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Questions and Answers
Can you get the dye back to the original color (green)?
Can you get the dye back to the original color (green)?
What are the products of the reaction between sodium hydrogen carbonate (NaHCO3) and heat?
What are the products of the reaction between sodium hydrogen carbonate (NaHCO3) and heat?
What is the purpose of heating the alum solution?
What is the purpose of heating the alum solution?
The reaction between aluminum and potassium hydroxide (KOH) is exothermic.
The reaction between aluminum and potassium hydroxide (KOH) is exothermic.
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What is the chemical formula for alum?
What is the chemical formula for alum?
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The theoretical yield of a reaction is calculated using the ______ ratios.
The theoretical yield of a reaction is calculated using the ______ ratios.
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Which of the following is NOT a type of experimental error?
Which of the following is NOT a type of experimental error?
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What is the purpose of vacuum filtration?
What is the purpose of vacuum filtration?
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What instrument is used to measure the pH of a solution?
What instrument is used to measure the pH of a solution?
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What is the name of the reagent used to test for the presence of aluminum ions?
What is the name of the reagent used to test for the presence of aluminum ions?
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What is the name of the reagent used to test for the presence of sulfate ions?
What is the name of the reagent used to test for the presence of sulfate ions?
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The mass of a hydrated compound will decrease when heated due to the loss of water.
The mass of a hydrated compound will decrease when heated due to the loss of water.
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Which type of balance is more precise, a top-loading balance or an analytical balance?
Which type of balance is more precise, a top-loading balance or an analytical balance?
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What is the purpose of a volumetric pipette?
What is the purpose of a volumetric pipette?
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What is the purpose of a graduated cylinder?
What is the purpose of a graduated cylinder?
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What is the formula for calculating density?
What is the formula for calculating density?
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What is the purpose of Job's plots?
What is the purpose of Job's plots?
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What does the term "neutralization equivalent" refer to?
What does the term "neutralization equivalent" refer to?
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Phenolphthalein is a commonly used indicator in acid-base titrations.
Phenolphthalein is a commonly used indicator in acid-base titrations.
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What happens when sodium alginate is added to a calcium chloride solution?
What happens when sodium alginate is added to a calcium chloride solution?
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What is the purpose of using a spectrophotometer in the salicylate level determination experiment?
What is the purpose of using a spectrophotometer in the salicylate level determination experiment?
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Study Notes
Acid-Base Reactions
- Goal: Determining if a dye can be returned to its original color.
- Procedure: Initial concentration of a substance (BB) was recorded. The color changes with dropwise addition of HCl (yellow/orange) and NaOH (blue) were observed.
Mass Change Reaction
- Goal: Hypothesizing reaction products using changes in mass.
- Procedure: An empty vial's weight was recorded. Sodium hydrogen carbonate was added to the vial. The vial was heated to 300°C, changes were observed, and the vial was reweighed after cooling.
Crystal Growth
- Goal: Creating a supersaturated alum solution and observing crystal growth.
- Procedure: Alum exceeding solubility was weighed and dissolved in deionized water. The solution was heated and stirred. The solution was stored to observe crystal growth.
Synthesis of Alum from Aluminum
- Goal: Determining the yield of alum synthesis starting with 1 gram of aluminum foil.
- Procedure: Aluminum foil was cut into squares and weighed. KOH was added to the aluminum, causing a reaction with bubbling. The mixture was heated in hot water. Gravity filtration was used to separate the solids. The filtrate was collected in a beaker. A second reaction produced alum: KAl(OH)4 + 2H2SO4 + 8H2O → KAI(SO4)2⋅12H2O. Sulfuric acid (H2SO4) was added, and the mixture was heated to 80°C. Cooling in an ice bath caused crystals to form.
Analysis of Alum
- Goal: Determining the pH of an alum solution and identifying Al ions, sulfate ions, and water.
- Procedure: The pH of a 5% alum solution was measured using pH paper (~3.0). Potassium hydroxide (KOH) was added dropwise. The presence of Al ions was confirmed using aluminon, which turns red in contact with Al ions. Sulfate ions were confirmed using barium chloride, which produces a cloudy solution with sulfate ions. Heating alum to a constant weight demonstrated the removal of water.
pH of Alum Solution
- Goal: Determining the pH of an aqueous alum solution.
- Procedure: A 5% alum solution was prepared, diluted, and its pH tested, which was found to be 3.0. The result was compared with expected pH values.
Raising pH of Solution
- Goal: Investigating the effect of raising the pH of an alum solution.
- Procedure: Alum solutions were exposed to increasing amounts of potassium hydroxide (KOH) and the pH changes were observed.
Identifying Aluminum Ions
- Goal: Confirming the presence of aluminum ions in the alum solution.
- Procedure: Alum, sodium sulfate, and aluminum nitrate solutions were tested with aluminon to confirm the presence of aluminum ions.
Identifying Sulfate Ions
- Goal: Confirming the presence of sulfate ions in the alum solution.
- Procedure: Alum, sodium sulfate, and aluminum nitrate solutions were tested with barium chloride to confirm the presence of sulfate.
Identifying Water
- Goal: Determining the presence of water in the alum.
- Procedure: Alum crystals were heated to observe the removal of water. Successive weighings were taken until no change in mass occurred.
Density Measurement of a Liquid
- Goal: Comparing the accuracy of volumetric pipettes and graduated cylinders for density calculations.
- Procedure: The mass of a 150 mL beaker was measured. 10 mL of deionized water was measured using a volumetric pipette and graduated cylinder and added to the beaker. The mass was measured again. Five determinations were performed for each method. Densities were calculated, and accuracy was evaluated using absolute errors and standard deviations. Volumetric pipettes were found to be more precise.
Stoichiometry
- Goal: Determining the stoichiometric ratio of elements A and B in a chemical reaction.
- Procedure: Concentrated solutions A and B were diluted and mixed in various ratios (1:4, 2:3, 2.5:2.5, 3:2, 4:1) in triplicate. Absorbance was measured using a spectrometer. The intersection point of linear portions of the graph indicated the stoichiometric ratio of A to B. Moles of A and B at this point were calculated, leading to the chemical formula and balanced reaction for A and B.
Neutralization Equivalent
- Goal: Accurately determining the concentration of NaOH by titrating it with KHP (Standardize).
- Procedure: A burette was filled with NaOH. The initial weight of the burette was recorded. KHP was weighed and transferred to an Erlenmeyer flask. Deionized water was added to the flask. Phenolphthalein was added as an indicator. Titration was performed by adding NaOH to the flask until the solution turned pink. The final weight of the burette was recorded, and titrations were repeated to ensure consistent concentrations.
Synthesis and Reaction of Calcium Chloride
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11.1: Synthesis of Calcium Chloride
- Goal: Synthesizing a calcium chloride solution.
- Procedure: Calcium metal was added to DI water, causing a reaction with smoking and opaqueness. HCl was gradually added until the solution cleared. A beaker was cooled in an ice bath.
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11.2: Reaction with Alginate
- Goal: Studying the effect of sodium alginate on calcium chloride solutions.
- Procedure: Sodium alginate was added dropwise to a calcium chloride solution, leading to the formation of gelatinous green solid balls. Observations were made regarding the effect of saltwater on the product.
Salicylate Level in Blood Serum
- Goal: Determining salicylate concentration in unknown serum samples.
- Procedure: Standard solutions with varying salicylate concentrations were prepared. Absorbance of each solution at 535 nm was measured. Three independent samples from an unknown serum were prepared, and their absorbance was measured. A calibration curve was used to calculate salicylate concentration in the unknown samples.
Dehydration
- Goal: Determining the mass loss of an unknown substance by heating.
- Procedure: Weight an empty vial, add a scoop of unknown powder, heat, allow to cool, and reweigh.
Density
- Goal: Determining the density of a liquid.
- Procedure: Record the temperature, measure the mass of a beaker, measure a specific volume of a liquid using a volumetric pipette, pour the liquid into the beaker, and weigh the beaker and liquid. Calculate density.
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