[ahawk1]

In the production of printed circuit boards for the electronics industry, a 0.575 mm layer of copper is laminated onto an insulating plastic board. Next a circuit pattern made of a chemically resistant polymer is printed on the board. The unwanted copper is removed by chemical etching and the protective polymer is finally removed by solvents. One etching reaction is:

Cu(NH3)4Cl2 (aq) + 4NH3 (aq) + Cu(s) -> 2 Cu(NH3)4Cl(aq)


A plant needs to manufacture 8200 printed circuit boards, each 7.45cm x 16.0cm in area. An average of 89.0% of the copper is removed from each board (density of copper=8.96g/cm3.)
What mass of Cu(NH3)4Cl2 reagent is required?


i am completely lost and dont know how to even start this problem!! can someone help walk me through step by step at a time? thanks!

[Arkcon]

Like a lot of word problems, this question is full of extraneous info, to make it seem more "real"to you and to make you work at picking out information, and putting it where you need it.

You have a balanced chemical equation.  Here's a question I tend to ask posters to this board -- What are the units of a balanced chemical equation?  And yes, it does have units, they may not be specified, but they are there.

[ARGOS++]

[ahawk1]

Like a lot of word problems, this question is full of extraneous info, to make it seem more "real"to you and to make you work at picking out information, and putting it where you need it.

You have a balanced chemical equation.  Here's a question I tend to ask posters to this board -- What are the units of a balanced chemical equation?  And yes, it does have units, they may not be specified, but they are there.

the balances equation tells u the ratio of moles needed to combine with one another to get the ratio of products, so i guess the units would be moles, or grams per mole?

[ahawk1]

[Arkcon]

the balances equation tells u the ratio of moles needed to combine with one another to get the ratio of products, so i guess the units would be moles, or grams per mole?

Nice, lots of people don't get that.  The units are moles.  So your reaction is a foumula, it tells you one mole of copper ammonium chloride, dissolves one mole of copper.  But, your question asks for grams of reagent, to remove an area of copper.  You have some conversions to do.

[ahawk1]

the balances equation tells u the ratio of moles needed to combine with one another to get the ratio of products, so i guess the units would be moles, or grams per mole?

Nice, lots of people don't get that.  The units are moles.  So your reaction is a foumula, it tells you one mole of copper ammonium chloride, dissolves one mole of copper.  But, your question asks for grams of reagent, to remove an area of copper.  You have some conversions to do.

thats where i get lost, #1 the 89% confuses me, #2 would i use density=mass/volume and solve for mass then mutiply by 8200 because theres 8200 chips?

[Arkcon]

Work slowly, start with what you know, try to figure out what you need to know, and try to figure out how to get there.  Write the units, at each step, trying to cancel them out as you go -- that's called dimensional analysis, you can find a hint on wikipedia, and also google for it.

This is, in fact, a pretty trivial sort of problem.  I know you'd like to have it written out for you, step by step.  But you'll be better off if you crack it yourself.  They will write something totally different come exam time, that somehow requires you to convert units multiple times.  It's just how it's done.

[ahawk1]

Work slowly, start with what you know, try to figure out what you need to know, and try to figure out how to get there.  Write the units, at each step, trying to cancel them out as you go -- that's called dimensional analysis, you can find a hint on wikipedia, and also google for it.

This is, in fact, a pretty trivial sort of problem.  I know you'd like to have it written out for you, step by step.  But you'll be better off if you crack it yourself.  They will write something totally different come exam time, that somehow requires you to convert units multiple times.  It's just how it's done.

thanks for the help i figured out the answer =]]