogen, and fluorine.
- C.
  
  Hydrogen is the only atom with an unshielded nucleus when it forms covalent bonds.
- D.
  
  More than one of the above.
Correct Answer
C. Hydrogen is the only atom with an unshielded nucleus when it forms covalent bonds.
7.

Which of the following is least strong?
- A.
  
  Polar covalent bond
- B.
  
  Ionic bond
- C.
  
  Hydrogen bond
- D.
  
  Dipole-dipole force
Correct Answer
D. Dipole-dipole force
8.

A buffer is 0.36 M in HNO2 and 0.21 M in NaNO2. If the ionization constant of HNO2 is 4.5 x 10^ -4, calculate the pH of the buffer.

Correct Answer
3.11

Explanation
The Henderson-Hasselbalch equation is
pH = pKa + log([A-]/[HA]) and pKa = -logKa

In your case, [A-] = nitrite concentration from NaNO2
[HA] = HNO2

pH = -log(4.5E-4) + log(.21/.36)
pH = 3.11

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Medical Chemistry: Class Test 2

What is the pH of a solution with [H+] = 1 x 10-6 M.

What is the pH of a 0.025 M solution of Hydrobromic Acid?

What is the pH of a 0.05 M solution of Potassium Hydroxide?

How many electrons does phosphorus have to gain in order to achieve a noble-gas electron configuration?

What is the effect of a surfactant on surface tension?

Why is hydrogen bonding only possible with hydrogen?

Which of the following is least strong?

A buffer is 0.36 M in HNO2 and 0.21 M in NaNO2. If the ionization constant of HNO2 is 4.5 x 10^ -4, calculate the pH of the buffer.

What is the pH of a solution with [H⁺] = 1 x 10^-6 M.