Question

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Review Topics) [References) Use the References to access important values if needed for this question. A solution contains 6.23x10' M potassium sulfate and 1.29x10-2 M ammonium carbonate. Solid barium nitrate is added slowly to this mixture. A. What is the formula of the substance that precipitates first? formula = formula = | B. What is the concentration of barium ion when this precipitation first begins? [Ba2+] = 1 Submit Answer Retry Entire Group 9 more group attempts remaining

Answer 1

Consider two precipitation reactions that occurs in the solution when we add solid barium nitrate.

1) Ba ²⁺ (aq) + SO ₄^2- (aq) $\rightleftharpoons$ BaSO₄ (S)

2) Ba ²⁺ (aq) + CO ₃^2- (aq) $\rightleftharpoons$ BaCO₃ (S)

To identify which precipitate will starts forming first, we need to calculate minimum concentration of Ba ²⁺ required to start precipitation of two compounds.

We have, Ksp = [ Ba ²⁺] [SO ₄^2- ] = 1.1 $\times$ 10 ^-10

$\therefore$ [ Ba ²⁺] minimum = 1.1 $\times$ 10 ^-10 / [SO ₄^2- ]

We have given [SO ₄^2- ] = 6.23 $\times$ 10 ^-03 M

$\therefore$ [ Ba ²⁺] minimum =  1.1 $\times$ 10 ^-10 / 6.23 $\times$ 10 ^-03 = 1.76 $\times$ 10 ^-08 M -------------> (1)

We have, Ksp = [ Ba ²⁺] [CO ₃ ^2- ] = 5.0 $\times$ 10 ^-09

$\therefore$ [ Ba ²⁺] minimum = 5.0 $\times$ 10 ^-09 / [CO ₃ ^2- ]

We have given [CO ₃ ^2- ] = 1.29  $\times$ 10 ^-02 M

$\therefore$ [ Ba ²⁺] minimum = 5.0 $\times$ 10 ^-09 / 1.29  $\times$ 10 ^-02 = 3.88 $\times$ 10 ^-07 M ---------------->(1)

From equation 1 and 2 , we found that [ Ba ²⁺] required for precipitation of BaSO₄ is lower than BaCO₃.

Hence, BaSO₄ will precipitate out first and [ Ba ²⁺] when this first precipitation begins is 1.76 $\times$ 10 ^-08 M.

ANSWER :

A) What is the formula of compound that precipitates out first

BaSO4

B) What is the concentration of Ba ²⁺ ions when this first precipitation begins?

[ Ba ²⁺] =

1.76 $\times$ 10 -08 M

( Note : IF your values of K sp values are different result value of second option may change slightly )