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Nikitich [7]
3 years ago
8

Suppose an EPA chemist tests a 250.0 ml sample of groundwater known to be contaminated with nickel(II) chloride, which would rea

ct with silver nitrate solution like this:
NiCl_2(aq) + 2AgNO_3 (aq) -------> AgCl (s) + Ni(NO_3)_2 (aq)
The chemist adds 58.0m silver nitrate solution to the sample until silver chloride stops forming. He then washes, dries, and weighs the precipitate. He finds he has collected of 3.6 mg of silver chloride.
1. Calculate the concentration of nickel(II) chloride contaminant in the original groundwater sample. Round your answer to 2 significant digits.
Chemistry
1 answer:
nataly862011 [7]3 years ago
6 0

Answer:

0.05 mM

Explanation:

NiCl_2(aq) + 2AgNO_3 (aq) -------> 2 AgCl (s) + Ni(NO_3)_2 (aq)

Molar mass of  NiCl_2 = 129.5994 g/mol

Molar mass of AgNO_3 = 169.87 g/mol

Molar mass of AgCl = 143.32 g/mol

The chemist added 58mM of silver nitrate = 58 / 1000 = 0.058 M

mass of silver nitrate present =0.058 × 169.87 = 9.85246 g

according to the equation of reaction

2 mole of silver nitrate is needed to produce 2 mole of silver chloride  

2 mole of silver nitrate = 339.74 g

2 mole of silver chloride = 286.64 g

339.74 g silver nitrate  produces 286.64 g silver chloride

unknown mass of silver nitrate produce 0.0036 g

unknown mass of silver nitrate = 339.74 × 0.0036 / 286.64 = 0.00427 g

then

1 mole of NiCl_2 reacts 2 mole of AgNO_3

129.5994 g of NiCl_2 react with 339.74 g AgNO_3

unknown mass of NiCl_2  react with  0.00427 g AgNO_3

mass of NiCl_2 = 0.00163 g

mole of NiCl_2 present = 0.00163 / 129.5994 = 0.0000126 mole

Molarity = 0.0000126 mole / 0.25 L = 0.0000504 M = 0.05 mM

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labwork [276]

Answer:

a) The slope of the line of best fit plot = -12629.507

b) ΔH∘ = 105 kJ

c) Intercept of the line of best fit plot = 39.099

d) ΔS∘ = 325.1 J/K

e) Option A is correct.

Solubility will increase as temperature increases, because as T increases the (−ΔH∘/RT) term becomes smaller therefore K will get larger.

f) Option D is correct. All of the options are correct.

Explanation:

The complete question is presented in the first attached image to this question. This complete question has the data readings required to plot the graph.

The second attached image has the plotted graph and the regression analysis to obtain the line of best fit.

The equation of the line of best fit obtained is

y = -12629.507x + 39.099

Comparing the given expression for the question with the equation of a straight line

ln (K) = (−ΔH∘/RT) + (ΔS∘/R)

y = mx + c

y = In K

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So, to answer the question now

a) The slope of the line of best fit plot = -12629.507

b) Slope = (−ΔH∘/R)

(−ΔH∘/R) = -12629.507

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c) Intercept of the line of best fit plot = 39.099

d) Intercept = (ΔS∘/R)

(ΔS∘/R) = 39.099

ΔS∘ = 39.099 × 8.314 = 325.069086 J/K = 325.1 J/K

e) Do you expect the solubility of Borax to increase or decrease as temperature increases?

Solubility will increase as temperature increases, because as T increases the (−ΔH∘/RT) term becomes smaller therefore K will get larger.

f) Why was it necessary to make sure that some solid was present in the main solution before taking the samples to measure Ksp? Select the option that best explains why.

A. To make sure no more sodium borate would dissolve in solution.

B. To ensure the dissolution process was at equilibrium.

C. To make sure the solution was saturated with sodium and borate ions.

D. All of the above

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