The [tex]$pH$[/tex] can be calculated using the equation [tex]$pH = -\log \left( [H^+] \right)$[/tex], where [tex]$[H^+]$[/tex] is the hydronium ion concentration. Find the hydronium ion concentration of a particular lemon juice if the [tex]$pH$[/tex] level is 2.1.

A. [tex]$3.222 \times 10^{-1}$[/tex]
B. [tex]$1.259 \times 10^2$[/tex]
C. [tex]$7.943 \times 10^{-3}$[/tex]
D. [tex]$1.668 \times 10^3$[/tex]



Answer :

To find the hydronium ion concentration from a given pH level, you can use the relationship between pH and hydrogen ion concentration, which is given by the equation:

[tex]\[ \text{pH} = -\log [H^+] \][/tex]

Where [tex]\( [H^+] \)[/tex] represents the concentration of hydronium ions (in moles per liter).

### Step-by-Step Solution

1. Understand the Problem:
You are given the pH level of a lemon juice, which is 2.1, and you need to find the hydronium ion concentration [tex]\([H^+]\)[/tex].

2. Rearrange the Formula:
To solve for [tex]\( [H^+] \)[/tex], we need to rearrange the equation:

[tex]\[ \text{pH} = -\log [H^+] \][/tex]

Rearrange it to isolate [tex]\( [H^+] \)[/tex]:

[tex]\[ [H^+] = 10^{-\text{pH}} \][/tex]

3. Substitute the Given pH Value:
Substitute [tex]\( \text{pH} = 2.1 \)[/tex] into the equation:

[tex]\[ [H^+] = 10^{-2.1} \][/tex]

4. Calculate the Hydronium Ion Concentration:
Calculate [tex]\( 10^{-2.1} \)[/tex]:

[tex]\[ [H^+] = 0.007943282347242814 \][/tex]

5. Express the Concentration in Scientific Notation:
The hydronium ion concentration [tex]\( [H^+] \)[/tex] can be expressed in scientific notation as:

[tex]\[ [H^+] \approx 7.943 \times 10^{-3} \][/tex]

6. Identify the Correct Answer:
Compare the calculated hydronium ion concentration to the provided options:

- [tex]\( 3.222 \times 10^{-1} \)[/tex]
- [tex]\( 1.259 \times 10^2 \)[/tex]
- [tex]\( 7.943 \times 10^{-3} \)[/tex]
- [tex]\( 1.668 \times 10^3 \)[/tex]

The correct choice is:

[tex]\[ 7.943 \times 10^{-3} \][/tex]

### Conclusion
The hydronium ion concentration of the lemon juice with a pH level of 2.1 is [tex]\( 7.943 \times 10^{-3} \)[/tex] M.

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