Scientiaestubique.weebly.com



NAME __________________________________ INDEPENDENT PACKET: MOLARITYGOAL(S): When you have completed this packet, you will be able to: 1) determine the molar concentration (MOLARITY) of an aqueous solution when given any TWO PIECES of the following information:a) moles of solute b) grams of solute and / orc) LITERS of solution 2) define the terms: aqueous solution, solute and solvent There are 2 types of Molarity problems. So, here's what you wish the textbook would tell you:Cutting To The Chase MOLARITY There are: and There are: 1 step problems 2 step problems give you 2 of the 3 variables of the equationask for or give you the number of grams ofsolute (rather than the number of moles). Use of Molarity = moles of solute the terms grams & molarity indicates that Liters of solution it’s 2 steps If you are given M, Liters &/or moles of soluteBegin with the equation then Molarity = moles of solute Liters of solutionall you need to do is substitute into the equation the two given values and solve for the third. and then, use unit cancellation to convert between grams moles Much of what you experience deals with "aqueous solutions". Apple juice, milk, soda, lake water, ocean water, tap water are all examples (complex and simple) of aqueous solutions. As in all mixtures, an aqueous solution is a physical combination of a SOLVENT and a SOLUTE. The solvent is the substance which does the "dissolving" or "breaks up the solid". The solute is the stuff that is dissolved. The solvent must always (powerful word) be in the greater quantity. In the case of aqueous solutions the solvent is water. Anything water can dissolve may be considered to be a water-soluble solute. Aqueous solutions (mixtures) are NOT substances. Rather, they are homogeneous mixtures made of 2 or more substances. For example, you would be unable to differentiate (visually) between a glass of pure water and (if made correctly) a glass of concentrated salt water (NaCl(aq)). When written, the solute is recordedfirst and the water solvent is recorded with the abbreviation (aq). Thus, the formula NaCl(aq) is known to be a solution (a homogeneous mixture) of sodium chloride dissolved COMPLETELY in water.These aqueous solutions may be described in terms of their concentration or their MOLARITY. If you were to update your Concept Map of Matter you would have the following:MATTERmay be divided into 2 large categoriesH e t e r o g e n e o u s M a t t e rH o m o g e n e o u s M a t t e r exemplified by is divided further into two different groupsemulsions & solid mixtures Mixtures like S u b s t a n c e s Mixtures or like those that often settle there are 2 types that don't settle out are called alloys & gas mixtures out into layers suspensions elements compounds solutions like made of only 1 type of made of 2 or more or for our class atom different species eg) sand + water eg) Fe(s) eg) C2H6(g) eg) aqueous solutionsThere are many types of homogeneous solutions. The "aqueous solution" is just one type. It is however, themost important to the understanding of the material contained in this Chemistry syllabus.SUMMARY: Aqueous solutions are not chemical combinations. Aqueous solutions are ______________ physical, water combinations of ______________ and some solute. Water acts as the dissolving agent.solvent In its role as the dissolving agent, water is called technically, the ____________________.homogeneous While they are not substances, aqueous solutions are ___________________, in that they aremolarity uniform in their properties. Concentration is expressed as ______________. Part 1: MOLARITY (symbol: M, or M ): a term of concentration which expresses the number of moles of solute completely dissolved in 1 liter of solution . A) unit: moles/Liter (read as moles per Liter)1) the unit expresses the definition: M, or M is the number of MOLES per LITERa) very often when you see M or M, you may "say" it as the word MOLAR so, 0.50 M HCl(aq) is read or spoken as: a 0.50 MOLAR solution of HCl B) Equation: M = # of moles of solute # of Liters of solution1) The volume of the solution must be in LITERS 2) If volume is given in milliliters (mL), you must convert from one to the other. Remember, 1 L = 1,000. mL _3) eg) Calculate the molarity of a 2,000 milliliter solution containing 3.0 moles of HCl(g)M = # of moles of solute # of liters of sol'nM = 3.0 moles HCl____ 2.0 Liters of sol'nM = 1.5 M4) eg) Calculate the molarity of 2.0 moles of HCl(g) dissolved in a 500. mL solution .M = # of moles of solute # of liters of sol'nM = 2.0 moles HCl did you remember to convert the 500. mL of solution 0.500 Liters of sol'n to 0.500 Liters of solution ??????? M = 4.0 M The answer has 2 sig figs because 2.0 has the fewer number of sig figs. 5) Practice for 1 step Molarity Problems a) What is the molarity of a 900. mL solution when 1.30 moles of CuSO4 are dissolved? Equation: M = moles LitersSubstitution:ANS: 1.44 M Answer: _________ M b) How many moles of NaCl are dissolved in a 0.20 M solution of 500. mL? Equation:Substitution:Ans: _________ molesAns: 0.10 moles of NaCl (note only 2 sig figs)c) Calculate the volume (Liters) of a 0.500 M solution made with 3.50 moles of NaOH? Equation:Substitution:Ans: 7.00 L Ans: ___________ Liters (note 3 sig figs)SUMMARY: dividing, solute The term molarity is found by _______________ the number of moles of _______solution by the number of liters of _________________. The most important thing to rememberLitersis that the VOLUME of the solution must be expressed in the unit, ___________.READ THIS ABOUT 2 STEP MOLARITY PROBLEMS!!!C) Many times you will not be given the number of moles DIRECTLY. When the question is a molarity question, BUT gives (or asks for) the number of grams of solute then you will need to use UNIT CANCELLATION.Read the following question carefully. Note how the key words that clue you in on the fact that it is a 2 step problem, have been identified.1) eg) A student made a 5.0 L solution by dissolving 80.0 grams of NaOH(s) into water.Calculate the molar concentration (molarity) of the solution. key words for2-step problemsStart: You can recognize this as a molarity problem. Begin with the molarity equation & try to fill in what you know….M = moles of solute Liters of solutionYou know the Liters of solution, but nothing else that fits the equation.However, you do know the grams, and you can convert to moles from grams.b) step 1: calculate moles from grams;moles of NaOH = 80.0 grams | 1 mole of NaOH| 40 grams ?(Na + O + H) 23g + 16g + 1g (calculating a mole mass) therefore: moles of dissolved NaOH = 2.00 moles (note 3 sig figs based on the "given")c) step 2: substitute into the M formula:M = # of moles of solute # of liters of solutionM = 2.00 moles NaOH 5.0 Liters of solutionM = 0.40 mol/L or 0.40 M or 4.0 x 10-1 molar solution …. each is equally correct, with 2 sig figs3) Practice: N.B. The following problems have been calculated using mole masses rounded to the nearest whole number, for convenience. In lab, we would use the decimalized values. If you use the decimalized values for theses problems, your answers would be just slightly different. _ Ans: 1.19 Ma) A 1500 mL solution has 100. grams of KOH completely dissolved. Calculate the molarity of the solution key words for 2-step problemsAns: 0.85 Mb) Calculate the molar concentration of a 750 mL solution when 54.0 grams of NaNO3(s) are dissolved completely in water. clues for a 2-step problemAns 0.552 Mc) Calculate the molarity of a 5.00 x 10-1 L solution with 94.5 grams of C12H22O11(s) completely dissolved in water. clues for a 2-step problemAns 2.0 Md) Calculate the molarity of a 250 mL solution with 53 grams of Na2CO3(s) completely dissolved Ans: 1.0 Me) Calculate the molarity of a 2.0 L solution with 320 grams of CuSO4(s) completely dissolved. Practice: 1) THIS IS A 1 STEP*: How many moles of NaI are required to make a 750. mL solution , of 0.80 M? (*You are given M, and the volume in Liters, simply plug into the equation and solve for moles… Do you need to use the molar mass?) a) 0.29 mole b) 7.0 moles c) 0.60 moled) 0.10 moleans. c2) THIS IS A 2 STEP**: What is the number of grams of AlCl3 dissolved in 0.500 L of a 0.900 M solution? **(Note, you're asked for grams, but you must first use the equation to get to moles and then use unit cancellation to calculate the grams... Will you need the molar mass?)a) 59.4 g b) 126 g c) 229 gd) 74.2 gans. a3) How many grams of KOH are dissolved in a 2.0 x 103 mL solution of 1.5 M KOH(aq)? How many steps is this? 1 or 2 How do you know?? a) 150 g? b) 140 gc) 90 gd) 170 gans d4) A student used 11.0 grams of NaOH to make a 3.0 L solution. Determine the molarity of the solution.a) 2.5 Mb) 0.092 Mc) 0.50 Md) 1.8 Mans b5) How many grams of LiCl are required to prepare 80.0 mL of a 0.150 M solution?a) 0.504 gramsb) 0.761 gramsc) 1.675 gramsd) 3.19 gramsans. a6) Calculate the number of liters of solution made from making a 0.50 M solution by dissolving 2 moles of KOH into water. (How many steps is this? 1 or 2 How do you know??) a) 1b) 2c) 3d) 4ans. d7) At 25?C, 0.0018 grams of NaCl dissolves in enough 1-petanol (CH3CH2CH2CH2CH2OH) to give 0.10 L of solution. Calculate the molar concentration of the solution. (What do you have? What do you need?)a) 0.0031b) 0.00031c) 0.00016d) 0.018ans. b8) A sugar-free soft drink contains 7.9 mg of saccharin, C7H5SNO3 in 1.0 ounce (31 mL). What is the molar concentration of saccharin in an ounce of the drink? (Note: you are given mg of solute, not grams….)a) 4.5 x 10-3 Mb) 1.4 x 10-1 Mc) 3.2 x 10-2 Md) 1.4 x 10-3 Mans. dPart 2: Going Further: Finding Molarity Given The Density Of A SolutionThis section deals with a slightly more advanced look at concentration. It uses the issue of density as well. When given the molarity and density of a solution, with a request to determine a volume or mass of solute, try this approach. Think about what you know and what you need to find .... Then...when asked for Molarity... ?Assume 1 Liter of solution and use the density to determine the mass in grams of the solution.?Use the % to determine what mass of that solution is actually due to the solute (the rest is due to water) ?Calculate the moles of solute using unit cancellation and ?Use the molarity equation (with a volume of 1.00 Liter) to find molarity. You'll note that this method equates the number of moles from the last step to the molarity9) What is the molarity of NaBr in a solution that is 40.0% NaBr and has a density equal to 1.42 g/mL? ? Think!: The density tells you that 1mL of solution is 1.42 grams ... and 40.0% of the mass is NaBr .... You want molarity ? Assume 1.00 liter of solution .... Thus at a density of 1.42 g/mL ..& 1.00 liter of solution, you have 1,420 grams of solution. How did I figure out that value? Recall: 1,000 mL = 1.00 Liter 1.42 g/mL means that 1.00 mL of solution has a mass of 1.42 grams. When1.00 mL=1.42 grams & you assume 1,000 mL, then the mass of solution is 1,420 grams. ? Use the 40.0% of solution mass that is due to NaBr ...& find the grams of NaBr (0.400 x 1420) = 568 grams of NaBr ? Calculate by converting 568 grams of NaBr to moles using unit cancellation moles NaBr = 568 grams NaBr | 1 mol | 103 grams NaBr ? Use that mole value to plug into the molartiy equation ...and keep assuming 1.00 Liter of solution.... you’ll find that as long as you have assumed 1 L of solution, the Molarity of the solution = the calculated number of moles...! Nicea) 5.51Mb) 6.42 M c) 5.78 M d) 6.89 M ans. a10) The density of a 72.0 % by mass (or by weight) aqueous solution of ethanol (CH3CH2OH) is 0.8644 g/cm3. Calculate the molarity of the solution. ? Think!: The density tells you that 1mL of solution is 0.8644 grams .. and 72.0% of the mass is ethanol .... You want molarity ? Assume you have 1.00 Liter of solution. So, you have * 864.4 grams of solution. (mass of 1.00L sol’n = the density x 1000) ? Use the fact that 72.0% of every 1.00 mL is ethanol. So ... use the percentage to determine the mass due to ethanol in solution ? Calculate the moles of ethanol by converting grams to moles ? Use the molarity equation ... assume 1.00 Liter of solution...a) 13.0b) 12.2 c) 13.5 d) 14.1 ans. c11) What is the molarity of a 21.9% by weight of a AgNO3 solution with a density of 1.220 g/cm3? Think: The density per mL of solution is 1.220 grams ... and 21.9% of the mass is AgNO3 .... You want molarity a) 1.66b) 1.42c) 0.158d) 1.57ans. d12) A 23.9% solution by weight of citric acid (H3C6H5O7) in water has a density of 1.10 g/cm3. Calculate the molarity of the solution.a) 1.55b) 1.37c) 2.01 d) 0.773ans. b13) The density of a 44.0% by mass aqueous solution of ethylene glycol (C2H6O2) is 1.0586 g/cm3. What is the molarity of the solution?a) 4.35b) 6.78c) 7.50d) 8.19ans. cQUIZ YOURSELF ! (SELF-QUIZ #1)___1. Which of the following represents a homogeneous mixture?a) Br2(l) b) Na2S(s) c) LiF(aq) d) Ne(g)___2. Calculate the molarity of a solution of sodium oxalate (Na2C2O4), containing 33.5 g of solute in 100.0 mL of solution ?a) 1.50 M b) 2.50 M c) 3.75 M d) 4.00 M___3. How many moles of NaCl are needed to prepare 5.0 L of a 2.0 M solution of NaCl(aq) ?a) 2.5 b) 5.0 c) 10. d) 20.4. Define the term: Molarity __________________________________________________________________________________________________________________________________5. Define the term: Solute _______________________________________________________________6 The density of a 48.0% by mass aqueous solution of H2SO4 is 1.3783 g/cm3. What is the molarity of the solution?a) 6.75 Mb) 10.2 Mc) 8.50 Md) 4.06 MANSWERS: 1 c 2. b 3. c 4. a term of concentration referring to the number of moles of solute dissolved completely in 1 liter of solution. 5. the solid, liquid, or gas which is dissolved into the solvent. The solute is always in the lesser molar quantity. 6. aIF AT FIRST YOU DON'T SUCCEED......(SELF - QUIZ #2)___1. What is the molarity of a solution of KNO3 that contains 404 grams of KNO3 in 2.00 liters of solution?a) 1.00 b) 2.00 c) 0.500 d) 4.00___2. Calculate the total number of grams of KCl dissolved in 1.00 L of 0.200 molar solution.a) 7.46 g b) 14.8 g c) 22.4 g d) 29.8 g___3. Calculate the molarity of a solution that contains 112 grams of KOH in 2.0 L of solution.a) 1.0 M b) 2.0 M c) 3.0 M d) 4.0 M 4 Define the term: Homogeneous Solution: ______________________________________________ __________________________________________________________________________________5 Which is has the greater mass of NaOH: a) 0.504 L of 0.0025 M NaOH(aq) OR b) 0.00393 L of 0.400 M NaOH(aq) ? ___6) The density of a 56.0% by weight aqueous solution of methanol (CH3OH) is 0.9046 g/cm3. What is the molarity of the solution?a) 17.0 Mb) 8.75 Mc) 15.8 Md) 11.6 MANSWERS: 1 b 2. b 3. a 4) a uniform mixture (when evaluated by the naked eye, for our course) composed of at least one solute evenly distributed/dissolved in solvent 5) b 6) c ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download