Question

calculate the hydroxide ion concentration for a solution with $h_3o^+_{eq}=2.8 \times 10^{-5}$ m. use \e\ for scientific notation.
respond with the correct number of significant figures in scientific notation (use e notation and only 1 digit before decimal e.g. 2.5e5 for $2.5 \times 10^5$)
type your numeric answer and submit

Explanation:

Step1: Recall water autoionization constant

At 25°C, $K_w = [\text{H}_3\text{O}^+][\text{OH}^-] = 1.0 \times 10^{-14}$

Step2: Rearrange to solve for $[\text{OH}^-]$

$[\text{OH}^-] = \frac{K_w}{[\text{H}_3\text{O}^+]}$

Step3: Substitute given values

$[\text{OH}^-] = \frac{1.0 \times 10^{-14}}{2.8 \times 10^{-5}}$

Step4: Calculate and format result

First compute the value: $\frac{1.0}{2.8} \approx 0.357$, and $\frac{10^{-14}}{10^{-5}} = 10^{-9}$. Adjust to 1 digit before decimal and use E notation: $3.6 \times 10^{-10}$ becomes $3.6\text{E}-10$ (rounded to 2 significant figures, matching the given value)

Answer:

3.6E-10