11. How would you prepare?
a) 250 mL of a 0.05 M solution of BaCl2 2H2O (MW = 244.27) starting with 80% pure BaCl2 2H2O and water?
b) 2000 mL of a 0.1 M nitric acid solution, beginning with concentrated nitric acid (15 M)?
 

12. Calculate the volume of solution containing 35 mg/mL of barium chloride dihydrate (BaCl2 2H2O, MW = 244.27). Which would be necessary to precipitate completely the sulfate from 1.420 grams of pure sodium sulfate (Na2SO4, MW = 142.0)
 

13. You prepared your NaOH (MW = 40.00) titrant by diluting a stock solution of NaOH provided for you in plastic bottles on top of your lab bench. Suppose, however, that these stock solutions were no longer available but instead you had to use a commercial product known to consist of a 3.0% (gm/100 mL) solution of NaOH in water. How much (in mL) of this commercially available NaOH solution would be needed to prepare 2.0 liter of a 0.10 M solution of NaOH?
 

14. A 0.3729 gram sample of impure Na2CO3 (MW = 106.00) requires 32.77 mL of a 0.1500 N H2SO4 (MW = 98.00) titrant for complete neutralization. Calculate the % Na2CO3 in the sample.
 

15. Calculate the pH of the solution which results when 38.50 mL of 0.2400 M benzoic acid (HOBz, MW=122.0, Ka = 6.3 × 10-5) is mixed with 41.50 mL of 0.2000 M potassium benzoate (KOBz , MW=160.0)
 

Clueless:

Both parts a) and b) are pure Chem 111 problems (P.S. 130). The other point here is the quality of measurements needed in the solutions as specified. This is importance in that the lower the quality of solution needed, the easier it is to accomplish in the lab (the less demanding the measurements, the simpler the equipment which can be used).

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Hints:

Here the low quality specified (0.05 M in part a, 0.1 M in part b) means that the solution preparation is not rigorous. Simple balances and glassware will work adequately. The only possible sticking point here is that the BaCl2 . 2H2O employed to prepare the solution is only 80% pure. The usual calculation assumes 100% purity of salt. Thus, to get the amount of salt needed to make the desired 0.05 M solution using only 80 %
BaCl2 . 2H2O it will be necessary to weigh out more salt than the "100 % pure" calculation gives you. This can be systematized by employing another conversion factor. The way to view this is to note that "80 % BaCl2 . 2H2O" means:

80 g Pure BaCl2 . 2H2O = 100 g Impure BaCl2 . 2H2O

Do the calculation as usual. When you determine the # g of Pure BaCl2 . 2H2O, simply employ the information above as your final conversion factor so that the final units come out as #g Impure BaCl2 . 2H2O.

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Clueless:

This is another Chem 111 problem set calculation. (P.S. 125). You are looking at a major reaction involving two species, BaCl2 . 2H2O, and Na2SO4.

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Hints:

Consider this a Limiting Reagent problem, with the value 1.420 g pure (100%) Na2SO4 being the limiting reagent. Convert this to moles and then to moles of BaCl2 . 2H2O, and finally to mL of the solution you've been given 35 mg/mL of BaCl2 . 2H2O.

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Clueless:

This is yet another Chem 111 type calculation (P.S. 130) where you're given a concentrated solution and asked to prepare a more dilute one.

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Hints:

Take the given concentration of NaOH and convert it to Molarity. Then a straightforward Chem 111 (P.S. 130) calculation should bring you to the desired value. Note the issue of quality here.

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Clueless:

This is nothing more than a commonplace titration calculation. Set up the usual template.

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Hints:

The only points of interest here are that the analyte, Na2CO3, corresponds to a diprotic system, as CO32- takes two protons to be completely neutralized. The second point is that the concentration of the titrant is given in NORMALITY. You need to convert this value to Molarity before you proceed.

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Clueless:

You're being asked for pH, so this is an Acid/Base problem. You need to look at each formula and decide what kind of acid properties it has. Then after the 2 formulas (as solutions) are mixed, you need to decide whether a major reaction takes place, which will change #mmoles of the given formulas and may produce new formulas with acid/base properties.

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Hints:

The best way to proceed is to draw the pH line and place each formula on its respective position, complete with #mmoles, on the pH line. Then, using the "neighbors rule", decide whether a major reaction takes place. If so, readjust #mmoles and formulas until you have the composition of the solution after the major reaction. This should lead you to deciding how to proceed to calculate the pH of the final solution at equilibrium

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