Lesson 53: Metric Unit Conversions, English Units to Metric Units, Weight Combination by Percent

The meter is the basic unit of length in the metric system The meter is the basic unit of length in the metric system. A meter is just s little longer than a yard. There are 100 centimeters in a meter, and there are 1000 meters in a kilometer, which is a little more than half a mile. From these relationships, we get two metric unit multipliers that can be used for distance and area conversion. 100 cm/1 m and 1000m/1 km

Example: Use unit multipliers to convert 7560 centimeters to kilometers.

Answer: 0.0756 km This problem illustrates the beauty of the metric system. All we have to do to change units in the metric system is to move the decimal point.

Example: Use unit multipliers to convert 15,740,000 square centimeters to square kilometers.

Answer: 0.001574 square kilometers

We need to know only one equivalence to change from English units of length to metric units of length. 2.54 cm = 1 in. This equivalence is exact.

Example: Use unit multipliers to convert 32 yards to meters.

Answer: (32)(3)(12)(2.54)(1) meters (1)(1)(1)(100)

Example: Use unit multipliers to convert 0 Example: Use unit multipliers to convert 0.042 square kilometers to square miles.

Answer: (0. 042)(1000)(1000)(100)(100) mi (2. 54)(2

Thus far, we have investigated the relative weights of the elements in chemical compounds by using ratios. For example, in a molecule of the compound Na S O There are two atoms of sodium (Na), two atoms of sulfur (S), and three atoms of oxygen (O). If we use the gram atomic weights of these elements, we can find the gram molecular weight of the molecule (Na, 23: S, 32: O, 16). = 158 grams 2 2 3

The decimal part of the total made up by an element can be found by dividing the atomic weight of the element by the molecular weight of the molecule. Sodium = 46/158 = 0.29 Sulfur = 64/158 = 0.41 Oxygen = 48/158 = 0.30

The percent of each element by weight is found by moving each of these decimal points two places to the right. If we do this we get, Sodium = 29% Sulfur = 41% Oxygen = 30% The sum of these percent's is 100%. sometimes, because of rounding, the sum will not be exactly 100%.

Example: What percent by weight of Na S O is sodium (Na)? 2 2 3

Answer: The compound is 29% sodium.

HW: Lesson 53 #1-30