L2-Scientific-Measurements PDF

SCIENTIFIC MEASUREMENTS LESSON 2 - GEN CHEMISTRY 1 PREPARED BY: RHODA MAE ALLERA  OBJECTIVES At the end of the lesson, you are expected to: Differentiate between accuracy and precision. Determine the different source of errors in measurements. Apply the rules fo...

SCIENTIFIC MEASUREMENTS LESSON 2 - GEN CHEMISTRY 1 PREPARED BY: RHODA MAE ALLERA  OBJECTIVES At the end of the lesson, you are expected to: Differentiate between accuracy and precision. Determine the different source of errors in measurements. Apply the rules for significant figures in calculations. Determine the density of liquids and solids. A Boeing 777-200ER Mass of the average Takeoff weight: mosquito is about 0.0000025 298,000 kilograms kilograms, which can be 2.98 x 10⁵ kg written as 2.5 x 10⁻⁶ kg ACCURACY AND PRECISION Accuracy is measuring near true value. Precision is getting consistent results.  Random Error and Systematic Error SIGNIFICANT FIGURES SIGNIFICANT FIGURES IN MEASUREMENT  SIGNIFICANT FIGURES IN MEASUREMENT Every measurement has uncertainty. Hence, it is important to write the precision of a measurement. Significant figures or digits are the digits in any measurement that are known with certainty, plus one uncertain digit which in the measurement is crucial.  SIGNIFICANT FIGURES IN MEASUREMENT 1. LEADING ZEROES in front of a number are not significant never count Examples: 1. 0.0025 = 2 significant figures 2. 0.26 = 2 significant figures  SIGNIFICANT FIGURES IN MEASUREMENT 2. CAPTIVE ZEROES trapped between two numbers always count all number means something Examples: 1. 305 = 3 significant figures 2. 2.007 = 4 significant figures  SIGNIFICANT FIGURES IN MEASUREMENT 3. TRAILING ZEROES end of numbers with 2 instances; with decimals – always count no decimals – do not count Examples: 1. 300 = 1 significant figure 2. 300. = 3 significant figures 3. 300.0 = 4 significant figures 4. 2600.0 = 5 significant figures SIGNIFICANT FIGURES IN MEASUREMENT ACTIVITY 1: COUNT THE NUMBER OF SIGNIFICANT FIGURES. 1. 3.000 2. 8.001 3. 48.00 4. 708 5. 0.002303 6. 2000 7. 1008.02 8. 2086.0 9. 20860 SIGNIFICANT FIGURES IN CALCULATIONS  SIGNIFICANT FIGURES IN CALCULATIONS Addition and Subtraction The rule is, the value with the lowest number of decimal places determines how many decimal places will appear in the answer. Example: SIGNIFICANT FIGURES IN CALCULATIONS  SIGNIFICANT FIGURES IN CALCULATIONS Multiplication and Division The rule is to count the number of significant figures in each number being multiplied or divided and then limit the significant figures base on the lowest count. Example: SIGNIFICANT FIGURES IN CALCULATIONS SIGNIFICANT FIGURES IN CALCULATIONS  UNIT OF MEASUREMENTS INTERNATIONS SYSTEM OF UNITS (SI) BASE UNITS INTERNATIONAL SYSTEM OF UNITS (SI) PREFIX AND NOTATION CONVERSION OF UNITS CONVERSION OF UNITS  CONVERSION OF UNITS TEMPERATURE ºC to K K to ºC K = ºC + 273.15 ºC = K -273.15 ºF to ºC ºC to ºF ºC = (ºF-32) x 5 ºF = (ºC x 9) +32 9 5 or or ºC = (ºF-32) ÷ 1.8 ºF = (ºC) 1.8 +32  CONVERSION OF UNITS Example 1: The lemon juice drink contains 500.0mg of Vitamin C. Express the Vitamin C content in grams. Solution: Known: 500.0mg Unknown: Mass in g (desired unit) Process: ……………. Answer: The Vitamin C in the lemon juice drink is 0.5g.  CONVERSION OF UNITS Example 2: What is the equivalent of 750ml red cane vinegar in gallons? Solution: Known: 750ml Unknown: Volume in gal (desired unit) Unit relationship: 1 gal = 3.785L and 1000ml = 1L Process: ……………. Answer: 750ml red cane vinegar = 0.20gal Activity 2: Convert the following. 1. 56 km to dm 2. 23 cm to mm 3 3 3. 4.35 hr. to s. 4. 58 ºF to ºC 5. 18 ºF to K WHAT WILL HAPPEN IF A NUMBER DOES NOT HAVE ANY UNIT? Meaningless Confusing Possibly life threatening  DENSITY MEASUREMENT  Density Measurement is one of the common measurements used in the laboratory. It involves getting the mass, volume and temperature of an object.  Mass Is the quantity of matter in an object. It is determined by weighing the object using a balance. SI basic units are g and kg.  Solids Volume Is the amount of space occupied by the substance. For liquids, it can be determined using graduated cylinder.  Temperature Commonly used using °C or °F; although the SI basic unit is the Kelvin. ºC to K K to ºC K = ºC + 273.15 ºC = K -273.15 ºF to ºC ºC to ºF ºC = (ºF-32) x 5 ºF = (ºC x 9) +32 9 5 or or ºC = (ºF-32) ÷ 1.8 ºF = (ºC) 1.8 +32  Density Is the ratio of the mass of an object to the volume it occupies. Density = Mass Volume  Density of some Common Matter Matter at 25ºC Density, g/ml Matter at 25ºC Density, g/ml Wood 0.75 Ethanol 0.79 Aluminum 2.70 Water 0.997 Lead 11.3 Wine 1.003-1.030 Gold 19.3 Milk 1.028-1.035 Gasoline 0.66 Urine 3.17 Example 1: A sample amount of sugar has a mass of 250.0g and a volume of 157.3cm. 3 What is its density in grams per cubic centimeter? Solution: Mass = 250.0g Volume = Process: Answer: Example 2: Gold metal has a density of 19.3g/cm3. What is the volume, in cubic centimeters of a 500.0g bar of a gold metal ? Solution: Density = 19.3g/cm3 Mass = 500.0g Volume = ? Process: Answer: ACTIVITY 3: Calculate the following. 1. A sample of mercury with a density of 13.6g/ml is put into a graduated cylinder containing 55 ml of water. The water level rises to 98ml. What is the mass of mercury in grams? 2. What is the density of a 56.3g rod that is 1.25cm long an has a diameter of 2.4cm?  REMINDERS Review your notes in Chemistry Lesson 2. Bring Periodic Table of Elements.