2. bromophenol blue is the indicator used in detecting the endpoint for the anta

Question

2. bromophenol blue is the indicator used in detecting the endpoint for the antacid analysis in this experiment. what is the expected color change at the endpoint?

3. a 0.204g sample of a CO3^2- antacid is dissolved with 25.0ml of 0.0981 M HCL. the hydrochloric acid that is not neutralized by the antacid is titrated to a bromophenol blue endpoint with 5.83 mL of 0.104 M NaOH.
a. calculate the number of moles of base in the antacid.

b. determine the moles of base per gram of antacid in the sample. express your answer with the correct number of significant figures.

Explanation / Answer

Solution:- (2) Bromophenol blue changes color from yellow to blue. yellow is at low pH and blue is at slight higher pH. since CO32- is a weak base and a strong acid HCl is added to it so the pH will decrease it means the color would change from blue to yellow.

(3)   CO32-(aq) + 2H+(aq) <----> CO2(g) + H2O(l)

OH-(aq) + H+(aq) ----> H2O(l)

From second equation, NaOH and HCl react in 1:1 mol ratio.

Total moles of HCl taken = 25.0 ml x (1L/1000ml) x (0.0981 mmol/L) = 0.00245 mol

moles of NaOH used to neutralize excess HCl = 5.83 ml x (1L/1000ml) x (0.104 mol/L) = 0.000606 mol

moles of HCl or H+ used to neutralize antacid present in sample = 0.00245 - 0.000606 = 0.00184 mol

(a) 0.00184 mol H+ x (1 mol CO32-/2 mol H+) = 0.000920 mol

(b) 0.000920 mol/0.204 g = 0.00451 mol/g

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