Lab Report: Solubility of Alkali Hydroxides

Abstract

In this experiment, we investigated the solubility of alkali hydroxides, specifically Ca(OH)2, LiOH, NaOH, and KOH, by titrating them against HCl. The solubility of these hydroxides was determined by measuring the concentration of the saturated solutions. The results were analyzed to understand the trends in solubility related to the periodic table and ionic bonding characteristics.

Introduction

When alkali metals from groups one and two of the periodic table combine with OH molecules, they form ionic bonds. In this type of bonding, metals lose electrons, becoming positively charged ions, while non-metal ions/molecules gain electrons, becoming negatively charged.

The attraction between oppositely charged ions leads to the formation of a rigid 3-D lattice structure.

Due to their polar nature, ionic compounds are usually soluble in polar solvents like water. This solubility occurs because water is a polar molecule with a partial positive (δ+) and partial negative (δ-) charge on its atoms.

The solubility of a solute in water at a given temperature is the maximum amount that will dissolve in 100 grams of water at that temperature, resulting in a saturated solution.

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In this experiment, we aim to determine the concentrations of saturated solutions of Ca(OH)2, LiOH, NaOH, and KOH by titrating them against HCl, a strong acid.

Our hypothesis is based on the periodic trends: as you move down groups one and two, the atomic radii of the atoms increase, making the hydroxides more soluble. Conversely, as you move across a period, the solubility decreases due to smaller atomic radii and increased ion charges, resulting in stronger electrostatic attractions within the lattice structure.

Materials and Methods

Apparatus:

• Burette
• White tile
• Ca(OH)2
• KOH (aq)
• NaOH (aq)
• LiOH (aq)
• Pipette and pipette filler
• Phenolphthalein indicator
• Distilled H2O
• Volumetric flasks
• Beaker
• Conical flasks (250 cm3 and 100 cm3)
• 0.05 moldm-3 HCl
• 0.10 moldm-3 HCl
• 0.20 moldm-3 HCl

Experimental Procedure

1. Determining Concentration of Ca(OH)2 solution:

1. Pipette 50 cm3 of Ca(OH)2 (aq) into a 250 cm3 conical flask. Add four drops of phenolphthalein.
2. Calculate moles of Ca(OH)2 = conc. x vol
3. Calculate suitable concentration of HCl for titration (approx 15 - 30 cm3 is a suitable titre).
4. Using a burette, titrate 0.05 moldm-3 HCl against Ca(OH)2 until the solution reaches neutralization, turning colorless.
5. Record the result and repeat the experiment until two readings are within 0.1 cm3 of each other.

2. Calculating Concentration of LiOH, NaOH, and KOH

1. Dilute the solutions as shown in the table below:

3. Calculate the concentrations of each diluted solution:

LiOH

• Moles = conc. x vol = 5.16 x 0.01 = 0.0516 moles in 250cm3
• Concentration in 1 dm3 = 0.0516 x 4 = 0.2064 moldm-3

NaOH

• Moles = conc. x vol = 10.5 x 0.025 = 0.2625 moles in 250cm3
• Concentration in 1 dm3 = 0.2625 x 4 = 1.05 moldm-3

KOH

• Moles = conc. x vol = 17.1 x 0.025 = 0.4275 moles in 250cm3
• Concentration in 1 dm3 = 0.4275 x 4 = 1.71 moldm-3

4. Select a suitable concentration of HCl to titrate with for each solution (based on 1:1 ratio):

5. Titrate the selected concentrations of HCl against the diluted solutions and record the titre value at the point of neutralization. Repeat the experiments as before.

6. Calculate the experimental concentrations of each saturated solution.

In order to determine the most concentrated alkali hydroxide, we will use stoichiometry and calculations to calculate the experimental values of the concentration of the saturated solutions.

Results

The results of the titration experiments are summarized in the following table:

Discussion

The results obtained from the titration experiments will be discussed in this section. We will analyze the experimental concentrations of the saturated solutions and draw conclusions regarding the solubility of the alkali hydroxides.

Conclusion

In this experiment, we determined the concentrations of saturated solutions of Ca(OH)2, LiOH, NaOH, and KOH by titrating them against HCl. Based on the experimental values, we will draw conclusions about the relative solubility of these alkali hydroxides.

Recommendations

Based on our findings, we may make recommendations for further experiments or applications related to the solubility of alkali hydroxides. These recommendations will depend on the specific outcomes of our study.

Possible Errors

There are several potential sources of error in this experiment that must be considered. These errors include inaccuracies in measuring, dilution, titration, and variations in room temperature. To improve the accuracy and reliability of the results, it is important to address and minimize these errors as much as possible.

Safety and Risk Assessment

Proper safety precautions were taken during this experiment to handle corrosive substances like KOH, NaOH, LiOH, and HCl. Eye protection and gloves were worn, and pipette fillers were used to prevent contact with these hazardous chemicals. Safety guidelines from Cleapss Hazcards were followed to ensure a safe laboratory environment.