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CHEM 1040 Chapter Notes - Chapter 4: Molar Concentration

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16 Dec 2015

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University of Guelph

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The majority of chemical reactions take place in solution because reactions between two solids often proceeds very slowly or not at all. When you run a reaction in a liquid it is convenient by measuring the amount out in volumes. When a substance is dissolved in a liquid, we call this substance the solute and the liquid the solvent. Concentration refers to the quantity of solute in a standard quantity of solution. A solution is dilute when the solute concentration is low and concentrated when the solute concentration is high. Usually these terms are used comparatively and are not specific. For commercially available solutions however, the term concentration refers to the maximum concentration available. Molar concentration or molarity (m): the moles of sulate dissolved in one liter (cubic decimeter) of solution. The advantage of molarity as a concentration unit is that the amount of solute is related to the volume of solution.

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Related Questions

Please help me solve for the molar mass of sample 1 and 2 and the molecular formula

Experiment 1084-03: Determination of M.M. by Freezing Point Depres sion Measure the freezing-point depressions solute whose empirical formula is known Pool the class hat occur with solutions containing mass of the solute and its Background Information However, as soon as the solution begins to freeze, Adding a solute to a pure, non-volatile lquid ature will remain constant untl all the (solvent) lowers the vapor pressure of the solvent raises its boiling point, and lowers (depresses) its freezing point. The extent to which these are aftected depends on the relative number of solute particlos in the solution. Properties of solutions that depend only on the number of solute molecules in a given quantity of solvent are called colligative properties. Such cyclohexane turns into solid. Once the substance again. The freezing point is the temperature where it stays constant, Le. the liquld phase and the sold phase of the cyclohexane coexists (Figure 3-1) boiling point elevation and osmotic pressure. They do NOT dopend on the nature of the solute, but DO depend on the nature of the solvent. As a consequence, colligative properties can be used to determine an unknown molar mass for a solute. In this experiment, we will be using cyclohexane (d " 0.779 gmL, K, . 20.5 oC/m) as the solvent to determine the molar mass of a white solid with an empirical formula of C,HC. The freezing point depression, Î7, is the difference between the freezing point of the pure solvent, TP, and the freezing point of the solution (solvent and solute). T As mentioned above, thits quantity is proportional only to the molal concentration of the solute, m Figure 3-1. Cooling Curves The proportionality constant, K, is called the freezing-point-depression constant. The K value of 20.5 C/m for Cyclohexane is one of the largest values one can find. Molal concentration is defined as the number of moles of substance in 1 kg of solvent. Now we can calculate the molar mass of a solute from ATã K,, the mass of the The freezing point of a solution in cyclohexane can be obtained in a similar way. Cooling results in an initial rapid decrease in the temperature until freezing begins as seen in the cooling curve of the pure solvent. However, the temperature of the solution does not remain constant while being frozen. As the cyclohexane in the solution treezes, cyclohexane is taken away from the solution and the concentration of the solute becomes higher In the liquid portion. Thus the molal concentration of the solute increases and the freezing point of the solute and the mass of the solvent. remaining liquid becomes lower. The result is a steadily decreasing freezing temperature until the solution is completely frozen. When all the solution In order to determine ATP, we will measure the freezing point of pure cyclohexane and the freezing point of a solution of the solute in is frozen, the temperature decreases more rapidly To evaluate the freezing point of pure cyclohexame, you will cool a sample of this substance, and measure the temperature as a The freezing point of the solution is the temperature at which the solution starts to freeze. portion represents the concentration of the starting function of time. As cooling begins, theOnly at this point, the concentration of the liquid temperature of the cyclohexane decreases rapidly.

Experiment 10 Colligative Properties Introduction A pinch of wa make boiling water hotter. A handful will clear the snow from your steps. Every day we the physical properties of materials around us, but often don't know why we use these particular s or what chemistry is involved. Modifying the temperature of phase changes, by adding a second chemical to the pure solvent are examples of manipulating the Colligative Properties of a solution. this lab, we will study how varying the concentration and type of a salt affects the point of a solution. Colligative properties are properties of a solution containing 2 or more components. Typically, the primary is the solvent and the other called the such as color or hardness, properties depend on the number of particles of astute in the not the identity of the In many cases, the rokute will determine the number of solute particles (degree of ionization, solubility, etc,) in the solvent, but a colligative property does not depend upon the nature of the particles. Two colligative properties commonly encountered are boiling point elevation and freezing point depression (the temperature of of a is lower than of pure solvent). We will be studying boiling point elevation in this Most of the previous work that you have done with solutions has involved units of molarity, M, or moles of solute per liter of solution. Boiling point elevation calculations (as well as those for freezing point depression) or moles of solute per kilogram of solvent. boili change of temperature. When the temperature of a solution changes, the volume of the solution also changes. Since molarity depends on a change in wil the solution's molarity. Molality depends on the mass of the solvent. and thus is independent of temperature. n't Hoff Factor salt into and the of moles inorganic salts in an aque the based on the addition of the number dissociates, the total number of particles in the solution will be of cations and anions produced from the dissociation. Thus; Nacion Na Choaa (2moles of particles) Cacbrs Ca +2ch (3moles of particles) The quantity of particles produced per mole of solute is called the van'tHoff factor and is given the symbol, i, If 1 mole of sodium chloride were completely dissociated, iwould be 2. This theory works very well for dilute solutions and non-electrolytes (i 1, no dissociation at all since nonelectrolytes not ionize), For does not always apply to more concentrated solutions. Thus, when there are a large number of particles in a solution, they have a tendency to recombine as the salt and you don't get 100% dissociation. example, at a NaCl concentration of 0.1M, iwill be 1.81 (90% dissociation) rather than 2 (100%). Boiling Point Elevation solute causes the solution to boil at a higher When a solution is heated, the presence of a non-volatile point of the pure liquid and the temperature than the pure The difference between the boiling boiling point of the solution is: 169

Need help answering the pre - lab questions

Chemistry 1010 Laboratory Fall 2016 Lab: Percent Sugar Content of Beverages ave you ever been to the ocean? Does it seem that you can float or swim much easier in the ocean than in a swimming pool? Seawater is more dense than freshwater due to the presence of dissolved salt in the cean As a result, our buoyancy-ability to float-is greater in salt water than in plain water. What factors of a particular substance is dissolved in it? Background The density of a pure substance is a characteristic physical property that can be used to identify the substance does not depend on the amount of the substance. The density of any material is determined by measuring its mass and volume and then dividing the mass by the volume. The mass of a substance can be measured directly using a balance. The volume of a liquid can be measured directly using special laboratory glassware, such as a graduated cylinder, buret, or pipet. In this experiment, liquild volumes will be measured using a graduated cylinder Density is defined as the ratio of mass per unit volume. It is an "intensive" property, that is, it The density of a solution depends on its concentration, that is, how much solid is dissolved in the liquid. The higher the concentration of solid, the greater the density of the solution. A convenient way to express concentration is in units of weight percent, which corresponds to the number of grams of sollid that are present in 100 g of solution. A 20% salt solution is prepared by dissolving 20 g of sodium chloride (table salt) in 80 g of water to give a final mass of 100 g of solution. When the density of a solution is plotted on a graph against the concentration of the solution, a regular pattern becomes evident, specifically that density is directly proportional to the concentration of solid in the solution. A 20% salt solution, for example, has a higher density and higher concentration of solid than a 10% salt solution. If the densities of several solutions of known concentration are determined experimentally and plotted on a graph, a calibration curve can be drawn to show a straight-line relationship between the density of a solution and the concentration of solid (note: the calibration curve in this lab reveals a linear (straight-line) relationship, but not all calibration curves are linear). The calibration curve can then be used to find the concentration of solid in an unknown solution simply based on experimentally measuring the density of the solution. Experiment Overview The purpose of this experiment is to determine the percent sugar content in beverages. The density of five reference" solutions will be determined in Part A. The reference solutions contain known amounts sugar " of sugar (0-20%). Their densities will be plotted on a graph to obtain a calibration curve of density versus nt sugar concentration. In Part 8, the densities of two beverages will also be determined, and the The results will be compared against the information provided on the nutrition labels for these beverages 1. if the following mass and volume data are used to calculate the density of solution, how many cal libration curve, created from the data in Part A, will be used to find the percentage of sugar they contain. Pre-Lab Questions significant figures are allowed in the calculated density? Mass of solution 12.53 g: volume of solution = 8.27 mL Calculate the density of the solution described in Question #1 (Hint: This is a 2-step problem. Then calculate the percent sugar in the beverage.) According to its nutrition label, orange soda 2. 3. First, use the density to convert the 355-mL serving size to grams. Lab: Percent Sugar Content of Beverages