General orrganic and biological chemistry structures off liffe 5th by karen timberlake03 worked examples

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a. Copper is an element, which is a pure substance

b. A chocolate-chip cookie does not have a uniform composition, which makes it a heterogeneous mixture

c. The gases oxygen and nitrogen have a uniform composition in nitrox, which makes it a homogeneous mixture

Study Check 3.1

A salad dressing is prepared with oil, vinegar, and chunks of blue cheese Is this a homogeneous or heterogeneous mixture?

Answer

heterogeneous

Classify each of the following as a pure substance (element or compound) or a mixture (homogeneous or heterogeneous):

a. copper in copper wire

b. a chocolate-chip cookie

c. nitrox, a combination of oxygen and nitrogen used to fill scuba tanks

Sample Problem 3.1 Classifying Mixtures

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General, Organic, and Biological Chemistry: Structures of Life, 5/e

Karen C Timberlake

Solution

a. A physical change occurs when the gold ingot changes shape

b. A chemical change occurs when gasoline burns and forms different substances with new properties

c. A physical change occurs when the size of the garlic pieces changes

Study Check 3.2

Classify each of the following as a physical or chemical change:

a. Water freezes on a pond

b. Gas bubbles form when baking powder is placed in vinegar

c. A log is cut for firewood

Answer

a. physical change b. chemical change c. physical change

Classify each of the following as a physical or chemical change:

a. A gold ingot is hammered to form gold leaf

b. Gasoline burns in air

c. Garlic is chopped into small pieces

Sample Problem 3.2 Physical and Chemical Changes

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Step 1 State the given and needed quantities

Step 2 Write a temperature equation

Step 3 Substitute in the known values and calculate the new temperature

TF = 38 + 32

= 70 °F Answer to the ones place

In the equation, the values of 1.8 and 32 are exact numbers, which do not affect the number of SFs used in the answer.

Sample Problem 3.3 Converting from Degrees Celsius to Degrees Fahrenheit

The typical temperature in a hospital room is set at 21 °C What is that temperature in degrees Fahrenheit?

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Karen C Timberlake

Study Check 3.3

In the process of making ice cream, rock salt is added to crushed ice to chill the ice cream mixture If the temperature drops to −11 °C, what is it in degrees Fahrenheit?

Answer

12 °F

Continued

Sample Problem 3.3 Converting from Degrees Celsius to Degrees Fahrenheit

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Step 2 Write a temperature equation

Step 3 Substitute in the known values and calculate the new temperature

Sample Problem 3.4 Converting from Degrees Fahrenheit to Degrees Celsius

In a type of cancer treatment called thermotherapy, temperatures as high as 113 °F are used to destroy cancer cells or make them more sensitive to radiation What is that temperature in degrees

Celsius?

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Karen C Timberlake

Study Check 3.4

A child has a temperature of 103.6 °F What is this temperature on a Celsius thermometer?

Answer

39.8 °C

Continued

Sample Problem 3.4 Converting from Degrees Fahrenheit to Degrees Celsius

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Step 2 Write a plan to convert the given unit to the needed unit

Step 3 State the equalities and conversion factors

A defibrillator gives a high-energy-shock output of 360 J What is this quantity of energy in calories?

Sample Problem 3.5 Energy Units

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Karen C Timberlake

Step 4 Set up the problem to calculate the needed quantity

Sample Problem 3.5 Energy Units

Continued

Study Check 3.5

When 1.0 g of glucose is metabolized in the body, it produces 3.8 kcal How many kilojoules are produced?

Answer

16 kJ

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Step 2 Use the energy value for each food type and calculate the kcal rounded off to the tens place Using the energy values for carbohydrate, fat, and protein (see Table 3.7), we can calculate

the energy for each type of food

The Nutrition Facts label for crackers states that 1 serving contains 19 g of carbohydrate, 4 g of fat, and 2 g of protein What is the energy from each food type and the total energy, in kilocalories,

for one serving of crackers? Round off the kilocalories for each food type to the tens place

Sample Problem 3.6 Energy Content for a Food Using Nutrition Facts

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Karen C Timberlake

Step 3 Add the energy for each food type to give the total energy from the food

Total energy = 80 kcal + 40 kcal + 10 kcal = 130 kcal

Sample Problem 3.6 Energy Content for a Food Using Nutrition Facts

Continued

Study Check 3.6

a. Using the nutrition values for one serving of crackers in Sample Problem 3.6, calculate the energy, in kilojoules, for each food type Round off the kilojoules for each food type to the tens place

b. What is the total energy, in kilojoules, for one serving of crackers?

Answer

a. carbohydrate, 320 kJ; fat, 150 kJ; protein, 30 kJ

b. 500 kJ

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Step 1 State the given and needed quantities.

Step 2 Calculate the temperature change (ΔT).

ΔT = 38.5 °C – 33.2 °C = 5.3 °C

During surgery or when a patient has suffered a cardiac arrest or stroke, lowering the body temperature will reduce the amount of oxygen needed by the body Some methods used to lower body

temperature include cooled saline solution, cool water blankets, or cooling caps worn on the head How many kilojoules are lost when the body temperature of a surgery patient with a blood volume of

5500 mL is cooled from 38.5 °C to 33.2 °C? (Assume that the specific heat and density of blood is the same as for water.)

Sample Problem 3.7 Calculating Heat Loss

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Karen C Timberlake

Step 3 Write the heat equation and needed conversion factors

Heat = m × ΔT × SH

Step 4 Substitute in the given values and calculate the heat, making sure units cancel

Study Check 3.7

How many kilocalories are lost when 560 g of water cools from 67 °C to 22 °C?

Answer

25 kcal

Continued

Sample Problem 3.7 Calculating Heat Loss

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Step 2 Write a plan to convert the given quantity to the needed quantity

Step 3 Write the heat conversion factor and any metric factor

Ice bag therapy is used by sports trainers to treat muscle injuries If 260 g of ice are placed in an ice bag, how much heat, in joules, will be absorbed to melt all the ice at 0 °C?

Sample Problem 3.8 Heat of Fusion

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Karen C Timberlake

Step 4 Set up the problem and calculate the needed quantity

Study Check 3.8

In a freezer, 150 g of water at 0 °C is placed in an ice cube tray How much heat, in kilocalories, must be removed to form ice cubes at 0 °C?

Answer

12 kcal

Continued

Sample Problem 3.8 Heat of Fusion

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In a sauna, 122 g of water is converted to steam at 100 °C How many kilojoules of heat are needed?

Sample Problem 3.9 Using Heat of Vaporization

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Karen C Timberlake

Step 4 Set up the problem and calculate the needed quantity

Study Check 3.9

When steam from a pan of boiling water reaches a cool window, it condenses How much heat, in kilojoules, is released when 25.0 g of steam condenses at 100 °C?

Answer

56.5 kJ released

Continued

Sample Problem 3.9 Using Heat of Vaporization

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a. A temperature of 120 °C occurs on the diagonal line above the boiling (condensation) point, which indicates that water is a gas

b. A temperature of 100 °C, shown as a horizontal line, indicates that the water vapor is changing to liquid water, or condensing

c. A temperature of 40 °C occurs on the diagonal line below the boiling point but above the freezing point, which indicates that the water is in the liquid state

Study Check 3.10

Using the cooling curve for water, identify the state or change of state for water as solid, liquid, gas, condensation, or freezing

a. at 0 °C b. at –20 °C

Answer

a. freezing b. solid

Using the cooling curve for water, identify the state or change of state for water as solid, liquid, gas, condensation, or freezing

a at 120 °C b at 100 °C c. at 40 °C

Sample Problem 3.10 Using a Cooling Curve

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Karen C Timberlake

Solution

Total heat = kilojoules needed to melt the ice and heat the water from 0.0 °C (freezing point) to 37.0 °C

Charles has increased his activity by doing more exercise After a session of using small weights, he has a sore arm An ice bag is filled with 125 g of ice at 0.0 °C The heat of fusion for ice is 334

J/g How much heat, in kilojoules, is absorbed to melt the ice, and to raise the temperature of the water to body temperature, 37.0 °C?

Sample Problem 3.11 Combining Heat Calculations

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Step 4 Set up the problem and calculate the needed quantity.

ΔT = 37.0 °C – 0.0 °C = 37.0 °C

Heat needed to change ice (solid) to water (liquid) at 0.0 °C:

Heat needed to warm water (liquid) from 0.0 °C to water (liquid) at 37.0 °C:

Calculate the total heat:

Melting ice at 0.0 °C 41.8 kJ Heating water (0.0 °C to 37.0 °C) 19.4 kJ Total heat needed 61.2 kJ

Continued

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Karen C Timberlake

Study Check 3.11

How many kilojoules are released when 75.0 g of steam at 100 °C condenses, cools to 0 °C, and freezes at 0 °C? (Hint: The solution will require three energy calculations.)

Answer

226 kJ

Continued

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