Ch.1 - Introduction: Matter, Energy, and Measurement

Problem 20a

Chapter 1, Problem 20a

(a) Read the following description of the element zinc and indicate which are physical properties and which are chemical properties. Zinc 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.

Verified step by step guidance

Identify the properties described in the problem: melting point, reaction with sulfuric acid, hardness, density, and reaction with oxygen.

Classify the melting point of zinc (420 °C) as a physical property because it describes a change in state without altering the chemical identity.

Classify the reaction of zinc with dilute sulfuric acid, where hydrogen is given off and the metal dissolves, as a chemical property because it involves a chemical reaction and formation of new substances.

Classify the hardness of zinc on the Mohs scale (2.5) and its density (7.13 g/cm^3 at 25 °C) as physical properties because they describe the physical characteristics of the element without changing its chemical structure.

Classify the reaction of zinc with oxygen gas at elevated temperatures to form zinc oxide (ZnO) as a chemical property because it involves a chemical change and the formation of a new compound.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Physical Properties

Physical properties are characteristics of a substance that can be observed or measured without changing its chemical identity. Examples include melting point, density, and hardness. In the case of zinc, its melting point of 420 °C, hardness of 2.5 on the Mohs scale, and density of 7.13 g/cm³ at 25 °C are all physical properties, as they describe the state and behavior of zinc without altering its chemical structure.

Chemical Properties

Chemical properties describe how a substance interacts with other substances and the changes it undergoes during chemical reactions. These properties are observed when a substance is transformed into a different substance. For zinc, the reaction with dilute sulfuric acid, which produces hydrogen gas and dissolves the metal, as well as its slow reaction with oxygen to form zinc oxide (ZnO), are examples of chemical properties.

Reactivity of Metals

The reactivity of metals refers to their tendency to undergo chemical reactions, particularly with acids and oxygen. Metals like zinc can react with acids to release hydrogen gas and form metal salts, and they can also oxidize when exposed to oxygen. Understanding zinc's reactivity helps in identifying its chemical properties, such as its behavior in reactions with sulfuric acid and oxygen, which are crucial for predicting its behavior in various chemical contexts.

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