AP Chem Topic #1 Foundations In-Class Notes Sample Exercises WS Name: ______Date: ______Per#: ___ Sample Exercise 1.1 – Uncertainty in Measurement In analyzing a sample of polluted water, chemist measured out a 25.00-mL water sample with a pipet. At another point in the analysis, the chemist used a graduated cylinder to measure 25mL of a solution. What is the difference between the measurements 25.00mL and 25mL? Sample Exercise 1.2 – Precision and Accuracy To check the accuracy of a graduated cylinder, a student filled the cylinder to the 25-ml mark using water delivered from a buret and then read the volume delivered. Trial Volume – Grad Cyl Volume – buret 1 25-mL 26.54-mL 2 25-mL 26.51-mL 3 25-mL 26.60-mL 4 25-mL 26.49-mL 5 25-mL 26.57-mL Average 25-mL 26.54-mL Is the graduated cylinder accurate? Is the graduated cylinder precise? Sample Exercise 1.3 – Significant Figures Give the number of significant figures for the following results. (a) A student’s extraction procedure on tea yields 0.0105g of caffeine. (b) A chemist records a mass of 0.050080g in an analysis. (c) In an experiment a span of time is determined to be 8.050x10-3s. Sample Exercise 1.4 – Significant Figures in Mathematical Operations Carry out the following mathematical operations, and give each result with the correct number of significant figures. (a) 1.05x10-3 ÷ 6.135 (b) 21 – 13.8 (c) As part of a lab assignment to determine the value of the gas constant (R), a student measured the pressure (P), volume (V), and temperature (T) for a sample of gas, where R = PV/T. The following values were obtained: P = 2.560, T = 275.15, and V = 8.8. Calculate R to the correct number of sig figs. Sample Exercise 1.5 – Unit Conversions I A pencil is 7.00in long. What is its length in centimeters? Ans: 17.8cm Sample Exercise 1.6 – Unit Conversion II You want to order a bicycle with a 25.5in frame, but the sizes in the catalog are given only in centimeters. What size should you order? Ans: 64.8cm Sample Exercise 1.7 – Unit Conversion III A student entered a 10.0km run. How long is the run in miles? Ans: 6.22 mi Sample Exercise 1.8 – Unit Conversion IV The speed limit on many highways in the U.S. is 55miles/hour. What number would be posted in km/hr? Ans: 88 km/hr Sample Exercise 1.9 – Unit Conversion V A Japanese car is advertised as having a gas mileage of 15lm/L. Convert this rating to miles/gallon. Ans: 35 mi/gal Sample Exercise 1.10 – Temperature Conversions I Normal body temperature is 98.6°F. Convert this temperature to °C and K. Ans: 37°C and 310.2K Sample Exercise 1.11 – Temperature Conversions II One interesting feature of the Celsius and Fahrenheit scales is that -40°C and -40°F represent the same temperature. Verify this true. Sample Exercise 1.12 – Temperature Conversions III Liquid nitrogen, which is often used as a coolant for low-temperature experiments, has a boiling point of 77K. What is this temperature on the Fahrenheit scale? Ans: -321°F

1 Sample Exercise 1.13 – Determining Density A chemist, trying to identify the main component of a compact disc cleaning fluid, finds that 25.00cm3 of the substance has a mass of 19.625g at 20°C. The following are the names and densities of the compounds that might be the main component. Compound Density (g/cm 3) Chloroform 1.492 Diethyl ether 0.714 Ethanol 0.789 Isopropyl alcohol 0.785 Toluene 0.867 Questions:

(1) (2) (3/4) (5) (1) What is the length of the pencil in the figure if the scale reads in centimeters? How many significant figures are there in this measurement? (2) An oven thermometer with a circular scale reading degrees Fahrenheit is shown. What temperature does the scale indicate? How many significant figures are in the measurement? (3) How many significant figures should be reported for the volume of the metal bar shown above? (4) If the mass of the bar is 104.7 g, how many significant figures should be reported when its density is calculated using the calculated volume? (5) Does the diagram shown above on far right represent a chemical or physical change? How do you know?

(6) (6) Which of the figures represents (a) a pure element, (b) a mixture of two elements, (c) a pure compound, (d) a mixture of an element and a compound? (More than one picture might fit each description.)

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