A chemist found a bottle of an unknown concentration of KOH solution sitting on
ID: 876411 • Letter: A
Question
A chemist found a bottle of an unknown concentration of KOH solution sitting on the shelf in the lab. She found that the pH was 12.0.
(a) Is the solution an acid or a base? How do you know?
(b) What is the concentration of H3O+ ions in the solution?
(c) The chemist decided to titrate the unknown solution with HCl to determine its concentration. She placed a 45.0 mL sample of the solution into a flask and mixed in a few drops of phenolphthalein. She then slowly added HCl and found that 75.0 mL of 1.5 M HCl was needed to neutralize the KOH. What is the concentration of KOH in the unknown solution?
Explanation / Answer
a- pH 12 indicates its a base because in pH scale so solution when have pH value is more than 7 it is called base while less than 7 called acid while pH 7 is nuetral.
b- [H3o]+ = 10-pH
= 10 -12 so on calculation it give value 0 for [H3O]+
c- concentraion is equal to mol / volume so for KOH M1 and V1 are 1.5 M and 75.0ml or75/1000 = 0.075 L and for HCl M2 =? , V= 45/1000 =0.045L
M1V1 =M2V2
1.5 * 0.075 = M2 * 0.045
M2 = 2.5 so 2.5 M KOH concentration nutralize 1.5M HCL
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