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Chemistry Test 1 Study Guide Wesley Painter Temperature Conversions Fahrenheit to Celsius – C = (F-32)/1.8 Celsius to Kelvin - K = C + 273.15 Scientific Method Hypothesis – A tentative interpretation or explanation of the observations. A good hypothesis is falsifiable – confirmed/rejected by further observation. Scientific Law – A brief statement that summarizes past observations and predicts future ones. Developed by a series of similar observations. Describes how nature behaves, nature does not follow laws. Scientific Theory – A model for nature that explains not only what it does, but why. Formed by one or more well established hypotheses. Experiments – Highly controlled procedures designed to generate observations. An example of Scientific Method The scientist Lavoisier once observed combustion and through these observations hypothesized, meaning he created a tentative explanation of the observations that was falsifiable, that for combustion to occur, oxygen was required. Through further experimentation, or the use of highly controlled procedures to generate observations, he came up with the law of conservation of mass. A law is a brief statement that summarizes past observations and predicts future ones. Through other experiments and the use of this law, Dalton was able to come up with atomic theory. A theory is a model for nature that explains what it does and why. Classification of matter Matter is simple to classify, and below is an easy chart to explain how. Matter Variable composition? Yes Mixture Uniform Throughout? Yes Homozygous No Pure Substance Separable into simpler substances? No Yes Heterozygous | Compound No Element Metric Prefixes Prefixes added to a metric unit that multiply that unit by a powers of 10. Prefix Symbol Multiplier Mega M 10^6 Kilo k 10^3 Deci d 10^-1 Centi c 10^-2 Milli m 10^-3 Micro 10^-6 Nano n 10^-9 Density Derived Unit – Any unit formed by combining other units (ex m/s) Density – Ratio of a substance’s mass to volume o D = M/V o Can be multiplied out so as to find any one of the variables (i.e. D = M/V, VD = M, V = M/D) Be sure to remember in volume that 1 mL = 1 cm^3 Significant Figures There are four easy rules to significant figures: i. Any non-zero number is significant o Ex: 1.02 ii. A zero surrounded by two significant figures is significant. o Ex: 1.02 iii. If a number is followed by a decimal, it is significant. o Ex: 120 has two sig. figs while 120. has three sig. figs. iv. A zero after the decimal is only significant if it has numbers before it. o Ex: 120.0 has four sig. figs. While 0.0120 has three sig. figs. When adding or subtracting significant figures, use the fewest number of decimal places for the significant figures. o Ex: 1.0362 + 0.19 = 1.23 When multiplying or dividing significant figures, use the amount with the fewest digits for significant figures. o Ex: 15.036/4.2 = 3.6 When using conversion factors and other things of that nature, do not factor those numbers into how many significant figures your answer has. Dimensional Analysis Dimensional Analysis – This is basically the simple task of converting units through the use of conversion factors, or amounts you can multiply the original number by to get the new units. o Ex: Convert 67.3 lbs to grams. (1 lb = 453.6 g) 67.3 lbs| 453.6 g| = 3.05 x 10^4 g | 1 lb | o Note that by dividing by one pound, you cancel out the lbs units of the original value, leaving grams as the sole value. Scientists John Dalton – Proposed several things o Atomic Theory, which has several parts: Each element is composed of tiny, indestructible particles called atoms. All atoms of a given sample of an element is the same as an atom from a different sample of the same element, but differs from an atom of a different element. Atoms combine in simple whole number ratios to form molecules of compounds. In a chemical reaction, atoms of one element cannot change into atoms of another element. o Law of Multiple Proportions: When two elements (called A and B) form two different compounds, the masses of element B that combine with 1 g of element A can be expressed as a ratio of small whole numbers. Antoine Lavoisier – Law of Conservation of Mass, which states: o In a chemical reaction, matter is neither created nor destroyed. Joseph Proupst – Law of Definite Proportions, which states: o All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements. J.J. Thomson – Through the use of the Cathode Ray, discovered the electron. o Electrons are low mass, negatively charged particles present within all atoms. Robert Millikan – Through the Oil Drop experiment, deduced that the mass of an electron was about 200 times lighter than a hydrogen atom. Ernest Rutherford – Through his gold foil experiment in which he shot particles through a piece of gold foil and recorded where these particles ended up, he disproved the plum-pudding model of the atom and proposed nuclear theory, which has three parts: o Most of the atom’s mass and all of its positive charge are contained in one small core called the nucleus. o Most of the volume of the atom is empty space, throughout which tiny, negatively charged electrons are dispersed. o There are as many negatively charged electrons outside the nucleus as there are positively charged particles (protons) within the nucleus, so that the atom is neutrally charged. Symbols according to protons, neutrons, and electrons The total mass of an element is represented by the letter A. The atomic number of an element, which represents the number of protons contained in the nucleus, is represented by the letter Z. To find the number of neutrons, subtract the A value from the Z value. The charge of an atom is determined by whether it is an ion or not. If it is not an ion, then the charge is 0. If it is an ion, than the charge is indicated in the top right corner of the symbol for the atom. To determine the number of electrons, subract the charge of the ion from the Z value. Natural Abundances The atomic mass of an element is weighted according to the natural abundance of each isotope. In order to calculate the atomic mass of an element, multiply the fraction of natural occurrence by the matching amu value for each isotope. Then add all of the calculated numbers together to get your atomic mass. Grams, Moles, and Avagadro’s number (Oh my!) Moles are the amount of a substance that you have. Because grams mean different things across different elements, it is a way to standardize the amount of a substance. One mole of an element is equal to its atomic number Avagadro’s number indicates the amount of particles, molecules, etc. in a mole. There are always 6.022 x 10^23 particles in one mole of a substance. If you are given grams of a substance, you can find the amount of moles by multiplying the grams of substance by 1 mol/ atomic mass of the substance. This will give you the amount of moles. If you want to see how many particles are in that certain amount of substance, multiply the number of moles by 6.022 x 10^23/ 1 mol. Naming Ionic and molecular compounds Ionic compounds are those that are made of a metal cation and a nonmetal anion. When naming these compounds there are a few things to keep in mind. o The metal cation always goes first in the name and is showed as is. The nonmetal anion goes second and is given as the root + ide. o If the metal anion is a transition metal, be sure to place the charge of the metal in roman numeral form inside brackets between the metal and the nonmetal. Molecular compounds are made up of two nonmetals and are easily distinguished from ionic compounds because of this. Naming of molecular ions requires you to know the prefixes that indicate the number of a certain thing. o For the first element, indicate the number that exist in the molecule with a prefix. o Do the same for the second molecule, but be sure to use the root and add ide to the end of the molecule root. Naming Acids Acids are compounds that release H+ ion when dissolved in water. Binary acids are composed of only two elements, Hydrogen and a nonmetal. o To name these acids, simply add hydro to the front of the root of the nonmetal, ic to the end of the root name of the nonmetal, and follow that with acid. This only works if the acids are aqueous and not if they are in a gaseous state. If they are in the gaseous state, name them as a molecular compound Oxyacids are acids that contain a hydrogen and an oxyanion (an anion containing a nonmetal and oxygen). These are the polyatomics ions that are listed below. o To name these acids, simply determine whether the oxyanion ends with ate or ite. If it ends with ate, change the ate to an ic and add acid after. It it ends with ite, replace the ite with ous and add acid onto the end. Polyatiomic ions and their names are as follows: Formula Acetate Carbonate Hydrogen Carbonate Hydroxide Nitrite Nitrate Chromate Dichromate Phosphate Name C2H3O2CO3-2 HCO3OHNO2NO3CrO4-2 Cr2O7-2 PO4-3 Hydrogen Phosphate Dihydrogen Phosphate Ammonium Ammonia Hypochlorite Chlorite Chlorate Perchlorate Permanganate HPO4-2 H2PO4NH4+ NH3+ ClOClO2ClO3ClO4MnO4- Sulfite Hydrogen Sulfite Sulfate Hydrogen Sulfate Cyanide Peroxide SO3-2 HSO3SO4-2 HSO4CNO2-2 (note that I and BR form the same pattern as Cl)