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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: wuzbob on September 28, 2009, 11:00:38 AM

Title: Homework help - how to do this problem??
Post by: wuzbob on September 28, 2009, 11:00:38 AM
Okay so basically before our big exam, we are required to do five practice problems. Well, I got through the first 4 but this is the only one left, any suggestions?

5.   Lead (II) ions can be precipitated from solution with potassium chloride to form lead sulfide and potassium ions.  Write the molecular, total, and net ionic equations for this reaction.  When 28.5 grams of potassium chloride is added to a solution containing 25.7 g of lead (II) ions the mass of lead (II) chloride that forms is 29.4 g.  Determine the theoretical yield of lead (II) chloride and calculate the percent yield for this reaction.
Title: Re: Homework help - how to do this problem??
Post by: Yggdrasil on September 28, 2009, 12:23:30 PM
Quote from: wuzbob on September 28, 2009, 11:00:38 AM
5.   Lead (II) ions can be precipitated from solution with potassium chloride to form lead sulfide and potassium ions.

This is probably a typo.  The products should be lead (II) chloride and potassium ions.

So, I would start by writing out the chemical formula for all of the chemical species involved (lead (II) ions, potassium chloride, lead (II) chloride, and potassium ions), then using these to write a balanced chemical reaction.
Title: Re: Homework help - how to do this problem??
Post by: wuzbob on September 28, 2009, 10:53:33 PM
5.   Lead (II) ions can be precipitated from solution with potassium chloride to form lead (II) chloride and potassium ions. Write the molecular, total, and net ionic equations for this reaction.  When 28.5 grams of potassium chloride is added to a solution containing 25.7 g of lead (II) ions the mass of lead (II) chloride that forms is 29.4 g.  Determine the theoretical yield of lead (II) chloride and calculate the percent yield for this reaction.


-----that's the real problem sorry about the typo.
Title: Re: Homework help - how to do this problem??
Post by: Borek on September 29, 2009, 02:54:33 AM
Now follow Ygg's advice.
Title: Re: Homework help - how to do this problem??
Post by: Yggdrasil on September 29, 2009, 12:51:26 PM
That is not a chemical reaction.  A chemical reaction has a left hand side with the reactants and a right hand side with the products.  For example, the reaction between silver nitrate and magnesium chloride to form solid silver chloride and magnesium nitrate can be written:

2AgNO3 (aq) + MgCl2 (aq) --> 2AgCl2 (s) + Mg(NO3)2 (aq)

You need to write a comparable equation for your reaction.
Title: Re: Homework help - how to do this problem??
Post by: sjb on September 29, 2009, 01:14:53 PM
Quote from: Yggdrasil on September 29, 2009, 12:51:26 PM
That is not a chemical reaction.  A chemical reaction has a left hand side with the reactants and a right hand side with the products.  For example, the reaction between silver nitrate and magnesium chloride to form solid silver chloride and magnesium nitrate can be written:

2AgNO3 (aq) + MgCl2 (aq) --> 2AgCl2 (s) + Mg(NO3)2 (aq)

You need to write a comparable equation for your reaction.

That ought to be AgCl, shouldn't it?
Title: Re: Homework help - how to do this problem??
Post by: Borek on September 29, 2009, 02:58:47 PM
Obvious typo.