40.0 ml of an acetic acid of unknown concentration is titrated with 0.100 m naoh. after 20.0 ml of the base solution has been added, the ph in the titration flask is 5.10. what was the concentration of the original acetic acid solution? [ka(ch3cooh) = 1.8 x 10â5]

Concentration of original the acetic acid = 0.11M

Explanation:

This neutralization reaction takes place between acetic acid,  CH 3 COOH , a weak acid, and sodium hydroxide,  NaOH , a strong base. Since the neutralization of the acid is not complete as indicated by the pH of the resulting solution, a buffer solution is formed that will contain acetic acid and its conjugate base, the acetate anion.

The balanced ionic equation of the reaction is as follows:

CH₃COOH + OH⁻ > CH₃COO⁻ + H₂O

Since the pH of the solution and Ka of the acid is given, the conjugate acid-base ratio is to be found using the Henderson-Hasselbalch equation:

pH = pKa + log ([conjugate base] / [conjugate acid])

where pH = 5.10, pKa= -log Ka

pKa = -log(1.8 x 10⁻⁵)

pKa = 4.74

log([conjugate base] / [conjugate acid]) = pH - pKa

log([conjugate base] / [conjugate acid]) = 5.10 - 4.74 = 0.36

[conjugate base] / [conjugate acid] = antilog(0.36) = 2.3

The moles of base reacted = no of moles of conjugate base

no of moles of NaOH reacted = molarity * vol in liters

no of moles of NaOH reacted= 0.100M * (20mL/1000mL*1L) = 0.002moles

[conjugate base] = no of moles / volume in liters

total volume of solution = (40 + 20)mL = 60mL

[conjugate base] = 0.002/ 60mL/1000mL*1L) = 0.033M

[conjugate acid] = 2.3 * [conjugate base] = 2.3 *0.033M

[conjugate base] = 0.076M

Concentration of original the acetic acid = [conjugate base] +[conjugate acid]

Concentration of original the acetic acid = 0.076M + 0.033M =  0.11M

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

while cooking a piece of 1/2 pound beef steak, a cast iron pan (2.4kg in weight) was heated 260 celsius.