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34 Cards in this Set
- Front
- Back
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electrolysis
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The use of electricity to break a molecule down into smaller units
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experimental error
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Experimental difficulties that can cause the results to be incorrect
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peer review
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The process through which scientists review the work of other scientists in an attempt to spot experimental error
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In the water electrolysis experiment, why did one test tube have about twice as much gas as the other did?
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Because when a water molecule is split, 2 hydrogen and 1 oxygen atom are made
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chemical formula
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A shorthand way of showing the number and type of atoms that make up a molecule
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What is a subscript?
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The number that comes after some atoms in a chemical formula. It indicates how many atoms of the element preceding it are present in each molecule. If there is no subscript after a chemical symbol in a chemical formula, there is one of that type of atom in each molecule.
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chemical bond
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the force that links atoms within a molecule. It occurs through sharing of an electron.
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polar molecule
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A molecule that has slight positive and negative charges due to an imbalance in the way electrons are shared
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nonpolar molecule
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A molecule that shares its electrons evenly such that no one part of the molecule is more negatively or positively charged than any other part.
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Why did the water stream bend slightly toward the charged comb?
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The negative charge on the comb attracted the hydrogen (slightly positive) end of the water molecules, causing all of the water molecules to line up and be pulled toward the comb.
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Why didn't the vegetable oil bend toward the comb?
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Vegetable oil is nonpolar, meaning that no one part of each molecule is more negative or positive than any other part. Thus, even though the comb was still negatively charged, there were no positive portions of the vegetable oil to be attracted to the negative comb.
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solution
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A liquid containing a dissolved substance.
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solvent
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A liquid substance capable of dissolving other substances
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solute
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A substance that is dissolved in a solvent.
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In soda pop, what is the solvent and what are some of the solutes?
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Water is the solvent, and syrup and carbon dioxide are some of the solutes.
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ionic compounds
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Substances made by one atom in a molecule stealing an electron from another atom in the molecule. This makes one part of the compound positive and one part negative. They are held together by the attractive forces of the opposite charges.
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Why does salt (NaCl) dissolve in water?
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The slightly negative oxygen end of a water molecule is attracted to the Na+, and working with several other water molecules, eventually separates a Na+ from the piece of salt, surrounding it with water molecules which have their negative O end facing the Na+. In a similar fashion, the slightly positive hydrogen ends of several water molecules work together to pull a Cl- from the salt, surrounding it with several water molecules which have their positive hydrogen ends facing the Cl-.
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Why don't nonpolar substances dissolve in polar substances?
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The polar substance is more attracted to itself (with its positive and negative ends) than to the nonpolar substance, which has no attractive charge to its molecules. Thus, the polar substance sticks to itself, preventing the nonpolar substance from mixing in with it.
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Explain what "like dissolves like" means
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Polar liquids dissolve polar substances and nonpolar liquids dissolve nonpolar substances
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Explain hydrogen bonding
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The negative oxygen end of a water molecule is attractive to the positive hydrogen end of another water molecule, whose own negative oxygen end attracts yet another water molecule's positive hydrogen end. This process brings the water molecules into close proximity to each other. These hydrogen bonds are quite weak, but are an important force in determining the behavior of water. Most chemically similar molecules are gases at room temperature, with their molecules far apart from each other, but water is a liquid because its molecules are held closely together through hydrogen bonds.
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What is the difference between a chemical bond and a hydrogen bond?
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A chemical bond is a bond holding atoms in a molecule. A hydrogen bond is a bond holding different molecules together in a substance. A chemical bond is much stronger than a hydrogen bond.
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How is hydrogen bonding responsible for the fact that ice floats in water, when most solids are denser than their liquid counterparts and would sink?
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When water is a solid, its molecules are locked into a rigid geometric formation that requires the molecules be a certain distance from each other. As a liquid, water molecules are actually pulled closer together by hydrogen bonding, making water denser than ice.
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Why doesn't hydrogen bonding keep pulling the molecules closer even as a solid?
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As water approaches 4 degrees Celcius, hydrogen bonding has to adjust to keep the negative oxygen molecules from different molecules a certain distance apart from each other. This results in a crystal lattice formation we know as ice, which is 9% less dense than water.
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Why is it important to life on earth that ice floats in water?
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If ice sunk, our lakes would completely freeze in the winter, killing all life in them and vastly changing the ecosystem we live in. Because ice floats, once a decently thick layer of ice forms on top of a lake, the water under it is insulated from the cold temperatures above, and life is able to continue through winter at the lower levels of the lake.
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cohesion
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The phenomenon that occurs when individual molecules are so strongly attracted to each other that they tend to stay together, even when exposed to tension.
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surface tension
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Cohesion that occurs at the surface of a liquid. Because of cohesion, the surface of a liquid can resist tension.
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Why did the paper clip float on the surface of the water?
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Surface tension which results from hydrogen bonding holding water molecules close together. The paper clip was not of sufficient mass to force the water molecules apart from each other.
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Why did the paper clip sink once dish soap was added?
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Dish soap is composed of long molecules which have one end that is strongly attracted to water. This forces the water molecules apart from each other, disrupting the hydrogen bonds, and therefore decreasing the surface tension, allowing the mass of the paper clip to push through the water molecules.
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How is cohesion important for plants?
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Water needs to travel up the xylem in a plant's stem, but there is no pump to force it up. Water actually travels up because of its cohesion to itself. This allows plants to grow to a much greater height than would be possible if water did not exhibit cohesion.
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Hard water
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Water that has certain dissolved ions in it - predominately calcium and magnesium ions
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What causes hard water?
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The source of the water. If the rock at the source of the water has a lot of limestone, the water dissolves some of the limestone, releasing calcium ions into the water.
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Why is hard water a problem?
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3 things: It affects the taste of the water. The calcium reacts with soap to make scum, which increases the amount of soap that you need to clean things. When the water containing the calcium changes temperature, the calcium comes out of solution and makes a tough scale in sinks, tubs, and toilets - "hard water stains."
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How does a water softener work?
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It uses a chemical process called ion exchange to remove the calcium and magnesium ions from the water, replacing them with sodium ions. Sodium ions don't taste as bad, they don't react with soap, and they don't build up scale. The sodium is supplied in the form of softener salt, which is sold in large bags and must be periodically added to the water softening equipment.
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Can water softening pose a health risk?
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It can be a minor health risk because some people with heart disease are sensitive to sodium in their diets. The amount of sodium in softened water is much less than in the food that people typically eat, but still these individuals should either not soften their water or use a different type of softening salt that utilizes potassium instead of sodium.
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