Investigating the Solubility of 5 Salts

1. Purpose

The experiments were carried out for measurement of solubility of 4 chosen salts in water to arrange these salts in the ascending order of solubility.

2. Introduction

Different salts dissolve in water to different extent. This fact is of great importance in our daily life as well as in industrial domain like extraction of useful mineral/metal, purification of salts, corrosion etc. Solubility of salts is quantitatively expressed in different units. The most common being maximum mass of a salt which can be completely dissolved in a unit mass of a solvent say 14 gm of KNO3 per 100 gm of water i.e. of gm solute/gm solvent type. Other units are Molarity (M), Molality (m), Normality (N), Mole fraction (X) etc. These different units are useful in different situations. It is easiest to experimentally determine the solubility of a salt in gm (of salt)/100 gm (of solvent) unit and this value can easily be converted into other units by using suitable formulae. The formula to convert gm solute/gm solvent solubility value into molarity (M) is following:

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M =              ……… (1)

Where,  is density of solution in g/liter and formula mass is in g/mol.

Materials are classified as insoluble, slightly soluble or soluble. Materials with solubility less than 0.01M are classified as insoluble.

Experiments were carried out to measure solubility of four salts Calcium Sulfate CaSO4, Copper (II) Nitrate Cu(NO3)2, Potassium Nitrate KNO3 and Sodium Chloride NaCl.

3. Materials:

Approximately five grams of each of salts Ammonium Nitrate NH4NO3, Calcium Sulfate CaSO4, Copper (II) Nitrate Cu(NO3)2, Potassium Nitrate KNO3 and Sodium Chloride NaCl, 250 ml beaker, 100 ml beaker, 50 ml burette and Parr DMA 35 density meter.

4. Procedure:

4.1. Ammonium Nitrate NH4NO3 salt was ground into fine powders using a mortar and pestle.

4.2. Approximately 5 gm of the salts was weighed using a balance and the exact mass was recorded for each of the salts.

4.3. The salt powder was placed in a clean 250 ml beaker.

4.4. Water was added slowly using 50 ml burette and the solution was continuously stirred while water was being added. Water addition was done until either all the salt powder was dissolved or 50 ml was reached, whichever occurred first.

4.5. Volume of water required for complete dissolution of the salt powder was recorded.

4.6. Density and temperature of the saturated salt solution was measured by using Parr Density meter and the same was recorded.

4.7. Steps 4.1 through 4.6. were repeated for the remaining four salts and the values were recorded in a table.

5. Data:

The data from this experiment is presented in table 1 below:

Table 1: Experimental data on solubility of the salts

Salt
Mass of Salt (gm)
Volume of H2O (ml)
Temperature (oC)
Density of Solution (gm/ml)
CaSO4
5.088
50
none
None
Cu(NO3)2
5.020
23
30.4
1.125
KNO3
4.956
48
16.9
1.065
NaCl
4.993
49
20.2
1.065

6. Results and Analysis:

From data it is very clear that CaSO4 is insoluble in water.

Solubility of remaining three salts was calculated using formula 1.

For Cu(NO3)2:

M = 1.07 at 30.4 oC; Hence soluble

For KNO3:

M = 1.00 at 16.9 oC; Hence soluble

For NaCl:

M = 1.20 at 20.2 oC; Hence soluble

The results are presented in table 2 in the ascending order of solubility.

Table 2: Solubility of given salts:

Salt
Solubility of Salt (g/100 g of water)
Solubility of Salt (M)
Temperature (oC)
CaSO4
0
Insoluble
Not recorded
KNO3
10.35
1.00
16.9
Cu(NO3)2
21.83
1.07
30.4
NaCl
10.20
1.20
20.2
The order of solubility of salts is following

CaSO4< KNO3< Cu(NO3)2< NaCl

This order may get slightly modified if we compare solubility of salts at same temperature. It should be noted that solubility value depends on temperature and this is the reason, why solubility value is reported along with temperature.

Glassware has been used in these experiments at visibility of solution was required to determine that salts were completely dissolved. Besides, these glass wares provide reasonable accuracy and are fairly less costly.

The salts were ground into fine powder because fine powders accelerate rate of dissolution of salts, hence the experiment can be finished in short span of time.

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