Question

which solution has the greatest number of hydroxide ions?
o baking soda, ph = 9
o milk, ph = 6
o tomato juice, ph = 3.5
o vinegar, ph = 2

Explanation:

Step1: Recall the relationship between pH and pOH

The sum of pH and pOH is 14 at 25°C, i.e., $pH + pOH=14$. Also, $[OH^-]=10^{-pOH}$.

Step2: Calculate pOH for baking soda

For baking - soda with $pH = 9$, $pOH=14 - pH=14 - 9 = 5$. Then $[OH^-]=10^{-5}\ M$.

Step3: Calculate pOH for milk

For milk with $pH = 6$, $pOH=14 - 6 = 8$. Then $[OH^-]=10^{-8}\ M$.

Step4: Calculate pOH for tomato juice

For tomato juice with $pH = 3.5$, $pOH=14 - 3.5 = 10.5$. Then $[OH^-]=10^{-10.5}\ M$.

Step5: Calculate pOH for vinegar

For vinegar with $pH = 2$, $pOH=14 - 2 = 12$. Then $[OH^-]=10^{-12}\ M$.

Answer:

Baking soda, pH = 9