What does the term \"endpoint\" mean in this experiment, specifically what obser

Question

What does the term "endpoint" mean in this experiment, specifically what observable changes, if any, occur and what are the chemical relationships at the endpoint for the following reaction? Answer each part below. HA (aq) + NaOH (aq) rightarrow NaN (aq) + H_2O (l). The endpoint is: At the endpoint, the observable changes are: At the endpoint, the chemical relationships (in moles) are: In determining the amount of unknown sample size to be used ion the titration, a student found that 0.115 g of the unknown used 6.45 ml of the standardized NaOH solution to reach the endpoint. What is the amount of unknown the student should be using when performing the titration? In order to receive credit you must show your work. If the endpoint is expected to occur at the calculated value in question 2, suggest a volume where the student should start adding titrant slowly Explain.

Explanation / Answer

Q1.

a.

endpoint --> point in which there is a change in color in indicator's solution, i.e. we assume equivalence point

b.

The chagnes are typically, a color from invisible to purple/pink

c.

In this endpoint, we assume

moles of H+ = moles of OH-

so

moles of acid = moles of base

Q2.

mol of acid = mol of base

mol of base = MV = Mbase*6.45 mL

mol of acid = masS/MW = 0.115

relate

Mbase*6.45 mL = (we require Concentration of bass)

Q3.

The volume where he should start adding slowly is near V = 6 mL, so each drop will be drstically changing the color

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