Unit-conversion method

That s why you need to know about the unit conversion method, which is sometimes called the factor label method. It will help you set up chemistry problems and calculate them correctly. Two basic rules are associated with the unit conversion method  

Rule 1 Always write the unit and the number associated with the unit. Rarely in chemistry will you have a number without a unit. Pi is the major exception that comes to mind. 

Rule 2 Carry out mathematical operations with the units, canceling them until you end up with the unit you want in the final answer. In every step, you must have a correct mathematical statement. 

How about an example so you can see those rules in action Suppose that you have an object traveling at 75 miles per hour, and you want to calculate its speed in kilometers per second. The first thing you do is write down what you start with  

Note that per Rule 1, the equation shows the unit and the number associated with it. 

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Basic study skills needed to study chemistry Macroscopic and microscopic properties of matter The SI (Metric) system Basic problem solving techniques Unit Conversion Method Significant figures... 

Chemistry is full of calculations. Our basic goal is to help you develop the knowledge and strategies you need to solve these problems. In this chapter, you will review the Metric system and basic problem solving techniques, such as the Unit Conversion Method. Your textbook or instructor may call this problem solving method by a different name, such as the Factor-Label Method and Dimensional Analysis. Check with your instructor or textbook as to for which SI (Metric) prefixes and SI-English relationships will you be responsible. Finally, be familiar with the operation of your calculator. (A scientific calculator will be the best for chemistry purposes.) Be sure that you can correctly enter a number in scientific notation. It would also help if you set your calculator to display in scientific notation. Refer to your calculator s manual for information about your specific brand and model. Chemistry is not a spectator sport, so you will need to Practice, Practice, Practice. 

Use the Unit Conversion Method (explained in Section 1-4) in solving for the desired quantity. 

In this section, we will introduce one of the two common methods for solving problems. (You will see the other method in Chapter 5.) This is the Unit Conversion Method. It will be very important for you to take time to make sure you fully understand this method. You may need to review this section from time to time. The Unit Conversion Method, sometimes called the Factor-Label Method or Dimensional Analysis, is a method for simplifying chemistry problems. This method uses units to help you solve the problem. While slow initially, with practice it will become much faster and second nature to you. If you use this method correctly, it is nearly impossible to get the wrong answer. For practice, you should apply this method as often as possible, even though there may be alternatives. 

Let s use the question of How many feet are in 3.5 mi to illustrate how to apply the Unit Conversion Method. First, we will organize the information by writing the given value (3.5 mi) and the unit for the answer, separated by an equals sign. 

According to the Unit Conversion Method, we may begin with any mass unit over any volume unit and have a density. Our isolated information supplies a mass and a volume. We can now enter this information into the definition ... 

Careful application of the Unit Conversion Method will make it much easier and quicker to master your chemistry problems. 

The measurement system that is most widely used in chemistry is the SI system. It incorporates a base unit for the various quantities and then uses prefixes to moderate the value of the base unit. The Unit Conversion Method is a way to generate easily the setup to a problem. Be sure to round off the final answer to the correct number of significant figures and include the units with the final answer. 

When solving a problem by the Unit Conversion Method, the question mark in the following should be replaced by. ... 

True/False. According to the Unit Conversion Method, the answer to the following calculation is 1728 in3. 

This is a critical chapter in your study of chemistry. Our goal is to help you master the mole concept. You will learn about balancing equations and the mole/mass relationships (stoichiometry) inherent in these balanced equations. You will learn, given amounts of reactants, how to determine which one limits the amount of product formed. You will also learn how to determine the empirical and molecular formulas of compounds. All of these will depend on the mole concept. Make sure that you can use your calculator correctly. If you are unsure about setting up problems, refer back to Chapter 1 of this book and go through Section 1-4, on using the Unit Conversion Method. Review how to find atomic masses on the periodic table. Practice, Practice, Practice. 

In this chapter, we will help you learn about the energy changes, especially heat, which occurs during both physical and chemical changes. You might need to review the Unit Conversion Method in Chapter 1 and the sections in Chapter 3 on balancing chemical reactions and the mole concept if you are not comfortable with them already. And remember to Practice, Practice, Practice. 

Dimensional analysis, sometimes called the factor label (unit conversion) method, is a method for setting up mathematical problems. Mathematical operations are conducted with the units associated with the numbers, and these units are cancelled until only the unit of the desired answer is left. This results in a setup for the problem. Then the mathematical operations can efficiently be conducted and the final answer calculated and rounded off to the correct number of significant figures. For example, to determine the number of centimeters in 2.3 miles ... 

The advantage of a unified system of units is that if all the quantities in a calculation are expressed in SI units, the final result must come out in SI units. Nevertheless, it is important to become familiar with the ways in which units are interconverted because units other than SI base units often appear in calculations. The unit conversion method provides a systematic approach to this problem. 

Using the "unit conversion method," derive an equation to calculate the heat produced from the HCl-NaOH reaction, and write your equation in Sample calculations A. 

I ve organized the topics in a logical progression — basically the same way I organize my courses for non-science and elementary education majors. I ve included a couple chapters on environmental chemistry — air and water pollution — because those topics appear so often in the news. And I ve included some material in appendices that I think might help you — especially Appendix C on the unit conversion method of working problems. 

I also include some appendixes that can give you help when dealing with mathematical problems. I cover scientific units, how to handle really big or small numbers, a handy unit conversion method, and how to report answers using what are called significant figures. 

By using the preceding conversions and the unit conversion method I describe in Appendbc C, you ll be able to handle most SI/English conversions you need to do. 

With a little practice, you ll reedly like and appreciate the unit conversion method. It got me through my introductory physics course ... 

By the unit-conversion method, we note that the concentration given in the problem statement is 1.4 mol per 250. mL (mol/mL). Since molarity = mol/L, the needed conversion is... 

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