SOLUBILITY OF SALTS CONCENTRATION AND TEMPERATURE

GEORGIA MILLITARY COLLEGE

NATURAL SCIENCE DEPARTMENT

ONLINE CAMPUS

CONCENTRATION, TEMPERATURE AND THE SOLUBILITY OF SALTS

NAME

STUDENT NUMBER

CLASS

PROFESSOR

Introduction

This laboratory measures and compares the water solubility of salts, and analyzes the effect of temperature increases on solubility. Concentration is the amount of solute contained in a given amount of solution. Molar concentration is defined as the quantity of solute in moles present in a liter of water. The experiment investigates the solubility of three salts/solutes: Cobalt (II) Nitrate (Co (NO3)2), potassium permanganate (KMnO4), and sodium chloride (NaCl). Solubility is defined as the amount of solute in grams that completely dissolves in 100 grams of solvent at a given temperature. A solution is considered saturated if it contains the maximum quantity of solute that completely dissolves in 100grams of solvent at any given temperature. A solution is unsaturated if it contains less solute than is needed to completely dissolve in 100g of solvent, and supersaturated if it contains more solute than is needed to dissolve completely in 100g of solute at a given temperature.

The solubility of solutes is influenced by multiple factors, including molar mass and temperature. Solutes with higher mass are likely to have bigger particles and are likely to be less soluble in liquids. At the same time, some solutes exhibit huge increases in solubility with temperature increases, while others show little variation. For this reason, it is important to measure the solubility of different solutes to see how they compare. The general hypothesis is that solutes with higher atomic mass will exhibit lower solubility, and that solubility will increase with increases in temperature.

The objectives of this laboratory are summarized as follows:

i) To enhance one’s ability to calculate a solute’s molar concentration at different temperatures.

ii) To increase one’s familiarity with the solubility curve.

iii) To enhance one’s understanding of solubility.

Materials and Methods

Preparing the Lab

1. Access the simulation environment on the course home page and click on the Concentration Link.

2. Once the Simulation environment loads, click on the bottom faucet to set the solvent volume at 0.1L.

3. If necessary, click on the top faucet to add solvent.

Performing the Environment

1. Select the saltshaker containing Cobalt (II) Nitrate from the solute category and shake it gently to add the salt to the solvent.

2. Keep adding the solute until the solution is saturated and record the molar concentration (M) of the solute at the saturation point in mol/L.

3. Repeat the procedure for sodium chloride (NaCl) and potassium permanganate (KMnO4).

Data Analysis

1. Calculate the quantity of solute that dissolved in 100g of water.

2. Using the solution concentration data, calculate n (the number of moles of solute) using the formula n = M (Molarity) x V (Volume).

3. Obtain the molar mass (MM) of each solute in g/mol from the periodic table atomic mass, and use the formula n = m/MM to calculate the solute mass in grams (m). Since the density of water is 1g/mL, m will be equal to solubility in g/100g of water.

4. Record the results.

Preparing Solubility Curve

5. Use the provided data to generate a solubility graph for cobalt (II) nitrate and obtain the temperature of the simulation.

Data and Discussion

Table 1: Summary of Solution Concentrations

Solute/Salt

Molar Concentration of Solution in mol/L

Solution Volume in L

Co(NO3)2

1.5

0.1

KMnO4

0.8

0.1

NaCl

1.2

0.1

Table 2: Calculation of Solubility from Solution Concentrations

Solute/salt

M in mol/L

n in mol

MM in g/mol

m in g

Solubility in g/100g of water

Co(NO3)2

1.5mol/L

0.15mol

182.94g/mol

27.44g

27.44

KMnO4

0.8mol/L

0.08mol

158.04g/mol

12.64g

12.64

NaCl

1.2mol/L

0.12mol

58.44g/mol

7.01g

7.01

Table 3: Cobalt (II) Nitrate Solubility Curve

Temperature oc

0

18

91

Solubility, g/100g of water

84.03

98.93

338.9

Figure 3: Cobalt (II) Nitrate Solubility Curve

Discussion

Table 1 shows the molar concentrations of the three solutes: Co (NO3)2, KMnO4, and NaCl. The solutions used in the laboratory contain1.5M cobalt (II) Nitrate, 0.8M potassium permanganate, and 1.2M sodium chloride. From the table, cobalt (II) Nitrate has the highest number of moles of solute present in a liter of water, implying that it is the most concentrated among the three solutions. Potassium permanganate (KMnO4) is the least concentrated of the three solutions.

Table 2 presents the relationship between concentration and solubility. Cobalt (II) Nitrate exhibits the highest solubility in grams per 100g of water, potassium permanganate has the second highest solubility, while sodium chloride has the least solubility in water. 27.44g of cobalt (II) nitrate can dissolve in 100grams of water, while only 7.01 grams of sodium chloride can dissolve in the same amount of water. This shows that cobalt (II) nitrate is more soluble than potassium permanganate, which is more soluble than sodium chloride. This is contrary to the hypothesis that solutes with higher molar mass are less soluble, since cobalt (II) nitrate exhibits the highest solubility despite having the highest molar mass, while sodium chloride, which has the lowest molar mass, is the least soluble per 100g of water. The procedure could be enhanced for accuracy by using more concentrated solutions since higher concentrations increase the accuracy of molar mass measurements, particularly for measurements involving low molar masses (Wypych, 2024). Improving the accuracy of the molar mass measurement would subsequently increase the accuracy of the calculated solute mass and solubility.

Figure 1 shows that the solubility of cobalt (II) nitrate increases with temperature. This supports the hypothesis that temperature increases the solubility of solutes. The solutes solubility increases slowly between 0 and 18 degrees Celsius, and then increases exponentially at temperatures above 18 degrees Celsius. The solubility of Cobalt (II) Nitrate at point 11 could be calculated by obtaining the rate of change (slope) in solubility between points 0 and 18 to obtain the effect of a unit change in temperature: