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11 Dec 2019

In the qualitative analysis scheme, magnesium and nickel precipitate from solution upon the addition of sodium hydroxide. Once separated from the remaining cations by filtration or decanting, the solid mixture is acidified and warmed to dissolve magnesium and nickel cations back into solution. Adding ammonia creates a buffer solution. (Remember, HCl and NH3 makes for NH4+ cation.) The buffered solution should just be basic (say, pH = 8). Adding sodium hydrogen phosphate (Na2HPO4) precipitates magnesium as MgNH4PO4 (Ksp = 3 x 10-13).

a. Write the Ksp expression for the dissociation of MgNH4PO4.

b. Calculate the molar solubility of the compound in pure water.

c.Calculate the [NH4+] in a pH of 8.

d. Calculate the molar solubility of MgNH4PO4 in a solution with pH of 8.

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Reid Wolff
Reid WolffLv2
13 Dec 2019

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Related questions

In the qualitative analysis scheme, magnesium and nickel precipitate from solution upon the addition of sodium hydroxide. Once separated from the remaining cations by filtration or decanting, the solid mixture is acidified and warmed to dissolve magnesium and nickel cations back into solution. Adding ammonia creates a buffer solution. (Remember, HCl and NH3 makes for NH4+ cation.) The buffered solution should just be basic (say, pH = 8). Adding sodium hydrogen phosphate (Na2HPO4) precipitates magnesium as MgNH4PO4 (Ksp = 3 x 10-13).

a)Write the dissociation equation and corresponding Ksp expression

b)Calculate the molar solubility of the compound

This is for the lab practical I take on Tuesday night. If you could answer each one and show your work/ explain that'd be amazing so I can do well on the actual practical on Tuesday! Thank you!

Chemistry 211 Lab Final Study Guide Spring 2015

Useful Information:
1 ampere =coulomb/sec
Faraday’s constant = 96,500 coulombs/mole of electrons
Molar mass of Au = 197.0 g/mole, Molar mass of Cu = 63.55 g/mole
m = moles , ' ’

c kg

ΔTf

= Tf

− Tf

where Tf is for the pure solvent and Tf

is for the mixture.

ΔT = (K

)(m ) ,

m = (

(mass of

solute, g )
)( ).

f f c

c molar

mass, g

mol −1

mass of

solvent, kg


7. Next question

(a) If you weigh 6.355 grams of copper, add concentrated nitric acid to dissolve it, and then dilute the solution to a total volume of 50 mL, how many moles of copper are in this solution?


(b) For the equilibrium reaction 3H2(g) + N2(g) → 2NH3(g), what is the equilibrium constant expression, Kc, for this reaction? (5pts)

8. Suppose at some temperature, the equilibrium concentration of H2 is 0.45M, the equilibrium concentration of N2 is 0.38M, and the equilibrium concentration of NH3 is 0.42M. What is the value of the equilibrium constant for the reaction 3H2(g) + N2(g) → 2NH3(g) at this temperature? (Show your work. No credit will be given if your work is not shown.)

9. Next question
(a) If you need 0.0534 moles of NaOH to reach equivalent point in the titration with acetic acid, how many mL of 0.09876M NaOH will you need?


(b) The Ksp of Cu(OH)2 is 2.2x10-20, what is the solubility of Cu(OH)2?


10. Next question
(a) In non-sulfide qualitative analysis of representative cations, the Group A cations comprising of Pb2+,

Hg2+, and Ag+ give a precipitate with solution.
(b) From a solution containing mixture of Pb2+, Fe3+, and Al3+, Pb2+ is removed by adding HCl solution. To the remaining cation mixture, on making the solution basic with NH3 (pH=9 – 10), both the cations form precipitate. Further analysis of the cation mixture containing Fe3+ and Al3+ is carried out by adding NaOH solution.


Aluminum hydroxide (dissolves/remains undissolved) in NaOH solution while Ferric hydroxide ( dissolves/remains undissolved).
(c) Fe(OH)3 precipitate is dissolved in minimal amount of aqueous HCl which gives a


yellow solution. To this solution addition of solution (at pH = 4 – 5) yields a dark blue solid known as Prussian Blue.

(d) Describe the method for checking for completeness of precipitate in qualitative analysis of ions.

QUESTION 1

Equal molar amounts of nitric acid (a strong acid) and methylamine (a weak base) are combined in an aqueous solution.

The pH of the resulting solution is:

greater than 7

close to 7

less than 7

QUESTION 2

A 1.00 L aqueous solution contains 0.10 mol acetic acid and 0.10 mol sodium acetate. The initial pH is 4.74. Calculate the pH after the addition of 0.049 mol of OH-.

QUESTION 3

Using the Henderson-Hasselbalch equation, calculate the pH of a buffer solution that contains 0.96 M NH4Cl and 0.33 M NH3.

QUESTION 4

A 10.0 mL volume of 0.49 M HNO3 is combined with a 15.0 mL volume of 0.58 M NaOH. Calculate the pH.

QUESTION 5

A diprotic acid is being titrated with a strong base. A volume of 0.0500 L of 0.0750 M diprotic acid (H2A+) is combined with 0.0150 L of 0.250 M NaOH.

Ka1 for the diprotic acid is 3.6 x 10-3.

Ka2 for the diprotic acid is 4.7 x 10-7.

Calculate the pH of the solution.

QUESTION 6

A saturated solution of Ca3(PO4)2 has a concentration of Ca2+ = 5.65 x 10-7 M and a concentration of PO43- = 9.80 x 10-8 M. Calculate Ksp for Ca3(PO4)2.

Answer in exponential notation. Examples:

Scientific Notation Exponential Notation

1.00 x 10-10 1.00e-10

5.00 x 105 5.00e5

QUESTION 7

A solution is prepared by combining 0.125 L of 0.020 M Pb(NO3)2 and 0.125 L of 0.050 M PbBr2. Does a precipitate of PbBr2 form? Ksp of PbBr2= 6.6 x 10-6

Yes, a precipitate forms.

No, a precipitate does not form.

QUESTION 8

Calculate the molar solubility of MgF2 in 0.37 M NaF at 25°C. Ksp = 7.4 x 10-11.

Answer in exponential format.

QUESTION 9

Determine the concentration of Ag+ in a solution prepared by adding 0.10 mol AgNO3 to 1.0 L of 3.9 M NH3.

Ag+(aq) + NH3(aq) [left right double arrow] AgNH3+(aq) K1 = 2.1 x 103

AgNH3+(aq) + NH3(aq) [left right double arrow] Ag(NH3)2+(aq) K2 = 8.1 x 103

Ag+(aq) + 2 NH3(aq) [left right double arrow] Ag(NH3)2+(aq) Kf = 1.7 x 107

QUESTION 10

Determine the molar solubility of MgCO3 at 25°C in pure water.

Ksp = 6.8 x 10-6

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