Measurement & Data Processing IB Chem

Objective: demonstrate knowledge of measurement & data processing. Warm up: Explain the difference between accuracy and precision. Objective: demonstrate knowledge of measurement & data processing. Warm up: Explain the difference between accuracy and precision.

Challenge… Hemoglobin (C 2952 H 4664 O 832 S 8 Fe 4 ) is the oxygen carrier in blood. Calculate its molar mass. An average adult has about 5.0 liters of blood. Every milliliter of blood has approximately 5.0 x 10 9 erythrocytes, or red blood cells, and every red blood cell has about 2 x 10 8 hemoglobin molecules. Calculate the mass of hemoglobin molecules in grams in an average adult. Hemoglobin (C 2952 H 4664 O 832 S 8 Fe 4 ) is the oxygen carrier in blood. Calculate its molar mass. An average adult has about 5.0 liters of blood. Every milliliter of blood has approximately 5.0 x 10 9 erythrocytes, or red blood cells, and every red blood cell has about 2 x 10 8 hemoglobin molecules. Calculate the mass of hemoglobin molecules in grams in an average adult.

Significant Figures g The certain (known) digits and one estimated digit of each measurement are significant. Remember! Every time you make a measurement, you record all of the certain digits and one estimated digit. Remember! Every time you make a measurement, you record all of the certain digits and one estimated digit. The certain (known) digits and one estimated digit of each measurement are significant. Remember! Every time you make a measurement, you record all of the certain digits and one estimated digit. Remember! Every time you make a measurement, you record all of the certain digits and one estimated digit.

Rules for Sig Figs 1.Non-zeros are always significant. 2.Zeros between non-zeros are significant. 3.All final zeros to the right of the decimal are significant. (estimated value) 4.Placeholder zeros are NOT significant. –Zeros preceding significant digits. –Zeros following significant digits without a decimal point. 1.Non-zeros are always significant. 2.Zeros between non-zeros are significant. 3.All final zeros to the right of the decimal are significant. (estimated value) 4.Placeholder zeros are NOT significant. –Zeros preceding significant digits. –Zeros following significant digits without a decimal point has 4 sig figs 5508 has 4 sig figs has 4 sig figs has 4 sig figs 45,670 has 4 sig figs Significant Figures

Adding and Subtracting Round to the fewest number of decimal places given in problem. Adding and Subtracting Round to the fewest number of decimal places given in problem. Sample Problem: (.01) (.001) (.1) Correct Answer: 47.9 Significant Figures

Sample Problem: 14.3 (3 sig figs) (5 sig figs) x (1 sig fig) Correct Answer: 0.07 Sample Problem: 14.3 (3 sig figs) (5 sig figs) x (1 sig fig) Correct Answer: 0.07 Multiplying and Dividing Round to the fewest number of significant digits given in the problem. Significant Figures

In chemistry, we work with very large and very small numbers. Number of particles in a mole = Mass of an electron = kg In chemistry, we work with very large and very small numbers. Number of particles in a mole = Mass of an electron = kg We need a simple way to write these numbers! Scientific Notation

1.Identify the significant digits 2.Write out the significant digits as a number greater than 1 but less than 10 3.Count the number of places you had to move the decimal to complete step 1 4.Write this number of decimal places as an exponent to 10 1.Identify the significant digits 2.Write out the significant digits as a number greater than 1 but less than 10 3.Count the number of places you had to move the decimal to complete step 1 4.Write this number of decimal places as an exponent to There are 4 sig figs in this number is 10 The decimal was moved 23 places x When the decimal place is moved to the left, the exponent is positive. Scientific Notation

Things you already know Significant figures Scientific notation Basic calculations without a calculator Significant figures Scientific notation Basic calculations without a calculator

Types of Uncertainty/Error Random: Error introduced has an equal probability of being too high or too low 50/50 chance Ex: Door open on analytical balance Random: Error introduced has an equal probability of being too high or too low 50/50 chance Ex: Door open on analytical balance Systematic Error introduced will always be too high or too low. Ex: Air bubbles in thermometer

Using equipment Analogue +/- Half of the smallest division Digital +/- The smallest scale division

UncertaintyUncertainty Absolute ± half of the smallest division Always include units 35.0 ± 0.5 cm 3 Absolute ± half of the smallest division Always include units 35.0 ± 0.5 cm 3 Percent Absolute uncertainty divided by the measurement x 100.4% 0.5/35.0 *100 = 1.4% Percent Absolute uncertainty divided by the measurement x 100.4% 0.5/35.0 *100 = 1.4%

Uncertainties in Calculations IB refers to this as propagating error

Uncertainties in Calculations

Percent error A measure of how close the experimental value is to the accepted/known value Not to be confused with percent uncertainty… (accepted value – experimental value) accepted value A measure of how close the experimental value is to the accepted/known value Not to be confused with percent uncertainty… (accepted value – experimental value) accepted value X 100

Equipment/technique uncertainty compared to literature values If % uncertainty > % error, the experimental value fits within the uncertainty range and is acceptable; the differences in the experimental and literature values is due to random errors If % uncertainty < % error, the experimental value does not fit within the uncertainty range and is unacceptable; the differences in the experimental and literature values is due to systematic errors If % uncertainty > % error, the experimental value fits within the uncertainty range and is acceptable; the differences in the experimental and literature values is due to random errors If % uncertainty < % error, the experimental value does not fit within the uncertainty range and is unacceptable; the differences in the experimental and literature values is due to systematic errors

Equipment/technique uncertainty compared to literature values Example: % uncertainty is 20 g +/- 5% < % error is 10% This indicates the data should fall between 19 and 21 grams. The error of 10% falls outside of this. Meaning the accepted or literature values are outside of this range produced. This must be due to systematic error and is UNACCEPTABLE! Example: % uncertainty is 20 g +/- 5% < % error is 10% This indicates the data should fall between 19 and 21 grams. The error of 10% falls outside of this. Meaning the accepted or literature values are outside of this range produced. This must be due to systematic error and is UNACCEPTABLE!

Accuracy vs. Precision

Accuracy measures how close a measured value comes to a predetermined target value (the set volume on your pipettor). Reproducibility (precision) measures how close repeated values are to one another. These concepts can be visualized using these cartoon (idealized) bulls-eye diagrams. Notice that accuracy and precision can vary independently, so they can be evaluated independently, as well. not accurate precise accurate not precise accurate precise not accurate not precise Accuracy vs. Precision Test yourself on identifying if these examples are precise, accurate, neither, or a mix

Graphing Always include: –Title –Axis titles with units –A best fit line –Identification of outliers –Consistent scales – no uneven jumps Always make the graph as large as possible…maximize axis usage and paper usage Always include: –Title –Axis titles with units –A best fit line –Identification of outliers –Consistent scales – no uneven jumps Always make the graph as large as possible…maximize axis usage and paper usage Graphing video

Extrapolation & Interpolation Extrapolation- Extending the graph to determine an unknown value outside the range of measured valuesExtrapolation- Extending the graph to determine an unknown value outside the range of measured values Interpolation- Determining an unknown value within the limits of the measured values Extrapolation- Extending the graph to determine an unknown value outside the range of measured valuesExtrapolation- Extending the graph to determine an unknown value outside the range of measured values Interpolation- Determining an unknown value within the limits of the measured values

Challenge… Hemoglobin (C 2952 H 4664 O 832 S 8 Fe 4 ) is the oxygen carrier in blood. Calculate its molar mass. An average adult has about 5.0 liters of blood. Every milliliter of blood has approximately 5.0 x 10 9 erythrocytes, or red blood cells, and every red blood cell has about 2 x 10 8 hemoglobin molecules. Calculate the mass of hemoglobin molecules in grams in an average adult. Hemoglobin (C 2952 H 4664 O 832 S 8 Fe 4 ) is the oxygen carrier in blood. Calculate its molar mass. An average adult has about 5.0 liters of blood. Every milliliter of blood has approximately 5.0 x 10 9 erythrocytes, or red blood cells, and every red blood cell has about 2 x 10 8 hemoglobin molecules. Calculate the mass of hemoglobin molecules in grams in an average adult.

Objective: demonstrate knowledge of measurement & data processing. Warm up: Explain the difference between accuracy and precision. Objective: demonstrate knowledge of measurement & data processing. Warm up: Explain the difference between accuracy and precision.