Chemistry!

10.2 g of Pb(NO3)2 are dissolved in 100 mL of water, and added to 250.0 mL of a 0.250 M solution of KI. Determine the mass in grams of Pbl2 produced, and find the number of moles of the excess reagent. PLZ explain



chemistry - DrBob222, Monday, December 13, 2010 at 4:30pm
..........Pb(NO3)2 + 2KI ==> PbI2 + 2KNO3
moles Pb(NO3)2 = grams/molar mass = ??
moles KI = M x L = ??

1 mol Pb(NO3)2 will produce 1 mole PbI2 and use 2 moles KI. DO YOU HAVE THAT MUCH KI? If so, then Pb(NO3)2 is the limiting reagent and KI is the excess reagent. Simply subtract moles KI from (2*moles Pb(NO3)2 to find moles KI in excess.
If you DON'T have enough KI, then KI is the limiting reagent and Pb(NO3)2 will be excess. You treat it the same way EXCEPT that moles Pb(NO3)2 used will be 1/2 moles KI.
Post your work if you get stuck.




chemistry - Jenni..can you look again i'm still not getting it thx, Monday, December 13, 2010 at 6:37pm
10.2g/331.208 = 0.0308

(0.25M)(0.25L) = 0.0625


now what? subtract those two #s?



chemistry - DrBob222, Monday, December 13, 2010 at 9:12pm
..........Pb(NO3)2 + 2KI ==> PbI2 + 2KNO3
initial...0.0308....0.0625.....0......0
change...-0.0308...0.0616.+0.0308.+0.0308
final.....0.......0.00090...0.0308....etc

First, the change line.
From the equation you can see that 1 mole Pb(NO3)2 will require 2 moles KI; therefore, I multiplied moles Pb(NO3)2 by 2 to arrive at moles KI used. Why didn't I do it the other way around (and it is possible to have done that but you know you started with the wrong one once that happens). Suppose we DID start with 0.0625 moles KI, how many moles Pb(NO3)2 will react with ALL of the KI. That is 0.0625 x (1 mole Pb(NO3)2/2 moles KI) = 0.0625*(1/2) = 0.03125 AND WE DON'T HAVE THAT MUCH Pb(NO3)2 so lead nitrate is the limiting reagent.
final line. Yes, we subtract the two moles to determine which one remains and how much is unreacted BUT we must first determine the limiting reagent as I did in the change line.
To convert moles PbI2 to grams, conert moles PbI2 x molar mass = grams.



chemistry - Anonymous, Tuesday, December 14, 2010 at 4:00pm
0.0308x 331.208 = 10.2 g


I am sorry but I still don't know what to do after this????

  1. 👍 0
  2. 👎 0
  3. 👁 264
asked by jenni

Respond to this Question

First Name

Your Response

Similar Questions

  1. chemistry

    10.2 g of Pb(NO3)2 are dissolved in 100 mL of water, and added to 250.0 mL of a 0.250 M solution of KI. Determine the mass in grams of Pbl2 produced, and find the number of moles of the excess reagent. PLZ explain

    asked by Lisa on December 13, 2010
  2. General Chemistry

    A student dissolved 4.00 g of Co(NO3)2 in enough water to make 100. mL of stock solution. He took 4.00 mL of the stock solution and then diluted it with water to give 275. mL of a final solution. How many grams of NO3- ion are

    asked by Dave on October 12, 2010
  3. chemistry

    Calculate the pH when 0.446 g of Cu(NO3)2 (s) are dissolved in 250.0 mL of water

    asked by Anonymous on October 10, 2010
  4. Chemistry

    1. Sugar can be dissolved in water because of the presence of bonds between _______ in its molecule. 2. If the maximum amount of a compound that can dissolve in 100 mL of water is 22 g, then a solution of 20 g of that substance in

    asked by Amanda on May 20, 2014
  5. Chemistry

    1. Sugar can be dissolved in water because of the presence of bonds between _______ in its molecule. 2. If the maximum amount of a compound that can dissolve in 100 mL of water is 22 g, then a solution of 20 g of that substance in

    asked by Amanda on May 20, 2014
  6. Chemistry

    A 1.250 g mass of standard aspirin is dissolved in approximately 20 mL of 1 M NaOH. This solution is added to a 250-mL volumetric flask and diluted to the mark with DI water. How many grams per mL of aspirin are in the resulting

    asked by Anonymous on January 26, 2014
  7. soran university

    1. Which salt is LEAST soluble at 0 ºC? 2. How many grams of sodium nitrate, NaNO3, are soluble in 100 g of water at 10 ºC? 3. When 50 grams of potassium chloride, KCl, is dissolved in 100 grams of water at 50 ºC, the solution

    asked by zagros on November 24, 2014
  8. Chemistry

    Pure water boils at 100ºC (212ºF). When a substance is added to the water the boiling point increases due to what is referred to as the boiling point elevation. (a) What is the molecular mass of sucrose (C₁₂H₂₂O₁₁)?

    asked by Hannah on March 18, 2012
  9. Chemistry

    What is the concentration in each of the following solutions? A) 240 mL of 0.200 M KNO3 is added to 160 mL of water. B) 2.25g of NaCl is dissolved in 250 ml of water.

    asked by Alan on October 12, 2016
  10. chemistry

    A 2.5 g sample of NaOH (Mw = 40.00) was dissolved in water to give a solution of final volume 250 cm3. (i) With reasons, state whether NaOH is a strong or a weak base. Give the conjugate acid of NaOH and decide whether this

    asked by LUx on April 21, 2013

More Similar Questions