Chapter 1 - Introduction: Matter and Measurement - Exercises - Page 34: 1.13b

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This question deals with classifying substances as pure substances, a heterogeneous mixture, or a homogeneous mixture. The specific substance is seawater. Seawater is a homogeneous mixture. Its main components are water ($H_{2}$O) and salt (NaCl). These parts are not chemically combined, but you can not see them separately with the naked eye. This makes it a homogeneous mixture.