Solved: Gold is alloyed (mixed) with other metals to

Does the following diagram represent a chemical or physical change? How do you know? [Section 1.3]

(a) How many picometers are there in one meter? (b) Express 6.0 * 103 using a prefix to replace the power of ten. (c) Use exponential notation to express 4.22 mg in grams. (d) Use decimal notation to express 4.22 mg in grams.

Problem 5E Visualizing Concepts (a) Three spheres of equal size are composed of aluminum (density = 2.70 g/cm3), silver (density = 10.49 g/cm3), and nickel (density = 8.90 g/cm3). List the spheres from lightest to heaviest. (b) Three cubes of equal mass are composed of gold (density = 19.32 g/cm3), platinum (density = 21.45 g/cm3), and lead (density = 11.35 g/cm3). List the cubes from smallest to largest. [Section]

Problem 3PE Converting Units of Temperature A weather forecaster predicts the temperature will reach 31 °C. What is this temperature (a) in K, (b) in °F? Ethylene glycol, the major ingredient in antifreeze, freezes at -11.5 °C. What is the freezing point in (a) K, (b) °F?

Identify each of the following as measurements of length, area, volume, mass, density, time, or temperature: (a) 25 ps, (b) 374.2 mg, (c) 77 K, (d) 100,000 \(km^2\), (e) 1.06 \(\mu m\), (f) 16 \(nm^2\), (g) \(-78^{\circ} \mathrm{C}\), (h) 2.56 \(g/cm^3\), (i) 28 \(cm^3\). [Section 1.4]

Problem 4PE Determining Density and Using Density to Determine Volume or Mass (a) Calculate the density of mercury if 1.00 × 102 g occupies a volume of 7.36 cm3. ________________ (b) Calculate the volume of 65.0 g of liquid methanol (wood alcohol) if its density is 0.791 g/mL. ________________ (c) What is the mass in grams of a cube of gold (density = 19.32 g/cm3) if the length of the cube is 2.00 cm? ________________ (a) Calculate the density of a 374.5-g sample of copper if it has a volume of 41.8 cm3. (b) A student needs 15.0 g of ethanol for an experiment. If the density of ethanol is 0.789 g/mL, how many milliliters of ethanol are needed? (c) What is the mass, in grams, of 25.0 mL of mercury (density = 13.6 g/mL)?

Problem 7PE Determining the Number of Significant Figures in a Calculated Quantity The width, length, and height of a small box are 15.5, 27.3, and 5.4 cm, respectively. Calculate the volume of the box, using the correct number of significant figures in your answer. It takes 10.5 s for a sprinter to run 100.00 m. Calculate her average speed in meters per second and express the result to the correct number of significant figures.

Problem 8E (a) How many significant figures should be reported for the volume of the metal bar shown here? (b) If the mass of the bar is 104.72 g, how many significant figures should be reported when its density is determined using the calculated volume? [Section]

Problem 6PE Determining the Number of Significant Figures in a Measurement How many significant figures are in each of the following numbers (assume that each number is a measured quantity)? (a) 4.003, (b) 6.023 × 1023, (c) 5000. How many significant figures are in each of the following measurements? (a) 3.549 g, (b) 2.3 × 104 cm, (c) 0.00134 m3.

Problem 9E Visualizing Concepts When you convert units, how do you decide which part of the conversion factor is in the numerator and which is in the denominator? [Section]

(a) What is the length of the pencil in the following figure if the ruler reads in centimeters? How many significant figures are there in this measurement? (b) An automobile speedometer with circular scales reading both miles per hour and kilometers per hour is shown. What speed is indicated, in both units? How many significant figures are in the measurements? [Section 1.5]

Problem 11PE If the volume of an object is reported as 5.0 ft3, what is the volume in cubic meters?

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: (a) rice pudding, (b) seawater, (c) magnesium, (d) crushed ice.

A car travels 28 mi per gallon of gasoline. How many kilometers per liter will it go?

Problem 9PE Converting Units If a woman has a mass of 115 lb, what is her mass in grams? (Use the relationships between units given on the back inside cover of the text.) At a particular instant in time the Earth is judged to be 92,955,000 miles from the Sun. What is the distance in kilometers to four significant figures? (See back inside cover for conversion factor). By using a conversion factor from the back inside cover, determine the length in kilometers of a 500.0-mi automobile race.

Classification and Properties of Matter (Sections) Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: (a)air, (b) tomato juice, (c) iodine crystals, (d) sand.

Problem 10E Visualizing Concepts Show the steps to convert the speed of sound, 344 meters per second, into miles per hour. [Section]

Problem 12PE The density of benzene is 0.879g/mL. Calculate the mass in grams of 1.00 qt of benzene.

Problem 15E Classification and Properties of Matter (Sections) A solid white substance A is heated strongly in the absence of air. It decomposes to form a new white substance B and a gas C. The gas has exactly the same properties as the product obtained when carbon is burned in an excess of oxygen. Based on these observations, can we determine whether solids A and B and gas C are elements or compounds? Explain your conclusions for each substance.

Read the following description of the element zinc and indicate which are physical properties and which are chemical properties. Zinc is a silver-gray–colored metal that melts at 420 °C. When zinc granules are added to dilute sulfuric acid, hydrogen is given off and the metal dissolves. Zinc has a hardness on the Mohs scale of 2.5 and a density of 7.13 g/cm3 at 25 °C. It reacts slowly with oxygen gas at elevated temperatures to form zinc oxide, ZnO.

Classification and Properties of Matter (Sections)You are hiking in the mountains and find a shiny gold nugget. It might be the element gold, or it might be “fool’s gold,” which is a nickname for iron pyrite, \(FeS_2\). What kinds of experiments could be done to determine if the shiny nugget is really gold?

Problem 13E Classification and Properties of Matter (Sections) Give the chemical symbol or name for the following elements, as appropriate: (a) sulfur, (b)gold, (c) potassium, (d) chlorine, (e) copper, (f) U, (g) Ni, (h) Na, (i) Al, (j) Si.

Problem 14E Classification and Properties of Matter (Sections) Give the chemical symbol or name for each of the following elements, as appropriate: (a)carbon, (b) nitrogen, (c) titanium, (d) zinc, (e) iron, (f) P, (g) Ca, (h) He, (i) Pb, (j) Ag.

Problem 21E Classification and Properties of Matter (Sections) Suggest a method of separating each of the following mixtures into two components: (a) sugar and sand, (b) oil and vinegar.

Classification and Properties of Matter (Sections) Label each of the following as either a physical process or a chemical process: (a) rusting of a metal can, (b) boiling a cup of water, (c) pulverizing an aspirin, (d) digesting a candy bar, (e) exploding of nitroglycerin.

Problem 17E Classification and Properties of Matter (Sections) In the process of attempting to characterize a substance, a chemist makes the following observations: The substance is a silvery white, lustrous metal. It melts at 649 °C and boils at 1105 °C. Its density at 20 °C is 1.738 g/cm3. The substance burns in air, producing an intense white light. It reacts with chlorine to give a brittle white solid. The substance can be pounded into thin sheets or drawn into wires. It is a good conductor of electricity. Which of these characteristics are physical properties, and which are chemical properties?

Problem 22E Classification and Properties of Matter (Sections) Three beakers contain clear, colorless liquids. One beaker contains pure water, another contains salt water, and another contains sugar water. How can you tell which beaker is which? (No tasting allowed!)

Problem 20E Classification and Properties of Matter (Sections) A match is lit and held under a cold piece of metal. The following observations are made: (a)The match burns. (b) The metal gets warmer. (c) Water condenses on the metal. (d) Soot (carbon) is deposited on the metal.Which of these occurrences are due to physical changes, and which are due to chemical changes?

Problem 26E Units and Measurement (Section) (a) The temperature on a warm summer day is 87 °F. What is the temperature in °C? (b) Many scientific data are reported at 25 °C. What is this temperature in kelvins and in degrees Fahrenheit? (c) Suppose that a recipe calls for an oven temperature of 400 °F. Convert this temperature to degrees Celsius and to kelvins. (d) Liquid nitrogen boils at 77 K. Convert this temperature to degrees Fahrenheit and to degrees Celsius.

Problem 23E What exponential notation do the following abbreviations represent: (a) d (b) c (c) f (d) ? (e) M (f) k (g) n (h) m (i) p?

Units and Measurement (Section)(a) A sample of tetrachloroethylene, a liquid used in dry cleaning that is being phased out because of its potential to cause cancer, has a mass of 40.55 g and a volume of 25.0 mL at 25 °C. What is its density at this temperature? Will tetrachloroethylene float on water? (Materials that are less dense than water will float.) (b) Carbon dioxide (CO2) is a gas at room temperature and pressure. However, carbon dioxide can be put under pressure to become a “supercritical fluid” that is a much safer dry-cleaning agent than tetrachloroethylene. At a certain pressure, the density of supercritical CO2 is 0.469 g/cm3. What is the mass of a 25.0-mL sample of supercritical CO2 at this pressure?

Use appropriate metric prefixes to write the following measurements without use of exponents: (a) \(2.3 \times 10^{-10}\) L, (b) \(4.7 \times 10^{-6}\) g, (c) \(1.85 \times 10^{-12}\) m, (d) \(16.7 \times 10^6\) s, (e) \(15.7 \times 10^3\) g, (f) \(1.34 \times 10^{-3}\) m, (g) \(1.84 \times 10^2\) cm.

Problem 28E Units and Measurement (Section) (a) A cube of osmium metal 1.500 cm on a side has a mass of 76.31 g at 25 °C. What is its density in g/cm3 at this temperature? (b) The density of titanium metal is 4.51g/cm3 at 25 °C. What mass of titanium displaces 125.0 mL of water at 25 °C? (c) The density of benzene at 15 °C is 0.8787g/mL. Calculate the mass of 0.1500 L of benzene at this temperature.

Units and Measurement (Section)(a) After the label fell off a bottle containing a clear liquid believed to be benzene, a chemist measured the density of the liquid to verify its identity. A 25.0-mL portion of the liquid had a mass of 21.95 g. A chemistry handbook lists the density of benzene at 15 °C as 0.8787 g/mL. Is the calculated density in agreement with the tabulated value? (b) An experiment requires 15.0 g of cyclohexane, whose density at 25 °C is 0.7781 g/mL. What volume of cyclohexane should be used? (c) A spherical ball of lead has a diameter of 5.0 cm. What is the mass of the sphere if lead has a density of 11.34 g/cm3? (The volume of a sphere is (4/3)\(\pi\)r3, where r is the radius.)

Problem 31E In the year 2007, an estimated amount of 31 billion tons of carbon dioxide (CO2) was emitted worldwide due to fossil fuel combustion and cement production. Express this mass of CO2 in grams without exponential notation, using an appropriate metric prefix.

Problem 33E Indicate which of the following are exact numbers: (a) the mass of a piece of paper, (b) the volume of a cup of coffee, (c) the number of inches in a mile, (d) the number of ounces in a pound, (e) the number of microseconds in a week, (f) the number of pages in this book.

(a) To identify a liquid substance, a student determined its density. Using a graduated cylinder, she measured out a 45-mL sample of the substance. She then measured the mass of the sample, finding that it weighed 38.5 g. She knew that the substance had to be either isopropyl alcohol (density 0.785 g/mL) or toluene (density 0.866 g>mL) . What are the calculated density and the probable identity of the substance? (b) An experiment requires 45.0 g of ethylene glycol, a liquid whose density is 1.114 g/mL. Rather than weigh the sample on a balance, a chemist chooses to dispense the liquid using a graduated cylinder. What volume of the liquid should he use? (c) A cubic piece of metal measures 5.00 cm on each edge. If the metal is nickel, whose density is 8.90 g/cm3, what is the mass of the cube?

Silicon for computer chips is grown in large cylinders called "boules" that are in diameter and in height. The density of silicon is . Silicon wafers for making integrated circuits are sliced from a boule and are typically thick and in diameter. (a) How many wafers can be cut from a single boule? (b) What is the mass of a silicon wafer? (The volume of a cylinder is given by , where is the radius and is its height.)

Problem 34E Indicate which of the following are exact numbers: (a) the mass of a 32-oz can of coffee, (b)the number of students in your chemistry class, (c) the temperature of the surface of the sun, (d) the mass of a postage stamp, (e) the number of milliliters in a cubic meter of water, (f) the average height of students in your school.

Problem 35E Uncertainty in Measurement (Section) What is the number of significant figures in each of the following measured quantities? (a) 601 kg, (b) 0.054 s (c) 6.3050 cm (d) 0.0105 L (e) 7.0500 × 10-3 m3, (f) 400 g.

Problem 25E Make the following conversions: (a) 72 °F to °C, (b) 216.7 °C to °F, (c) 233 °C to K, (d) 315 K to °F, (e) 2500 °F to K, (f) 0 K to °F.

Problem 37E Round each of the following numbers to four significant figures, and express the result in standard exponential notation: (a) 102.53070, (b) 656,980, (c) 0.008543210, (d) 0.000257870, (e)–0.0357202

Problem 39E Uncertainty in Measurement (Section) Carry out the following operations and express the answers with the appropriate number of significant figures. (a) 14.3505 + 2.65 (b) 952.7 - 140.7389 (c) (3.29 × 104)(0.2501) (d)0.0588/0.677

Problem 40E Uncertainty in Measurement (Section) Carry out the following operations and express the answer with the appropriate number of significant figures.

Problem 38E Uncertainty in Measurement (Section) (a) The diameter of Earth at the equator is 7926.381 mi. Round this number to three significant figures and express it in standard exponential notation. (b) The circumference of Earth through the poles is 40,008 km. Round this number to four significant figures and express it in standard exponential notation.

Dimensional Analysis (Section)Using your knowledge of metric units, English units, and the information on the back inside cover, write down the conversion factors needed to convert (a) mm to nm (b) mg to kg, (c) km to ft (d) in.3 to cm3.

Problem 45E Dimensional Analysis (Section) (a) A bumblebee flies with a ground speed of 15.2 m/s. Calculate its speed in km/hr. (b) The lung capacity of the blue whale is 5.0 × 103 L. Convert this volume into gallons. (c) The Statue of Liberty is 151 ft tall. Calculate its height in meters. (d) Bamboo can grow up to 60.0 cm/day. Convert this growth rate into inches per hour.

Problem 42E Uncertainty in Measurement (Section) You have a graduated cylinder that contains a liquid (see photograph). Write the volume of the liquid, in milliliters, using the proper number of significant figures.

Problem 44E Dimensional Analysis (Section) Using your knowledge of metric units, English units, and the information on the back inside cover, write down the conversion factors needed to convert (a) mm to mm, (b) ms to ns, (c) mi to km, (d) ft3 to L.

You weigh an object on a balance and read the mass in grams according to the picture. How many significant figures are in this measurement?

Problem 46E Dimensional Analysis (Section) (a) The speed of light in a vacuum is 2.998 × 108 m/s. Calculate its speed in miles per hour. (b) The Sears Tower in Chicago is 1454 ft tall. Calculate its height in meters. (c) The Vehicle Assembly Building at the Kennedy Space Center in Florida has a volume of 3,666,500 m3. Convert this volume to liters and express the result in standard exponential notation. (d) An individual suffering from a high cholesterol level in her blood has 242 mg of cholesterol per 100 mL of blood. If the total blood

Problem 47E Dimensional Analysis (Section) Perform the following conversions: (a) 5.00 days to s, (b) 0.0550 mi to m, (c) $1.89/gal to dollars per liter, (d) 0.510 in./ms to km/hr, (e) 22.50 gal/min to L/s, (f) 0.02500 ft3 to cm3.

Problem 48E Dimensional Analysis (Section) Carry out the following conversions: (a) 0.105 in. to mm, (b) 0.650 qt to mL, (c) 8.75 ?m/s to km/hr, (d) 1.955 m3 to yd3, (e) $3.99/lb to dollars per kg, (f) 8.75 lb/ft3 to g/mL.

(a) How many liters of wine can be held in a wine barrel whose capacity is 31 gal? (b) The recommended adult dose of Elixophyllin ®, a drug used to treat asthma, is 6 mg/kg of body mass. Calculate the dose in milligrams for a 185-lb person. (c) If an automobile is able to travel 400 km on 47.3 L of gasoline, what is the gas mileage in miles per gallon? (d) A pound of coffee beans yields 50 cups of coffee (4 cups = 1 qt) . How many milliliters of coffee can be obtained from 1 g of coffee beans?

Problem 51E Dimensional Analysis (Section) The density of air at ordinary atmospheric pressure and 25 °C is 1.19 g/L. What is the mass, in kilograms, of the air in a room that measures 14.5 ft × 16.5 ft × 8.0 ft?

Problem 50E Dimensional Analysis (Section) (a) If an electric car is capable of going 225 km on a single charge, how many charges will it need to travel from Seattle, Washington, to San Diego, California, a distance of 1257 mi, assuming that the trip begins with a full charge? (b) If a migrating loon flies at an average speed of 14 m/s, what is its average speed in mi/hr? (c) What is the engine piston displacement in liters of an engine whose displacement is listed as 450 in.3? (d) In March 1989 the Exxon Valdez ran aground and spilled 240,000 barrels of crude petroleum off the coast of Alaska. One barrel of petroleum is equal to 42 gal. How many liters of petroleum were spilled?

Problem 53E By using estimation techniques, arrange these items in order from shortest to longest: a 57-cm length of string, a 14-in.-long shoe, and a 1.1-m length of pipe.

The concentration of carbon monoxide in an urban apartment is 48 \(\mu g/m^3\) . What mass of carbon monoxide in grams is present in a room measuring 11.0 ft X 11.5 ft X20.5 ft?

Problem 54E By using estimation techniques, determine which of the following is the heaviest and which is the lightest: a 5-lb bag of potatoes, a 5-kg bag of sugar, or 1 gal of water (density = 1.0 g/mL).

Problem 55E Gold can be hammered into extremely thin sheets called gold leaf. An architect wants to cover a ceiling with gold leaf that is five-millionths of an inch thick. The density of gold is , and gold costs $953 per troy ounce ( ). How much will it cost the architect to buy the necessary gold?

A copper refinery produces a copper ingot weighing 150 lb. If the copper is drawn into wire whose diameter is 7.50 mm, how many feet of copper can be obtained from the ingot? The density of copper is 8.94 \(g/cm^3\). (Assume that the wire is a cylinder whose volume \(V = \pi r^2h\), where r is its radius and h is its height or length.)

(a) Classify each of the following as a pure substance, a solution, or a heterogeneous mixture: a gold coin, a cup of coffee, a wood plank. (b) What ambiguities are there in answering part (a) from the descriptions given?

Problem 58AE (a) What is the difference between a hypothesis and a theory? (b) Explain the difference between a theory and a scientific law. Which addresses how matter behaves, and which addresses why it behaves that way?

Problem 59AE A sample of ascorbic acid (vitamin C) is synthesized in the laboratory. It contains 1.50 g of carbon and 2.00 g of oxygen. Another sample of ascorbic acid isolated from citrus fruits contains 6.35 g of carbon. How many grams of oxygen does it contain? Which law are you assuming in answering this question?

Two students determine the percentage of lead in a sample as a laboratory exercise. The true percentage is 22.52%. The students’ results for three determinations are as follows: (1) 22.52, 22.48, 22.54 (2) 22.64, 22.58, 22.62 (a) Calculate the average percentage for each set of data and state which set is the more accurate based on the average.(b) Precision can be judged by examining the average of the deviations from the average value for that data set. (Calculate the average value for each data set; then calculate the average value of the absolute deviations of each measurement from the average.) Which set is more precise?

Problem 61AE Is the use of significant figures in each of the following statements appropriate? Why or why not? (a) Apple sold 22,727,000 iPods during the last three months of 2008. (b) New York City receives 49.7 inches of rain, on average, per year. (c) In the United States, 0.621% of the population has the surname Brown. (d) You calculate your grade point average to be 3.87562.

What type of quantity (for example, length, volume, density) do the following units indicate: (a) mL, (b) \(cm^2\), (c) \(mm^3\), (d) mg/L, (e) ps, (f) nm, (g) K?

Problem 63AE Give the derived SI units for each of the following quantities in base SI units: (a) acceleration = distance/time2 (b) force = mass × acceleration (c) work = force × distance (d) pressure = force/area (e) power = work/time (f) velocity = distance/time (g) energy = mass × (velocity)2

The distance from Earth to the Moon is approximately 240,000 mi. (a) What is this distance in meters? (b) The peregrine falcon has been measured as traveling up to 350 km/ hr in a dive. If this falcon could fly to the Moon at this speed, how many seconds would it take? (c) The speed of light is 3.00 × 108 m/s. How long does it take for light to travel from Earth to the Moon and back again? (d) Earth travels around the Sun at an average speed of 29.783 km/s. Convert this speed to miles per hour.

Problem 65AE The US quarter has a mass of 5.67 g and is approximately 1.55 mm thick. (a) How many quarters would have to be stacked to reach 575 ft, the height of the Washington Monument? (b) How much would this stack weigh? (c) How much money would this stack contain? (d) The US National Debt Clock showed the outstanding public debt to be $11,687,233,914,811.11 on August 19, 2009. How many stacks like the one described would be necessary to pay off this debt?

Problem 66AE In the United States, water used for irrigation is measured in acre-feet. An acre-foot of water covers an acre to a depth of exactly 1 ft. An acre is 4840 yd2. An acre-foot is enough water to supply two typical households for 1.00 yr. (a) If desalinated water costs $1950 per acre-foot, how much does desalinated water cost per liter? (b) How much would it cost one household per day if it were the only source of water?

Problem 67AE Suppose you decide to define your own temperature scale with units of O, using the freezing point (13 °C) and boiling point (360 °C) of oleic acid, the main component of olive oil. If you set the freezing point of oleic acid as 0 °O and the boiling point as 100 °O, what is the freezing point of water on this new scale?

Problem 68AE The liquid substances mercury (density = 13.6 g/mL), water (1.00 g/mL), and cyclohexane (0.778 g/mL) do not form a solution when mixed but separate in distinct layers. Sketch how the liquids would position themselves in a test tube.

Problem 69AE Two spheres of equal volume are placed on the scales as shown. Which one is more dense?

Problem 70AE Water has a density of 0.997 g/cm3 at 25 °C; ice has a density of 0.917 g/cm3 at -10 °C. (a) If a soft-drink bottle whose volume is 1.50 L is completely filled with water and then frozen to -10 °C, what volume does the ice occupy? (b) Can the ice be contained within the bottle?

Problem 71AE A 32.65-g sample of a solid is placed in a flask. Toluene, in which the solid is insoluble, is added to the flask so that the total volume of solid and liquid together is 50.00 mL. The solid and toluene together weigh 58.58 g. The density of toluene at the temperature of the experiment is 0.864 g/mL. What is the density of the solid?

Problem 72AE A thief plans to steal a gold sphere with a radius of 28.9 cm from a museum. If the gold has a density of 19.3 g/cm3, what is the mass of the sphere in pounds? [The volume of a sphere is V= (4/3)?r3.] Is the thief likely to be able to walk off with the gold sphere unassisted?

Automobile batteries contain sulfuric acid, which is commonly referred to as “battery acid.” Calculate the number of grams of sulfuric acid in 1.00 gal of battery acid if the solution has a density of 1.28 g/mL and is 38.1% sulfuric acid by mass.

Problem 74AE A 40-lb container of peat moss measures 14 × 20 × 30 in. A 40-lb container of topsoil has a volume of 1.9 gal. (a) Calculate the average densities of peat moss and topsoil in units of g/cm3. Would it be correct to say that peat moss is “lighter” than topsoil? Explain. (b) How many bags of peat moss are needed to cover an area measuring 15.0 ft × 20.0 ft to a depth of 3.0 in.?

Problem 75AE A package of aluminum foil contains 50 ft2 of foil, which weighs approximately 8.0 oz. Aluminum has a density of 2.70 g/cm3. What is the approximate thickness of the foil in millimeters?

Problem 77AE A 15.0-cm long cylindrical glass tube, sealed at one end, is filled with ethanol. The mass of ethanol needed to fill the tube is found to be 11.86 g. The density of ethanol is . Calculate the inner diameter of the tube in centimete

Problem 78AE Gold is alloyed (mixed) with other metals to increase its hardness in making jewelry. (a) Consider a piece of gold jewelry that weighs 9.85 g and has a volume of 0.675 cm3. The jewelry contains only gold and silver, which have densities of 19.3 and 10.5 g/cm3, respectively. If the total volume of the jewelry is the sum of the volumes of the gold and silver that it contains, calculate the percentage of gold (by mass) in the jewelry. (b) The relative amount of gold in an alloy is commonly expressed in units of carats. Pure gold is 24 carat, and the percentage of gold in an alloy is given as a percentage of this value. For example, an alloy that is 50% gold is 12 carat. State the purity of the gold jewelry in carats.

Problem 80AE You are assigned the task of separating a desired granular material with a density of 3.62 g/cm3 from an undesired granular material that has a density of 2.04 g/cm3. You want to do this by shaking the mixture in a liquid in which the heavier material will fall to the bottom and the lighter material will float. A solid will float on any liquid that is more dense. Using an Internet-based source or a handbook of chemistry, find the densities of the following substances: carbon tetrachloride, hexane, benzene, and diiodomethane. Which of these liquids will serve your purpose, assuming no chemical interaction between the liquid and the solids?

Problem 81AE In 2009, a team from Northwestern University and Western Washington University reported the preparation of a new “spongy” material composed of nickel, molybdenum, and sulfur that excels at removing mercury from water. The density of this new material is 0.20 g/cm3, and its surface area is 1242 m2 per gram of material. (a) Calculate the volume of a 10.0-mg sample of this material. (b) Calculate the surface area for a 10.0-mg sample of this material. (c) A 10.0-mL sample of contaminated water had 7.748 mg of mercury in it. After treatment with 10.0 mg of the new spongy material, 0.001 mg of mercury remained in the contaminated water. What percentage of the mercury was removed from the water? (d) What is the final mass of the spongy material after the exposure to mercury?

Problem 82AE The concepts of accuracy and precision are not always easy to grasp. Here are two sets of studies: (a) The mass of a secondary weight standard is determined by weighing it on a very precise balance under carefully controlled laboratory conditions. The average of 18 different weight measurements is taken as the weight of the standard. (b) A group of 10,000 males between the ages of 50 and 55 is surveyed to ascertain a relationship between calorie intake and blood cholesterol level. The survey questionnaire is quite detailed, asking the respondents about what they eat, smoke, drink, and so on. The results are reported as showing that for men of comparable lifestyles, there is a 40% chance of the blood cholesterol level being above 230 mg/dL for those who consume more than 40 calories per gram of body weight per day, as compared with those who consume fewer than 30 calories per gram of body weight per day. Discuss and compare these two studies in terms of the precision and accuracy of the result in each case. How do the two studies differ in ways that affect the accuracy and precision of the results? What makes for high precision and accuracy in any given study? In each of these studies, what factors might not be controlled that could affect the accuracy and precision? What steps can be taken generally to attain higher precision and accuracy?