To determine the amount of sodium chloride (NaCl) required to make a 0.200 molar (M) solution with a total volume of 500 milliliters (ml), we need to use the relationship between molarity, moles of solute, and liters of solution.
Molarity (M) is defined as the number of moles of solute dissolved per liter of solution. It is calculated by dividing the moles of solute by the liters of solution:
Molarity (M) = Moles of solute (mol) / Liters of solution (L)
Since we know the desired molarity (0.200 M) and the desired volume in liters (0.500 L for 500 ml), we can rearrange this equation to solve for the number of moles of NaCl needed:
Moles of NaCl = Molarity x Liters of solution
= 0.200 mol/L x 0.500 L
= 0.100 moles NaCl
Once we know the number of moles of NaCl required, we can use the molar mass of NaCl (58.44 g/mol) to convert from moles to grams:
Grams of NaCl = Moles of NaCl x Molar mass of NaCl
= 0.100 mol NaCl x 58.44 g/mol
= 5.844 g NaCl
Therefore, to make 500 ml of a 0.200 M sodium chloride solution, 5.844 grams of sodium chloride is required.
Detailed Explanation
Let’s go through the full calculation step-by-step:
Step 1: Write the known values
– Concentration (molarity) of NaCl solution = 0.200 M
– Volume of solution = 500 ml
To convert volume in ml to volume in liters:
500 ml x (1 L / 1000 ml) = 0.500 L
Step 2: Use the molarity equation to calculate moles of NaCl
Molarity = Moles / Liters
0.200 M = Moles NaCl / 0.500 L
Rearrange and solve:
Moles NaCl = Molarity x Liters
= 0.200 mol/L x 0.500 L
= 0.100 mol NaCl
Step 3: Use moles and molar mass to convert to grams of NaCl
The molar mass of NaCl from the periodic table is 58.44 g/mol.
Use the mole-gram conversion:
Grams = Moles x Molar mass
Grams NaCl = 0.100 mol NaCl x 58.44 g/mol
= 5.844 g NaCl
Step 4: Write the final answer
To make 500 ml of a 0.200 M sodium chloride solution, 5.844 grams of sodium chloride is required.
Why Molarity is Used
Molarity (M) is a convenient unit for expressing the concentration of solutions. Some key reasons why molarity is commonly used include:
- Molarity provides a direct connection between moles of solute and volume of solution.
- Using molarity allows chemists to easily convert between mass of solute, volume of solution, and moles using molar mass and density.
- Molarity simplifies the mathematics involved in stoichiometric calculations and reaction yields.
- Molar concentrations can be easily diluted or concentrated by adding more solvent or solute.
- Molarity is independent of temperature and pressure, so it provides a consistent way to express concentration.
Overall, molarity provides a very useful, convenient unit for chemists to work with when making solutions, performing experiments, and doing chemical calculations. The utility and simplicity of molarity is why it is so commonly used to express the concentration of solutions.
How Molarity Relates to Moles and Mass
Molarity, moles, and mass are fundamentally interconnected quantities. Here is how they relate:
- Molarity (M) is defined as moles of solute per liter of solution.
- Moles are a count of the number of molecules or formula units of a substance.
- The mass of a substance can be converted into moles using its molar mass from the periodic table.
- Molar mass relates grams of a compound to moles by providing the mass per mole ratio.
For example, the molar mass of table salt or sodium chloride (NaCl) is 58.44 g/mol. This means one mole of NaCl has a mass of 58.44 grams.
If we had 100 g of NaCl, we could convert to moles:
100 g NaCl x (1 mol NaCl / 58.44 g NaCl) = 1.71 mol NaCl
We could then use the moles to find the molarity if we dissolve the NaCl in enough water to make a 1 liter solution:
Molarity = Moles / Liters
= 1.71 mol NaCl / 1 L solution
= 1.71 M NaCl
This example shows how mass in grams is connected to moles using molar mass, and moles then relate to molar concentration depending on the volume of solution in liters. Being able to interconvert between mass, moles, and molarity is very useful for performing chemical calculations.
Role of Sodium Chloride as an Electrolyte
Sodium chloride or NaCl is an important electrolyte in biology and medicine. Here is an overview of what electrolytes are and the key functions of sodium chloride in the body:
What Are Electrolytes?
Electrolytes are minerals that carry an electric charge when dissolved in body fluids like blood or cytoplasm. They separate into positively charged cations and negatively charged anions. Important electrolytes in the body include:
- Sodium (Na+)
- Chloride (Cl-)
- Potassium (K+)
- Calcium (Ca2+)
- Magnesium (Mg2+)
- Bicarbonate (HCO3-)
- Phosphate (PO43-)
These charged ions allow electrolytes to conduct electricity and are essential for nerve transmission, muscle contraction, fluid balance, and more.
Functions of Sodium Chloride
As the main components of table salt, sodium and chloride ions play crucial roles:
- Maintaining osmotic balance between cells and body fluids
- Allowing transmission of nerve impulses
- Enabling muscle contraction and relaxation
- Regulating blood pressure and blood volume
- Supporting digestion and nutrient absorption
Sodium chloride is the most abundant electrolyte in extracellular fluid. Having the right levels of sodium and chloride ions in blood, sweat, and tissues is essential for normal body function.
Sodium Chloride Imbalance
Too much or too little sodium chloride can cause problems:
- Hyponatremia – Low sodium levels can lead to muscle cramps, fatigue, and confusion.
- Hypernatremia – High sodium levels can cause high blood pressure, swelling, and fluid retention.
- Hypochloremia – Low chloride can affect pH balance and cause neurological issues.
- Hyperchloremia – High chloride impacts fluid regulation in the body.
Maintaining the right concentration of sodium chloride and other electrolytes is critical for health. Sodium chloride plays diverse and vital roles as an electrolyte in the human body.
Preparing Solutions from a Solid Solute
When preparing an aqueous solution from a solid solute like sodium chloride, there are a few key steps involved:
1. Calculate the amount of solute needed
– For our example problem, we used the desired molarity and volume to calculate the moles and mass of NaCl needed.
– The molar mass from the periodic table converts moles to mass in grams.
2. Measure out the solid solute
– Use an analytical balance to accurately measure out the mass calculated in the first step.
– It’s good practice to add a little extra solute to account for transfer losses.
3. Transfer the solid to a volumetric flask
– Volumetric flasks allow accurate volumes to be measured.
– Transfer the weighed solute to the volumetric flask.
4. Add solvent to reach final volume
– For an aqueous solution, slowly add distilled water up to the volume mark on the flask.
– Cap the flask and mix thoroughly until all solute is dissolved.
Following this general procedure allows accurate and reproducible solutions to be prepared from solid reagents. Proper technique and high quality glassware are important for creating solutions with precise concentrations.
Different Units Used to Express Concentration
There are several different units that can be used to express the concentration of chemical solutions, including:
Molarity (M)
– Moles solute per liter of solution
– Discussed extensively already
Molality (m)
– Moles solute per kilogram of solvent
– Uses mass of solvent instead of volume
Normality (N)
– Equivalents of solute per liter of solution
– Accounts for molecular charge by using equivalents
Mass Percentage
– Mass solute per mass solution x 100%
– Simple to measure using mass alone
Volume Percentage
– Volume solute per volume solution x 100%
– Convenient for solutions of liquids
Parts Per Million (ppm)/Parts Per Billion (ppb)
– Amount solute per 10^6/10^9 parts total solution
– Used for very dilute concentrations
Different concentration units are useful for different applications and situations. Chemists choose the most appropriate way to express concentration based on what is being measured and the level of accuracy needed.
Importance of Proper Laboratory Technique
Proper laboratory technique is extremely important when preparing solutions to ensure accuracy and precision:
Measuring Chemicals
– Use high quality analytical balances and volumetric glassware.
– Carefully measure out reagents according to calculations.
– Follow safety guidelines for handling chemicals.
Mixing Solutions
– Mix thoroughly to ensure even distribution of solute.
– Gently swirl or invert sealed containers.
– Stir continuously when adding one solution to another.
Accounting for Errors
– Make measurements slightly in excess to account for transfer losses.
– Take care when transferring liquids or powders.
– Check for spills or use of incorrect amounts.
Repeatability
– Precisely follow protocols and recipes each time.
– Use consistent equipment and methods.
– Take detailed notes about each step.
Cleaning Equipment
– Clean all glassware thoroughly between uses.
– Use solvents appropriate for the chemicals involved.
– Rinse multiple times with distilled water.
Cutting corners with solution preparation risks introducing significant errors. Chemists must make precision and attention to detail a top priority in the lab.
Common Problems Encountered
Some common problems encountered when preparing solutions include:
Inaccurate concentrations
– Caused by errors in measuring reagents or volumes.
– Avoid by carefully following calculations, using quality equipment.
Unsaturated solutions
– Occurs when solute is not fully dissolved.
– Can remedy by heating, stirring, or sonicating solution.
Supersaturated solutions
– Develop if too much solute precipitates upon standing.
– Prevent by carefully monitoring solubility limits.
Contaminated solutions
– Caused by unclean glassware or impure reagents.
– Use very clean equipment and high purity chemicals.
Leaks or spills
– May occur if containers are capped improperly.
– Check seals and caps before mixing or moving solutions.
With practice and care, these potential pitfalls can be avoided in the lab. Meticulous technique is key for obtaining high quality chemical solutions.
Laboratory Safety
When preparing solutions, proper laboratory safety should always be followed:
Personal Protective Equipment (PPE)
– Wear lab coat, gloves, and eye protection.
Review Chemical Hazards
– Consult safety data sheets and bottle labels.
Limit Exposure
– Use fume hoods when handling toxic substances.
Manage Spills
– Clean up any leaks or spills immediately.
Handle Waste Properly
– Follow protocols for disposing of excess solutions.
Decontaminate Equipment
– Fully clean all glassware and surfaces after use.
Follow Safety Training
– Listen to guidelines from lab supervisors and training.
Strict adherence to safety practices reduces the risks of accidents or chemical exposures when working with solutions. A culture of safety should permeate every action in the laboratory.
Conclusion
In summary, preparing a 0.200 M 500 ml sodium chloride solution requires:
- Determining moles of NaCl using the molarity equation
- Converting moles to mass of NaCl using molar mass
- Carefully measuring out the calculated mass of NaCl solid
- Dissolving the NaCl in 500 ml of water in a volumetric flask
Proper technique, high quality equipment, and careful calculations are necessary to accurately prepare solutions. Understanding how to correctly make standardized solutions is an essential skill in chemistry.
