Differences between pure substances and mixtures Characteristics of

Differences between pure substances and mixtures

Characteristics of Pure Substances �Fixed composition �Distinct properties is h t s e o What d ? mean �Cannot be separated into simpler substances by physical methods �Can only be changed in identity and properties by chemical methods (Unit 4) �Properties do not vary one sample to another sample

Mixtures �Form when elements and/or compounds are combined physically �Properties of a mixture are related to its components �Composition varies from sample to sample �Can be separated by physical methods �Examples of Mixtures: Tea, Perfume, Air, Salad, Beach sand, oil and vinegar salad dressing, etc.

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How can we distinguish between a pure substance and an homogeneus mixture?

How can we distinguish between a pure substance and an homogeneus mixture? If pure water is heated until it boils, we will observe that temperature remains constant at 100 ºC during the change of state. However when water is not pure the temperature will increase progressively.

What are differences and similarities between a pure substance and a homogeneous mixture? Pure substances Homogeneous Mixtures Consists of a single type of substance It is a system that consists of two or more pure substances Cannot be separated into other substances by physical methods. Can be separated into its components by physical methods (distillation, evaporation, chromatography. . ) Has its own fixed specific properties (density, boiling point, …) Mixtures shows the properties of its components and these properties change with the proportion of the components (concentration) Temperature is constant when boiling. Temperature changes when boiling, the boiling point is unclear. Examples: iron, copper, water, Examples: sea water, air, sugar in water sodium chlorine, copper BOTH ARE sulfate, HOMOGENEOUS

Learning more What would you do? Do you drink chemically pure H 2 O? What is the difference between chemically pure versus “Clean” water?

Watching videos �UNICEF � Tap project � How far would you walk to find clean drinking water?

Working in groups �What's the difference between salt and fresh water? �What would you do to differentiate them?

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