PREPARATION OF SOLUTIONS FROM LIQUID SOLUTES

Introduction

The method of dilution is a common technique used to prepare solutions from liquid solutes. It involves adding a solvent, typically water, to a concentrated solution to decrease its concentration and create a more diluted solution. The following steps can be used to prepare a solution by dilution:

1. Determine the desired concentration of the final solution. This will depend on the specific application or experiment you are performing.
2. Measure out a known volume of the concentrated solution using a graduated cylinder or pipette. This volume should be small enough to allow for the addition of the solvent but large enough to accurately measure.
3. Add the solvent to the concentrated solution slowly while stirring or swirling. The amount of solvent added will depend on the desired final concentration and the volume of the concentrated solution used.
4. Measure the final volume of the solution and calculate the actual concentration using the equation: C1V1 = C2V2, where C1 is the initial concentration of the concentrated solution, V1 is the initial volume used, C2 is the final concentration of the diluted solution, and V2 is the final volume of the diluted solution.
5. Mix the solution thoroughly to ensure the solute is uniformly distributed throughout the solution.

It’s important to note that the solvent should be chosen carefully to ensure it will not react with or change the properties of the solute. Additionally, accurate measurement of the volumes and concentrations is crucial to ensure the final solution is prepared to the desired specifications.

 

Steps involved in the preparation of solutions from liquid solutes

The preparation of solutions from liquid solutes typically involves the following steps:

1. Determine the desired concentration: The first step in preparing a solution is to determine the desired concentration. This will depend on the application and the specific solute being used.
2. Weigh out the solute: Once the desired concentration has been determined, the solute must be weighed out using a balance. It is important to use an accurate balance and to measure the solute to the correct number of significant figures.
3. Add the solute to a volumetric flask: The solute is then added to a volumetric flask. A volumetric flask is a specially calibrated flask that allows for the precise measurement of a specific volume of liquid. The solute should be added to the flask using a funnel to prevent spills.
4. Add solvent to the flask: After the solute has been added to the volumetric flask, the solvent is added to the flask until it reaches the desired volume. The solvent should be added slowly and carefully to avoid splashing or spills.
5. Mix the solution: Once the solvent has been added to the flask, the solution should be mixed thoroughly to ensure that the solute is evenly distributed throughout the solvent. This can be done by shaking the flask gently or by using a magnetic stirrer.
6. Verify the concentration: Finally, the concentration of the solution should be verified using an appropriate analytical method, such as titration or spectrophotometry. If the concentration is not within the desired range, the solution can be adjusted by adding more solute or solvent as needed.

Note: It is important to follow proper safety procedures when handling solutes and solvents, including wearing appropriate personal protective equipment and working in a well-ventilated area.

 

To determine the concentration of a liquid solute (stock solution), several pieces of information are needed, including:

1. Density: The density of a substance is defined as its mass per unit volume. It is usually expressed in grams per milliliter (g/mL) or kilograms per liter (kg/L).
2. % Purity: The percentage purity of a substance is the amount of pure substance in a given sample, expressed as a percentage. For example, if a sample of a substance is 90% pure, it means that 90% of the sample is the pure substance, and the remaining 10% is impurities.
3. Molar Mass: The molar mass of a substance is the mass of one mole of the substance. It is usually expressed in grams per mole (g/mol).
4. Specific Gravity: Specific gravity is the ratio of the density of a substance to the density of a reference substance (usually water) at a specified temperature.
5. w/v: It refers to the weight of the solute (in grams) per volume of solution (in milliliters) and is expressed as a percentage.
6. w/w: It refers to the weight of the solute (in grams) per weight of the solution (in grams) and is expressed as a percentage.

 

Once you have all this information, you can use the following formulas to determine the concentration of the solute:

1) For w/v and density:

Concentration (in g/mL) = (weight of solute in grams / volume of solution in mL) / density of solution in g/mL

2) For w/w and density:

Concentration (in g/mL) = (weight of solute in grams / weight of solution in grams) / density of solution in g/mL

3) For % purity and molar mass:

Concentration (in mol/L) = (% purity / 100) x (density of solution in g/mL) / (molar mass of solute in g/mol)

4) For specific gravity:

Concentration (in g/mL) = (specific gravity of solution) x (density of water at the same temperature)

Note: If you have the molarity (concentration in moles per liter) of the solution instead of the density, you can use the following formula:

Concentration (in mol/L) = (mass of solute in grams / molar mass of solute in g/mol) / volume of solution in liters.

 

Calculations

Here are some examples of how to calculate the concentration of liquid solutes given different parameters:

Determining concentration in terms of weight per volume (w/v):

Example: A 500 mL solution contains 25 grams of NaCl. What is the concentration of the solution in terms of weight per volume (w/v)?

Solution:

Concentration (w/v) = (mass of solute (g) / volume of solution (mL)) x 100% Concentration (w/v) = (25 g / 500 mL) x 100% Concentration (w/v) = 5%

Therefore, the concentration of the NaCl solution in terms of weight per volume (w/v) is 5%.

 

Determining concentration in terms of weight per weight (w/w):

Example: A solution contains 50 grams of salt dissolved in 450 grams of water. What is the concentration of the solution in terms of weight per weight (w/w)?

Solution:

Concentration (w/w) = (mass of solute (g) / total mass of solution (g)) x 100% Concentration (w/w) = (50 g / (50 g + 450 g)) x 100% Concentration (w/w) = 10%

Therefore, the concentration of the salt solution in terms of weight per weight (w/w) is 10%.

 

Determining concentration in terms of specific gravity:

Example: A solution has a specific gravity of 1.2. What is the concentration of the solution?

Solution:

Specific gravity = density of solution / density of water Density of solution = specific gravity x density of water

Assuming the density of water is 1 g/mL:

Density of solution = 1.2 x 1 g/mL Density of solution = 1.2 g/mL

Therefore, the concentration of the solution cannot be determined solely based on its specific gravity. Additional information is needed, such as the molecular weight or molarity of the solute.

 

Determining concentration in terms of relative molecular mass:

Example: A solution contains 5 grams of glucose (C6H12O6) dissolved in 100 mL of water. What is the concentration of the solution in terms of relative molecular mass?

Solution:

Relative molecular mass of glucose = (6 x atomic mass of carbon) + (12 x atomic mass of hydrogen) + (6 x atomic mass of oxygen) Relative molecular mass of glucose = (6 x 12) + (12 x 1) + (6 x 16) Relative molecular mass of glucose = 180 g/mol

Concentration (in moles/L) = mass of solute (g) / (relative molecular mass (g/mol) x volume of solution (L)) Concentration (in moles/L) = 5 g / (180 g/mol x 0.1 L) Concentration (in moles/L) = 0.2778 mol/L

Therefore, the concentration of the glucose solution in terms of relative molecular mass is 0.2778 mol/L.

 

Determining concentration in terms of molar mass

1) What is the concentration of a solution that contains 10 grams of sodium chloride (NaCl) in 500 mL of water?

Step 1: Determine the molar mass of NaCl The molar mass of NaCl is 58.44 g/mol.

Step 2: Convert the mass of NaCl to moles 10 g / 58.44 g/mol = 0.171 moles

Step 3: Calculate the molarity of the solution Molarity = moles of solute / volume of solution (in liters) Molarity = 0.171 mol / 0.5 L = 0.342 M

Therefore, the concentration of the NaCl solution is 0.342 M.

 

2) Suppose you have a solution containing 5.0 grams of glucose (C6H12O6) in 500 milliliters of water. To determine the concentration of glucose in moles per liter (M), you can use the following formula:

M = (mass of solute in grams ÷ molar mass of solute in grams per mole) ÷ volume of solution in liters

The molar mass of glucose is 180.16 g/mol.

First, convert the volume of the solution from milliliters to liters: 500 mL ÷ 1000 mL/L = 0.5 L

Next, plug in the values and solve for M: M = (5.0 g ÷ 180.16 g/mol) ÷ 0.5 L M = 0.055 M

Therefore, the concentration of glucose in the solution is 0.055 M.

 

Determining % purity

Question 1: A sample of calcium carbonate (CaCO3) has a mass of 5 grams. After it is heated and the carbon dioxide (CO2) is released, the mass of the remaining calcium oxide (CaO) is found to be 3.5 grams. What is the % purity of the original sample?

Step 1: Calculate the molar mass of CaCO3 The molar mass of CaCO3 is 100.09 g/mol.

Step 2: Determine the moles of CaCO3 in the original sample 5 g / 100.09 g/mol = 0.050 mol

Step 3: Determine the theoretical yield of CaO The theoretical yield of CaO can be calculated by multiplying the moles of CaCO3 by the molar mass ratio of CaO to CaCO3 (i.e. 1 mol CaO / 1 mol CaCO3) and the molar mass of CaO (i.e. 56.08 g/mol). Theoretical yield of CaO = 0.050 mol x 1 x 56.08 g/mol = 2.804 g

Step 4: Determine the actual yield of CaO The actual yield of CaO is 3.5 g.

Step 5: Calculate the % purity of the original sample % purity = (actual yield / theoretical yield) x 100% % purity = (3.5 g / 2.804 g) x 100% = 124.6%

Therefore, the % purity of the original sample is 124.6%. This value is greater than 100% because there may have been impurities present in the sample that were not accounted for in the calculation.

 

Question 2: Suppose you have a sample of aspirin (acetylsalicylic acid, C9H8O4) that weighs 1.2 grams. You dissolve the sample in a small amount of ethanol and then add water to make a total volume of 100 milliliters. You then titrate the solution with a standardized sodium hydroxide (NaOH) solution and find that it requires 16.2 milliliters of the NaOH solution to reach the endpoint. The concentration of the NaOH solution is 0.100 M. To determine the % purity of the aspirin sample, you can use the following formula:

% purity = (moles of pure solute ÷ moles of impure sample) x 100%

First, calculate the number of moles of NaOH used in the titration: 0.100 M x 0.0162 L = 0.00162 moles

Next, use stoichiometry to determine the number of moles of aspirin in the sample: 1 mole of aspirin reacts with 1 mole of NaOH 0.00162 moles of NaOH ÷ 1 mole of NaOH ÷ 2 moles of aspirin = 0.00081 moles of aspirin

Then, calculate the mass of pure aspirin in the sample: 0.00081 moles of aspirin x 180.16 g/mol = 0.146 g

Finally, calculate the % purity of the aspirin sample: % purity = (0.146 g ÷ 1.2 g) x 100% % purity = 12.2%

Therefore, the % purity of the aspirin sample is 12.2%.

 

Primary standard, secondary standard, and standardized solution are terms used in analytical chemistry to describe different types of chemical standards used for the calibration and quality control of analytical instruments and methods.

1. Primary standard: A primary standard is a highly purified compound with a known and precise amount of a particular substance. Primary standards are used as reference materials for the calibration of analytical methods and instruments. They are typically used to determine the concentration of other solutions or compounds in a sample. Primary standards are often used for titrations, where a solution of known concentration is used to determine the concentration of an unknown solution.
2. Secondary standard: A secondary standard is a solution of known concentration that is used to calibrate or standardize analytical instruments or methods. Secondary standards are less pure than primary standards and are typically prepared by diluting a primary standard solution to a known concentration. Secondary standards are used to ensure that analytical instruments are working correctly and that results are accurate and precise.
3. Standardized solution: A standardized solution is a solution of known concentration that is used for chemical analysis or as a reference material. Standardized solutions are often prepared by accurately measuring a primary standard or secondary standard and diluting it to the desired concentration. Standardized solutions are used in a variety of analytical methods, such as titrations, spectrophotometry, and chromatography, to determine the concentration of unknown solutions or compounds in a sample.