Comparisons and contrasts Element and compound Comparison: Both are pure substances Contrast: Elements can only be composed of one type atom, Compounds are composed 2 or more types atoms (elements)
Atom and Molecule Comparison: The smallest unit that still retains material’s properties Contrast: Atom is the smallest unit of an element, Molecule is the smallest unit of a compound. Molecules can be composed of different types of atoms
What does it mean to be a pure substance? “100% pure Honey” “100% pure salt or sugar”
Pure substance Substance composed of either a single type of element or compound chemically combined If a Compound, a pure substance has a fixed composition or proportions of elements every molecule of water has 2 hydrogen and one oxygen atom All compounds can be written with a chemical formula
Pure Substance An amount of matter, either single element or one compound that exhibits distinct chemical and physical properties Table Salt (if just made with NaCl) is a pure substance Grape Juice is not (Water, Sugars, Vitamins)
Mixture A combination of 2 or more pure substance combined physically Classified by how thoroughly they are mixed Properties of mixture similar to properties of components
Mixtures If you can separate the substances, it’s a mixture If it has ingredients, it’s a mixture
Types of Mixtures Heterogeneous Homogeneous Miscible Immiscible Alloy
Heterogeneous mixture Mixtures with ingredients that do not mix well or stay mixed long Examples: Chocolate syrup and milk
Homogeneous Mixture Mixtures that mix very well Solutions where substances dissolve well into each other Can not visually see any separation of the ingredients Examples: Gasoline, Soda
Pure substance and mixtures Comparison: both are composed of elements Contrast: Pure substance is composed of an element or compound whose composition is fixed. Mixture is composed of a combination of pure substances whose composition can vary
WHAT IS THE DIFFERENCE BETWEEN HETEROGENEOUS AND HOMOGENEOUS MIXTURES?
Heterogeneous and homogeneous mixtures Comparisons: both mixtures Contrast: Heterogeneous materials do not mix well or evenly. They are easily separated. Homogeneous mixtures do mix well and evenly, not easily separated
Difference… Heterogeneous mixtures: are mixtures of 2 or more substances that are not completely soluble (bits of each are seen in mixture) Homogeneous mixtures: are mixtures of 2 or more substances that are completely soluble (blend completely, can not tell components)
Miscible mixture Extremely homogeneous Dissolves completely Example: Air
Miscibilitity How well substances mix together The greater the ability to mix (solubility), the more miscible it is. Oil and water are immiscible (insoluble) Carbon dioxide and water (very soluble)
Immiscible mixture Extremely heterogeneous Don’t mix well at all Examples water and granite
Alloy An alloy is a solid homogenous mixture of two or more metals. The there is not chemical reaction occurring, and the original materials can be recreated by melting. There are thousands of different alloys, and people use them for many different purposes.
Different common alloys AlloyCompositionPropertiesRepresentative Uses Brass,copper, zincCorrosion resistance Instruments castings Bronzecopper, tinGood for castingCastings Pewtertin, copper, lead, antimony Easy to work withUtensils Soldertin, leadLow melting pointMelted to join metal surfaces Stainless steeliron, chromium, nickel Hard, strong, rust resistance Machines, utensils
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