Problem 92 - Chemistry The Central Science In Si Units

Question

Judge the following statements as true or false. If you believe a statement to be false, provide a corrected version. (a) Air and water are both elements. (b) All mixtures contain at least one element and one compound. (c) Compounds can be decomposed into two or more other substances; elements cannot. (d) Elements can exist in any of the three states of matter. (e) When yellow stains in a kitchen sink are treated with bleach water, the disappearance of the stains is due to a physical change. (f) A hypothesis is more weakly supported by experimental evidence than a theory. (g) The number 0.0033 has more significant figures than 0.033 . (h) Conversion factors used in converting units always have a numerical value of one. (i) Compounds always contain at least two different elements.

Step-by-Step Solution

Answer

(a) False; air is a mixture, water a compound. (b) False; mixtures vary in components. (c) True. (d) True. (e) False; it's a chemical change. (f) True. (g) False; both have two significant figures. (h) True. (i) True.

Step 1: Analyze Statement (a)

Statement (a) is "Air and water are both elements." Air is a mixture of gases, and water is a compound composed of hydrogen and oxygen elements. Therefore, neither air nor water is an element. The statement is false. The corrected version is: "Air is a mixture, and water is a compound."

Step 2: Analyze Statement (b)

Statement (b) is "All mixtures contain at least one element and one compound." Mixtures can contain only elements (like air), only compounds, or a combination. The statement is false. A corrected version is: "Mixtures can contain different combinations of elements and compounds."

Step 3: Analyze Statement (c)

Statement (c) is "Compounds can be decomposed into two or more other substances; elements cannot." This statement is true. Compounds are made of elements bonded together and can be decomposed, while elements are the simplest substances and cannot be decomposed.

Step 4: Analyze Statement (d)

Statement (d) is "Elements can exist in any of the three states of matter." Elements can exist as solids, liquids, or gases, depending on their nature and conditions. This statement is true.

Step 5: Analyze Statement (e)

Statement (e) is "When yellow stains in a kitchen sink are treated with bleach water, the disappearance of the stains is due to a physical change." The disappearance is due to a chemical change because the bleach reacts with the stain. The statement is false. A corrected version is: "The disappearance of yellow stains is due to a chemical change."

Step 6: Analyze Statement (f)

Statement (f) is "A hypothesis is more weakly supported by experimental evidence than a theory." A hypothesis is a testable statement, while a theory is a well-substantiated explanation. The statement is true.

Step 7: Analyze Statement (g)

Statement (g) is "The number 0.0033 has more significant figures than 0.033." Both numbers have two significant figures. The statement is false. The corrected version is: "The number 0.0033 has the same number of significant figures as 0.033, which is two."

Step 8: Analyze Statement (h)

Statement (h) is "Conversion factors used in converting units always have a numerical value of one." Conversion factors represent the ratio between two equivalent quantities and have a numerical value of one. This statement is true.

Step 9: Analyze Statement (i)

Statement (i) is "Compounds always contain at least two different elements." A compound is defined by having two or more different elements bonded together. This statement is true.

Key Concepts

Elements and Compounds

Elements are pure substances that consist entirely of one type of atom. They are the simplest form of matter and cannot be broken down into simpler substances through chemical reactions. The periodic table showcases all currently known elements by their atomic number and other characteristics.
Compounds, on the other hand, are substances formed when two or more different elements are chemically bonded together. These bonds can be covalent, ionic, or metallic, depending on the nature of the elements involved. The composition of a compound is constant, meaning it always contains the same elements in the same proportions by mass.
For example, water is a compound composed of hydrogen and oxygen (H₂O). Unlike elements, compounds can be decomposed into their constituent elements through chemical reactions. Understanding the distinction between elements and compounds is fundamental to studying chemistry and understanding how complex substances are formed.

Mixtures

Mixtures consist of two or more substances physically combined. These substances can be elements, compounds, or both, and they retain their individual properties within the mixture. Mixtures can be classified into two types: homogeneous and heterogeneous.
A homogeneous mixture, also called a solution, has a uniform composition throughout. An example of this is salt dissolved in water. On the other hand, a heterogeneous mixture has a non-uniform composition where you can see or separate the distinct components, like salad or sandy water.
Unlike compounds, the components of a mixture can be separated by physical means such as filtration, distillation, or evaporation. This makes mixtures versatile and crucial in various applications, from culinary arts to industrial processes.

States of Matter

Matter typically exists in one of three states: solid, liquid, or gas. Each state has distinct characteristics based on the arrangement and behavior of its particles.
Solids have a fixed shape and volume due to tightly packed particles, which only vibrate in place. Liquids have a definite volume but take the shape of their container, as their particles are loosely packed and can slide past each other. Gases have neither a definite shape nor volume, as their particles are widely spaced and move freely.
Some elements can exist in more than one state under different conditions, such as temperature and pressure. Understanding these states is essential for grasping how matter interacts and changes under various circumstances.

Physical vs Chemical Change

Changes in matter usually occur in two forms: physical changes and chemical changes. A physical change alters some properties of a material but not its fundamental identity. Examples include changes in state, like ice melting to water or evaporating to steam.
Chemical changes, on the other hand, involve a transformation in which a substance or substances convert into new products with different properties. This occurs through the making and breaking of chemical bonds. For instance, when baking a cake, the ingredients undergo chemical changes to form a new product altogether.
Recognizing the difference between these two types of changes is critical in predicting how substances will behave during reactions and processes, which is a core part of chemistry.