Suppose you add a solution of calcium hydroxide to a solution of sodium carbonat
ID: 887472 • Letter: S
Question
Suppose you add a solution of calcium hydroxide to a solution of sodium carbonate and a precipitate forms. You measure the total amount of the precipitate (in g) as a function of time. At time 0, 20.0 s, 40.0 s and 60.0 s you get a cumulative weight of 0.00 g, 4.85 g, 7.15 g and 8.15 g of the precipitate, respectively. What is the average rate of reaction between 20 and 40 seconds in mol/s? Enter a numerical value below without any units or symbols. If you use scientific notation, then be sure to format it using the "E" notation like "1.0E-5" and do not put spaces between the "E" and the numbers.
Explanation / Answer
Ca(OH)2 + Na2CO3 ----> 2NaOH + CaCO3(S)
No of moles of CaCO3 produced after 20 sec =w/mwt = 4.85/100.0869 = 0.04846 mol
mwt of CaCO3 = 100.0869 g/mol
No of moles of CaCO3 produced after 40 sec = 7.15/100.0869 = 0.0714 mol
average rate = change in concentration / dt
= (0.0714 - 0.04846)/20
= 0.001147 mol/s