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## Ch.2 Measurements and Calculations

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**Ch.2 Measurements and Calculations**System – specific portion of matter in a given region of space that has been selected for study during an experiment or observation.**Scientific Method**Hypothesis – testable statement controls – remain constant variable – is changed Model – explanation of how phenomena occur and how data or events are related. Theory – broad generalization that explains a body of facts or phenomena.**Accuracy and Precision**• Accuracy – close to the expected value • Precision – a number of measurements close to each other.**What is more accurate?**Graduated cylinder Or Beaker**Significant Figures**• Indicates how precise a measurement is.**Sig fig practice**Perform these calculations following the rules for sig figs. • 26 x 0.02584 = ? • 15.3 / 1.1 = ? • 782.45 - 3.5328 = ? • 63.258 + 734.2 = ?**SI unit – measurements in science.**Density = m/v A sample of aluminum metal has a mass of 8.4g. The volume of the sample is 3.1 cm3. calculate the density of aluminum.**Dimensional analysis – math technique that allows you to**use units to solve problems involving measurements. Express a mass of 5.712 grams in milligrams and in kilograms.**PercentageError**• Calculated by subtracting the accepted value from the experimental value, dividing the difference by the accepted value, and then multiplying by 100. Percentage error = valueexperimental – valueexpectedx 100 valueexpected**Direct Proportions**• Two quantities are directly proportional to each other if dividing one by the other gives a constant value. y/x = k 2/4 = 0.5 4/8 = 0.5 y = kx**Indirect Proportions**• Two quantities are inversely proportional to each other if their product is constant. If x and y are inversely proportional to each other, the relationship can be expressed as follows: y ∞ 1/x xy = k