Help!! Chemistry question!

[Cofo]

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Hello, this question is going to make probably all of you laugh, but for some reason it is not clicking for me. How do I convert MILLImeters to Meters to KILOmeters? I am horrible at conversions. I really need help....fast too! I am taking chemistry 1 this summer, and I understand everything so far except conversions. Any advice??? If my given unit is 103 mm, and I need to convert 103 mm to kilometers...would my answer be 103 mm x 10^4? Why is the exponent 4? HEEEEEEEEEELP!!!😕

 

[vj212306]

1km=1000m =10^3
1m=1000 mm=10^3
so 1km= 10^6 mm and so 1mm=10^-6km

103mm=103* 10^-6 =1.03*10^-4 km

hope it helps

 

[wannabDMD]

what i do is:

KHDUDCM = Kilo Hecta Deca Unit Deci Centi Milli

so you basically count how many letters it takes to get from M (mm) to K, and it takes 6. So you move the decimal point 6 places to the left...

103. mm ---> .000103 or 1.03 x 10^-4 km

also realize that 103 x 10^-4 is NOT the same as 1.03 x 10^-4

 

[Robert Paulsen]

One thing they should hit hard in chem 1 is dimensional analysis.

You have mm and you want km. Work backwards, starting from km:
(1 km)/(1000 m)=
here we have the desired km, but we also have 1/m that we need to get rid of.

(1 m)/(1000 mm) x (1 km)/(1000 m) =
now we have gotten rid of the 1/m (by multiplying by m) but we need to get rid of 1/mm

finally, to get your answer:
1.03 mm x (1 m)/(1000 mm) x (1 km)/(1000 m) =
the 1/mm is canceled by multiplying by mm (your given value).

Treat units just like numbers. 5/5 = 1 so you just drop it. mm/mm = 1 so you just drop it. In the equation above, mm/mm and m/m are dropped. leaving only km in the answer. Try rewiting the above with the fractions written out so the numerator is above the denominator. I tried but couldn't get the right formatting in this forum...

Some scientific calculators can handle units and this is exactly how it is done.

You should have a LOT of homework problems that use this sort of analysis to convert units from one type to another. I remember doing some that had strings of 10-12 ratios before the final answer was complete.

This is one of the things that always bugged me about physics. Physicists are so eager to reward the egos of their more accomplished practitioners that you lose the meaning that can be derived from dimensional analysis. What are units of energy? The Joule! What is a Joule? It is Watt-second. What is a Watt? You spend so much time and energy trying to figure out the meaning of the units when if they had stuck to mks or cgs units all would be clear. Ohm got the Ohm named after him for figuring out that electrical resistance was E/I. What about Siemen? He got the unit of electrical conductivity named after him for figuring out that conductivity = I/E. And you guys thought surgeons had big egos!

RP

 

[Cofo]

what i do is:

KHDUDCM = Kilo Hecta Deca Unit Deci Centi Milli

so you basically count how many letters it takes to get from M (mm) to K, and it takes 6. So you move the decimal point 6 places to the left...

103. mm ---> .000103 or 1.03 x 10^-4 km

also realize that 103 x 10^-4 is NOT the same as 1.03 x 10^-4

In words, are we saying that there are 0.000103 mm in 103 km? Now I am confused. I thought my question was "How many km are in 103 mm?" So should I do this?: (103mm)(1km/10^6)= 0.000103 km ...or 1.03 km X 10^-4 Did I do this equation correctly? If I did or did not, lemme know! I think I understand it now! (I am taking chemistry 1 and chemistry 2 this SUMMER, currently in chem1 as we speak. My professor spent ONLY 5 MINUTES on dimensional analysis. I did not know it was this important. He is going reeeeeeeally fast.)

 

[tooth decay]

In words, are we saying that there are 0.000103 mm in 103 km? Now I am confused. I thought my question was "How many km are in 103 mm?" So should I do this?: (103mm)(1km/10^6)= 0.000103 km ...or 1.03 km X 10^-4 Did I do this equation correctly? If I did or did not, lemme know! I think I understand it now! (I am taking chemistry 1 and chemistry 2 this SUMMER, currently in chem1 as we speak. My professor spent ONLY 5 MINUTES on dimensional analysis. I did not know it was this important. He is going reeeeeeeally fast.)

Millimeters is expressed as 10 to the minus 3 power meters(Don't know how to type that out). And to convert meters to kilometers, you must divide (not multiply) your meters by 10 to the third power. Thus your answer will be 103 x 10 to the minus 6 power kilometers.