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Conversions

Yttrium2 - 21-3-2018 at 07:47

So I was doing conversions the other day and it seemed to all make sense, but today the question arose how many grams are in 1/8th of an ounce and I had difficulty. This should be simple

How many grams are in a lb and ounce.

1/16 x a lb should equal grams in an ounce, then from there what is the technique to taking an eighth of that number. There is a decimal number with several digits I get and I'm not sure about the rounding.

Knowing there are 2.205 lbs in a kilogram how do I go from there to grams in 1/8th an ounce, and knowing a lb is 16/1 ounces.

Thank you

JJay - 21-3-2018 at 07:54

You absolutely have to know how to do this sort of thing to do any kind of hard science, and you can't really get by without it in biology, psychology, political science, earth science, etc. either: https://www.youtube.com/watch?v=UBzVf8XeMYA

ELRIC - 21-3-2018 at 08:06

I agree with jjay. Any decent chemistry text should go over this. I found that just practicing this over and over again will make it become easy with time. You can get online and find practice problems with answers provided so you can gauge you’re progress. Some conversion factors will need to be memorized. Look up the “factor label method”. Some people may call it dimensional analysis.

Tsjerk - 21-3-2018 at 08:18

If an ounce is 30 grams you multiply 1/8 with 30. I'm so happy we don't use these units!

1000/2.205x1/16 is 28,3

[Edited on 21-3-2018 by Tsjerk]

aga - 21-3-2018 at 08:55

Google (as in google.com itself, not the search results) has quite a few converters built-in.

Typing in the search box: "1/8oz in g" comes up with 3.54g

It's really useful for converting obscure units, like a 'pennyweight', 'cup' or 'dram'.

Yttrium2 - 21-3-2018 at 09:23

Quote: Originally posted by JJay

You absolutely have to know how to do this sort of thing to do any kind of hard science, and you can't really get by without it in biology, psychology, political science, earth science, etc. either: https://www.youtube.com/watch?v=UBzVf8XeMYA

I know how to set them up, I just forgot the conversion factor.

I forgot the conversion factor they wanted us to use.

I cant remember if grams in an ounce were given or if they wanted us to go from pounds to ounces to grams by a 1/8th conversion factor, if it is such.

knowing 454 grams are in a lb (which we don't know, do we?)

can someone walk me through the steps

[Edited on 3/21/2018 by Yttrium2]

JJay - 21-3-2018 at 09:54

Write out the quantity and then multiply it by quantities that are equal to one to get the units you want.

Code:


1 oz           28.35 grams        
-         x   ----------------- = 
8               1 oz

Cancel factors that are the same in the numerator and the denominator.

Code:


XXXX           28.35 grams        28.35 grams
-         x   ----------------- = ------------------- =
8               XXXX                        8

Do the math.

Code:


    28.35 grams
------------------- = 3.544 grams
         8

I think this forum supports LaTeX, which I happen to know... I should probably look into that....

sodium_stearate - 21-3-2018 at 10:09

454 divided by 16, then divided by 8 again.

Or 454 x .0625 x .125

It helps to know your "eighths" and your "sixteenths"
from memory, to do it the 2nd way.

Both methods yield 3.546875, which is the quick approximation.

[Edited on 21-3-2018 by sodium_stearate]

JJay - 21-3-2018 at 10:12

Write out the quantity and then multiply it by quantities that are equal to one to get the units you want.

$$\frac{1 \textrm{oz.}}{8} \cdot \frac{28.35 \textrm{g}}{1 \textrm{oz.}} = $$

Cancel factors that are the same in the numerator and the denominator.

$$\frac{\color{red}{\textrm{cancel}} \rightarrow 1 \textrm{oz.}}{8} \cdot \frac{28.35 \textrm{g}}{\color{red}{\textrm{cancel}} \rightarrow 1 \textrm{oz.}} = $$

Do the math.

$$\frac{28.35 \textrm{g}}{8} = 3.544 \textrm{g}$$

Yttrium2 - 21-3-2018 at 11:15

Where are you getting 28.35 for an ounce?

I've seen different numbers.

Look, at my question, I know how to do dimensional analysis but I forgot the conversion factor they were using. I don't think anyone can answer this because I forgot the question but remembered the answer was to simply multiple by 1/8 and or 1/16th.

What you can answer is how you got to 28.35 grams for an ounce.

Ill really have to see the problem again to be more clear. Pretty sure we just went from grams to ounces and the number only went out 2 digits past the decimal place.

I know how to do dimensional analysis!!!!!!!!!!!

I just forgot what the question was really, but remember it didn't involve rounding off digits, it was a ounce to gram question, or pound to ounce to grams question -- but it didn't involve the rounding.

[Edited on 3/21/2018 by Yttrium2]

Yttrium2 - 21-3-2018 at 11:28

Ultimately I had difficulty tackling the problem because I didn't know how many grams are in an ounce. Can someone give me a specific number?

It made me remember back to learning the common conversions to decimals ike 1/10th, 2/10ths, 2/5ths, 3/5ths, 4/10ths and it made me remember that I recently solved a problem, pretty sure it was asking what 1/8th of an ounce is, but it did not require rounding off digits

Yttrium2 - 21-3-2018 at 11:32

Ahh, I confused myself here, didn't remember the question tmand information that's troubling me. No one can help me now! Yikes.

But I do get the dimensional analysis, atleast, I should.

LearnedAmateur - 21-3-2018 at 11:34

1/2.205 = 0.454 kg/lb = 454 g/lb.
454/16 = 28.375 g/oz.
28.375/8 = 3.547 grams per eighth ounce.

To change between units when given a value for one, just use the reciprocal - equation 1. Glad metric is the system I’ve always used.

Sorry if this still hasn’t answered your question, if so then I’m lost.

Oh yeah, and a thing to remember is that you always round your numbers to the decimal point of the value you are given, such as what I’ve done (3 d.p).

[Edited on 21-3-2018 by LearnedAmateur]

aga - 21-3-2018 at 11:46

Either use fractions to get Perfect numbers, such as Pi
$$\frac {22}{7}$$
or better
$$\frac {355}{113}$$
or rounding is always involved
$$3.1415927$$

[Edited on 21-3-2018 by aga]

JJay - 21-3-2018 at 11:51

Quote: Originally posted by Yttrium2

Ultimately I had difficulty tackling the problem because I didn't know how many grams are in an ounce. Can someone give me a specific number?

It made me remember back to learning the common conversions to decimals ike 1/10th, 2/10ths, 2/5ths, 3/5ths, 4/10ths and it made me remember that I recently solved a problem, pretty sure it was asking what 1/8th of an ounce is, but it did not require rounding off digits

Yeah, just type "how many grams are in an ounce" into your favorite search engine. If you're asking how to calculate it, it's a factor label problem. I'm not trying to do your homework for you.

Yttrium2 - 21-3-2018 at 12:55

Out of curiosity, how much gets chocked off when converting from pounds to ounces to grams if you rounded to the nearest hundredth in both conversions?

I don't mean to derail the thread.

Thank you

[Edited on 3/21/2018 by Yttrium2]

aga - 21-3-2018 at 12:58

Not enough to bother with.

Most of the time we cannot measure things precisely, so a few decimal places makes absolutely no difference at all.

Yttrium2 - 21-3-2018 at 13:01

Does it depend upon sign figs..?

[Edited on 3/21/2018 by Yttrium2]

ELRIC - 21-3-2018 at 13:06

I think you’re problem about the whole ounce thing is: who is defining an ounce? Is it a Troy, which is the same as an apothecarie, or is it an Avoirdupois? I only mention this because my search engine gives a hit of 28.35, whereas my Merriam-Webster’s Collegiate Dictionary gives three values (the other two are both 31.103).

ELRIC - 21-3-2018 at 13:12

Quote: Originally posted by Yttrium2

Does it depend upon sign figs..?

[Edited on 3/21/2018 by Yttrium2]

Generally, your answer should have no more decimal places than any of the numbers you were given. In other words, if I ask you how man grams are in 3.56 ounces, you shouldn’t give me an answer with 3-4 decimal places. This is how it was taught to me by my chem text. Your answer shouldn’t exceed three sig-figs regardless of what a calculator says it is. Also, the last sig fig is to be rounded according to the following decimal place. 3.56 x 28.35 = 100.926. Answer would be 101 grams. Hope this helps. Others may have been taught differently

[Edited on 21-3-2018 by ELRIC]

[Edited on 21-3-2018 by ELRIC]

[Edited on 21-3-2018 by ELRIC]

[Edited on 21-3-2018 by ELRIC]

aga - 21-3-2018 at 13:44

Good point ELRIC.

When it comes to answering question for an exam, the required precision of the answer is always in the question.

If the values in the question are like 1.14 then an answer like 0.2355677890234 is automatically Wrong.

Unless otherwise stated, answer to the Least precision given.

ELRIC - 21-3-2018 at 14:01

Quote: Originally posted by aga

Good point ELRIC.

When it comes to answering question for an exam, the required precision of the answer is always in the question.

If the values in the question are like 1.14 then an answer like 0.2355677890234 is automatically Wrong.

Unless otherwise stated, answer to the Least precision given.

That’s the phrase I was thinking of, but the wording slipped my mind. “ least precision given”. You’re answer can’t be anymore precise than the least precise value given.

aga - 21-3-2018 at 14:16

Serious Grammar/Spelling Error Detected : Grammar Nazi Engine Activated.
Offending Phrase: You’re answer
Correct version: Your answer
Autocorrect Disabled.
Select Y/N, then press the Any Key.

JJay - 21-3-2018 at 14:20

Significant figures do matter, especially if this is a homework problem. The best approach IMHO is to retain as many decimal places as possible until the final answer and then use significant digit rules to do the rounding.

ELRIC - 21-3-2018 at 14:22

Quote: Originally posted by aga

Serious Grammar/Spelling Error Detected : Grammar Nazi Engine Activated.
Offending Phrase: You’re answer
Correct version: Your answer
Autocorrect Disabled.
Select Y/N, then press the Any Key.

Was that directed to me? I know my grammar/spelling sucks lol. I do appreciate you putting what I was trying to say into simpler terms btw. Until the OP gets back online, it’s hard to tell if we’ve been any help. I would like to see the original question, and his answer myself

[Edited on 21-3-2018 by ELRIC]

ELRIC - 21-3-2018 at 14:29

Quote: Originally posted by JJay

Significant figures do matter, especially if this is a homework problem. The best approach IMHO is to retain as many decimal places as possible until the final answer and then use significant digit rules to do the rounding.

Yes, you are correct. I forgot to mention that. That is also in my chem text, and hopefully everyone else’s. If you start rounding before you get you’re final value, you’re gonna be in a mess.

ELRIC - 21-3-2018 at 14:45

Quote: Originally posted by ELRIC

Quote: Originally posted by aga

Serious Grammar/Spelling Error Detected : Grammar Nazi Engine Activated.
Offending Phrase: You’re answer
Correct version: Your answer
Autocorrect Disabled.
Select Y/N, then press the Any Key.

rsneha - 3-11-2020 at 02:00

Quote: Originally posted by aga

Google (as in google.com itself, not the search results) has quite a few converters built-in.

Typing in the search box: "1/8oz in g" comes up with 3.54g

It's really useful for converting obscure units, like a 'pennyweight', 'cup' or 'dram'.

Also try this unit converter to convert it.