Chemistry conversion question

[swimmermom3]

I am currently working on atoms to grams (among other things) and I keep the following notation at the top of my page to help me keep it all straight:

 

1 mol x = y grams of x = 6.022 x 10^23 atoms

 

x = element in question

y = molar mass of x

 

When I compare my answers to the solutions manual, I leave out a step but come up with the correct answer.

 

The official answer for finding the number of atoms present in 3.14g Cu is:

 

3.14 g Cu x 1 mol Cu     x 6.022 x 10^23 Cu atoms  = 2.98 x 10^22 atoms Cu

                   63.55 g Cu                 1 mol Cu

 

 

Because of the equivalencies at the top of the page, I do the following:

 

3.14 g Cu  x  6.022 x 10^23 atoms  =  2.98 x 10^22 atoms Cu

                                 63.55 g Cu

 

 

Is my time-saving strategy just sloppy math? If I teach my son to leave out the mol conversion, would he be counted down on a test like SAT 2? The official answer seems to me to include an unnecessary step (except for example).

[Julie of KY]

I would say your way is accurate, but harder to follow if someone doesn't know exactly how you came up with the numbers. Most will recognize Avogadro's number, but not everyone will recognize where the 63.55 g came from (1 mole).

 

Writing it out will help the student go back and know what he did, help others find where he made a mistake more easily and potentially earn more partial credit if the grader can follow it more easily.

 

That said, I have a major struggle to teach my son to show any work.

[anne1456]

I always teach my students to do it the way the solution manual shows.  As the problems get longer and more complicated the more steps that are written out the easier it is to keep track of what you are doing.  So while your way isn't wrong, it is taking a shortcut, and I'd discourage that.

[swimmermom3]

I would say your way is accurate, but harder to follow if someone doesn't know exactly how you came up with the numbers. Most will recognize Avogadro's number, but not everyone will recognize where the 63.55 g came from (1 mole).

 

Writing it out will help the student go back and know what he did, help others find where he made a mistake more easily and potentially earn more partial credit if the grader can follow it more easily.

 

That said, I have a major struggle to teach my son to show any work.

 

 

I always teach my students to do it the way the solution manual shows.  As the problems get longer and more complicated the more steps that are written out the easier it is to keep track of what you are doing.  So while your way isn't wrong, it is taking a shortcut, and I'd discourage that.

 

This all makes perfect sense since I have always made my students write out every step for math when handling conversions. I work out all of the chemistry problems in advance even if I have answers for them, so I am aware of any pitfalls. I think I am getting a bit  lazy.

 

Do only boys skip showing their work. My dd and I (usually ;) ) show all our work. The boys can't be bothered; I always have to resort to some form of, er, "correction," to get them to show everything. How can you study problems before a test if you don't have the problem written out with all of the steps you performed?

[Julie of KY]

Do only boys skip showing their work. My dd and I (usually ;) ) show all our work. The boys can't be bothered; I always have to resort to some form of, er, "correction," to get them to show everything. How can you study problems before a test if you don't have the problem written out with all of the steps you performed?

My second son shows his work beautifully without any guidance from me.

 

My oldest, dyslexic and severely dysgraphic, does everything in his head. It is very hard for him to translate his visual picture of the solution to a written stepwise solution. Math problems that take me two pages of writing, he does correctly in his head. It has always been struggle to find a balance between teaching and challenging him, without the frustration of figuring out how to "show work". I try to separate the two for him. His learns by speeding along absorbing and learning lots. He has separate assignments to "show work". He detests busywork so it is hard to find practical ways that he needs to show his work that isn't just busywork.

 

It is easy to say that we need to teach our kids to show their work, but I think in reality we need to tailor this to our student's abilities.

 

As far as how to study the problem for a test, my oldest would ask why anyone would want to go back and "study" a problem. Once he has figured it out it is filed away in his brain and he can reproduce it. He'll come across a math problem on a past competition test and state he doesn't want to do it again since he already did it once with same/different answers two years ago. He can then point to the exact page in any book that the problem was previously done. I know this isn't normal... but it is his normal and he has no clue why anyone would want to go back to "study" previous problems once it has been figured out.

[8filltheheart]

Completely OT, Lisa, but thought I would offer you some humor. :)

 

What is an undertaker's favorite element? (Atomic number 56......didn't want to post the answer directly. ;) ). My dd and I both dislike chemistry. :p. We have to find a way of making it palatable. LOL! How I managed to raise a chemE and 2 other kids so far that love chemistry, I have no idea. This dd is so much more like me, poor thing.

[Dicentra]

I totally missed this the first time around, SM3!  I agree with Julie - you're right but didn't exactly show ALL of your steps. :)

 

Hee, hee...  Good one 8!  I follow "Chemistry Cat" on Facebook because of the truly awesome/awful chemistry puns. :D

 

Here's a good one for organic chemistry...

 

Ahem.

 

Organic chemistry is difficult.

 

Those who study it have alkynes of problems.

 

:D

 

Or this... :D :D