PHC Chapter 15 only Quiz Show

Size: px

Start display at page:

Download "PHC Chapter 15 only Quiz Show"

Verity Cameron Short
6 years ago
Views:

1 version Q, 01/19/2016 PHC Chapter 15 only Quiz Show Multiple choice 1. Why is the covalent bond between an oxygen atom and a hydrogen atom polar? a. Oxygen has a higher average atomic mass than hydrogen. c. Oxygen has a higher electronegativity than hydrogen. b. Oxygen has a higher density than hydrogen. d. Oxygen has a higher atomic number than hydrogen. 2. Which of the following is a consequence of the high strength of the intermolecular forces between water molecules? a. Water has a lower boiling point than hydrogen sulfide. c. Water has a relatively low vapor pressure. b. Water mixes with nonpolar hydrocrabons more easily than gasoline does. d. Water has a very low surface tension, but it can be increased by adding a surfactant. 3. What kinds of bonds must be broken in order for water to vaporize? a. covalent bonds c. ionic bonds b. metallic bonds d. hydrogen bonds 4. dissolves in to create. a. an element, a compound, an isotope c. a solute, a solution, a solvent b. a compound, an isotope, an element d. a solute, a solvent, a solution 5. Why is water known as the universal solvent? a. Water reacts explosively with so c. Water dissolves so many solutes. many chemicals. b. Water is very difficult to boil. d. Water forms heterogeneous mixtures with hydrocarbons. 6. Wasitra pours some blue crystals into a pitcher of water. The crystals dissolve, turning the water blue. By dissolving in water, the crystals became a. a product. c. a solute. b. a hydrocarbon. d. an acid. 7. Which of the following helps salt dissolve in water? a. formation of a crystal lattice c. attractive intermolecular forces between molecules of the same compound b. random molecular motion d. molecules forming covalent cross-links page 1

2 version Q, 01/19/ Which of the following occurs as NaCl dissolves in water? a. More and more sodium and chloride ions join crystal lattices until crystallization is complete. b. Sodium ions develop a 2- electrical charge. c. Sodium ions become surrounded by water molecules. d. Chlorine ions transfer electrons to sodium ions. 9. Which of the following would help sugar dissolve in a flask full of water? a. heating the water c. cooling the water b. evaporating some of the water from the flask first d. melting the sugar into a single glob and allowing it to solidify and cool down to room temperature before attempting to dissolve it 10. Which of the following does NOT break up into separately-wandering ions when it dissolves in water? a. salts c. bases b. oils d. acids 11. Pure water is not a. a substance. c. a compound. b. an electrolyte. d. a liquid at room temperature. 12. Anything that breaks up into positive and negative ions when melted or dissolved in water is a. nonpolar. c. an electrolyte. b. a noble gas. d. a nonmetallic element. page 2

3 PHC Chapter 15 only Quiz Show Answer Section MULTIPLE CHOICE 1. ANS: C All four facts comparing oxygen to hydrogen are true, but the one that explains the polarity of the bond between oxygen and hydrogen is that oxygen has a higher electronegativity than hydrogen. Electronegativity is the tendency of the atoms of an element to draw electrons toward themselves when they bond with atoms of another element. In other words, electronegativity is a rating that says how much of an electron hog an element is. Oxygen has an electronegativity of 3.5, but hydrogen has an electronegativity of only 2.1. They re both nonmetals, so when they bond with each other, they share electron pairs covalently. However, the sharing is not equal. Oxygen gets far more than a 50% of the shared electron pair and hydrogen gets far less than 50%. That results in the oxygen atom developing a partial negative charge and hydrogen a partial positive charge. It s not quite as unequal as when a nonmetal completely steals an electron from a metal to form an ionic bond, but it s halfway there. PTS: 1 OBJ: STA: 2g 2. ANS: C Because of the large difference in electronegativity between oxygen (3.5) and hydrogen (2.1) the bond between an oxygen atom and a hydrogen atom is quite polar, meaning that the oxygen atom has a significant negative charge and the hydrogen atom is quite positive. The positive hydrogen atoms on one water molecule are strongly attracted to the negative oxygen atoms on nearby water molecules. This intermolecular attraction is the most famous example of a hydrogen bond. Because water molecules have strong attractions for each other, they don t fly away from each other easily, so water has a relatively low vapor pressure, especially considering how small its molecules are. Most other materials with molecular weights as low as water are gases at room temperature. The other three answer choices are false statements. * Water has a very high surface tension, not a low one. Furthermore, surface tension is decreased by adding a surfactant. * Water has a higher boiling point than hydrogen sulfide, precisely because of the high strength of the intermolecular attractions between water molecules. (If molecules are strongly attracted to each other, it s more difficult to boil the material.) * Water does NOT mix with nonpolar materials easily. Water is a polar material. It mixes with other polars and with ionics nicely, but not with nonpolars. Gasoline is much better at mixing with oily chemicals than water is. PTS: 1 OBJ: STA: 2h page 1

4 3. ANS: D When a positive atom on one molecule is attracted to a negative atom on a totally different molecule, the attractive intermolecular force between these two atoms is called a hydrogen bond. The classic case, but not the only example, is when a negative oxygen atom on one water molecule is attracted to a positive hydrogen atom on a different water molecule. Hydrogen bonding makes water molecules stick to each other pretty hard, hard enough, for instance, to make water much harder to vaporize than methane or ammonia, whose molecular masses are comparable to that of water. Water (H 2 O) is a liquid because of the + s and - s on a water molecule. Ammonia (NH 3 ) and methane (CH 4 ) are gases because their + s and - s are not as powerful as those on water. The atoms get their charges because they are covalently bonded to atoms with very different electronegativities. For instance, oxygen has an electronegativity of 3.5, so if it s bonded to a hydrogen atom, whose electronegativity is only 2.1, they will share electrons with each other, but not very equally. Oxygen will end up with >50% of the electron pair, so oxygen will become negative. Hydrogen, having <50% of the negative electrons, will become positive because it has lost part of its ownership of one of its negative particles. Nitrogen has an electronegativity of only 3.0, so while it can tug electrons away from hydrogens to which it is bonded, it can t tug them as hard as oxygen (3.5) can, so nitrogen doesn t become as negative as oxygen does, and the hydrogens that nitrogen bond to don t become as positive as the hydrogens that are bonded to oxygen. The + s and - s in H 2 O (water, a liquid) are stronger than the + s and _ s in NH 3 (ammonia, a gas). PTS: 1 OBJ: STA: 2d 4. ANS: D My favorite example is Kool-Aid. Kool-Aid is a solution made by dissolving sugar, the solute, in water, the solvent. PTS: 1 OBJ: STA: 6a 5. ANS: C Water dissolves anything polar or ionic, pretty much, with certain exceptions. It dissolves acids, bases, salts, sugars, alcohols, soaps, golly, so many things. Water doesn t dissolve everything, though. It s not truly universal, despite its nickname. It doesn t dissolve nonpolar things like grease, fat, wax, and oil, though. It s a good thing it doesn t dissolve everything, or it would dissolve the whole world and there would be no place to stand. PTS: 1 OBJ: STA: 6a 6. ANS: C The blue crystals are the solute. The water is the solvent. The water with the crystals dissolved in it is a solution. PTS: 1 OBJ: STA: 6a page 2

5 7. ANS: B Random molecular motion helps break up a solid crystal. If you speed up that random molecular motion by heating up the solvent, it will disolve it even better, with few exceptions. Contrary to this, the solubility of gases in water actually decreases with increasing temperature. To keep a gas dissolved in a liquid, you need to keep it cold. A liquid has less entropy (disorder) than a gas, so if you give it entropy in the form of heat, it s harder for it to stay in the more orderly state. PTS: 1 OBJ: STA: 6b 8. ANS: C When an ion becomes surrounded by water molecules, which then wander away with the ion, kidnapping the ion from the crystal, this is called hydration. Regarding the wrong answers: Sodium ions do not become negative. They become positive. Chlorine does not give electrons to sodium. It steals electrons from sodium. Crystallization is the very opposite of dissolving. PTS: 1 OBJ: STA: 6b 9. ANS: A Solids dissolve easier in hot water than in cold water. The dissolved, liquid state is more disorderly than the solid state. Thermal energy is a very disorderly form of energy, since it increases the random motion of molecules. Thermal energy and the colisions and mixing it causes helps crystals dissolve. Regarding the wrong answers: Melting the sugar into one glob would decrease its surface area, making it harder to dissolve it. Evaporating water from the flask would decrease the amount of solvent. Solute needs solvent to dissolve, so less solvent means less dissolving. Cooling the water would make it harder for the sugar to dissolve. On the other hand, if sugar were a gas instead of a solid, cooling would help. Cold water holds more dissolved oxygen than warm water, which may help explain the rich marine life in arctic and antarctic waters. PTS: 1 OBJ: STA: 6c 10. ANS: B Acids, bases, and salts are all, generally, electrolytes. They are all known for breaking up into positive and negative ions when they dissolve in water, though some do a better job than others. This is why aqueous solutions of acids, bases, and salts are all good conductors of electricity. Oil, on the other hand, does not break up into ions in water. In fact, oil molecules don t even separate from one another in water. Oil not only does not dissociate into ions in water; it doesn t even dissolve in water. Oil isn t even water-soluble. Oil and water don t mix. PTS: 1 OBJ: STA: 5a page 3

6 11. ANS: B Water does not break up into ions very easily. Pure water, therefore, does not conduct electricity very well at all. It is not an electrolyte. The water that comes out of a faucet, however, typically has lots of mineral ions dissolved in it for various reasons, so typical tap water is not pure. Regular tap water does conduct electricity, so it s deadly dangerous to use a hair dryer in the bathtub. Distilled water, however, does not conduct electricity because it is nearly pure. SEMI-APOLOGY: The book doesn t mention this on pp , but Mr. Barnes always tests the conductivity of distilled water during the conductivity demo he does during chapter 15. Distilled water never makes the light bulbs light up on the conductivity apparatus. Water most definitely is a compound. It is made of two elements bonded together, hydrogen and oxygen. Water most definitely is a liquid at room temperature. Pure water is a substance. Its chemical formula is H 2 O. If anything is dissolved in it, it becomes a solution, but when it s pure, it s a substance. PTS: 1 OBJ: STA: 5a 12. ANS: C Because electrolytes break up into positive and negative ions when dissolved in water and/or when melted, they conduct electricity when they do so. Nonpolar materials typically do not break up into ions. If there s a polar bond between two elements, why would either one of them become the positive and the other become the negative? You need at least a polar bond or even an ionic bond to have a definite positive and a definite negative. A nonmetallic element has no reason to break up into ions. A nonmetallic element, even if diatomic, will not break up into ions. Why would it? The two atoms in a molecule of a diatomic element share electrons with perfect equality. Who s going to be the positive? Who s going to be the negative? The two atoms in a diatomic molecule of a nonmetal element are identical twins. Noble gas atoms have full outer electron shells, so noble gas atoms almost never form bonds, including covalent bonds. Therefore, noble gas atoms never form molecules, so how can a noble gas particle break up when it s only made of single, unbonded atoms? You can t break up something that never bonded together in the first place. PTS: 1 OBJ: STA: 5a page 4

Valence Electrons. 1. The electrons responsible for the chemical properties of atoms, and are those in the outer energy level, the valence level.

Valence Electrons. 1. The electrons responsible for the chemical properties of atoms, and are those in the outer energy level, the valence level. Valence Electrons 1. The electrons responsible for the chemical properties of atoms, and are those in the outer energy level, the valence level. 2. Electrons that make bonds are called valence electrons.