Hello. I have an experiment that deal with trying to find the concentration of c

Question

Hello. I have an experiment that deal with trying to find the concentration of copper in solution.

I weighed 0.2015 g of CuO and transfered it into a 150 beaker. Then Added 30 mL 6M HCl. Then Added 50 mL 6M Ammonia. The solution was transfered into a 100 mL volumetric flask and filled to line.

I then transfered the contents into 6 , 10mL volumetric flasks at the following volumes. Filled to line. and measured absorbance

I need to find the :

1) Initial concentration of copper solution (in the 100 mL) : ____________________M

2) Concetration of copper in the solution: __________________M

Flask 1 0 mL 0 abs Flask 2 1 mL 0.1730 abs Flask 3 2 mL 0.3470 abs Flask 4 4 mL 0.6139 abs Flask 5 6 mL 0.8751 abs Flask 6 8 mL 1.1821 abs

Explanation / Answer

the series of reactions that take place in the process are

CuO + H2O = Cu(OH)2

Cu(OH)2 + 2 HCl = CuCl2 + 2 H2O

CuCl2 + 2 NaOH = Cu(OH)2 + 2 NaCl

in the initial stages, 30 ml of HCl is added.

but in the second step, 50 ml of NaOH is added in order to make sure that all the HCl is neutralised and all the amount of CuO is converted to Cu(OH)2 and hence excess NaOH is added.

the moleculasr weight of CuO is 63.5 + 16 = 79.5

then 1 M CuO contains 79.5 gms of CuO in 1000 ml.

then , in 100 ml the weight of CuO dissolved is 0.2015 g

then, the initial concentration in 100 ml of CuO is 0.2015*.0.1/ 79.5 = 0.00025 M

when we have plotted the absobance on X-axis and volume of the solution on Y-axis,

we get a slightly straight line at a bend at 0.8751 abs.

we can observe that the solution is less acidic means more basic than the o ml volume original solution .

and the concentration of the solution is around 0.00245 M

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