Struggling with first two modules of Apologia Chemistry

[Hunter's Moon]

I am really struggling with the first two modules of Apologia Chem. I am horrible at conversions. I understand the first part of the equation (1g/1) but then the second part, I never understand what goes where. Say I want to convert to mg, do I put how many mg are in 1 g in the numerator, or how many mg there are in 1 g in the denominator. I understand mg would go on top so both grams would cancel out, but I don't understand what number to put there.

 

Sorry, I am bad at explaining.

 

Ex: Convert 3 grams to milligrams.

 

There are 1000 milligrams in 1 gram.

 

1gram/1 x 1mg/1000g OR 1gram/1 x 1000mg/1g.

 

It seems they keep changing the rules.

 

I am also having trouble with calorimeters and specific heat and such. The equation and word problems confuse me beyond belief.

 

Would someone please help me understand at least the conversion problems??

 

Thanks.

[jld]

I'll ask dd if she can pm you. She did mention the second module was pretty hard, the hardest in the book, if I recall correctly. She wonders why they start off with something so difficult.

 

She's still sleeping (9:17 a.m. here :D), but I'll ask her when she gets up.

 

Hang in there!

[Hunter's Moon]

I'll ask dd if she can pm you. She did mention the second module was pretty hard, the hardest in the book, if I recall correctly. She wonders why they start off with something so difficult.

 

She's still sleeping (9:17 a.m. here :D), but I'll ask her when she gets up.

 

Hang in there!

 

Thank you so much!

 

I'm glad it is the hardest because I couldn't take much more head-banging :banghead:

[Guest Cheryl in SoCal]

I am really struggling with the first two modules of Apologia Chem. I am horrible at conversions. I understand the first part of the equation (1g/1) but then the second part, I never understand what goes where. Say I want to convert to mg, do I put how many mg are in 1 g in the numerator, or how many mg there are in 1 g in the denominator. I understand mg would go on top so both grams would cancel out, but I don't understand what number to put there.

 

Sorry, I am bad at explaining.

 

Ex: Convert 3 grams to milligrams.

 

There are 1000 milligrams in 1 gram.

 

1gram/1 x 1mg/1000g OR 1gram/1 x 1000mg/1g.

 

It seems they keep changing the rules.

 

I am also having trouble with calorimeters and specific heat and such. The equation and word problems confuse me beyond belief.

 

Would someone please help me understand at least the conversion problems??

 

Thanks.

1 mg does not equal 1000 grams. 1 mg equals .001 gram.

 

The conversion factor must equal 1. You could use either .001 g/1 mg (or the inverse 1 mg/.001 g) or 1 g/1000 mgs (or the inverse 1000 mgs/1gm). Most would use the latter but it really doesn't matter. You can invert whichever you choose to get the labels where you need them because it equals 1 no matter which is on the top or bottom (1/1 is the same as 1/1).

 

For your example - convert 3 grams into milligrams. Here it is with both conversion factors:

 

3g x 1000mg = 3000mg = 3000mg (the grams cancel each other so you are left with 3000 mg/1, which equals 3000 mg)

-1-----1 g-------1

 

3g x -1mg- = 3mg = 3000mg

-1---.001g---.001

 

They both give you the same answer because both conversion factors are true.

Edited July 15, 2010 by Cheryl in SoCal

[Guest Cheryl in SoCal]

I posted again to try to post better looking fractions and couldn't delete this post after I edited my original.

Edited July 15, 2010 by Cheryl in SoCal

[kiana]

One way to think about it -- When you have a statement like "There are 1000 milligrams in one gram", the 1000 will always go with the mg. If you want the mg on the bottom, you have 1 g/1000mg. If you want the mg on the top, you have 1000mg/1g. There's no other way to write it which makes it equal to 1.

 

A good way to check -- in the question you gave, you know that grams are bigger than milligrams, so if you have 3 grams, when you convert to milligrams, the number of milligrams should get bigger. If you divide by 1000 accidentally, you get a number much smaller than 3, which tells you that you made an error.

[Luckymama]

If it makes you feel any better, dimensional analysis is always at the start of a chemistry program/textbook because it's a fundamental skill to master :)

 

Get in the habit of writing down all units used in any problem. Go through the units before doing the actual math, to make sure you will end up with the correct unit in your answer.

[MyThreeSons]

She did mention the second module was pretty hard, the hardest in the book, if I recall correctly. She wonders why they start off with something so difficult.

 

 

Our co-op teacher skips the second module at the beginning of the year and comes back to it later.

[MyThreeSons]

When you're doing unit conversions, remember that your answer is the same thing you started with, it just looks different as you convert to the desired units. The way you keep it the same is by multiplying by 1 in each step. It's just like when you convert two-thirds to four-sixths: you multiplied the numerator and denominator both by 2; two over two is 1.

 

So as you do your conversions, make sure you're multiplying by one in each step. In a single step problem, your "one" will be the units you want to end up with over the units you started with.

 

HTH

[Hunter's Moon]

Thank you everyone!

 

I am starting to understand the conversions more and more.

[Teachin'Mine]

Khan Academy has this awesome video on conversions:

 

 

 

It starts out basic, and goes into a problem just like the one you had. :)

 

He has entire chemistry topics available. I need to remember to use his site more. I just wish it had a search engine in it.