Objectives: The student will be able to: Describe properties in order to describe materials. Classify pure substances as elements or compounds. Distinguish pure substances from mixtures. Classify mixtures.

Inquiry Activity P.37 in book

Mixtures, elements, compounds Scientists like to classify things. One way that scientists classify matter is by its composition. Ultimately, all matter can be classified as mixtures, elements and compounds.

Why isn’t it a good idea to classify matter by its phases? Because one kind of substance can exist in more than one phase – such as H20. And matter changes phases rather easily.

Why isn’t matter classified according to its physical characteristics, such as color? Scientists wouldn’t find it very useful to group gold, sunflowers, and the sun together.

Scientists ask themselves these questions? Is the matter uniform throughout? Can it be separated by physical means? Can it be separated by chemical means?

By asking these questions scientists can classify matter into: Mixtures – two or more substances that are not chemically combined with each other and can be separated by physical means. The substances in a mixture retain their individual properties. Solutions – a special kind of mixture where one substance dissolves in another. Elements – simplest form of pure substance. They cannot be broken into anything else by physical or chemical means. Compounds – pure substances that are the unions of two or more elements. They can be broken into simpler substances by chemical means.

Each piece of your clothing has a label that recommends cleaning methods. A 100%-cotton shirt may need to be ironed after washing. A cotton and polyester blend fabric may come out of the dryer wrinkle free. There is no cleaning process that works for all materials.

Pure Substances Why are elements and compounds classified as pure substances?

Pure Substances A pure substance is matter that always has exactly the same composition. Table salt and table sugar are two examples of pure substances. Substances can be classified into two categories—elements and compounds.

Pure Substances Every sample of a given substance has the same properties because a substance has a fixed, uniform composition.

Elements How do mixtures differ from pure substances? An element is a substance that cannot be broken down into simpler substances. An element has a fixed composition because it contains only one type of atom. No two elements contain the same type of atom.

Elements All elements are made of atoms. Atoms of the same element are alike. Atoms of different elements are different.

Elements In 1813, a system of representing elements with symbols was introduced. Each symbol consists of one or two letters. Two letters are needed for a chemical symbol when the first letter of that element’s name has already been used.

Common Elements Aluminum Al Bromine Br Calcium Ca Carbon C Gold Au Helium He Hydrogen H Nitrogen N

Elements Examples of Elements Some elements are solids at room temperature. Most soft drink cans are made from aluminum. Carbon is the main element in the marks you make with a pencil. The elements oxygen and nitrogen are the main gases in the air you breathe. Two elements are liquids at room temperature–bromine and mercury.

Elements Symbols for Elements Chemists use symbols of one or two letters to represent elements. The first letter is always capitalized. If there is a second letter, it is not capitalized. C represents carbon. Al represents aluminum. Au represents gold. (The Latin name for gold is aurum.)

Elements Symbols for Elements Symbols allow scientists who speak different languages to communicate without confusion. For example, nitrogen is azote in France, stickstoff in Germany, and nitrógeno in Mexico. But all scientists use N as the symbol for the element nitrogen.

Elements Aluminum, carbon, and gold are elements that you can see in common objects, such as cans, pencils, and rings. Mixtures containing iodine are used to prevent and treat infections. Gold Aluminum Carbon Iodine

Compounds How do mixtures differ from pure substances?

Compounds A compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances. A compound always contains two or more elements joined in a fixed proportion.

Compounds The properties of a compound differ from those of the substances from which it is made. Water is composed of the elements hydrogen and oxygen. Oxygen and hydrogen are gases at room temperature, but water is a liquid. Hydrogen can fuel a fire, and oxygen can keep a fire burning, but water does not burn or help other substances to burn.

Compounds Compounds are also pure substances. But compounds are made from more than one element. Water is a compound. Water can be broken down into simpler substances – hydrogen and oxygen.

Compounds Silicon dioxide is a compound found in most light-colored grains of sand and in crystals of quartz. It is a colorless, transparent solid. Yet, silicon dioxide is made from a colorless gas (oxygen) and a gray solid (silicon). In silicon dioxide, there are always two oxygen atoms for each silicon atom. Oxygen Silicon Silicon dioxide

Mixtures How do mixtures differ from pure substances?

Mixtures If you make salsa, a recipe can guide you. You can use exactly the amounts in the recipe, or you can adjust the ingredients to your own taste. Salsa is a mixture. Each batch may be slightly different.

Mixtures The properties of a mixture can vary because the composition of a mixture is not fixed. Mixtures can retain some of the properties of their individual substances. The properties of a mixture are less constant than the properties of a substance.

Mixtures Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture. Heterogeneous Mixtures In a heterogeneous mixture, the parts of the mixture are noticeably different from one another. Homogeneous Mixtures In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another.

Is it uniform throughout? If the answer is no, the matter is a heterogeneous mixture. Considered the “least mixed.” Does not appear to be the same throughout. Particles are large enough to be seen and to be separated from the mixture.

Examples of heterogeneous mixtures Sand and pebbles Oil and water Powdered iron and powdered sulfur

Granite is a heterogeneous mixture.

Is it uniform throughout? If the answer is yes, the matter is homogeneous (looks the same throughout). That leads us to another question.

Can it be separated by physical means? If the answer is yes, the matter is a homogeneous mixture or solution.

Homogeneous Mixtures A mixture that appears to be the same throughout. It is “well mixed.” The particles that make up the mixture are very small and not easily recognizable.

Examples of homogeneous mixtures Milk, toothpaste, and mayonnaise are homogeneous mixtures. They are also colloids.

Mixtures The sand is a heterogeneous mixture of different kinds of grains. The spoon is stainless steel, a homogeneous mixture of iron, chromium, and nickel.

Mixtures Do the Contents of Two Cans of Mixed Nuts Meet FDA Regulations? According to Food and Drug Administration (FDA) regulations, a can labeled mixed nuts must contain at least four types of shelled nuts other than peanuts. The mass of each type of nut must be not less than 2 percent of the total mass and not more than 80 percent of the total mass.

Mixtures Comparing and Contrasting How are the two brands of mixed nuts alike? How are they different? Answer:

Mixtures Comparing and Contrasting How are the two brands of mixed nuts alike? How are they different? Answer: Both brands contain the same types of nuts but the amount of each type differs.

Mixtures 2. Calculating What is the percent by mass of each type of nut in each can? Answer:

Mixtures 2. Calculating What is the percent by mass of each type of nut in each can? Answer: Brand A: 44.2% peanuts, 13.64% almonds, 16.79% Brazil nuts, 13.4% cashews, 5.77% hazelnuts, and 6.21% pecans Brand B: 54.8% peanuts, 8.90% almonds, 5.59% Brazil nuts, 21.06% cashews, 4.82% hazelnuts, and 4.82% pecans

Mixtures 3. Drawing Conclusions Do the contents of each can meet the FDA regulations? Explain. Answer:

Mixtures 3. Drawing Conclusions Do the contents of each can meet the FDA regulations? Explain. Answer: Yes. Both brands contain more than four types of nuts other than peanuts. The masses are within the 2% to 80% range.

Mixtures 4. Inferring On the Brand A label, the nuts are listed in this order: peanuts, Brazil nuts, almonds, cashews, pecans, and hazelnuts. What do you think determines the order? Answer:

Mixtures 4. Inferring On the Brand A label, the nuts are listed in this order: peanuts, Brazil nuts, almonds, cashews, pecans, and hazelnuts. What do you think determines the order? Answer: The ingredients are listed in order by total mass. The ingredient with the largest mass is listed first.

Solutions, Suspensions, and Colloids What is the main difference among solutions, suspensions, and colloids? The size of the particles in a mixture has an effect on the properties of the mixture. Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.

Solutions, Suspensions, and Colloids When substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution. Suspensions A suspension is a heterogeneous mixture that separates into layers over time.

Solutions A solution is a type of homogeneous mixture formed when one substance dissolves in another. It is the best mixed of all mixtures. A solution always has a substance that is dissolved and a substance that does the dissolving. The substance that is dissolved is the solute and the substance that does the dissolving is the solvent.

Ocean water is a solution

The universal solvent: Water

Solutions, Suspensions, and Colloids A colloid contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension. Like solutions, colloids do not separate into layers. You cannot use a filter to separate the parts of a colloid.

Colloids A colloid will not separate upon standing. The particles are constantly colliding, and this allows a colloid to scatter light – thus colloids often seem cloudy.

Water as a solvent Many liquid solutions contain water as the solvent. Ocean water is basically a water solution that contains many salts. Body fluids are also water solutions.

Metals dissolved in metals are called alloys. Types of solutions Solute Solvent Example Gas Air (oxygen in nitrogen) Liquid Soda water (carbon dioxide in water) Solid Ocean water (salt in water) Solid Gold jewelry (copper in gold) Metals dissolved in metals are called alloys.

Air is a solution of oxygen and other gases dissolved in nitrogen

Alloys Stainless steel is a mixture of iron and chromium. Brass is an alloy of copper and zinc.

Solutions, Suspensions, and Colloids These liquids represent three categories of mixtures. Windshield wiper fluid is a solution. Muddy water collected from a swamp is a suspension. Milk is a colloid.

Homogeneus Mixtures (Solutions) Homogeneous mixture: a mixture in which the components are evenly distributed among each other. You cannot see the component parts. Homogeneous means the same throughout. It has a constant composition Examples: Salt dissolved in water, sugar dissolved in water, apple juice, tea, copper (II) sulfate solution in water, alloys....

Solutions Well-mixed (uniform) – single phase homogeneous transparent (if liquid) cannot be separated by filter do not separate on standing

States of Matter in Solution Examples of Solutions gas in gas air ( N2, O2 , Ar, CO2 , other gases) gas in liquid soda pop (CO2 in water) liquid in liquid gasoline (a mixture of hydrocarbon compounds) solid in liquid Salt water gas in solid H2 in platinum or palladium liquid in solid dental amalgams (mercury in silver) solid in solid alloys ( brass, (Cu/Zn), sol-der (Sn/Pb), Steel (Fe/C ))

Q: Can a solution be separated by filtration? Yes No

Heterogeneous Mixtures Heterogeneous Mixture (Suspension or Colloid): the components are not evenly distributed among each other has two or more distinct phases that are usually visible does NOT have uniform properties. Heterogeneous mixtures that look like solutions can be distinguished because they scatter light (Tyndall Effect). Ex: muddy water, oil and water, milk, sulfur and iron, granite, blood...

Suspensions A suspension is a mixture where the particles are dispersed but are big enough to settle out or be filtered out. A mixture that needs to be shaken before use is probably a suspension. Ex. Mud or muddy water, where soil, clay, or silt particles are suspended in water. Paint (needs to be mixed before use) Snow globe (eventually settles) Orange Juice (needs to be shaken before use)

Suspensions like coffee are easily filtered to take out the tiny solid clumps floating in the liquid. Solutions are mixtures that have particles that are so small they pass through most filters.

Non-transparent, uniform, large particles, cloudy (milky) Colloids Colloids Non-transparent, uniform, large particles, cloudy (milky) but stable system

Colloids Tyndall Effect You can see the light beam as it passes through a colloid or suspension. particles scatter light

Mixtures and Solutions

Kahoot

Which of these substances is a compound? Assessment Questions Which of these substances is a compound? copper water oxygen carbon

Which of these substances is a compound? Assessment Questions Which of these substances is a compound? copper water oxygen carbon ANS: B

Assessment Questions Which of these groups of letters could be used as a symbol for an element? HF Cm Car fe

Assessment Questions Which of these groups of letters could be used as a symbol for an element? HF Cm Car fe ANS: B

Which of the following statements does not apply to a compound? Assessment Questions Which of the following statements does not apply to a compound? It is made of two or more elements. It has components that are joined in fixed proportions. It can be separated into components by physical methods. It can be broken down into elements or other compounds.

Which of the following statements does not apply to a compound? Assessment Questions Which of the following statements does not apply to a compound? It is made of two or more elements. It has components that are joined in fixed proportions. It can be separated into components by physical methods. It can be broken down into elements or other compounds. ANS: C

How does a compound differ from a mixture? Assessment Questions How does a compound differ from a mixture? A compound cannot be broken down into simpler substances. Compounds can be separated by physical processes and mixtures cannot. The composition of a mixture cannot vary. A compound is made of two or more elements in fixed proportion.

How does a compound differ from a mixture? Assessment Questions How does a compound differ from a mixture? A compound cannot be broken down into simpler substances. Compounds can be separated by physical processes and mixtures cannot. The composition of a mixture cannot vary. A compound is made of two or more elements in fixed proportion. ANS: D

Which of these materials is a heterogeneous mixture? Assessment Questions Which of these materials is a heterogeneous mixture? air seawater sand steel

Which of these materials is a heterogeneous mixture? Assessment Questions Which of these materials is a heterogeneous mixture? air seawater sand steel ANS: C

Which of the following can be separated with a filter? Assessment Questions Which of the following can be separated with a filter? colloids compounds solutions suspensions

Which of the following can be separated with a filter? Assessment Questions Which of the following can be separated with a filter? colloids compounds solutions suspensions ANS: D