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You will need to read through the lab procedure and background information to solve this question. Need help? See a TA or your instructor in office hours. CaCrO4 is a slightly soluble solid. In the lab, you find that addition of 357.73 µL of 1 M H2CrO4 to 7.924 mL of 0.3 M Ca(NO3)2 results in formation of a persistent precipitate. Addition of water (1.878 mL) just dissolves the precipitate. What is the experimental value of Ksp for CaCrO4 according to the information above? Provide your response to 4 digits after the decimal.

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Jarrod Robel
Jarrod RobelLv2
13 Dec 2019

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Related questions

This is for the lab practical I take on Tuesday night. If you could answer each one and show your work/ explain that'd be amazing so I can do well on the actual practical on Tuesday! Thank you!

Chemistry 211 Lab Final Study Guide Spring 2015

Useful Information:
1 ampere =coulomb/sec
Faraday’s constant = 96,500 coulombs/mole of electrons
Molar mass of Au = 197.0 g/mole, Molar mass of Cu = 63.55 g/mole
m = moles , ' ’

c kg

ΔTf

= Tf

− Tf

where Tf is for the pure solvent and Tf

is for the mixture.

ΔT = (K

)(m ) ,

m = (

(mass of

solute, g )
)( ).

f f c

c molar

mass, g

mol −1

mass of

solvent, kg


7. Next question

(a) If you weigh 6.355 grams of copper, add concentrated nitric acid to dissolve it, and then dilute the solution to a total volume of 50 mL, how many moles of copper are in this solution?


(b) For the equilibrium reaction 3H2(g) + N2(g) → 2NH3(g), what is the equilibrium constant expression, Kc, for this reaction? (5pts)

8. Suppose at some temperature, the equilibrium concentration of H2 is 0.45M, the equilibrium concentration of N2 is 0.38M, and the equilibrium concentration of NH3 is 0.42M. What is the value of the equilibrium constant for the reaction 3H2(g) + N2(g) → 2NH3(g) at this temperature? (Show your work. No credit will be given if your work is not shown.)

9. Next question
(a) If you need 0.0534 moles of NaOH to reach equivalent point in the titration with acetic acid, how many mL of 0.09876M NaOH will you need?


(b) The Ksp of Cu(OH)2 is 2.2x10-20, what is the solubility of Cu(OH)2?


10. Next question
(a) In non-sulfide qualitative analysis of representative cations, the Group A cations comprising of Pb2+,

Hg2+, and Ag+ give a precipitate with solution.
(b) From a solution containing mixture of Pb2+, Fe3+, and Al3+, Pb2+ is removed by adding HCl solution. To the remaining cation mixture, on making the solution basic with NH3 (pH=9 – 10), both the cations form precipitate. Further analysis of the cation mixture containing Fe3+ and Al3+ is carried out by adding NaOH solution.


Aluminum hydroxide (dissolves/remains undissolved) in NaOH solution while Ferric hydroxide ( dissolves/remains undissolved).
(c) Fe(OH)3 precipitate is dissolved in minimal amount of aqueous HCl which gives a


yellow solution. To this solution addition of solution (at pH = 4 – 5) yields a dark blue solid known as Prussian Blue.

(d) Describe the method for checking for completeness of precipitate in qualitative analysis of ions.

Information

Day 1. Synthesis and characterization of HA and CHA. Preparation of ceramics. Prepare two solutions, 100 mL each: (1) 0.5 M Ca2+ solution (from Ca(NO3)2·4H2O) with pH adjusted to 11 using 1 M NaOH; (2) 0.3 M solution of PO4 3- ions (from Na2HPO4). For the synthesis of CHA add the carbonate source (NaHCO3) to the phosphate solution such that the PO4 3- : CO3 2- ratio is 5:1 or 2:1. Dropwise add the phosphate and carbonate solutions over the course of 10 minutes to the calcium solution. Heat and mix the solution to 80 °C for 1 hour adjusting the pH to 11 if needed by adding 1 M NaOH. Cool it down and vacuum filter your precipitate, wash three times with DI water. Dry the powder in the oven and calculate your yield. Use some of the dry powder to press a pellet. This pellet will be annealed at ~1000 °C overnight to fabricate dense ceramic material, which will be used later in the SBF test. Submit some of the sample to your TA for XRD measurements. If time permits, perform FTIR measurements of your sample and compare it to bovine CHA.

Day 2. Preparation of SBF.6 Thoroughly clean 1000 mL glass beaker, try to avoid heavily scratched glassware. 1) Add 960 mL of deionized water and dissolve 6.5456 g of NaCl, stir vigorously at RT for 5 min 2) Dissolve 2.2682 g of NaHCO3 and stir vigorously at RT for 5 min 3) Dissolve 0.373 g of KCl and stir vigorously at RT for 5 min 4) Dissolve 0.1419 g of Na2HPO4 and stir vigorously at RT for 5 min 5) Heat the solution to 36.5-37 °C 6) Dissolve 0.3049 g of MgCl2·6H2O and stir vigorously for 5 min 7) Add 9 mL of 1 M HCl solution (use a pipette and add it slowly) and stir vigorously for 5 min 8) In small portions add 0.3675 g of CaCl2·2H2O and stir vigorously for 5 min 9) Add 0.071 g of Na2SO4 and stir vigorously for 5 min 10) In small portions add 6.057 g of Tris [=(CH2OH)3CNH2]. Upon adding Tris, the solution should become turbid; keep stirring. 11) Insert the pH electrode into the solution, which should be at around 37°C until now 12) Add 30 mL of 1 M HCl slowly in 5 mL portions, by using a pipette, your addition plan is 5 + 5 + 5 + 5 + 5 + 5 mL = 30 mL (with the addition of each 5 mL portion of 1 M HCl, pH will gradually drop towards 7.4) 13) Keep stirring and be careful when adding the last “5 mL portion” of 1 M HCl, add this 5 mL portion quite slowly (i.e., drop by drop) while watching the pH meter reading 14) You can easily adjust the pH at 7.4 (at 36.5 or 37°C), pH=7.38, 7.37, 7.41 or 7.39 are also OK 15) Measure the total volume of the transparent solution, if it is not exactly equal to 1000 mL, you must add deionized water to complete the volume to 1000 mL Table 2. Order and amounts of reagents for 1000 mL of SBF.

# Reagent Amount 1 NaCl 6.5456 g 2 NaHCO3 2.2682 g 3 KCl 0.373 g 4 Na2HPO4 0.1419 g 5 MgCl2·6H2O 0.3049 g 6 1.0M HCl 9 mL 7 CaCl2·2H2O 0.3675 g 8 Na2SO4 0.071 g 9 Tris 6.057 g 10 1.0M HCl 30 mL

Prepare a water bath heated to ~37 °C. Put the SBF solution into a 25 mL glass vial and heat it to 36.5 °C on a water bath. Place a pellet of ceramic material such that the entire sample is submerged in the SBF, seal the container and leave it at 36.5 °C until the next lab period.

question: Not all of the carbonate ions used in the reaction actually incorporate in the final structure of CHA. Propose a characterization method to quantitatively study amount of carbonate in your CHA samples (for instance, carbonate to phosphate ratio, which might be different from what you have in your solution at the beginning). Propose a method to estimate the ratio between A- and B- type carbonates and explain how/why this method can distinguish the A- and B- type carbonate substitution.

Procedure Reaction 1: Dissolving the Copper 1. Obtain a clean, dry, glass centrifuge tube. 2. Place a piece of copper wire in a weighing paper, determine the mass of the wire and place it in the centrifuge tube. The copper wire should weigh less than 0.0200 grams. 3. In a fume hood, add seven drops of concentrated nitric acid to the reaction tube so that the copper metal dissolves completely. Describe your observations in the lab report. (Caution, Concentrated nitric acid and nitrogen dioxide are very corrosive. Either will turn your skin yellow on contact. Do not leave any spills on the lab bench or in the fume hood.) 4. When the copper has dissolved, add seven drops of distilled water to the tube. Reaction 2: Preparation of Copper(II) Hydroxide 1. Add 15 drops of 3.0 M aqueous sodium hydroxide to the tube. Make sure that the reactants are well mixed. Shake the tube carefully or gently flick the bottom of the tube with your finger. Remember that the contents of the tube may still be corrosive. 2. Add a second 15 drops of NaOH(aq), mix well, and record your observations. If you have two layers at this point it means that you have not mixed the solution well enough. 3. Centrifuge the reaction mixture. 4. The liquid at the top of the centrifuged mixture is called the supernatant while the solid is called a precipitate. Before separating the supernatant from the precipitate it is necessary to ensure that all of the copper(II) hydroxide has been precipitated. The supernatant should be clear and colorless indicating the absence of any Cu+2 ions in the solution. It should also be basic due to an excess of OH- ions. Using a clean glass stirring rod, transfer a drop of the supernatant onto a piece of red litmus paper. If the litmus paper turns blue then the solution is basic and enough NaOH has been added. If the paper does not turn blue, add more NaOH, mix well, recentrifuge, and repeat the litmus paper test until the paper does turn blue. 5. An efficient separation of supernatants and precipitates is key to obtaining a good final yield of copper. The supernatant liquid can be separated from the precipitate by expelling the air from the bulb of a Pasteur pipet, inserting the tip of the pipet into the supernatant, then gently sucking the supernatant into the pipet. If you expel air or liquid into the precipitate with the pipet, you will stir up the precipitate and will have to repeat the centrifugation step. Remove as much liquid as possible and discard it in the waste container provided on the instructor’s cart. It is better to leave a small amount of supernatant liquid than to remove some of the copper(II) hydroxide precipitate. Reaction 3: Formation of Copper(II) Oxide 1. Set up a hot water bath by placing a beaker of water on a hotplate, placing an iron ring around the beaker, and heating the water to boiling. 2. Place the centrifuge tube containing the copper(II) hydroxide into the boiling water. Carefully hold the tube with a test tube clamp so that it doesn’t get water into it. Record your observations. Reaction 4: Formation of Copper(II) Sulfate 1. Add 20 drops of 3.0 M H2SO4 to the solid in the centrifuge tube. Stir carefully to ensure that the copper(II) oxide dissolves completely. Complete dissolution of the mixture will require thorough mixing and possibly heating of the solution. 2. Obtain the mass of a small, clean, glass test tube as accurately as possible. 3. Transfer the liquid from the centrifuge tube into the test tube. Rinse the centrifuge carefully with 1.0 mL of distilled water and transfer the rinse into the test tube containing your sample. 4. Record your observations on the data sheet. Reaction 5: Formation of Copper Metal 1. Add a small quantity of zinc powder to the sample solution. Continue adding zinc in small quantities until the solution loses the blue copper(II) color. Any excess zinc added will need to be removed so don’t add it too quickly or in large quantities. When the solution has turned colorless, add several drops of 3.0 M H2SO4 to the tube to dissolve any left over zinc. You can tell that the zinc has dissolved when addition of sulfuric acid does not generate bubbles. 2. Allow the copper metal to sink to the bottom of the tube and carefully remove the supernatant liquid using a Pasteur pipet. 3. Wash the red-brown copper metal in the tube with 1.0 mL of water. Allow the copper metal to settle to the bottom and remove the excess water. Repeat this rinsing process two more times. 4. Describe your observations on the data sheet. Drying the copper metal 1. After removing as much of the third rinse water as possible you are ready to dry the metal. This must be done carefully in a cool Bunsen Burner flame. If the tube is heated too quickly there is a risk of ejecting the contents of the tube as the water boils. Also, if the flame is too hot you may convert the copper metal back into black copper(II) oxide. The objective is to drive the water from the tube as steam. Make sure that as water condenses on the walls of the tube that you continue to heat until all of the water if gone from the tube. 2. Once all of the water is removed from the tube, cool the tube and its contents then determine the mass of copper by weighing the tube and subtracting the tube + copper weight from the weight of the empty tube (Reaction 4 step 2). If the mass of copper is higher than the original mass of the copper wire it either contains water or zinc or has been converted to copper(II) oxide. Excess water can be removed by reheating the tube and reweighing to constant mass. Excess zinc requires addition of sulfuric acid followed by re-rinsing with water and re-drying. Chemistry 1215 Experiment 9 Lab Report Name ______________________________ Data Sheet Mass of copper wire _______________ Mass of clean, dry test tube _______________ Mass of test tube plus copper _______________ Mass of final copper sample _______________ Percent recovery of copper. Show all calculations. Observations 1. Describe your observations for Reaction 1 including colors, gases formed, etc. 2. Describe your observations for Reaction 2 including colors, gases formed, etc. 3. Describe your observations for Reaction 3 including colors, gases formed, etc. Estimate the temperature of the decomposition of Copper(II) hydroxide. 4. Describe your observations for Reaction 4 including colors, gases formed, etc. 5. Describe your observations for Reaction 5 including colors, gases formed, etc. Write a brief discussion of your results including a statement of the final percent recovery of copper and a discussion of reasons why the recovery differs from 100%. Chemistry 1215, Experiment #9; Copper and its compounds, Pre-lab Name ____________________________________ 1. Write a balanced chemical equation including phase labels for the reaction between aqueous copper (II) nitrate and aqueous sodium hydroxide. 2. Nitrogen monoxide (NO) and nitrogen dioxide (NO2) are toxic, corrosive gases that significantly lower blood pressure when inhaled. How are these gases produced in today’s experiment? What should you do to protect yourself against their toxicity? 3. Iron reacts with oxygen from the atmosphere to produce iron (III) oxide, also known as rust (Fe2O3). What chemical species is oxidized in this reaction? What is the reducing agent? Jaffrey Zagnut couldn’t find any nitric acid so he tried to dissolve his copper sample in hydrochloric acid instead. Unfortunately his copper wouldn’t dissolve in HCl. Why will copper dissolve in nitric acid but not in hydrochloric acid (after all, HCl is a stronger acid than HNO3). Chemistry 1215, Experiment #9; Copper and its compounds, Post-lab Name ____________________________________ 1. Copper (II) hydroxide is converted into copper (II) oxide by heating the test tube containing Cu(OH)2 in a hot water bath. Is it necessary to use distilled water in this water bath? Why or why not? 2. Copper metal doesn’t “rust” in the presence of oxygen at room temperature. However, it will react with O2 at elevated temperatures. Write a balanced chemical equation describing the formation of copper (II) oxide when copper metal is heated in air. 3. When zinc is dissolved in sulfuric acid a gas is produced. What is the chemical identity of this gas? How is it produced? 4. Jaffrey Zagnut started with a 0.032 g sample of copper which he took through the series of reactions described in this experiment. At the end of the experiment he obtained 0.038 g of a black product. What was his percent yield? What is the most likely source of the error in his experiment? (Hint: consider question 2 above)

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