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All Textbook Solutions for Chemical Principles in the Laboratory

Finding the volume of a flask. A student obtained a clean, dry glass-stoppered flask. She weighed the flask and stopper on an analytical balance and found the total mass to be 34.166g. She then filled the flask with water and obtained a mass for the full stoppered flask of 68.090g. From these data, and the fact that at the temperature of the laboratory the density of water was 0.9975g/mL, find the volume of the stoppered flask. a. First we need to obtain the mass of the water in the flask. This is found by recognizing that the mass of a sample is equal to the sum of the masses of its parts. For the filled, stoppered flask: Massoffilledstopperedflask=massofemptystopperedflask+massofwater,somassofwater=massoffilledflaskmassofemptyflask Massofwater=gg=g Many mass and volume measurements in chemistry are made by the method used in la. This method is called measuring by difference, and is a very useful one. b. The density of a pure substance is equal to its mass divided by its volume: Density=massvolume or volume=massdensity The volume of the flask is equal to the volume of the water it contains. Since we know the mass and density of the water, we can find its volume and that of the flask. Make the necessary calculation. Volumeofwater=volumeofflask=mL Finding the density of an unknown liquid. Having obtained the volume of the flask, the student emptied the flask, dried it, and filled it with an unknown liquid whose density she wished to determine. The mass of the stoppered flask when completely filled with liquid was 57.418g. Find the density of the liquid. a. First we need to find the mass of the liquid by measuring the difference: Massofliquid=gg=g b. Since the volume of the liquid equals that of the flask, we know both the mass and volume of the liquid and can easily find its density using the equation in lb. Make the calculation. Densityofliquid=g/mL Finding the density of a solid. The student then emptied the flask and dried it once again. To the empty flask she added pieces of a metal until the flask was about three-fourths full. She weighed the stoppered flask and its metal contents and found that the mass was 116.150g. She then filled the flask with water, stoppered it, and obtained a total mass of 119.827g for the flask, stopper, metal, and water. Find the density of the metal. a. To find the density of the metal we need to know its mass and volume. We can easily obtain its mass by the method of differences: Massofmetal=gg=g b. To determine the volume of metal, we note that the volume of the flask must equal the volume of the metal plus the volume of water in the filled flask containing both metal and water. If we can find the volume of water, we can obtain the volume of metal by the method of differences. To obtain the volume of the water we first calculate its mass: Massofwater=massof(flask+stopper+metal+water)massof(flask+stopper+metal)Massofwater=gg=g The volume of water is found from its density, as in lb. Note that 1mL=1cm3. Make the calculation. Volumeofwater=mL=cm3 c. From the volume of the water, we calculate the volume of metal: Volumeofmetal=volumeofflaskvolumeofwaterVolumeofmetal=cm3cm3=cm3 From the mass and volume of metal, we find the density, using the equation in 1b. Make the calculation. Densityofmetal=g/cm3 1ASA 2ASA 3ASA 4ASA Using Figure 3.1, determine a. the number of grams of CuSO45H2O that will dissolve in 100g of H2O at 100C. gCuSO45H2O b. the number of grams of water required to dissolve 4.0g of CuSO45H2O at 100C. Hint: your answer to Problem 1a gives you the needed conversion factor for g CuSO45H2O to gH2O. gH2O c. the number of grams of water required to dissolve 18gKNO3 at 100C. gH2O d. the number of grams of water required to dissolve a mixture containing 18gKNO3 and 4.0g CuSO45H2O, assuming that the solubility of one substance is not affected by the presence of another. gH2O 2ASA To find the mass of a mole of an element, one looks up the atomic mass of the element in a table of atomic masses see Appendix III or the Periodic Table. The molar mass of an element is simply the mass in grams of that element that is numerically equal to its atomic mass. For a compound substance, the molar mass is equal to the mass in grams that is numerically equal to the sum of the atomic masses in the formula of the substance. Find the molar mass of Cu_g/molCl_g/molH_g/mol O_g/molH2O_g/mol If one can find the ratio of the number of moles of the elements in a compound to one another, one can find the formula of the compound. In a certain compound of copper and oxygen, CuxOy, we find that a sample weighing 0.9573g contains 0.7649gCu. a. How many moles of Cu are there in the sample? (MolesofCu=massofCumolarmassofCu) _moles b. How many gram of O are there in the sample? The mass of the sample equals the mass of the Cu plus the mass of O. _g c. How many moles of O are there in the sample. _moles d. What is the mole ratio (molesofCu/molesofO) in the sample? _:1 e. What is the formula of the oxide? The atom ratio equals the mole ratio and is expressed using the smallest integers possible. _ f. What is the molar mass of the copper oxide? _g/mol A student attempted to identify an unknown compound by the method used in this experiment. She found that when she heated a sample weighing 0.5032g, the mass dropped to 0.2663g. When the product was converted to a chloride, the mass went back up, 0.3747g. a. Is the sample a carbonate? Yes / no Circle one Please provide reasoning below. b. What are the two compounds that might be in the unknown? _ or _ c. Write the balanced chemical equation for the overall reaction that occurs when each of these two original compounds is converted to a chloride. If the compound is a hydrogen carbonate, use the sum of Reactions 1 and 2. If the sample is a carbonate, use Reaction 2. Write the equation for a sodium salt and then for a potassium salt. d. How many moles of the chloride salt would be produced from one mole of the original compound? _ e. How many grams of the chloride salt would be produced from one molar mass of the original compound? Molarmasses:NaHCO3_g/molNa2CO3_g/molNaCl_g/molKHCO3_g/molK2CO3_g/molKCl_g/mol If a sodium salt, _g original compound _g chloride If a potassium salt, _g original compound _g chloride f. What is the theoretical value of Q, as found by Equation 3, if she has the Na salt? _ if she has the K salt? _ g. What was the observed value of Q? _ h. Which compound did she have as an unknown? _A student is given a sample of a pink manganese (II) chloride hydrate. She weighs the sample in a dry, covered crucible and obtains a mass of 26.742g for the crucible, cover, and sample. Earlier she had found that the crucible and cover weighed 23.599g. She then heats the crucible to drive off the water of hydration, keeping the crucible at red heat for about 10 minutes with the cover slightly ajar. She then lets the crucible cool and finds it has a lower mass; the crucible, cover and contents then weigh 25.598g. In the process the sample was converted to off-white anhydrous MnCl2. a. What was the mass of the hydrate sample? _ghydrate b. What is the mass of the anhydrous MnCl2? _gMnCl2 c. How much water was driven off? _gH2O d. What is the percent by mass of water in the hydrate? water=massofwaterinsamplemassofhydrateinsample100 _massH2O e. How many grams of water would there be in 100.0g hydrate? How many moles? _gH2O; _molesH2O f. How many grams of MnCl2 are there in 100.0g hydrate? How many moles? What percentage of the hydrate is MnCl2? Convert the mass of MnCl2 to moles. The molar mass of MnCl2 is 125.85g/mol. _gMnCl2; _molesMnCl2 g. How many moles of water are present per mole MnCl2? _ h. What is the formula of the hydrate? _1ASA 2ASA 1ASA 2ASA 1ASA 2ASA 1ASA 2ASA 1ASA As pure elements, all of the halogens are diatomic molecular species. Their melting points are: F2. 54K; Cl2, 172K; Br2,. 266K; and I2, 387K. Using the Periodic Table, predict as best you can the molecular formula of elemental astatine, At, the only radioactive element in this family. Also predict whether it will be a solid, liquid, or gas at room temperature. Elemental formula: ______ Phase at room temperature: ______Substances A2, B2, and C2 can all act as oxidizing agents. In solution, A2 is green, B2 is yellow, and C2 is red. In the reactions in which they participate, they are reduced to A, B, and C ions, all of which are colorless. When a solution of C2 is mixed with one containing B ions, the color changes from red to yellow. Which species is oxidized? __________ Which is reduced? __________ When a solution of C2 is mixed with one containing A ions, the color remains red. Is C2 a better oxidizing agent than A2? __________ Is C2 a better oxidizing agent than B2? __________ Arrange A2, B2, and C2 in order of increasing strength as an oxidizing agent. ___________________ _______________ ______________ weakest oxidizing agentstrongest oxidizing agent You are given a colorless unknown solution that contains one of the following salts: NaA, NaB, NaC. In solution, each salt dissociates completely into the Na+ ion and the anion A, B, or C, whose properties are given in Problem 2. The Na+ ion is effectively inert. Given the availability of solutions of A2, B2, and C2, develop a simple procedure for identifying the salt that is present in your unknown.First you need to find the number of valence electrons in NH2Cl. For counting purposes with Lewis structures, the number of valence electrons in an atom of a main group element is equal to the last digit in the group number of that element in the Periodic Table. N is in Group ________ H is in Group ________ Cl is in Group _________ In NH2Cl there is a total of ____________ valence electrons.The model consists of balls and sticks. a. How many holes should be in the ball you select for the N atom? ___________ b. How many holes should be in the ball you select for the H atoms? ____________ c. How many holes should be in the ball you select for the Cl atom? ____________ The electrons in the molecule are paired, and each stick represents a valence electron pair. d. How many sticks do you need? ____________Assemble a skeleton structure for the molecule, connecting the balls and sticks to make one unit. Use the rule that N atoms form three bonds, whereas Cl and H atoms usually form only one. Draw a sketch of the skeleton below:a. How many sticks did you need to make the skeleton structure?____________ b. How many sticks are left over? ____________ If your model is to obey the octet rule, each ball must have four sticks in it except for hydrogen atom balls, which need and can only have one. Each atom in an octet rule species is surrounded by four pairs of electrons. c. How many holes remain to be filled? ____________ Fill them with the remaining sticks, which represent nonbonding electron pairs. Draw the complete Lewis structure for NH2Cl using lines for bonds and pairs of dots for nonbonding electrons.5ASA 6ASA 1ASA 2ASA 1ASA 2ASA 1ASA In an FCC structure, the atoms are found on the corners of the cubic unit cell and at the center of each face. The unit cell has an edge whose length is the distance from the center of one corner atom to the center of another corner atom on the same edge. The atoms on the diagonal of any face are touching. One of the faces of the unit cell is shown below in the following: a. Show the distance dO on the sketch. Draw the boundaries of the unit cell. b. What is the relationship between the length of the face diagonal and the radius of the atoms in the cell? Face diagonal = ______________ c. How is the radius of the atoms related to dO? r= ______________ d. Silver metal crystals have an FCC structure. The unit cell edge in silver is 0.4086nm long. What is the radius of a silver atom? ______________nm 1ASA If we classify substances as ionic, molecular, macromolecular, or metallic, in which if any categories are all the members a. soluble in water? b. electrical conductors in the melt? c. insoluble in all common solvents? d. solids at room temperature?A given substance is a white, granular solid at 25C that does not conduct electricity. It melts at 750C without decomposing, and the melt conducts an alternating electric current. It dissolves readily in water, to produce an electrically conductive solution. What would be the proper classification of the substance, based on this information?4ASA 1ASA 2ASA 3ASA 4ASA 5ASA 6ASA 7ASA 8ASA 9ASA A student determined the molar mass of an unknown non-dissociating liquid by the method described in this experiment. She found that the equilibrium temperature of a mixture of ice and pure water was indicated to be +0.4C on her thermometer. When she added 9.9g of her sample to the mixture, the temperature, after thorough stirring, fell to 3.7C. She then poured off the solution through a screen into a beaker. The mass of the solution was 84.2g. a. What was the freezing point depression? ____________C b. What was the molality of the unknown liquid? ____________ m c. What mass of unknown liquid was in the decanted solution? ____________ g d. What mass of water was in the decanted solution? ____________ g e. How much unknown liquid would there be in a solution containing 1kg of water, with her unknown liquid at the same concentration as she had in her experiment? ___________ g unknown liquid f. Based on these data, what value did she calculate for the molar mass of her unknown liquid, assuming she carried out the calculation correctly? ____________ g/mol In a reaction involving the iodination of acetone, the following volumes were used to make up the reaction mixture: 5mL4.0M acetone+10mL1.0M HCl+10mL0.0050MI2+25mLH2O a. How many moles of acetone were in the reaction mixture? Recall that, for a component A, moles A=MAV, where MA is the molarity of A and V is the volume in liters of the solution of A that was used. __________ moles acetone b. What was the molarity of acetone in the reaction mixture? The volume of the mixture was 50 mL, 0.050 L, and the number of moles of acetone was found in Part a. Again, MA=moles ofAV of soln. in liters __________ M acetone c. How could you double the molarity of the acetone in the reaction mixture, keeping the total volume at 50 mL and keeping the same concentrations of H+ ion and I2 as in the original mixture?2ASA 3ASA 4ASA 1ASA 2ASA Methyl orange, HMO, is a common acid-base indicator. In solution it ionizes according to the equation: HMOaqH+aq+MO-aqredyellow If methyl orange is added to distilled water, the solution turns yellow. If 1 drop or two of 6 M HCl is added to the yellow solution, it turns red. If to that solution one adds a few drops of 6 M NaOH, the color reverts to yellow. a. Why does adding 6 M HCl to the yellow solution of methyl orange tend to cause the color to change to red? Note that in solution HCl exists as H+ and Cl- ions. b. Why does adding 6 M NaOH to the red solution tend to make it turn back to yellow? Note that in solution NaOH exists as Na+ and OH- ions. How does increasing OH- shift Reaction 3 in the discussion section? How would the resulting change in H+ affect the dissociation reaction of HMO?2ASA 1ASA 2ASA 1ASA In an acid-base titration, 21.16 mL of an NaOH solution are needed to neutralize 20.04 mL of a 0.0997 M HCl solution. To find the molarity of the NaOH solution, we can use the following procedure: First note the value of MH in the HCl solution. ____________M Find MOH- in the NaOH solution. Use Eq.3. ____________M Obtain MNaOH from MOH. ____________M A 0.3012g sample of an unknown monoprotic acid requires 24.13mL of 0.0944MNaOH for neutralization to a phenolphthalein end point. There are 0.32mL of 0.0997MHCl used for back titration. a. How many moles of OH are used? How many moles of H+ from HCl? _______moles OH ________moles H+ b. How many moles of H+ are there in the solid acid? Use Eq.5. ____________ moles H+ in solid c. What is the molar mass of the unknown acid? Use Eq.4. ____________ g/mol 1ASA 2ASA The pH of a 0.10 MHOBr solution is 4.8. What is H in that solution? ____________M What is OBr-? What is HOBr? Where do the H and OBr- ions comes from? ____________M; ____________M What is the value of Ka for HOBr? What is the value of pKa?____________ ____________4ASA 5ASA 1ASA 2ASA 3ASA 1ASA 2ASA 1ASA 2ASA A 100-mL sample of hard water is titrated with the EDTA solution in Problem 2. The same amount of Mg2 is added as previously, and the volume of EDTA required is 31.84 mL. a. What volume of EDTA is used in titrating the Ca2 in the hard water? _____________mL b. How many moles of EDTA are there in that volume? _____________ moles c. How many moles of Ca2 are there in the 100 mL of water? _____________ moles d. If the Ca2 comes from CaCO3, how many moles of CaCO3 are there in one liter of the water? How many grams of CaCO3 are present per liter of the water? _____________ mol / L _____________ g / L e. If 1 ppm CaCO3 = 1 mg per liter, what is the water hardness in ppm CaCO3? _____________ ppm CaCO3 1ASA 1ASA 2ASA 3ASA What is the mass percent of iron in iron II ammonium sulfate hexahydrate, FeNH42SO42.6 H2O? ____________mass 1ASA 2ASA 1ASA 2ASA 1ASA 2ASA 3ASA 4ASA 5ASA 1ASA Each of the observations in the following list was made on a different solution. Given the observations, state which ion studied in this experiment is present. If the test is not definitive, indicate that with a question mark. A. Addition of 6 M NAOH and A1 to the solution produces a vapor that turns red litmus blue. Ion present: B. Addition 6 M HCI produces a vapor with an acrid odor. Ion present: C. Addition of 6 M HCI produces an effervescence. Ion present: D. Addition of 6M HNO3 plus 0.1 M AgNO3 produces a precipitate. Ion present: E. Addition of 6 M HNO3 plus 1 M BaCl2 produces a precipitate. Ion present: F. Addition of 6 M HNO3 plus 0.5 M NH42MoO4 produces a precipitate. Ion present:2ASA 3ASA 1ASA 2ASA 3ASA 4ASA 1ASA 2ASA 3ASA 1ASA 2ASA 3ASA 1ASA 2ASA 3ASA 4ASA 1ASA 2ASA 3ASA 1ASA 2ASA 3ASA 4ASA 5ASA 1ASA 1ASA 2ASA 3ASA

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