# Why use Liter?

1. Jan 23, 2016

### brycenrg

I'm taking my 3rd chem course and I was just wondering why do we use the Liter?
Shouldn't we just use cm^3 on the instruments and use dm^3? I never got it.

2. Jan 23, 2016

### Staff: Mentor

Since a liter is $1000 cm^3$ or $1 dm^3$ it doesn't make a difference. Liter is allowed within the SI system so it's just a matter of taste.

3. Jan 23, 2016

### Dr. Courtney

It's not too hard to go back and forth between metric units. 1 L = 1000 cm^3.

4. Jan 23, 2016

### Ygggdrasil

It's also easier to convert between different orders of magnitude (the relationship between L, mL, µL is more apparent than between cm^3, dm^3 etc).

5. Jan 23, 2016

### brycenrg

For a sec I thought order of magnitude was a good enough reason but then I realized when you use maths you don't ever use liter, you convert it to cm^3. So it doesn't make it easier :( lol I guess it's just our primordial slime

6. Jan 23, 2016

### Ygggdrasil

Chemists and biochemists typically do a lot of math involving L. For example, today in lab, I had to figure out how many µL of specific solution (whose concentration was in mg/mL) to get a final concentration of 10 µM in a 20µL reaction. Not impossible to do in terms of cm^3 etc, but using the L system helps a little.

7. Jan 24, 2016

### Staff: Mentor

In some areas mL (or c3) is preferred over liter, in others it is not.

In general, you choose a unit that is most convenient to use.

I wouldn't say my car burns 7500 mL gasoline per 100 km, I would say it needs 7.5 L per 100 km.

The volume of gas collected at STP when you decompose 1 mole of CaCO3 is commonly listed as 22.4 L, not 22400 mL.

And the hydrogen tanks of the LZ 129 Hindenburg had a volume of about 200 000 m3, I wouldn't report it neither using L nor mL.

8. Jan 24, 2016

### epenguin

If you look in old textbooks till the 1950's or so I think you will find cc's. I don't know the exact history and the whys of it, but I did see the changeover mnyah mnyah. In the years of school up to English 'O level' (around age 16) I remember nothing but cc's. But then the next two years ('A levels) from the start it had switched over entirely to litres and ml.

I think, at least this is my memory, if you look into scientific book reviews for 10 or 20 years around that time, you'll find them a very often saying 'the MKS system is used' or 'unfortunately the CGS system is used' (or maybe if they were reactionary the other way round). I guess this was important for school purchasing decisions. I seem to remember we had books with both systems; as the conversion is so easy it never bothered me, in fact I never saw what the fuss was about

9. Jan 24, 2016

### ogg

Most of the world uses the liter as THE measuring unit of ( human use size) volume. When is the last time you measured a liquid by measuring its (container's) length, width and height? Who does that? When I was in school, warning! ancient history alert!, the liter was NOT exactly 1000 cm^3, believe it or not. Anyway. You can easily measure volumes (liquids and gasses) in terms of intuitive units of volume, whether gallons or liters, cups or barrels. It requires a bit of abstract thinking to understand that a cubic cm is a unit of volume. Also, (and while this may seem like a restatement of the previous, it really is different) using what to a lot of people is the same unit for length, area, and volume (ie the meter or the centimeter) would cause confusion. It takes some training to understand that multiplying cm x cm does NOT result in cm. If you really think about it, can you explain why cm x cm = cm² ? (Hint: the directions of the basis vectors are orthogonal...but why do you get ANYTHING meaningful when you multiply two orthogonal vectors? And why should we assume that as soon as the "same" units are multiplied, the bases (abstract coordinate system) are orthogonal? See, its a rat hole, better left to those geeks amongst us who can do algebra, etc.

10. Jan 25, 2016

### rootone

11. Jan 25, 2016

### Staff: Mentor

I actually did not believe you, because the original definition of the liter after the French revolution was dm3. But you are right! from 1901 to 1964, the liter was defined based on the properties of water, so it was about 1.000028 dm3. Learned something today...

12. Jan 25, 2016

### Staff: Mentor

Actually I was taught of liter not being exactly 1000 cm3 somewhere in mid seventies. Probably because it took time for the altered SI definition to seep down.

13. Jan 25, 2016

### Rx7man

While it's not exact, you're still accurate to 5 significant digits...
The meter is also defined as a portion (is it 1/1,000,000) of the distance from the equator to the north pole?.. A second is also defined as a period of the earth's rotation (1/(24*60*60)), but the earth's rotation is measurably slowing down, so either you keep the time period of the old definition and most everyone is happy, or you change it, and every physics constant involving time will have to be recalculated. Just as a year isn't exactly 365 days, a day is not exactly 86400 seconds, and THERE ARE LEAP SECONDS every once in a while.

14. Jan 25, 2016

### Staff: Mentor

Why don't you google that instead of guessing? No, it was never a part of the distance from the equator to the north pole (even if the equator was definitely involved).

15. Jan 25, 2016

### Rx7man

16. Jan 25, 2016

### Staff: Mentor

Sigh, you learn all your life and you die stupid I swear I was taught it was 1/40000000 of the equator length.

Honestly, I feel like in those films where someone learns he doesn't exist and nobody recognizes him. It was always the equator based definition! Have you edited everything in the world just to make me feel like an idiot?

17. Jan 25, 2016

### MrAnchovy

Most of the world calls it a litre.

I assume the French, who invented the metre chose their prime meridian as the defining circumference because it passes through Paris whereas the equator does not.

18. Jan 26, 2016

### Rx7man

If you're talking about my post, I only edited it for styling and spelling... I didn't edit Wikipedia though.

As for the spelling of meter/metre.. Being in Canada I should abide by the international spelling, but it doesn't make any sense phonetically... If I were speaking french I'd be fine with Metre because then it's phonetically correct.

19. Jan 28, 2016

### epenguin

Ah, but if the earth were spherical it would be exactly the same thing. Perhaps in seventeen ninety-noo they thought it was.

20. Jan 30, 2016

### sophiecentaur

and they also call a metre a metre. A meter is a measuring instrument and a liter is not part of SI, afaiaa. Liter is, presumably, and Americanism, which is a bit of a librety as they don't even use the damn thing.