Processing Lab Data MRS. PAGE 2014-2015 After Collecting Data = Process Data Raw Data: the data you collect during lab without any calculations Qualitative Data: Descriptive data – observed with senses, (i.e. what does it look like, sound like, feel like) Quantitative Data: Measured data using tools. Will be number values. Processed Data: data as a result of performing calculations AFTER all data has been collected Raw Data & Processed Data are kept on SEPARATE DATA TABLES!!! DENSITY Density is a physical property of matter Density refers to how tightly packed the particles are in an object Tightly packed = more dense Loosely = packed = less dense or = Units for density are or 3 (note: 1 = 13 ) Practice Calculating Density If you measure an object that has a mass of 8.47 g and a volume of 3.1 cm3. Calculate the density of the object. = = 8.47 3.13 = 8.4 3.13 = 2.7 3 Remember Sig. Fig. Rules YOU TRY What is the density of an 84.70 g sample of an unknown substance if the sample occupies 49.6 mL? . What volume would be occupied by 7.75 g of the same substance? (Use the density from the first problem) . Accuracy vs. Precision Accuracy: how close a measurement is to an accepted value (literature value) Precision: how close the measurements are to each other Percentage Error You can determine how accurate your data is by calculating the percentage error = The larger the percentage error, the more inaccurate your data is The smaller the percentage error, the more accurate and reliable your results are. Note: error can be positive or negative, this just means your values are higher or lower than the accepted value − × 100 Practice Calculating Percentage Error What is the percentage error for a mass measurement of 17.8 g, given that the correct value is 21.2 g? − % = × 100 17.8 − 21.2 % = × 100 21.2 −3.4 = × 100 21.2 = −16.0% Remember Sig. Fig. Rules YOU TRY… A volume is measured experimentally as 4.26 mL. What is the percentage error, given that the correct value is 4.15 mL? . % A student measures the mass and volume of a substance and calculates its density as 1.40 g/mL. The correct, accepted, value of the density is 1.30 g/mL. What is the percentage error of the student’s measurement? . % Experimental Errors 2 Types: Random & Systematic Random Errors: unpredictable, chance variations that experimenter has little control over– using many trials and averaging results helps alleviate this type of error. (ex: parallax error) Systematic Errors: caused by the way in which the experiment was conducted (design). Systematic errors can not be eliminated by averaging. Must change how experiment is conducted. (ex: not calibrating instruments) Human Error: should not occur if you are focused and careful HOMEWORK Read/review pages 44-57 in your textbook. Complete questions 1-8 on page 57. SHOW ALL WORK.