1. A sample contains BaCl2.2H2O and NaCl. After 0.678 g of sample was heated and

Question

1. A sample contains BaCl2.2H2O and NaCl. After 0.678 g of sample was heated and residue weighted 0.648 g. What is the percent of BaCl2.2H2O in the sample? 2. Do solid NaCl, MgCl2 conduct electricity? Why? What happens after you add distilled water into solid NaCl? What is the conductivity of the solution? 3.For the following reaction: Al2(SO4)3(aq) + 3BaCl2 (aq) ? 3 BaSO4(s) + 2 AlCl3 (aq) 0.780 g of aluminum sulfate was mixed with 0.950 g of barium chloride. A white precipitate barium sulfate was formed. (show calculations for all the questions) a. Write the balanced equation for the reaction b. Which one is limiting reagent? c. What is the theoretical yield? d. If the actual yield is 0.456g , what is the percent yield of barium sulfate? 4. Which of the following will conduct electricity? Which ones are strong electrolytes, weak electrolytes and non-electrolytes. Write down the dissociation equations for electrolytes in water. a. 0.1 M NaOH b. 0.1 M HCl c. 0.1 M CH3COOH d. 0.1 M NH3 e. 0.1 M sugar (C11H22O11)

Explanation / Answer

1)Assuming there was no furthermass losswith continued heating ... all the water is evaporated and the difference in mass is due to the loss of water in the BaCl2.2H2O

change in mass = 0.678 - 0.648 = 0.030 g

so mass of water lost = 0.030 g



molar masswater = 1.01 x 2 + 16.00 = 18.02 g / mol

molH2Olost = 0.030 g H2O x [1 mol / 18.02 g] = 1.665 x 10^(-3) mol H2O



each mol BaCl2.2H2O contains 2 mol water

so mol BaCl2.2H2O in sample = 1.665 x 10^(-3) / 2 = 8.33 x 10^(-4) mol BaCl2.2H2O



molar mass BaCl2.2H2O = 137.33 + 35.45 x 2 + 2 x 18.02 = 244.27 g / mol

mass BaCl2.2H2O in sample = 8.33 x 10^(-4) mol BaCl2.2H2O x [244.27 g / mol]

= 0.203 g BaCl2.2H2O



Edit: oopps ... it wants the % BaCl2.2H2O

so % BaCl2.2H2O = (mass BaCl2.2H2O in sample / mass sample) x 100%

= (0.203 / 0.678) x 100%

= 29.9%

2) no solid salts cannot conduct electricity becauseIn the solid state the cations(+vly charged ions) and anions(-vly charged ions)are held together by strong electrostatic forces and hence they behave neutral.but when distilled water is added they conduct electricity becausewhen they are in fused state the oppositely charged ions get separated giving room to electric conductivity (cation of the salt is associated to -ve part of the solvent while anion is with +vly charged part).

Pure water does not

conduct; therefore the bulb does

not light. Right: A solution of

sodium chloride allows the

current to pass through it, and

the bulb lights.

4) c

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