Solution Concentration Problem Set Discussion

CHEM25415 Instrumental Analysis 1

Solution Concentration Problem Set

  1. Calculate the molarity of ethanol in an aqueous solution that contains 2.30 g of C2H5OH in 3.50 L of solution. (Ans: 0.0143 M)

 

  1. Describe the preparation of the following from solid BaCl2 ∙ 2H2O:

a) 2.00 L of 0.108 M BaCl2 ∙ 2H2O (Ans: Dissolve 52.8 g of BaCl2 ∙ 2H2O in water and dilute to

2.00 L)

b) 500.0 mL of 0.0740 M Cl (Ans: Dissolve 4.52 g of BaCl2 ∙ 2H2O in water and dilute to 500.0 mL)

 

  1. A solution contains 6.0 µmol of Na2SO4 in 250.0 mL. How many ppm of sodium does it contain?

(Ans: 1.1 mg/L Na+)

 

  1. What is the molarity of K+ in a solution that contains 63.3 ppm of K3Fe(CN)6? (Ans: 5.77 × 10-4 M)

 

  1. Calculate the molar concentration of a 1.00 ppm solution of (NH4)4Ce(SO4)4H2O. What is the molarity of SO42- in this solution? (Ans: 1.63 × 10-6 M Ce salt; 6.52 × 10-6 M SO42-)

 

  1. How many grams of NaCl must be weighed out to prepare 500.0 mL of a 1000.0 ppm solution of

Cl? (Ans: 0.8239 g)

 

  1. How many grams of K+ are in 1000.0 mL of a 500.0 ppm solution of KClO3? (0.1592 g)

 

  1. Determine the molarity of 37.0 % (w/w) HCl that has density of 1.19 g/mL. (Ans: 12.1 M)

 

  1. A 6.42 % (w/w) Fe(NO3)3 solution has a density of 1.059 g/mL. Calculate the molar concentration of

Fe(NO3)3 in this solution. (Ans: 0.281 M)

 

  1. Describe the preparation of:
    1. 500 mL of 4.75 % (v/v) aqueous ethanol. (Ans: Dilute 23.8 mL of ethanol to 500 mL with water)
    2. 500 mL of 4.75 % (w/v) aqueous ethanol. (Density of ethanol = 0.789 g/mL). (Ans: Dilute 30.1 mL of ethanol to 500 mL with water)

 

  1. A 0.489 g sample of ore is analyzed for chromium and found to contain 0.355 mg of Cr2O3. Express the concentration of Cr2O3 as % (w/w). (Ans: 0.0726 % (w/w))

 

  1. A 250.0 ppm solution of K+ is prepared from KCl. From this solution, you wish you prepare a 0.00100 M solution of Cl. How many mL of the 250.0 ppm solution must be diluted in 1000.0 mL to prepare this solution? (Ans: 156 mL)

 

  1. What is the molarity of Fe2+ in a solution that contains:
    1. 75.6 pg FeCl2 in 1.00 L? (Ans: 5.96 x 10-13 M)
    2. 62.4 ppm (NH4)2Fe(SO4)2? (Ans: 2.19 × 10-4 M)

 

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  1. Calculate the following for 250.0 mL of a solution containing 0.250 g of MgCl2•2H2O:
    1. % (w/v) (Ans: 0.100 % (w/v))
    2. ppm (Ans: 1.00 × 103 ppm)
    3. molarity (Ans: 7.62 × 10-3 M)

 

  1. Water is considered “hard” when it contains 100 ppm (w/v) of CaCO3. How many mg of Ca2+ and how many mg of CO32- are in 0.5 L of a 100 ppm calcium carbonate solution? (Ans: 20 mg Ca2+ and

30 mg CO32-)

 

  1. In many states, a person is considered legally intoxicated if his or her blood contains 0.100 % ethanol (v/v). What volume of ethanol in the blood is enough to produce legal intoxication in a 70 kg person with a total blood volume of 5.45 L? (Ans: 5.45 mL)

 

  1. Calculate the grams of salt required to prepare 250.0 mL of the following solutions:
    1. 0.100 M potassium hydrogen phthalate (MM = 204.23 g/mol) (Ans: 5.11 g)
    2. 2.00 ppm Na+ from Na2CO3 (Ans: 0.00115 g)
    3. 2.50 ppb Cr3+ from Cr(NO3)3 (Ans: 2.86 × 10-6 g)

 

  1. For the preparation of a 1000.0 ppm stock solution of Na+:
    1. Determine the theoretical mass of pure sodium required to prepare this solution in a 250.0 mL volumetric flask. (Ans: 250.0 mg)
    2. Determine the theoretical mass of Na2SO4 required to prepare this solution in a 250.0 mL volumetric flask. (Ans: 0.7720 g)

 

  1. Aliquot dilution method: To prepare a stock Na+ solution, 0.8562 g of Na2SO4 was weighed on an analytical balance, dissolved, and diluted to the mark in a 250.0 mL volumetric flask. A substock Na+ solution was then prepared by transferring 10.00 mL of stock solution to a 100.00 mL volumetric flask and diluting to the mark. A set of Na+ calibration standards were then prepared using the aliquot dilution method by transferring volumes of 0.500 mL, 1.000 mL, 1.500 mL, 2.000 mL and 2.500 mL to 50.00 mL volumetric flasks. Determine the actual concentration of Na+ in each calibration standard. (Ans: 1.11 ppm, 2.218 ppm, 3.327 ppm, 4.436 ppm, 5.545 ppm)

 

  1. Serial dilution method: To prepare a stock Na+ solution, 0.6997 g of Na2SO4 was weighed on an analytical balance, dissolved, and diluted to the mark in a 250.0 mL volumetric flask. A substock Na+ solution was then prepared by transferring 5.00 mL of stock solution to a 50.00 mL volumetric flask and diluting to the mark. A set of Na+ calibration standards were then prepared using the serial dilution method by transferring the following volumes into 25.00 mL volumetric flasks and diluting to the mark:

 

Std #1: 1.000 mL of substock

Std #2: 15.00 mL of Std #1

Std #3: 15.00 mL of Std #2

Std #4: 15.00 mL of Std #3

 

Determine the actual concentration of Na+ in each calibration standard. (Ans: 3.63 ppm, 2.18 ppm,

1.31 ppm, 0.784 ppm)

 

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