Chemistry: Midterm Review

Name______Date______Per______Chemistry: Midterm Review

1) Know your safety rules, including things like fire safety and diluting acids. Fire—don’t run to the safety shower, stop drop and roll while your partner gets the fire blanket. Acids—do what you “otter” and pour acid into water. 2) What are qualitative/quantitative measurements? Give examples. Qualitative—measurement using description without numbers (IE yellow ppt forms, liquid emits a brown gas, etc.) Quantitative—measurements involving numerical data (IE water density is 1.0g/ml, boils at 100oC, etc.) 3) In scientific notation, what would the following be:160 000 1.6x105 0.00075 7.5x10-4 2.7x103 + 4.1x104 4.37x104 4) How many significant figures are in:2.0100 5 45000 2 0.0062 2 5) Report in correct sig. figs: 22.1 x 0.015 0.33 33/16.77 2.0 1.256 x 77.76 97.67 6) What is the difference between accuracy and precision? Give examples. Accuracy is closeness of measurement to the actual value; precision is the closeness of a set of measurements to each other; think of throwing darts at a target—the most accurate would be the one closest to the bullseye, the most precise would be the thrower whose group of three were closest to each other, regardless of their position on the dartboard 7) How do you calculate percent error? If a 3.35g rock is found to weigh 2.92g, what percent error did they have? % error = |accepted value – experimental value|x 100 (3.35-2.92)/3.35 x 100 = 12.8% Accepted value 8) Convert 1500m into: km 1.5 mm 1,500,000 cm 150,000 Convert 120L to: kL 0.12 mL 120,000 9) If water, oil, corn syrup and mercury were put into a container, what order would they layer into? Highest density on bottom to lowest on top, so: mercury, corn syrup, water, oil 10) Dimensional Analysis: If a car is going 65m/s, how many km/hr is that? How many inches are in 33.7 miles? 65mx 1km x 60s x 60min = 230 km/hr 33.7mix 5280ft x 12in= 2.14x106 in s 1000m 1min 1hr 1mi 1ft 11) Density: What is the density of a fluid that has a mass of 24g and a volume of 8.83mL? Remember sig. figs. D = m/v D = 24g/8.83mL = 2.7g/mL 12) What is the difference between chemical and physical properties? Chemical/physical change? Give examples. A physical property is one that can be observed without changing the composition of the sample, such as color, hardness, melting point, state, solubility, etc. whereas chemical properties are observed through changing the composition of the substance, such as flammability, oxidizer, corrosive, inert, etc. A physical change is a change in a substance that does not alter its composition, like boiling, tearing in half, melting, etc. A chemical change is a change that by definition alters composition, like burning, rusting, tarnishing, etc. 13) What are the four evidences chemical reactions have occurred? Color change, heat/light produced or absorbed, a solid forming from two liquids (precipitate) a gas forming 14) Give several examples of ways to separate mixtures. Filtration, distillation, evaporation, separation by hand, magnetism, etc. Anything that takes advantage of a difference in physical properties of the substances mixed together. 15) What is the law of conservation of mass? What are the implications for mass of products vs. reactants in a reaction? The law of conservation of mass states that matter cannot be created or destroyed. For a chemical reaction, this means that the total mass of reactants and the total mass of the products should be equal. 16) Writing formulas/naming: Write formulas for compounds, like calcium fluoride CaF2, copper (II) nitrate Cu(NO3)2, cobalt (III) arsenide CoAs. Name compounds, like: Zn(NO3)2 zinc nitrate, CF4 carbon tetrabromide, SnBr4 tin (IV) bromide, etc. 17) What is the smallest part of an element an atom, ionic compound a formula unit, covalent compound a molecule. 18) What is the relationship between pressure and volume? It is an inverse relationship If you double the volume of a gas, what would happen to the pressure in the container—it should half the pressure. 19) What is absolute zero and what happens to the particles at that temperature? Absolute zero is the lowest possible temperature. Because temperature is based on kinetic energy, the lowest possible temperature would be the temperature when all particle motion ceases…so at absolute zero particles stop moving. 20) Gas Law Problems: If you have 75mL of gas at -50oC, what would the new volume be at 70oC? V1= V2 75= V2 V2 = 115.358 = 120mL T1 T2 223 343 If a balloon with 250L of gas at 30oC and 150kPa are changed to 50oC and 200kPa, what is the new volume? P1V1 = P2V2 = 150x250 200xV2 V2 = 199.876 = 200L T1 T2 303 323 What pressure would be needed to keep 1.15mol of gas in a 22.8L container at 40oC? PV = nRT P(22.8L) = (1.15mol)(8.31)(313K) P = 131.19 = 130kPa 21) Be able to use a graph of solubility vs. temperature to determine solubilities (see worksheet online). Look for worksheet on my website in the solubility unit 22) What happens when more solute is added to a saturated solution without changing temperature? Since the solution is already saturated, then any more solute added will just sit on the bottom of the container if temperature is not increased to increase saturation point. 23) Molarity: what is the molarity of a solution made by adding 1.88mol salt to make a 0.85L solution. Molarity = moles/Liter solution Molarity = 1.88mol/0.85L = 2.2M 24) What is a solution? What are the parts? What does miscible mean? A solution is the same thing as a homogeneous mixture. The solute is the part being dissolved and the solvent is the part doing the dissolving (more often than not its water). Miscible liquids are ones that will dissolve into each other, the opposite of which is immiscible, which do not dissolve into each other, like oil and water. 25) What factors affect solubility in gases? Give examples of each. Temperature affects gas solubility, with increasing temperature decreasing solubility, like thermal pollution we discussed in class, where fish die when hot water is added to their environment b/c it decreases dissolved oxygen in the water and they suffocate. Pressure affects gas solubility, with increasing pressure increasing solubility, like making carbonated beverages, where high pressure carbon dioxide is introduced to the top of a carbonated beverage, causing a relatively large amount to dissolve, which is released in the form of bubbles when the high pressure gas is released as the container is opened. 26) Why is water a good solvent? Because it is polar, it will dissolve most things that have a charge associated with it, like ionic and polar compounds. 27) What is the Tyndall effect? What substances exhibit it? The Tyndall effect is exhibited by colloids (like milk, jello, etc.) where a beam of light shined through a sample of the mixture is visible, but not the particles. This is because particles in a colloid are in between homogeneous and heterogeneous mixtures, so the particles are big enough to scatter light (unlike in homogeneous mixtures) but are too small to see (unlike heterogeneous mixtures). 28) Solubility rules: soluble/insoluble: calcium hydroxide S, ammonium nitrate S, lithium sulfide S what precipitates form if the following mix: sodium carbonate and iron (II) nitrate iron (II) carbonate, calcium nitrate and lithium chloride No rxn 29) What subatomic particle is negative? What happens if an atom loses one? Electrons, when an atom loses one the charge becomes positive 30) What were the major contributions of Dalton, Rutherford and Thomson? Dalton came up with the general idea about how atoms behaved, as lined out in Dalton’s atomic theory, Rutherford led the gold foil experiment, where it was determined that the atom is made of mostly empty space with a dense positively charged center (the nucleus) and Thomson used the Crooke’s tube experiments to prove the existence of particles smaller than the atom, and demonstrated one is negative, which he called the electron 31) What are isotopes? How many neutrons are in an isotope of carbon-14? Isotopes are atoms that have the same number of protons but a different number of neutrons. Carbon-14 would have 6 protons (because its carbon) and 14-6 = 8 neutrons. 32) What is the average atomic mass of carbon if 99.2% occurs as carbon-12 and the remaning 0.8% is carbon-14? Avg atomic mass = (0.992 x 12) + (0.008 x 14) = 12.016amu* *note this is not in correct # of sig figs 33) What are the types of natural radioactive decay, what is the charge and penetration of each? Alpha decay—which has the lowest penetration (can’t go through paper) and a +2 charge Beta emission—has medium penetration (goes through paper, but not wood or foil) and a -1 charge Gamma radiation—has highest penetration (needs over 3” lead or 3’ concrete) and no charge 34) Half life: if the half life of a substance is 10 years, how long does it take for a sample to decay from 8g to 1g? Determine how many half lives: 8g  4g  2g  1g so three half lives 3 x 10 = 30 years 35) If radon-222 undergoes alpha decay, what is the particle formed? 222Rn  He4 + 218Po so polonium-218 is formed 86 2 84 36) What are fission and fusion? Fission is the breaking apart of a large nucleus into two similarly sized smaller nuclei. Fusion is the combining of two very small nuclei into one larger one. Both processes are associated with the release of large amounts of energy. 37) What is the most current model of the atom? The quantum mechanical model 38) How many electrons are possibly held by s 2, by p 6, by d 10 or by f 14? 39) Electron configuration: Write electron configuration for elements like: Co S Al Cs Co = 1s22s22p63s23p64s23d7 S = 1s22s22p63s23p4 Al = 1s22s22p63s23p1 Cs = 1s22s22p63s23p64s23d104p65s24d105p66s1 40) What does each part mean in 5s2? 5 is the energy level, s is the sublevel, 2 is the number of electrons in the sublevel 41) What are the Aufbau principle, Pauli’s exclusion principle and Hund’s Rule? Aufbau—German for “building up” means that electrons fill from the lowest energy orbitals upwards Pauli’s Exclusion Principle—an orbital can describe at most the location of two electrons, and they must spin opposite Hund’s Rule—when filled, orbitals of equal energy will each get one electron before one gets two, and they spin parallel 42) Explain how Mendeleev set up the first periodic table. What were groups based on? How is this different than now? He put elements in order of increasing atomic mass, then grouped them according to similar physical/chemical properties. They are still grouped the same, but are now ordered by increasing atomic number. 43) Know the location of halogens group 17 (7A), alkali metals group 1 (1A), alkaline earth metals group 2 (2A), transition metals groups 3-12 (B groups), noble gases group 18 (8A), metalloids elements touching stairstep line (not Al) 44) How many protons, neutrons, electrons are in an element that has an atomic number of 15 and a mass number of 20. Protons = 15, so electrons = 15; neutrons = 20-15 = 5, which couldn’t really happen, but it is what it is. 45) When an atom loses three electrons, what charge would it have? Electrons have a -1 charge each, so losing three would give the ion an overall +3 charge 46) Why are positive ions always smaller than neutral atoms? Why are negative ions bigger? A positive ion has lost enough electrons so that it has one fewer energy level than as a neutral atom. Negative ions have more electrons without any extra protons, so increased repulsion causes a larger radius 47) How do you predict oxidation number the pattern is +1 +2 skip middle +3 +/-4 -3 -2 -1 0, biggest radius increases to the right and down, most electronegative increases up and right, noble gases are zero, and ionization energy increases up and right? Predict between the following elements: nitrogen, oxygen, phosphorus and sulfur. Phosphorus would be biggest, oxygen the most electronegative and highest ionization energy, N and P are -3, S and O are -2 48) Be able to predict shape, polarity and number of sigma/pi bonds for molecules like H2O, CO2, NH3, PCl5

H2O—bent, polar, 2 CO2—linear, NP, 22 NH3—pyramidal, polar, 3 PCl5—tr. bipyramidal, NP, 5 49) Be able to tell if bonds are polar, like between carbon and oxygen, carbon and sulfur, sodium and fluorine. C-O: EN Diff. = 1.0, polar bonds C-S: EN Diff. = 0.0, NP bonds Na-F: EN Diff. = 3.1. ionic bonds 50) Know the bond angles for linear, trigonal planar and tetrahedral molecules. Linear = 180o, trigonal planar = 120o, tetrahedral = 109.5o