Dimensional Analysis or Factor-Label Method PDF

CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method Many problems in chemistry require a change of units. To make a conversion, a conversion factor is required. A conversion factor is derive...

CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method Many problems in chemistry require a change of units. To make a conversion, a conversion factor is required. A conversion factor is derived from an existing relationship between two units of measurement. It is written or expressed in fraction form having a numerator and denominator. The conversion factor is used to produce the desired cancellation of unit. CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method What is Dimensional Analysis? (also called Factor-Label Method or the Unit Factor Method) is a problem-solving method that uses the fact that any number or expression can be multiplied by one without changing its value. It is a useful technique. The only danger is that you may end up thinking that chemistry is simply a math problem - which it definitely is not. CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method Unit Factors Unit factors may be made from any two terms that describe the same or equivalent "amounts" of what we are interested in. Now, we can solve some problems. Set up each problem by writing down what you need to find with a question mark. Then set it equal to the information that you are given. The problem is solved by multiplying the given data and its units by the appropriate unit factors so that only the desired units are present at the end. CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method (1) How many centimeters are in 6.00 inches? (2) Express 24.0 cm in inches. CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method (3) How many seconds are in 2.0 years? You can also string many unit factors together. CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method How many atoms of hydrogen can be found in 45 g of ammonia, NH3? We will need three-unit factors to do this calculation, derived from the following information: 1 mole of NH3 has a mass of 17 grams. 1 mole of NH3 contains 6.02 x 1023 molecules of NH3. 1 molecule of NH3 has 3 atoms of hydrogen in it. We also can use dimensional analysis for solving problems. CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method POST TEST POST TEST CHAPTER 1.4: MEASUREMENT Dimensional Analysis or Factor-Label Method