Mr. Lerchenfeldt

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An atom is the smallest unit of an element that still has all the properties of that substance.
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Consists of protons, neutrons, and electrons.

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The protons and neutrons are found in the center of the atom, which is a dense, tightly packed structure called the atomic nucleus.
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The electrons move around outside the nucleus.

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Each proton has a positive charge of +1.
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Neutrons have no charge.
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Each electron has a negative charge of -1.
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It can be electrically neutral.

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If the number of electrons is the same as the number of protons, the atom will not have a charge.
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If an atom gains or loses electrons, it becomes a charged particle called an ion.

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All materials are made up of atoms. Atoms are too small to be seen without being greatly magnified.
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When grouped together with other atoms of the same type, they make up elements, such as copper.

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There are over 100 different kinds of atoms.
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A substance made up of only one kind of atom is called an element.
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Helium is made up of only helium atoms.

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Different elements have different physical and chemical properties.
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Iron, carbon, hydrogen, and oxygen are other examples of elements.

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A chart displaying information about the elements.
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Elements are arranged in the table in a specific pattern that helps to predict their properties and to show their similarities and differences.

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The periodic table was developed by Dimitri
Mendeleev in 1869.
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It provides a powerful tool for studying the elements and how they combine.

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There are over 100 elements, so it is necessary to use a systematic method to organize them.
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The periodic table indicates each element's atomic symbol, atomic number, and average atomic mass.

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The placement of an element on the periodic table gives clues about the element's chemical and physical properties, like its melting point, density, hardness, and thermal and electrical conductivities.

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The periodic table is so named because it is organized into "periods."
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A period is defined as an interval required for a
cycle to repeat itself.

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In the periodic table, the periods are the horizontal rows that extend from left to right.
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These periods consist of as few as two elements and as many as thirty-two elements.

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Both the atomic number and the atomic mass of the elements increase moving across the table from left to right and down the table from top to bottom.

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The division of elements into vertical groups by column creates families of elements.
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Elements in the same group all have similar chemical properties.

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Lithium (Li), group 1, can combine with chlorine (Cl), group 17, and form lithium chloride (LiCl).
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Sodium (Na) is also in group 1, it has similar chemical properties to lithium.

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Some individual groups (or families) in the periodic table also have special names.
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Groups 3-12: Transition metals–tend to be hard metallic solids with high heat conductivities.

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All of the elements in group 1 of the periodic table
(except hydrogen) are alkali metals.
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They are soft metallic solids with low melting points and they are the most reactive metals.

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They are hard metallic solids and have higher melting points than alkali metals.
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Though they are also highly reactive, they are less reactive than alkali metals.

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Group 17: Halogens - They have low boiling points and low melting points.
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Group 18: Noble gases – They tend to be stable and do not react or combine with any element.

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The elements in the periodic table can be subdivided into metals, nonmetals, and metalloids.
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The stair step line that begins by boron, B, and moves down and right to polonium, is dividing line.

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This division is shown by the different colors in the periodic table below.

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Metals are the elements to the left of the stairstep.
Metals are typically dense solids with a shiny luster.
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They tend to form positive ions and are capable of conducting electricity.

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Nonmetals are elements to the right of the stairstep plus hydrogen.
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Tend to have low densities, a dull luster, low melting points, and do not conduct electricity (brittle).

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Metalloids are along the stairstep that have some of the properties of both metals and nonmetals.
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The metalloid elements are B, Si, Ge, As, Sb, and Te.
Some of these elements, Si, are semiconductors.

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A compound is made up of molecules, which contain two or more different types of atoms.
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If two or more atoms join together, they form a connection called a bond.

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Particles made up of two or more bonded atoms are called molecules.
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Sometimes, atoms of the same element are bonded together.

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Other times, atoms of different elements are bonded together.
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The molecules that make up carbon dioxide each contain two oxygen atoms and one carbon atom.

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A drawing of the molecules of carbon dioxide gas is shown below.

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When two different kinds of atoms bond together to form molecules, a new substance called a
compound is formed.
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A compound is a kind of pure substance.

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When two elements bond together to make a compound, the physical and chemical properties of the compound are different from those of the original elements.

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Molecules that make up a compound cannot be split apart to form elements unless the molecules go through a chemical reaction.
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Molecules of a kind of compound are the same.

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They have the same number of each atom, and the atoms are bonded together in the same way.
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For example, each molecule of water contains one oxygen atom bonded to two hydrogen atoms (H
2
O).

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In the drawing below, atoms of oxygen are drawn in red. Atoms of hydrogen are drawn in white.
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The number of hydrogen and oxygen atoms in each molecule of water is the same.

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Sometimes, instead of bonding together to form small molecules, atoms can form larger structures called crystals.
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Crystals are solid particles in which many atoms arrange themselves in a regular pattern.

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The drawing below shows how atoms of sodium and chlorine in regular table salt arrange themselves to form a crystal.

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While atoms and molecules cannot be seen with the naked eye or a common microscope, crystals can be large enough to see with a hand lens or even the eyes alone.

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Each substance has its own unique combination of
physical and chemical properties, and substances can be identified based on these properties.

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Characteristics of a substance that can be observed without changing the identity of the substance.
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Properties that the substance already has.
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Color, density, mass, and solubility.

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Some physical properties change depending on the amount of the substance present.
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These properties are called extensive properties.
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Mass and volume are examples of this.

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Other physical properties are not dependent on how much of the substance is present.
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These are called intensive properties.
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Boiling point and density are two examples.

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A cup of water or an entire pot filled with water, the water in both will boil at 100 °C (at sea level).
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The water in both containers will also have the same density of about 1.0 g/mL (at 25 °C).

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Intensive properties are useful when identifying an unknown substance.
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During a physical change, substances are not altered chemically.

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They simply change from one state of matter to another, or they separate or combine without breaking or making bonds.
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Changes of state are physical changes.

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Making and separating mixtures are also physical changes.
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Mixtures can be separated using the differences in physical properties of each substance.

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The following list provides the definitions of some important physical properties.
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Mass is the amount of matter in an object.
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Mass is different from weight.

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Volume is the amount of space occupied by a substance; size.
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Density is how much mass a material has per unit of volume.

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Denser materials have more matter in a given space than less dense materials.
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Density is found by dividing the mass of an object by its volume.

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The boiling point is the temperature at which a liquid changes to a gas (water: 100 °C or 212 °F).
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The melting/freezing point is the temperature at which a liquid changes from a solid to a liquid 0 °C.

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Solubility refers to the ability of a substance to dissolve in a solvent such as water or the amount of a substance that can dissolve in a certain amount of water.

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Conductivity refers to the ability of a substance to transmit energy.
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Usually this refers to its ability to conduct electricity, but it may also refer to its ability to conduct heat.

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Magnetism refers to the ability of a substance to respond to a magnetic field.
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Metals such as iron, nickel, and cobalt are magnetic because they can be attracted by magnetic fields.

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Chemical properties are the characteristic ways in which a substance chemically behaves.
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They describe how substances react under certain conditions and with other substances.

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Chemical properties primarily depend on the types of atoms and bonds that are in a substance.
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During a chemical change, a chemical reaction takes place.

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Atoms are rearranged to form new substances with different properties.
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Chemical properties and changes can be used to identify a substance.

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The following list gives the definitions of some important chemical properties.
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Flammability describes the ability of a substance to ignite or burn.

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Reactivity describes whether a substance reacts with other substances. (Metals react with acids.)
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Combustibility describes the ability of a substance to react rapidly with oxygen and release energy.

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The ability to oxidize (rust) refers to the tendency of some metals to corrode by reacting with oxygen.
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The ability to tarnish refers to the tendency of some metals to react easily with certain gases.

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Acids and bases are important classes of materials with unique and useful properties.
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The pH scale is a mathematical scale that is used to indicate how acidic or basic a solution is.

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Acids are corrosive substances characterized by a strong smell, a sour taste, and a pH of less than 7.
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Acids produce hydronium ions when dissolved in water.

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Examples of acids include lemon juice, hydrochloric acid, vinegar, and sulfuric acid.
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Bases are corrosive substances characterized by a bitter taste, slippery feel, and a pH greater than 7.

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Bases produce hydroxide ions when dissolved in water.
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Examples of bases include antacids, ammonia, soap, baking soda, and drain cleaner.

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A basic solution is also called alkaline.
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Both acids and bases can be dangerous and can burn skin.
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They should only be worked with if an adult or trained individual is present.

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The pH of a solution is a chemical property that is related to the concentration of hydronium ions in a solution.
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The higher the concentration of hydronium ions in a solution, the lower its pH.

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The pH scale has a range of 0 to 14.
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Solutions with a pH less than 7 are acidic.
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Solutions with a pH greater than 7 are basic.
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Solutions with a pH of 7 are neutral.

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Several kinds of indicators have been developed to measure whether a substance is acidic or basic.
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Litmus paper is a special type of paper that changes color when it comes in contact with an acid or base.

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It can be used to determine the relative pH of a substance.
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Red litmus paper will remain red if it contacts an acidic liquid, but it will turn blue if it contacts a basic liquid.

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Blue litmus paper will remain blue if it contacts a basic liquid, but it will turn red if it contacts an acidic liquid.
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Both types of litmus paper will turn purple when contacting a neutral liquid.

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Some other acid/base indicators are listed in the table below:

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When equal amounts of an acid and base react chemically, they neutralize each other.
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The products of a neutralization reaction always include a salt and water.

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Some insect stings, such as bee stings, inject acid into the skin.
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A paste of baking soda (a base) can relieve the pain of a bee sting by neutralizing the acid.

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Salts are formed during neutralization reactions, which occur when acids react with bases.
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Neutralization reactions produce molecules of water in addition to molecules of salt.

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This type of reaction generally takes the form:
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For instance, hydrochloric acid (HCl) reacts with the base sodium hydroxide (NaOH) to produce water
(H
2
O) and the salt sodium chloride (NaCl).

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Salt solutions can have characteristic odors. Or, they can be odorless.
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Solutions containing salts can possess a variety of tastes (e.g., salty, sweet, bitter, sour, savory).

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Sodium benzoate, for example—the sodium salt of benzoic acid—is used as a preservative in food.
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At low concentrations, it is not detectable, but in higher concentrations, it is perceived to be sweet or bitter.

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Finally, many salts have colors that are characteristic of the metal they contain.
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Copper salts, for instance, often produce solutions that are blue or blue green.

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Iron salts can be yellow, orange, or red. Some mercury salts, such as mercury sulfide (HgS), appear reddish.
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Sodium chloride (NaCl) solutions are colorless.