# Help/Support ►Any Chemistry Experts?

Status
Not open for further replies.

#### Coffee Lover

##### Bronze Member
I am currently taking my very first chemistry class. Not only is it my first chem, but it's college chem! Anyway, after talking to the instructor, I have found that I am going to need help because I lack the desired chemistry or math background. So, are there any chemistry experts on this forum or is there anyone who can recommend how I can get help?

#### TheMuffinMan

what do you need help on

the amount of math you need for Chemistry is like, ridiculously simple. It's basic algebra + fractions some of the time.

#### KeyofEvil'sBane

##### Space Duck
A lot of the chem i have done (and this was AP chem, so it was college difficulty) is just knowing what order to push buttons on the calculator. The hardest part of chem is really knowing when to use a specific formula when they give you data

#### Coffee Lover

##### Bronze Member
Well, right now we're converting Metric to Metric, English to Metric or reversal, and English to English. I can do the work, but there was some stuff I didn't understand. I'll give you an example of a problem I don't understand in a little while.

#### afrobutt

##### Silver Member
if you don't already know it, learn Kids Over Come Metrics

#### TheMuffinMan

you're having a problem with english to metric and vice versa? uh

metric to metric is just moving over decimal places and scientific notation, that's honestly stuff you should have established in middle school, but if you need help then yeah just give us example problems and we'll help

English to Metric and vice-versa you need formulas and conversion factors. if you're taking a test they should honestly be provided on a separate sheet of conversion factors and formulas, but after a certain point you'll have them memorized, such as there being 453 grams in a pound, and 2.54 cm in an inch

#### LongLiveLife

##### Bronze Member
It's not really chemistry to do basic conversions...

If you want to convert X inches to Y cm, for example, you'd just need to know how many centimeters there are in one inch (Z) then multiply the number of inches you have by that number. I.e. Y = X * Z

Once you have that basic concept sorted, you can adjust the formula to have X, Y, Z represent any unit measurement, and rearrange to find the unit that you're looking for.

#### TheMuffinMan

yeah, you're not really into any chemistry at all right now, but I mean I suppose it's good to have this thread open for when you do actually get into electron structure and polyatomic ions and acid/base stuff

#### TheMuffinMan

yeah, you're not really into any chemistry at all right now, but I mean I suppose it's good to have this thread open for when you do actually get into electron structure and polyatomic ions and acid/base stuff

#### Coffee Lover

##### Bronze Member
I can do the work. It's just that I don't understand the work. Here's an example I don't understand:

18 yrs = ______ seconds.
365 days = 1 yr
24 hours = 1 day
60 min = 1 hour
60 secs = 1 min

This is how he did it.

365 days/1 x 24hrs/1 day x 60min/1hr x 60seconds/1min = 570,000,000 seconds (rounded significantly)

So my question is . . . I think I'm beginning to get it. Like, the day on 1 day cancels the days on 365 and so on. They're being divided. But why is it done this way?

#### TheMuffinMan

Dimensional analysis is fractions, just think of it as fractions

Say you have 1/2. you wanna get rid of 1/2, what do you do? multiple it by a reciprocal

1 2
- - = cancelled
2 1

So, you don't WANT your answer to be in days, right? So you need to cancel away "days". therefore, put "days" in the opposite end of the next fraction, and then an equivalent of what a day equals. ie, 24 hours. now, you don't want HOURS either, right? So, hours goes in the next denominator, and then something that "hours" equals, such as 60 minutes. etc.

you slowly work your way from what kind of unit you don't want, to using a series of equivalent values until you reach the units you do want. This is extremely helpful for many things without having to ever actually conceptualize what units you're even using, all you need to do is plug in numbers. you can find out how fast something is going in MPH, and turn that into centimeters per nanosecond for all you care, you don't have to ever actually think about it, just plug in conversion factors and forget about it

#### Coffee Lover

##### Bronze Member
Okay. I get it now. I'll come back to this thread if I need some more help. Thank you! #### Coffee Lover

##### Bronze Member
I'm lost. I feel so fustrated that I feel like crying. It's called Dimensional Analysis and I made a 3 out of 10 on the first quiz. However, I'm not the only one having trouble in my class. I heard most of my classmates did worse, even one got a 0 out of 10.

You make 6 dollars an hour. Each shift is 75 minutes. Each laundry load requires 6 quarters. How many shifts must you work to wash 10 loads? I hate this stuff.

##### Iron Tomato
TheMuffinMan gave a pretty good explanation. The goal is to get from the undesired units given, to the units you want to work with using a series of ratios (fractions).

A general formula looks like this:

x [wanted unit] = y [undesired unit] * [wanted unit] /[undesired unit]

Where the ratio of [wanted unit] / [undesired unit] is always equal to 1, so the multiplication is allowed (ie 60 minutes / 1 hour, 200 cm / 2 m, etc).

Notice how the undesired unit is in the numerator first, then it's multiplied by a ratio with it in the denominator? This will "cancel out" the undesired unit.
Example: How many minutes in 2.5 hours?
x minutes = 2.5 hours * 60 minutes / 1 hour Cancel out the hours
x minutes = 2.5 * 60 minutes / 1 multiply through
x minutes = 150 minutes

Then, you can go even further, "chaining" these equations.
This generally looks like this:
x [wanted unit] = y [first undesired unit] * [second undesired unit] / [first ] * [third] / [second] * ... * [wanted] / [last]

Notice again, how the first time each unit is seen, it's "on top" and the next time, it's "on bottom" of the ratios. Again, this is to "cancel out" that unit each time you multiply.
From the example above:
How many seconds in 2.5 hours?
x seconds = 2.5 hours * 60 minutes / 1 hour * 60 seconds / 1 minute
x seconds = 2.5 * 60 / 1 * 60 seconds / 1
x seconds = 9000 seconds.

Okay, that's it for the lesson, on to the question
So let's look at the given information:
6 dollars per hour
1 shift = 75 minutes

We want to know:

If 1 load = 6 quarters, then 10 loads = 60 quarters. We now have:
x shifts = 60 quarters

That's still not what we want, so let's turn the quarters into dollars:
(60 quarters) (1 dollar / 4 quarters ) = (60/4) dollars = 15 dollars.
Note here: the "quarters" cancelled out, and left us with dollars.

So thus, x shifts = 15 dollars. Let's see how many hours this is.
(15 dollars) (1 hour / 6 dollars) = (15/6) hours = 2.5 hours
Giving us:
x shifts = 2.5 hours

Getting closer to the final answer. Now let's convert those hours into shifts. BUT WAIT! We only know that 1 shift = 75 minutes. There's nothing about hours! No problem! Let's turn those hours into minutes, then turn it into shifts!
(2.5 hours) ( 60 minutes / 1 hour) = 150 minutes
(150 minutes) (1 shift / 75 minutes) = 2 shifts!

And there's the answer! It would take 2 shifts to do 10 loads.

In one step:
x shifts = (10 loads) * (6 quarters / 1 load) * (1 dollar / 4 quarters) * (1 hour / 6 dollars) * (60 minutes / 1 hour) * (1 shift / 75 minutes)
x shifts = (10) * (6 / 1) * (1 / 4) * (1 / 6) * (60 / 1) * (1 shift / 75)
x shifts = 2 shifts

#### TheMuffinMan

BanishingBlade gave a very thorough answer. One of the easiest ways I find to handle Dimensional Analysis at this level (see: easy peasy lemon squeezy) is to just not think about anything. Seriously. Do not think about shit of what anything means, just plug in numbers. Dimensional analysis problems will give you every single piece of conversion factor you will need at this level, so frankly you just need to go through a checklist of the information they've provided

This is how i would go about thinking through this problem:

You make 6 dollars an hour. Each shift is 75 minutes. Each laundry load requires 6 quarters. How many shifts must you work to wash 10 loads?

"Okay, I wanna know how many shifts equal 10 loads of laundry. The unknown factor is shifts, the known factor is how many loads I'm doing. I'm going from # loads -> # shifts"

*looks up at the problem sentences*

How many loads do I have to do?
How many quarters does a load cost?
6 quarters
How many quarters are in a dollar?
4 quarters
How many dollars do I get paid?
6 dollars
Per what?
hour (60 minutes)
But how many minutes are in a shift?
75 minutes

Now, write this out in a sequence of cancelling fractions

Q = quarters
\$ = dollars
M = minutes
S = shift

Code:
``````10L   6Q    \$1   60M   1S
-  *  -  * -  *  -  * -
1    1L    4Q   \$6    75M``````

Now then, all you do from this point is multiply directly across and see what it gives you.

10 * 6 * 1 * 60 * 1
-----divided by------
1 * 1 * 4 * 6 * 75

In this instance you get:

3600
-
1800

Now then, all you do is simplify your answer. 3600 divided by 1800? 2. What is the only conversion factor we did not cancel in that process? Shifts.

2 Shifts.

#### Coffee Lover

##### Bronze Member
I'm dropping Chemistry. It's not the material, it's the people in the class I can't deal with.

Thank you BB and TMM. I really appreciate it.

Status
Not open for further replies.