Question

Ques- For analyzing your water sample for Cu and Zn , you have to prepare your stock solution from the scratch by weighing copper(2)sulphate and anhydrous zinc sulphate.

1- How would you prepare one litre of 1000ppm of Cu and Zn from their salt? and after how would you prepare your following standards in HNO 2% from your 1000ppm (Cu and Zn) stock solution you have prepared?

a) Stock solution: 1000ppm of Cu and Zn from copper(2)sulfate and anhydrous zinc sulfate

b) HNO3 (2% in 500ml )

c) 50ml of 50ppm Cu, Zn in HNO3, 2%

d) 50ml of 10ppm Cu, Zn in HNO3, 2%

e) 50ml of 5ppm Cu, Zn in HNO3, 2%

F) 100ml of 25ppb Cu, Zn in HNO3, 2%

Answer 1

a) We know that

1 ppm = 1 mg/L.

The stock solutions of copper (II) sulfate, CuSO₄ and zinc sulfate, ZnSO₄ are 1000 ppm each, i.e, the stock solutions contains 1000 mg/L CuSO₄ and 1000 mg/L ZnSO₄.

The volume of the solution = 1 L.

Therefore,

Mass of anhydrous CuSO₄ required = (volume of solution in L)*(concentration of solution in mg/L) = (1 L)*(1000 mg/L) = 1000 mg = (1000 mg)*(1 g)/(1000 mg) = 1 g (ans).

Mass of anhydrous ZnSO₄ required = (volume of solution in L)*(concentration of solution in mg/L) = (1 L)*(1000 mg/L) = 1000 mg = (1000 mg)*(1 g)/(1000 mg) = 1 g (ans).

The stock solution is prepared by adding 1 g each of anhydrous CuSO₄ and ZnSO₄ to a 1 L volumetric flask and diluting upto the mark with DI water.

b) We are required to prepare 500 mL of 2% HNO₃ solution (w/v).

We know that 1% solution contains 1 g of the solute in 100 mL solvent.

Here the solvent is water and we have 500 mL solvent.

Therefore,

Mass of HNO₃ required to prepare 2% solution = (500 mL)*(2%)*(1 mg)/(100 mL)*1/(1%) = 10 g (ans).

c) The test solution contains 50 ppm Cu, Zn in 2% HNO₃.

Use the dilution equation:

C₁*V₁ = C₂*V₂

where C₁ = concentration of stock solution = 1000 pm; V₁ = volume of stock solution required.; C₂ = concentration of the reagent in the test solution and V₂ = volume of the test solution = 50 mL.

Plug in values and obtain

(1000 ppm)*V₁ = (50 ppm)*(50 mL)

=====> V₁ = (50 ppm)*(50 mL)/(1000 ppm)

=====> V₁ = 2.5 mL.

The test solution is prepared by adding 2.5 mL of the 1000 ppm stock solution to a 50 mL volumetric flask and diluting upto the mark with 2% HNO₃ solution.

d) Again, use the dilution equation.

C₁*V₁ = C₂*V₂

where C₁ = 1000 pm; C₂ = 10 ppm and V₂ = 50 mL.

Plug in values and obtain

(1000 ppm)*V₁ = (10 ppm)*(50 mL)

=====> V₁ = (10 ppm)*(50 mL)/(1000 ppm)

=====> V₁ = 0.5 mL.

The test solution is prepared by adding 0.5 mL of the 1000 ppm stock solution to a 50 mL volumetric flask and diluting upto the mark with 2% HNO₃ solution.

e) We will use the 50 ppm test solution prepared in part (c) above as the stock solution.

C₁*V₁ = C₂*V₂

where C₁ = 50 pm; C₂ = 5 ppm and V₂ = 50 mL.

Plug in values and obtain

(50 ppm)*V₁ = (5 ppm)*(50 mL)

=====> V₁ = (5 ppm)*(50 mL)/(50 ppm)

=====> V₁ = 5.0 mL.

The test solution is prepared by adding 5.0 mL of the 50 ppm test solution to a 50 mL volumetric flask and diluting upto the mark with 2% HNO₃ solution.

f) We know that

1000 ppb = 1 ppm; therefore,

1 ppb = (1 ppb)*(1 ppm)/(1000 ppb) = 0.001 ppm.

Therefore,

25 ppb = (25 ppb)*(0.001 ppm)/(1 ppb) = 0.025 ppm.

Prepare this test solution from the test solution prepared in (e) above, i,e, the concentration of the stock solution is 5 ppm.

Use the dilution equation. C₁*V₁ = C₂*V₂

where C₁ = 5 pm; C₂ = 0.025 ppm and V₂ = 100 mL.

Plug in values and obtain

(5 ppm)*V₁ = (0.025 ppm)*(100 mL)

=====> V₁ = (0.025 ppm)*(100 mL)/(5 ppm)

=====> V₁ = 0.5 mL.

The test solution is prepared by adding 0.5 mL of the 5 ppm stock solution to a 100 mL volumetric flask and diluting upto the mark with 2% HNO₃ solution.