Answer :
Let's begin addressing each question:
9. When [tex]\([ H^{+}]=4.0 \times 10^{-9} M\)[/tex] in water at [tex]\(25^{\circ} C\)[/tex]:
To determine the pH of the solution, use the pH formula:
[tex]\[ pH = -\log [ H^{+} ] \][/tex]
Given that [tex]\([ H^{+}] = 4.0 \times 10^{-9} M\)[/tex], the calculations will yield:
[tex]\[ pH = 8.40 \][/tex]
Thus, the correct answer is:
b. [tex]\( pH = 8.40 \)[/tex].
10. A solution with an [tex]\([ OH^{-}] \)[/tex] concentration of [tex]\(1.20 \times 10^{-7} M\)[/tex] has a pOH and pH:
To determine pOH:
[tex]\[ pOH = -\log [ OH^{-} ] \][/tex]
Given that [tex]\([ OH^{-}] = 1.20 \times 10^{-7} \)[/tex], the calculations will yield:
[tex]\[ pOH = 6.92 \][/tex]
Since pH and pOH are related by:
[tex]\[ pH + pOH = 14 \][/tex]
Calculating pH:
[tex]\[ pH = 14 - 6.92 = 7.08 \][/tex]
Thus, the correct answer is:
a. 6.92 and 7.08
11. The acidic ingredient in vinegar is acetic acid. The pH of vinegar is around 2.4 and the molar concentration of acetic acid in vinegar is around 0.85 M. Determine the value of the acid ionization constant, [tex]\(K_a\)[/tex] for acetic acid.
Given:
[tex]\[ pH = 2.4 \][/tex]
[tex]\[ [HA] = 0.85 \, M \][/tex]
First, calculate the [tex]\([H^+]\)[/tex] using the pH:
[tex]\[ [H^+] = 10^{-pH} = 10^{-2.4} \approx 4.0 \times 10^{-3} \][/tex]
Assuming [tex]\( [H^+] \approx [A^-] \)[/tex] for a weak acid, we use:
[tex]\[ K_a = \frac{ [H^+][A^-] }{ [HA] } \][/tex]
[tex]\[ K_a \approx \frac{(4.0 \times 10^{-3})(4.0 \times 10^{-3})}{0.85} \approx 1.9 \times 10^{-5} \][/tex]
Thus, the correct answer is:
b. [tex]\(1.9 \times 10^{-5}\)[/tex]
12. A cup of coffee has a hydroxide ion concentration of [tex]\(1.0 \times 10^{-10} M\)[/tex]. What is the pH of this coffee?
To determine pOH:
[tex]\[ pOH = -\log [ OH^{-} ] \][/tex]
Given that [tex]\([OH^{-}] = 1.0 \times 10^{-10} \)[/tex], the calculations will yield:
[tex]\[ pOH = 10 \][/tex]
Since pH and pOH are related by:
[tex]\[ pH + pOH = 14 \][/tex]
Calculating pH:
[tex]\[ pH = 14 - 10 = 4 \][/tex]
Thus, the correct answer is:
c. 4
13. What is the concentration of [tex]\([OH^{-}]\)[/tex] in a 0.20 M solution of ammonia? The [tex]\(K_b\)[/tex] value for ammonia is [tex]\(1.8 \times 10^{-5}\)[/tex].
Given:
[tex]\[ [NH_3] = 0.20 \, M \][/tex]
[tex]\[ K_b = 1.8 \times 10^{-5} \][/tex]
Use the formula for [tex]\(K_b\)[/tex]:
[tex]\[ K_b = \frac{ [OH^-][NH_4^+] }{ [NH_3] } \][/tex]
Assuming [tex]\([OH^-] = [NH_4^+]\)[/tex]:
[tex]\[ K_b = \frac{ [OH^-]^2 }{ [NH_3] } \][/tex]
[tex]\[ 1.8 \times 10^{-5} = \frac{ [OH^-]^2 }{ 0.20 } \][/tex]
[tex]\[ [OH^-]^2 = (1.8 \times 10^{-5})(0.20) \][/tex]
[tex]\[ [OH^-]^2 = 3.6 \times 10^{-6} \][/tex]
[tex]\[ [OH^-] = \sqrt{ 3.6 \times 10^{-6} } = 1.9 \times 10^{-3} \][/tex]
Thus, the correct answer is:
c. [tex]\(1.9 \times 10^{-3} M\)[/tex]
14. Which of the following is not true about Lewis base?
Considering the properties of Lewis bases:
a. Incorrect - Lewis bases are not necessarily cationic; they are typically anionic or neutral with lone pairs of electrons.
b. True - Lewis base strength does depend on the pKa of the parent acid.
c. True - Lewis bases are electron-rich species.
d. True - Water is an example of a Lewis base due to its lone pairs of electrons.
Thus, the correct answer is:
a. Lewis bases are cationic in nature
15. Which one of the following salts forms aqueous solutions with [tex]\( pH = 7 \)[/tex]?
a. [tex]\(Na_2S\)[/tex] - forms basic solution
b. [tex]\(NaNO_2\)[/tex] - forms basic solution
c. NaBr - NaBr is a salt derived from a strong acid (HBr) and a strong base (NaOH), thus forms neutral solution.
d. [tex]\(Na_2CO_3\)[/tex] - forms basic solution
Thus, the correct answer is:
c. NaBr
9. When [tex]\([ H^{+}]=4.0 \times 10^{-9} M\)[/tex] in water at [tex]\(25^{\circ} C\)[/tex]:
To determine the pH of the solution, use the pH formula:
[tex]\[ pH = -\log [ H^{+} ] \][/tex]
Given that [tex]\([ H^{+}] = 4.0 \times 10^{-9} M\)[/tex], the calculations will yield:
[tex]\[ pH = 8.40 \][/tex]
Thus, the correct answer is:
b. [tex]\( pH = 8.40 \)[/tex].
10. A solution with an [tex]\([ OH^{-}] \)[/tex] concentration of [tex]\(1.20 \times 10^{-7} M\)[/tex] has a pOH and pH:
To determine pOH:
[tex]\[ pOH = -\log [ OH^{-} ] \][/tex]
Given that [tex]\([ OH^{-}] = 1.20 \times 10^{-7} \)[/tex], the calculations will yield:
[tex]\[ pOH = 6.92 \][/tex]
Since pH and pOH are related by:
[tex]\[ pH + pOH = 14 \][/tex]
Calculating pH:
[tex]\[ pH = 14 - 6.92 = 7.08 \][/tex]
Thus, the correct answer is:
a. 6.92 and 7.08
11. The acidic ingredient in vinegar is acetic acid. The pH of vinegar is around 2.4 and the molar concentration of acetic acid in vinegar is around 0.85 M. Determine the value of the acid ionization constant, [tex]\(K_a\)[/tex] for acetic acid.
Given:
[tex]\[ pH = 2.4 \][/tex]
[tex]\[ [HA] = 0.85 \, M \][/tex]
First, calculate the [tex]\([H^+]\)[/tex] using the pH:
[tex]\[ [H^+] = 10^{-pH} = 10^{-2.4} \approx 4.0 \times 10^{-3} \][/tex]
Assuming [tex]\( [H^+] \approx [A^-] \)[/tex] for a weak acid, we use:
[tex]\[ K_a = \frac{ [H^+][A^-] }{ [HA] } \][/tex]
[tex]\[ K_a \approx \frac{(4.0 \times 10^{-3})(4.0 \times 10^{-3})}{0.85} \approx 1.9 \times 10^{-5} \][/tex]
Thus, the correct answer is:
b. [tex]\(1.9 \times 10^{-5}\)[/tex]
12. A cup of coffee has a hydroxide ion concentration of [tex]\(1.0 \times 10^{-10} M\)[/tex]. What is the pH of this coffee?
To determine pOH:
[tex]\[ pOH = -\log [ OH^{-} ] \][/tex]
Given that [tex]\([OH^{-}] = 1.0 \times 10^{-10} \)[/tex], the calculations will yield:
[tex]\[ pOH = 10 \][/tex]
Since pH and pOH are related by:
[tex]\[ pH + pOH = 14 \][/tex]
Calculating pH:
[tex]\[ pH = 14 - 10 = 4 \][/tex]
Thus, the correct answer is:
c. 4
13. What is the concentration of [tex]\([OH^{-}]\)[/tex] in a 0.20 M solution of ammonia? The [tex]\(K_b\)[/tex] value for ammonia is [tex]\(1.8 \times 10^{-5}\)[/tex].
Given:
[tex]\[ [NH_3] = 0.20 \, M \][/tex]
[tex]\[ K_b = 1.8 \times 10^{-5} \][/tex]
Use the formula for [tex]\(K_b\)[/tex]:
[tex]\[ K_b = \frac{ [OH^-][NH_4^+] }{ [NH_3] } \][/tex]
Assuming [tex]\([OH^-] = [NH_4^+]\)[/tex]:
[tex]\[ K_b = \frac{ [OH^-]^2 }{ [NH_3] } \][/tex]
[tex]\[ 1.8 \times 10^{-5} = \frac{ [OH^-]^2 }{ 0.20 } \][/tex]
[tex]\[ [OH^-]^2 = (1.8 \times 10^{-5})(0.20) \][/tex]
[tex]\[ [OH^-]^2 = 3.6 \times 10^{-6} \][/tex]
[tex]\[ [OH^-] = \sqrt{ 3.6 \times 10^{-6} } = 1.9 \times 10^{-3} \][/tex]
Thus, the correct answer is:
c. [tex]\(1.9 \times 10^{-3} M\)[/tex]
14. Which of the following is not true about Lewis base?
Considering the properties of Lewis bases:
a. Incorrect - Lewis bases are not necessarily cationic; they are typically anionic or neutral with lone pairs of electrons.
b. True - Lewis base strength does depend on the pKa of the parent acid.
c. True - Lewis bases are electron-rich species.
d. True - Water is an example of a Lewis base due to its lone pairs of electrons.
Thus, the correct answer is:
a. Lewis bases are cationic in nature
15. Which one of the following salts forms aqueous solutions with [tex]\( pH = 7 \)[/tex]?
a. [tex]\(Na_2S\)[/tex] - forms basic solution
b. [tex]\(NaNO_2\)[/tex] - forms basic solution
c. NaBr - NaBr is a salt derived from a strong acid (HBr) and a strong base (NaOH), thus forms neutral solution.
d. [tex]\(Na_2CO_3\)[/tex] - forms basic solution
Thus, the correct answer is:
c. NaBr
