The Ultimate Guide To Si Units And Unit Conversions
- The Albert Team
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Units are extremely important in the study of science. Without them, a number is just a number without any meaning. The Système international dunités is a standard that simplifies international scientific communication. This system comprises seven base quantities and 16 prefixes that designate amount.
These reference tables show the different bases and prefixes used to designate metric units with the SI system.
Quantity |
1 gigameter = 109 meters | ||
Mega | 1 megameter = 106 meters | |
Kilo | 1 kilometer = 103 meters | |
1 decimeter = 10-1 meters | ||
Centi | 1 centimeter = 10-2 meters | |
Milli | 1 millimeter = 10-3 meters | |
Micro | 1 micrometer = 10-6 meters | |
Nano | 1 nanometer = 10-9 meters | |
Pico | 1 picometer = 10-12 meters | |
Femto | 10-15 | 1 femtometer = 10-15 meters |
These base units can be combined with any of the prefixes to create units that are most appropriate for what is being measured. For example, you wouldnt measure the distance from LA to New York in meters, the base unit. Instead, you would use kilometers, or even megameters. The different base units can also be combined to form what are called derived units. For example, speed can be measured in meters per second, or in kilometers per nanosecond. The combinations are endless.
955kg\times \frac =0.995Mg
How To Set Up Unit Conversion Problems For Chemistry
In chemistry, the information being processed is seldom expressed in the units needed in the final result. In order to show the outcome in the proper units of measure, set up a unit conversion problem. This type of problem allows you to translate one size measure to another. For example, you may need to change inches to feet or convert inches into centimeters.
Find the conversion factor that will allow you to get from the units that you have to the units that you need. For example, to get from inches to centimeters , you will need to know that the conversion factor is 2.54 cm/1 in . If you have 5 inches to convert, the problem is set up like this: 5 in/1 x 2.54 cm/1 in. When you multiply, you will cancel the 1 inch into the 5 inches so that the “inches” go away. This leaves 5 x 2.54 cm = 12.7 cm.
Use the same type of unit conversion technique when converting one size measurement into a different type of unit within the same system. To convert milliliters into liters , use the conversion factor 1 L/1,000 mL. 5,000 mL would convert to liters this way: 5,000 mL x 1 L / 1,000 mL. The milliliters and the thousands cancel each other out, leaving 5 x 1 L= 5 L.
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- Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
- B.A., Physics and Mathematics, Hastings College
Fahrenheit and Celsius are the scales most often used for reporting room, weather, and water temperatures. The Fahrenheit scale is used in the United States, while the Celsius scale is used worldwide.
Indeed, most countries around the world measure their weather and temperatures using the relatively simple Celsius scale. But the United States is one of just a few remaining countries that use Fahrenheit, so it’s important for Americans to know;how to convert one to the other, especially when traveling or doing scientific research.
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How Do You Convert From Grams To Atoms
You can take this kind of dimensional analysis one step further by asking how many atoms of a particular element in a compound there are in some mass of that compound. For example, how many atoms of nitrogen are there in imidazole ?
You’ll need another conversion factor! The conversion factor here is how many nitrogen atoms are there per molecule of imidazole? The molecular formula has the answer! There are two nitrogen atoms in one molecule of imidazole.
Say you have 21 grams of imidazole. How many atoms of nitrogen are there in that 21 grams of imidazole? You will need the following conversion factors: molar mass .
Here’s how to set it up:
This means that in 21 grams of imidazole there are 3.72×1023 atoms of nitrogen.
Always remember to think about conversion factors and the units you want to end up with!
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How Do You Convert From Grams To Molecules
Given the different conversion factors mentioned above, there is enough information to convert from grams to molecules. You just have to be careful to set it up so that units cancel correctly and that you are left with molecules of the substance at the end.
Say your chemistry lab instructor asks you: How many molecules of methane are there in 105 grams of methane?
Where would you begin?
Knowing that the conversion factor to get to molecules involves the number of mols, the first conversion you need to do from grams is to mol. For this, you need to know the molar mass of methane, which is 16.04 g/mol.
Now, you know that in 105 g of methane there are 6.55 mol of methane. Next, you can make use of Avogadro’s number to find the number of molecules of methane in 6.55 mol of methane.
This means that in 105 grams of methane, there are 3.94×1024 molecules of methane. It’s hard to even comprehend a number that big!
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How Do You Use Conversion Factors
We all know from elementary school math that if you multiply any quantity by 1 you get the same quantity back. You can do this as many times as you want. For example, 2×1 = 2, and 18×1×1×1 = 18.
Multiplication by 1 is what you do whenever you do a problem involving conversion factors. The best way to explain how to solve using conversion factors is to work through some simple examples.Problem: How many days are there in 3 years? Solution: Here we basically want to convert years to days. Our conversion factor is:
;;; |
3 years× = 1, 095 days | ;;; |
Conversion Factor = | ;;; |
When doing any type of problem involving conversion factors, feel free to draw a line through any unit you see on the top and bottom of the fraction to make it visually obvious that the units cancel.
3 years× = 1, 095 days | ;;; |
Here’s another, slightly harder problem: How many seconds are there in 3 years?Solution: It is easiest to use multiple conversion factors for this problem. Starting with the units you are given, find the conversion factor needed to express to current unit in terms of the next smaller unit.
3 years× |
Performing Grams And Moles Conversions
Here are some tips for performing these conversions:
- The two problems most commonly encountered are setting up the problem incorrectly, so the units don’t cancel out and give the correct result. It helps to write out the conversion and make sure units cancel. You may want to draw a line through them in complex calculations to keep track of active units.
- Watch your significant figures. Chemistry professors are unforgiving when it comes to reporting an answer, even if you set up the problem correctly.
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Why Do We Use Kelvin Instead Of Celsius
Kelvin 0 degrees stands for zero kinetic energy or temperature. Changes in Celsius or Fahrenheit are not directly related to kinetic energy or volume because these scales do not begin at zero. Researchers use the Kelvin scale because it is an absolute scale of temperature which is directly related to kinetic energy and volume.
How To Convert Grams To Molecules
Whenever you convert from one unit to another, you need a conversion factor. For example, when you convert from minutes to seconds, you use the fact that in one minute there are 60 seconds. You need to know the same kind of conversion factors when trying to convert grams of a substance into molecules of that substance.
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Part 1 Of 2: Calculating The Molecular Mass
Significant Figures In Conversions
How do conversion factors affect the determination of significant figures? Numbers in conversion factors based on prefix changes, such as kilograms to grams, are not considered in the determination of significant figures in a calculation because the numbers in such conversion factors are exact. Exact numbers are defined or counted numbers, not measured numbers, and can be considered as having an infinite number of significant figures. Counted numbers are also exact. If there are 16 students in a classroom, the number 16 is exact. In contrast, conversion factors that come from measurements or are approximations have a limited number of significant figures and should be considered in determining the significant figures of the final answer.
Example \
Solution
We use the conversion factor that will cancel out the original unit, liters, and introduce the unit we are converting to, which is milliliters. The conversion factor that does this is the one on the right.
Exercise \
- Answer a
- Answer b
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Converting Between Units With Conversion Factors
A conversion factor is a factor used to convert one unit of measurement into another. A simple conversion factor can convert meters into centimeters, or a more complex one can convert miles per hour into meters per second. Since most calculations require measurements to be in certain units, you will find many uses for conversion factors. Always remember that a conversion factor has to represent a fact; this fact can either be simple or more complex. For instance, you already know that 12 eggs equal 1 dozen. A more complex fact is that the speed of light is \ miles/\. Either one of these can be used as a conversion factor depending on what type of calculation you are working with ).
Table \: Conversion Factors from SI units to English UnitsEnglish Units | |
---|---|
0.95 liters | volume |
*Pounds and ounces are technically units of force, not mass, but this fact is often ignored by the non-scientific community.
Of course, there are other ratios which are not listed in Table \. They may include:
- Ratios embedded in the text of the problem .
- Conversions in the metric system, as covered earlier in this chapter.
- Common knowledge ratios 1 minute).
If you learned the SI units and prefixes described, then you know that 1 cm is 1/100th of a meter.
Suppose we divide both sides of the equation by \ :
We know that 100 cm is 1 m, so we have the same quantity on the top and the bottom of our fraction, although it is expressed in different units.
Key Takeaways: Converting Moles To Grams
- Grams and moles are two units to express the amount of matter in a sample. There is no “conversion formula” between the two units. Instead, you must use atomic mass values and the chemical formula to do the conversion.
- To do this, look up atomic masses on the periodic table and use the formula mass to know how many atoms of each element are in a compound.
- Remember, subscripts in a formula indicate number of atoms. If there is no subscript, it means there is only one atom of that element in the formula.
- Multiply the number of atoms of an element by its atomic mass. Do this for all the atoms and add the values together to get the number of grams per mole. This is your conversion factor.
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Why Are The Units Of Measurement So Important
I am a bit of a stickler on units of measurement thanks to my high school chemistry teacher. She always told us that a number in chemistry meant nothing without its units, which is so true.
After all, if I say that I need 2 of sugar for a recipe, do you know if I mean 2 tablespoons, 2 grams, 2 cups or 2 kilos?
Thats why from the very first time I introduce measurements to my students I always emphasize the importance of not forgetting to write the units. I know from experience how key it is to lay a foundation for remembering these units of measurement early on.
Knowing the units of measurement that correspond with a number can give you so much more information than a digit sitting there by itself. Units can:
- Help to show another person the exact amount you have
- Assist in solving a mathematical problem, especially in chemistry, where you can follow the units to get to the answer
- Show which measurement system the person is using
In a nutshell, the unit of measurement in science serves as the supporting pillar upon which a number rests.
How Can Carbon Dioxide Be Converted Into Carbon And Oxygen
How can $\ce$ be converted into carbon and oxygen?
$$\ce$$
Alternatively:
$$\ce$$
I’m aware that plants are capable of transforming $\ce$ to glucose and oxygen via photosynthesis, but I’m interested in chemical or physical means rather than biological.
- 6$\begingroup$Plants do not exaclty do this, they do $2n CO_2 + 2n H_2O + photons \rightarrow 2_n + 2n O_2$ according to en.wikipedia.org/wiki/Photosynthesis In quite a complicated reaction schema.$\endgroup$;LaarAug 7 ’12 at 21:19
- $\begingroup$You can use scrubbing process. Using $\ce$$\endgroup$
In my opinion, the catalytic, solar-driven conversion of carbon dioxide to methanol, formic acid, etc. is much more interesting and promising, but since Enrico asked for the conversion of carbon dioxide to carbon itself:
The group around Yutaka Tamaura was/is active in this field. In one of their earlier publications, they heated magnetite at 290;°C for 4 hours in a stream of hydrogen to yield a material which turned out to be stable at room temperature under nitrogen. This material, $\ceO4}$ $$, i.e. the metastable cation-excess magnetite is able to incorporate oxygen in the form of $\ce$.
Under a $\ce$ atmosphere, the oxygen-deficient material converted to “ordinary” $\ce$ with carbon deposited on the surface.
$\ce$
Edit from another deleted answer:
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Applying The Concept Of Moles
Remember that the relationship of moles to a number of atoms holds constant, regardless of how complicated a molecule is. As a simple example, a molecule of water is made out of one hydrogen atom and two oxygen atoms. That means that in a mole of water, there would be one mole of oxygen and two moles of hydrogen.
Grams To Moles Conversion Problem
Determine the number of moles of CO2 in 454 grams of CO2.
Solution
First, look up the atomic masses for carbon and oxygen from the periodic table. The atomic mass of C is 12.01, and the atomic mass of O is 16.00. The formula mass of CO2 is:
12.01 + 2 = 44.01
Thus, one mole of CO2 weighs 44.01 grams. This relation provides a conversion factor to go from grams to moles. Using the factor 1 mol/44.01 g:
moles CO2 = 454 g x 1 mol/44.01 g = 10.3 moles
Answer
There are 10.3 moles of CO2 in 454 grams of CO2.
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Example 1: Using A Unit Conversion Factor
The mass of a competition frisbee is 125 g. Convert its mass to ounces using the unit conversion factor derived from the relationship 1 oz = 28.349 g .
If we have the conversion factor, we can determine the mass in kilograms using an equation similar the one used for converting length from inches to centimeters.
\largex\text=\text\times \text
We write the unit conversion factor in its two forms:
\large\frac}}\text\frac}}
The correct unit conversion factor is the ratio that cancels the units of grams and leaves ounces.
\large\beginx\text\hfill & \text\hfill & 125\cancel}\times \frac}\cancel}}\hfill \\ \hfill & =\hfill & \left\text\hfill \\ \hfill & =\hfill & \text\hfill \end
Check Your Learning
Convert a volume of 9.345 qt to liters.
Beyond simple unit conversions, the factor-label method can be used to solve more complex problems involving computations. Regardless of the details, the basic approach is the sameall the factors involved in the calculation must be appropriately oriented to insure that their labels will appropriately cancel and/or combine to yield the desired unit in the result. This is why it is referred to as the factor-label method. As your study of chemistry continues, you will encounter many opportunities to apply this approach.