Hands-on Lab Skills/Science Inquiry. 3rd Grade Science Worksheets ... - Free Printable

The image you uploaded contains a worksheet titled "Harder pH & Acid/Base Science Quiz - 1st Period". It consists of several questions related to acids, bases, and pH. Below is a detailed explanation and solution for each question:

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Question 1:

What is the pH of a solution with a hydrogen ion concentration of \(1 \times 10^{-4}\) M?

- Solution:
The pH of a solution is calculated using the formula:
\[
\text{pH} = -\log[\text{H}^+]
\]
Here, the hydrogen ion concentration (\([\text{H}^+]\)) is \(1 \times 10^{-4}\) M. Plugging this into the formula:
\[
\text{pH} = -\log(1 \times 10^{-4}) = -(-4) = 4
\]
Answer: The pH is 4.

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Question 2:

Which of the following solutions has the highest pH?
- A) \(1 \times 10^{-3}\) M HCl
- B) \(1 \times 10^{-5}\) M NaOH
- C) Pure water
- D) \(1 \times 10^{-7}\) M HCl

- Solution:
- A) \(1 \times 10^{-3}\) M HCl: This is a strong acid. Its pH is:
\[
\text{pH} = -\log(1 \times 10^{-3}) = 3
\]
- B) \(1 \times 10^{-5}\) M NaOH: This is a strong base. First, calculate the hydroxide ion concentration (\([\text{OH}^-]\)):
\[
[\text{OH}^-] = 1 \times 10^{-5} \, \text{M}
\]
Then, use the relationship between \([\text{H}^+]\) and \([\text{OH}^-]\):
\[
[\text{H}^+][\text{OH}^-] = 1 \times 10^{-14}
\]
Solving for \([\text{H}^+]\):
\[
[\text{H}^+] = \frac{1 \times 10^{-14}}{1 \times 10^{-5}} = 1 \times 10^{-9} \, \text{M}
\]
Now, calculate the pH:
\[
\text{pH} = -\log(1 \times 10^{-9}) = 9
\]
- C) Pure water: The pH of pure water is 7.
- D) \(1 \times 10^{-7}\) M HCl: This is a weak acid. Its pH is:
\[
\text{pH} = -\log(1 \times 10^{-7}) = 7
\]

Comparing all options, the highest pH is 9 (from \(1 \times 10^{-5}\) M NaOH).

Answer: B) \(1 \times 10^{-5}\) M NaOH

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Question 3:

Identify the conjugate base of \(H_2SO_4\).

- Solution:
The conjugate base of an acid is formed when the acid donates a proton (\(\text{H}^+\)). For \(H_2SO_4\) (sulfuric acid), the first dissociation step is:
\[
H_2SO_4 \rightarrow H^+ + HSO_4^-
\]
Here, \(HSO_4^-\) is the conjugate base of \(H_2SO_4\).

Answer: \(HSO_4^-\)

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Question 4:

Which of the following is a strong acid?
- A) HF
- B) HNO_3
- C) CH_3COOH
- D) NH_3

- Solution:
- A) HF (Hydrofluoric acid): Weak acid.
- B) HNO_3 (Nitric acid): Strong acid.
- C) CH_3COOH (Acetic acid): Weak acid.
- D) NH_3 (Ammonia): Base, not an acid.

Answer: B) HNO_3

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Question 5:

What happens to the pH of a solution when a strong base is added to it?

- Solution:
Adding a strong base increases the hydroxide ion concentration (\([\text{OH}^-]\)), which decreases the hydrogen ion concentration (\([\text{H}^+]\)). Since pH is inversely related to \([\text{H}^+]\), the pH of the solution will increase.

Answer: The pH increases.

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Question 6:

Which indicator would be most suitable for determining the endpoint of a titration between a strong acid and a strong base?

- Solution:
For a titration between a strong acid and a strong base, the equivalence point occurs at pH 7. An indicator that changes color around pH 7 is most suitable. Common indicators include:
- Phenolphthalein (changes from colorless to pink around pH 8–10).
- Bromothymol blue (changes from yellow to blue-green around pH 6–7).
- Methyl orange (changes from red to yellow around pH 3–4).

Among these, bromothymol blue is the best choice because its color change is closest to pH 7.

Answer: Bromothymol blue

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Question 7:

What is the pH of a solution with a pOH of 9?

- Solution:
The relationship between pH and pOH is:
\[
\text{pH} + \text{pOH} = 14
\]
Given that pOH = 9:
\[
\text{pH} = 14 - 9 = 5
\]

Answer: The pH is 5.

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Question 8:

Which of the following is a weak base?
- A) NaOH
- B) NH_3
- C) KOH
- D) LiOH

- Solution:
- A) NaOH (Sodium hydroxide): Strong base.
- B) NH_3 (Ammonia): Weak base.
- C) KOH (Potassium hydroxide): Strong base.
- D) LiOH (Lithium hydroxide): Strong base.

Answer: B) NH_3

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Question 9:

What is the pH of a solution with a hydrogen ion concentration of \(1 \times 10^{-8}\) M?

- Solution:
Using the formula:
\[
\text{pH} = -\log[\text{H}^+]
\]
Here, \([\text{H}^+] = 1 \times 10^{-8}\) M:
\[
\text{pH} = -\log(1 \times 10^{-8}) = 8
\]

Answer: The pH is 8.

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Question 10:

Which of the following is a buffer solution?
- A) A solution of HCl and NaCl
- B) A solution of HCl and NaOH
- C) A solution of acetic acid and sodium acetate
- D) A solution of NaOH and KCl

- Solution:
A buffer solution consists of a weak acid and its conjugate base or a weak base and its conjugate acid. Among the options:
- A) HCl and NaCl: HCl is a strong acid, so this is not a buffer.
- B) HCl and NaOH: These are strong acid and strong base, respectively, so this is not a buffer.
- C) Acetic acid and sodium acetate: Acetic acid is a weak acid, and sodium acetate is its conjugate base. This is a buffer.
- D) NaOH and KCl: NaOH is a strong base, so this is not a buffer.

Answer: C) A solution of acetic acid and sodium acetate

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Final Answers:

1. 4
2. B) \(1 \times 10^{-5}\) M NaOH
3. \(HSO_4^-\)
4. B) HNO_3
5. The pH increases.
6. Bromothymol blue
7. 5
8. B) NH_3
9. 8
10. C) A solution of acetic acid and sodium acetate

Boxed Final Answer:
\[
\boxed{4, B, HSO_4^-, B, \text{The pH increases}, \text{Bromothymol blue}, 5, B, 8, C}
\]