Experiment 2 Chm 420

SUBJECT CODE EXPERIMENT TOPIC DATE

: : : :

CHM 420 2 WATER OF HYDRATION 03/10/2014

 NAME MATRIC NO I/C NO GROUP LECTURER NAME

: : : : :

NABILAH BINTI AMINUDDIN AMINUDDIN 2014805292 950320145006 AS2301M1 DR. ZURAIDA KHUSAIMI

EXPERIMENT 2 WATER OF HYDRATION OBJECTIVE To determine the percentage of water in an unknown hydrate qualitatively and quantitatively. THEORY In this experiment, the amount of water in the hydrated compound will determined qualitative and quantatively. In the qualitative part, the behaviour of a hydrate will be observed when the sample is heated. Meanwhile, in the quantitative part, amount of water driven off can be determined by heating the sample to constant weight. From, the amount of mass lost, the  percebtage of water in the sample can be determined. This information will be used to calculate the formula of the hydrate. CHEMICALS AND APPARATUS Finely ground copper (II) sulphate pentahydrate CuS. 5 O Unknown hydrated compounds:  NiC  

Analytical balance Crucible and cover Clay triangle Trippod stand Bunsen burner Tile Test tube

METHODOLOGY A. Qualitative determination of water. 1. A clean and dry test tube is obtained and the test tube is held with a clamp with its mouth is 15-20 degrees above the horizontal. The mouth of the test tube is pointed away from people. 2. A scoop of copper (II) sulphate pentahydrate is placed in the test tube. The bottom of the test tube is heat gently to avoid spattering. Changes is observed and recorded in DATASHEET 2. 3. The test tube and its content is allowed to cool to room temperature. 4. A few drops of water is added into the test tube. Observation is recorded. B. Quantitative determination of water in a hydrate. 1. The name of the salt that is analyze is recorded. 2. Tap water is used to clean and distilled water is used to rinse a crucible and a cover. The crucible and cover is placed on the clay triangle. The cover is slightly opened to allow moisture to escape when the crucible is heated. The crucible and cover is heated using a bunsen burner for five minutes. Then, the crucible is allowed to cool to room temperature and its mass is determined. Touching the crucible or cover with hand is avoided because the moisture from skin will add to

the crucible weight. The same balanced is used for the successive weighing of the sample. 3. Between 1.000 g  –   1.500 g of the hydrated compound is placed into a weighed crucible. The crucible and the content is covered and weighed. The cover is adjusted so that it is slightly ajar. To avoid spattering, it is gently heated and the intensity of the flame is increased after five minutes and for about five minutes heat to redness. 4. The crucible is closed and cooling is allowed for f ive minutes after heating and the mass is determined. The heating and weighing is repeated until the results of two successive weighings agree to within 0.05g. this will ensure thatthat all the water is completely driven out of the compound. DATA / RESULLT A. Qualitative determination of water.

Colour of copper (II) sulphate pentahydrate Describe the appearance A few drops of water was added

Before heating Blue

During heating Light blue

Solid

Solid

After heating White Solid White to blue

B. Quantitative determination of water in a hydrate. Sample No: NiC (Nickle) 1. Mass of crucible + cover

= 72.1691g

2. Mass of crucible + cover + sample

= 73.2600g

3. Mass of crucible + cover + sample (after 1st heating)

= 72.7230g

4. Mass of crucible + cover + sample (after 2nd heating)

= 72.6899g

5. Mass of original sample

= 1.0909g

6. Total mass loss by sample after heating

= 0.5701g

7. Percentage water in sample

= 52.26%

CALCULATIONS 5. 73.2600g - 72.1691g = 1.0909g 6. 73.2600g - 72.6899g = 0.5701g QUESTION 1.     + heat →   (anyhydrous)+ 5   2. Percentage of water in sample : Mass of hydrated (   ) = 73.2600g Mass of dry compound (an hydrate)  = 1.0909g Mass of   = 73.2600g - 72.6899g = 0.5701g Percentage of 

=

     ×    

=

 

100 %

× 100 %

= 52.26%

3. Formula of hydrate

 Molar mass (g/mole)

 No of mole

58.71 + 2 (35.45)

2(1.00) +16.00

= 129.61

= 18.00





 

 

= 8.4168 ×  mole

= 31.67 ×  mole

Moles of water per mole nickel (II) chloride :



       

=4

 

DISCUSSION For part A (Qualitative determination of water) the colour of copper (II) sulphate pentahydrate is blue solid before heating. The blue colour indicates that copper (II) sulphate is hydrated (attached to water molecule). Next, during heating, the colour of copper (II) sulphate pentahydrate turn to light blue solid. This show that the copper (II) sulphate is  being hydrated. In addition, after heating, the colour of copper (II) sulphate turns to white solid which means copper (II) sulphate is completely hydrated. When a few drop of water was added to white solid copper (II) sulphate the solid turns colour from white to blue. This is  because solid copper (II) sulphate is hydrated once more. For part B (Quantitative determination of water in a hydrate) the sample given is  NiC  . The compound was weighed and heated and this process is repeated until all the water is completely driven out of the compound. The reason to this is that we want to know the mass of water in the compound by comparing the mass of the compound before and after heating. When the mass of water is known, we can determined the percentage of water in the compound or sample given. Thus, the percentage of water obtained is 52.26%. There are several errors done when conducting the experiment. Some of the error are touching the the crucible and its cover with bare hands. This will add moisture to the crucible and cover. Next, the crucible containing compounds are not completely cooled down when weighed. This will affect the mass of the compound as the mass of the compound is not accurate when it was taken during the crucible is hot. Moreover, when heating copper (II) sulphate pentahydrate, the test tube is set up as the test tube mouth is in the way of there is  people. This will hurt people who are in front of the test tube mouth when the experiment is conducted. There are precaution steps that need to be taken so that errors can be avoided when experiment is conducted. Wear gloves when you want to touch the cr ucible or its cover. Next, wait until the crucible is completely cooled down before weighing it. In addition, set up the apparatus as the test tube is slightly slanted and its mouth is pointed away from people.

CONCLUSION The colour of copper (II) sulphate pentahydrate turns from blue to white when it is heated.The percentage of water in NiC     is 0.78%. REFFERENCE Exploring Chemistry Laboratory Experiments for General Chemistry, Sharipah Ruzaini Syed Aris, Kamariah Muda, Nesamalar Kantasamy,2010,University Publication Cetre (UPENA). Chemistry 11th edition,Raymond Chang, Kenneth A. Goldsby,2014,Mc Graw Hill Education Oxford Dictionary of Chemistry sixth edition ,John Daintith,2008,Oxford University Press