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Chapter 1: Problem 8

In each case, decide whether the change is a chemical or physical change. (a) A cup of household bleach changes the color of your favorite T-shirt from purple to pink. (b) Water vapor in your exhaled breath condenses in the air on a cold day. (c) Plants use carbon dioxide from the air to make sugar. (d) Butter melts when placed in the sun.

Short Answer

Expert verified
(a) Chemical, (b) Physical, (c) Chemical, (d) Physical.

Step by step solution

01

Analyze Reaction (a)

The reaction of household bleach with the fabric of your T-shirt changes its color from purple to pink. Bleach is a chemical agent that alters the molecular structure of the dyes causing a change in color, indicating a new substance is formed. Hence, this is a chemical change.
02

Analyze Reaction (b)

When water vapor condenses in the air, it changes from a gas to a liquid. This process involves a change in state, but the substance remains water (H鈧侽). Therefore, this is a physical change.
03

Analyze Reaction (c)

In photosynthesis, plants convert carbon dioxide and water into glucose (sugar) and oxygen using sunlight. This process involves the formation of new chemical substances, making it a chemical change.
04

Analyze Reaction (d)

Butter melting in the sun changes from a solid to a liquid but remains butter. Since the substance itself does not change chemically, this is a physical change.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Chemical Reactions
Chemical reactions occur when the molecular structure of a substance is changed to form a new substance. These reactions often involve breaking existing chemical bonds and forming new ones. Common indicators of a chemical reaction include a change in color, temperature, or the production of gas or a precipitate. For example, when household bleach is applied to fabric, it chemically alters the dye molecules, thus changing the color of the fabric, as seen in Exercise (a).
  • New substances are created.
  • Indicators include color change, temperature change, and gas production.
  • An example includes using bleach on a T-shirt.
Physical Transformations
Physical transformations involve changes in the state or appearance of a substance, without altering its molecular structure. This means the substance remains the same chemically, but its form may change. Common physical changes include melting, boiling, freezing, and condensing. In Exercise (b), when water vapor condenses, it changes from a gas to a liquid, yet it remains H鈧侽.
  • No new substances are formed.
  • States of matter may change, such as solid to liquid.
  • Example: condensation of water in breath.
Photosynthesis
Photosynthesis is a process that occurs in plants, algae, and some bacteria. During photosynthesis, sunlight is used to convert carbon dioxide and water into glucose (a sugar) and oxygen. In Exercise (c), the transformation of carbon dioxide into sugar is a chemical change because new substances (glucose and oxygen) are created. This process is vital because it produces oxygen for us to breathe and creates food for the plant itself.
  • Occurs in plants and some bacteria.
  • Involves conversion of carbon dioxide and water into glucose and oxygen.
  • Essential for providing energy and oxygen.
Condensation
Condensation is the process by which water vapor in the air is converted into liquid water. This is a type of physical transformation because the molecular structure of water (H鈧侽) remains unchanged. As seen in Exercise (b), when you exhale on a cold day, the water vapor in your breath condenses, forming tiny droplets. This change in state is key to many natural phenomena, such as the formation of dew, clouds, and even rain.
  • Involves change from gas to liquid.
  • Molecular structure remains unchanged.
  • Examples include formation of dew and breath on cold days.
Molecular Structure Changes
Changes in molecular structure involve breaking and forming chemical bonds. In chemical reactions, such as those involving bleach reacting with fabric dyes, the original molecules are transformed completely. The molecular structure of the reactants changes to form new products. This concept is crucial in understanding why chemical reactions result in substances with new properties and compositions.
  • Involves breaking and forming chemical bonds.
  • Results in new molecules with different properties.
  • Example: fabric dye alteration by bleach.

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Most popular questions from this chapter

The fluoridation of city water supplies has been practiced in the United States for several decades. It is done by continuously adding sodium fluoride to water as it comes from a reservoir. Assume you live in a medium-sized city of 150,000 people and that \(660 \mathrm{L}(170 \mathrm{gal})\) of water is consumed per person per day. What mass of sodium fluoride (in kilograms) must be added to the water supply each year (365 days) to have the required fluoride concentration of 1 ppm (part per million)-that is, 1 kilogram of fluoride per 1 million kilograms of water? (Sodium fluoride is \(45.0 \%\) fluoride, and water has a density of \(1.00 \mathrm{g} / \mathrm{cm}^{3} .\) )

You have a white crystalline solid, known to be one of the potassium compounds listed below. To determine which, you measure the solid's density. You measure out \(18.82 \mathrm{g}\) and transfer it to a graduated cylinder containing kerosene (in which salts will not dissolve). The level of liquid kerosene rises from \(8.5 \mathrm{mL}\) to \(15.3 \mathrm{mL}\). Calculate the density of the solid, and identify the compound from the following list. (a) \(\mathrm{KF}, d=2.48 \mathrm{g} / \mathrm{cm}^{3} \quad\) (c) \(\mathrm{KBr}, d=2.75 \mathrm{g} / \mathrm{cm}^{3}\) (b) \(\mathrm{KCl}, d=1.98 \mathrm{g} / \mathrm{cm}^{3} \quad\) (d) \(\mathrm{KI}, d=3.13 \mathrm{g} / \mathrm{cm}^{3}\)

Diamond has a density of \(3.513 \mathrm{g} / \mathrm{cm}^{3} .\) The mass of diamonds is often measured in "carats," where 1 carat equals \(0.200 \mathrm{g} .\) What is the volume (in cubic centimeters) of a 1.50 -carat diamond?

Suppose you have a cylindrical glass tube with a thin capillary opening, and you wish to determine the diameter of the capillary. You can do this experimentally by weighing a piece of the tubing before and after filling a portion of the capillary with mercury. Using the following information, calculate the diameter of the capillary. Mass of tube before adding mercury \(=3.263 \mathrm{g}\) Mass of tube after adding mercury \(=3.416 \mathrm{g}\) Length of capillary filled with mercury \(=16.75 \mathrm{mm}\) Density of mercury \(=13.546 \mathrm{g} / \mathrm{cm}^{3}\) Volume of cylindrical capillary filled with mercury \(=(\pi)(\text { radius })^{2}(\text { length })\)

What experiment can you use to: (a) Separate salt from water? (b) Separate iron filings from small pieces of lead? (c) Separate elemental sulfur from sugar?
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