hydrated copper sulphate

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Analysis

Experiment 1

Mass of crucible + lid = 20.82 g

Mass of hydrated CuSO4 = 23.36 – 20.82 = 2.54 g

Mass of anhydrous CuSO4 = 22.41 – 20.82 = 1.59 g

Mass of water = 2.54 – 1.59 = 0.95 g

% of water by mass = (0.95/2.54) x 100

= 37.401575

= 37.4 % (3.s.f)

Mr of H2O = 18

No. of moles in 2.54g of H2O = 0.95/18 = 0.05278 moles

No. of moles in 1g of H2O = 0.05278/2.54

= 0.020778652 moles

Experiment 2

Mass of hydrated CuSO4 used = 5.83g

Average titre = (23.5+24.1)/2 = 23.80 cm3

Volume of S2O32- = 23.80 cm3

Concentration of S2O3 = 0.1 mol dm-3

Moles of S2O32- in 25ml = (0.1 x 23.80) / 1000 = 0.00238 moles

Moles of S2O32- in 250ml = 10 x 0.00238 = 0.02380 moles

To find the number of moles of Cu 2+, we need to see what ratio the Cu 2+ and S2O32- react in:

They react in a 1:1 molar ratio.

Therefore the no. of moles of Cu2+ = 0.02380

Mass of Cu2+ in this number of moles = 0.02380 x 63.5

=  1.5113g

Percentage by mass of Cu2+ in 1g of copper sulphate =

(1.5113/5.83) x 100

= 25.9228130387 % = 25.9% (3.s.f)

Mass of sulphate ion = 1g – (0.259228g + 0.374016g)

                                                        = 0.366756g 

Deducing the formula of hydrated copper sulphate crystals:

The ratio is:

Cu2+ : SO42- : H2O

63.5 : 96.0 : 18.0 (Mr)

0.259228g : 0.374016g : 0.366756g (mass in 1g)

0.004082 : 0.003896 : 0.020375 (moles)

= 1 : 0.954434 : 4.991426

≈ 1 : 1 : 5  (simplest ratio)

Therefore the formula for the hydrated copper suphate crystals is CuSO4.5H2O 

Evaluation

In experiment 2 an anomalous result was found. The second titre read 25cm³. In comparison to 23.1(1st titre) and 24.5 (3rd titre) this value was relatively large, therefore would affect the average, so it was not included. This was to ensure as accurate results as possible.

As a whole my experiment was accurate because the formula I produced was correct. However this experiment was open to various errors which hindered the chances of obtaining accurate results. Furthermore on many occasions in my calculations, I had to round off number of moles in order to deal with simpler numbers. The reasons for these inaccuracies may have been due to errors in measurement and procedure as will be explained later.

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Errors in procedure and measurement

  • Some soot was formed at the bottom of the crucible. In turn this adds to the total mass, thus preventing me from obtaining the mass purely of the copper sulphate and crucible + lid.
  • After the hydrated crystals were heated to become anhydrous crystals, they were left to cool. During this time, water in the air could have reacted with the anhydrous crystals to become hydrous again. This would add onto the mass and cause inaccuracies, thus making the experiment less reliable.
  • A lot of thermal energy is required to remove ...

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