A chemist needed some potassium nitrate, KNO3, for an experiment. Because there

Question

A chemist needed some potassium nitrate, KNO3, for an experiment. Because there was none in her laboratory, she decided to make it from potassium iodide, KI and sodium nitrate, NaNO3 by means of the following reaction:

KI (aq) + NaNO3 (aq) ---> KNO3 (s) + Nal (aq) .

The success of this synthesis depends onthe fact that KNO3 is much less soluble in water than KI, NaNO3, or NaI. When she dissolved 0.50 mol KI and 0.75 mol NaNO3 in 100ml of water and cooled the solution to 0 degrees celcius, 37g of pure KNO3 crystallized from solution.

1. What is the theoretical yield, in grams, of KNO3 for this synthesis?

2. What is her percent yield for this synthesis?

Explanation / Answer

OK, as you say, a how-to answer without the answer itself. Since I teach Chem, I was concerned about doing someone's homework...

The reaction is balanced as written and says that every 1 mole of KI needs 1 mole of NaNO3 to make 1 mole of KNO3 (we can ignore the NaI since it's not part of the question), so if the chemist used only half the KI shown in the equation, or 0.5 moles of KI, the KI is the limiting reactant (it's the *least available reactant*) and only 0.5 moles of the NaNO3 will be used up making KNO3. Since the ratio of moles of KNO3 produced for each mole of the controlling/limiting reactant (here, KI) is 1, only 0.5 moles of KNO3 will be produced.

a. To get the theoretical yield, you'll need the FW of KNO3 (the sum of atomic weights (=1 mole). Remember, the chemist made only 0.5 moles of KNO3.

b. To get the % yield, divide the actual yield in grams by the theoretical yield in grams to get a fraction. Multiply the fraction by 100%.

ok now ,

mol (0.5 mol) * Molar mass = mass of KNO3 (find the molar mass from the table of elements) = 0.5*101.1 = 50.55 gm

u will then get the theorical yeild.

the experimental yeild is 37 g

percentage yeild = [ 100 * absolute value of(theorical yield - experimental yeild)] / theorical yield

= 100* (37 ) / 50.55 =73.19%

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