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Molarity

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Intros
Lessons
  1. Molarity and concentration
  2. Definition of molarity
  3. Finding the concentration of a solution
  4. Changing concentration of a solution
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Examples
Lessons
  1. Apply the formula to find the concentration of solutions.
    1. Find the concentration of a solution where 0.7 mol NaOH is dissolved into 120 mL of water.
    2. Find the concentration of another solution where 0.45 mol HCl is dissolved into 95 mL of water.
    3. Find the concentration of the solution that will be made if 32 grams of NaOH pellets are weighed out and dissolved in a container with 200 mL water.
  2. Apply the formula to find changing concentration and volume of solutions.
    1. Find the molarity of this solution.
    2. 45 mL extra water is added to dilute this solution. Find the new concentration of this solution.
    3. This solution is diluted down further and the concentration is measured to be 0.55 M. What must the new volume of the solution be?
    4. In a separate experiment, a 50 mL solution of .450 M MgCl2 was mixed with 20 mL of 0.3 M AlCl3. Find the concentration of all the ions present in this combined mixture.
Topic Notes
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Introduction to Molarity

Welcome to our exploration of molarity, a fundamental concept in chemistry that's crucial for understanding solution chemistry and their concentrations. Molarity is a measure of the concentration of a solute in a solution, expressed as moles of solute per liter of solution. It's an essential tool for chemists and students alike, used in various calculations and experiments. Our introduction video will guide you through the basics of molarity, making this sometimes challenging concept more accessible. You'll discover how molarity relates to everyday life and its applications in laboratory settings. Understanding molarity is key to mastering solution chemistry, helping you analyze and prepare solutions accurately. Whether you're studying for an exam or preparing for lab work, grasping molarity will significantly enhance your chemistry skills. Let's dive in and unravel the mysteries of molarity together!

Understanding Molarity and Concentration

Molarity is a fundamental concept in chemistry that helps us understand and quantify the concentration of solutions. At its core, molarity is all about "how much stuff in how much space." This simple analogy makes the concept more accessible and easier to grasp for students and chemistry enthusiasts alike.

To define molarity more precisely, it is the number of moles of a solute dissolved in one liter (or one cubic decimeter) of solution. The equation for molarity is:

M = moles of solute / volume of solution in liters

Where M represents molarity, moles represent the amount of solute, and volume is measured in liters. This equation is the key to calculating and understanding concentration in chemical solutions.

Let's break down each component of the molarity equation:

  • Moles: This represents the amount of substance, typically the solute in a solution. It's a way to count particles on an atomic or molecular level.
  • Volume: This is the total volume of the solution, including both the solute and solvent. It's crucial to note that the volume is always expressed in liters for molarity calculations.
  • Molarity (M): The resulting value gives us the concentration in moles per liter (mol/L) or moles per cubic decimeter (mol/dm³).

The units used for molarity are typically moles per liter (mol/L) or moles per cubic decimeter (mol/dm³). These units are interchangeable since one liter is equal to one cubic decimeter. This standardization makes it easier to compare concentrations across different solutions and experiments.

To illustrate how molarity works in practice, let's consider some examples:

1. Imagine you have 1 mole of sugar dissolved in 1 liter of water. The molarity of this solution would be 1 mol/L or 1 M.

2. Now, if you keep the same amount of sugar (1 mole) but increase the volume to 2 liters, the molarity would decrease to 0.5 mol/L or 0.5 M. This demonstrates how increasing the volume while keeping the amount of solute constant decreases the concentration.

3. Conversely, if you have 2 moles of sugar in 1 liter of water, the molarity would be 2 mol/L or 2 M. This shows that increasing the amount of solute while keeping the volume constant increases the concentration.

These examples highlight a crucial aspect of molarity: it's a ratio. Changing either the amount of solute or the volume of the solution will affect the overall concentration. This relationship is at the heart of many chemical calculations and is essential for preparing solutions in laboratories and industrial settings.

Understanding molarity is vital for various applications in chemistry, including:

  • Preparing solutions for experiments or industrial processes
  • Calculating reaction rates and equilibrium constants
  • Determining the concentration of unknown solutions through titration
  • Predicting the outcomes of chemical reactions

When working with molarity, it's important to remember that temperature can affect the volume of a solution, which in turn can impact the molarity. For precise measurements, chemists often specify the temperature at which the molarity was calculated or measured.

In conclusion, molarity is a powerful tool for understanding and quantifying concentration in chemistry. By relating the amount of solute to the volume of solution, it provides a standardized way to describe and work with solutions. Whether you're a student learning the basics of chemistry or a professional working in a lab, mastering the concept of molarity is essential for success in the field. Remember, it's all about "how much stuff in how much space" a simple yet profound way to approach the complexities of chemical concentrations.

Expressing Concentration and Ionic Compounds

Understanding how to express concentration using square brackets for ions in solution is crucial in chemistry, especially when dealing with ionic compounds. This knowledge is essential for accurately calculating the concentration of ions and finding molar concentration. When working with chemical formulas, it's important to recognize that one molecule of an ionic compound can produce multiple ions when dissolved in solution.

To express the concentration of ions in solution, we use square brackets [ ] around the chemical formula of the ion. For example, [Na+] represents the concentration of sodium ions in solution. This notation is widely used in chemistry to denote molar concentration, typically measured in moles per liter (mol/L).

When calculating the concentration of ions from ionic compounds, it's crucial to understand the chemical formulas and how these compounds dissociate in solution. Let's consider two examples to illustrate this concept:

1. Hydrochloric acid dissociation (HCl): When HCl dissolves in water, it completely dissociates into H+ and Cl- ions. The chemical equation for this dissociation is:

HCl H+ + Cl-

In this case, one molecule of HCl produces one H+ ion and one Cl- ion. Therefore, the concentration of H+ ions [H+] and Cl- ions [Cl-] will be equal to the concentration of HCl in solution.

2. Magnesium chloride (MgCl2): When MgCl2 dissolves in water, it dissociates into one Mg2+ ion and two Cl- ions. The chemical equation for this dissociation is:

MgCl2 Mg2+ + 2Cl-

Here, one molecule of MgCl2 produces one Mg2+ ion and two Cl- ions. This means that the concentration of Cl- ions [Cl-] will be twice the concentration of Mg2+ ions [Mg2+] and twice the concentration of MgCl2 in solution.

These examples highlight the importance of understanding chemical formulas when calculating the concentration of ions from ionic compounds. It's essential to consider the stoichiometry of the dissociation reaction to accurately determine the concentration of each ion in solution.

When calculating molar concentration for ionic compounds, it's crucial to take into account the number of ions produced by each molecule. Molarity (M) is defined as the number of moles of solute per liter of solution. For ionic compounds, you need to consider whether you're calculating the molarity of the compound itself or the molarity of the ions it produces.

For instance, if you have a 0.1 M solution of MgCl2, the concentration of Mg2+ ions [Mg2+] would also be 0.1 M, but the concentration of Cl- ions [Cl-] would be 0.2 M because each MgCl2 molecule produces two Cl- ions.

To find the molarity of ions in solution, follow these steps:

1. Identify the chemical formula of the ionic compound.

2. Write the dissociation equation to determine how many ions are produced per molecule.

3. Calculate the molarity of the compound in solution.

4. Use the stoichiometric ratios from the dissociation equation to calculate the concentration of each ion.

By mastering these concepts and understanding how to express concentration using square brackets, you'll be better equipped to solve problems involving ionic compounds and their concentrations in solution. This knowledge is fundamental in various fields of chemistry, including analytical chemistry, electrochemistry, and solution chemistry.

Calculating Changes in Concentration

Understanding how to calculate changes in concentration is a fundamental skill in chemistry. The equation M1V1 = M2V2 is a powerful tool for determining new concentrations or volumes after dilution or combination of solutions. This formula, known as the dilution equation, is essential for various laboratory procedures and real-world applications.

Let's break down the components of the equation:

  • M1: Initial concentration (molarity)
  • V1: Initial volume
  • M2: Final concentration (molarity)
  • V2: Final volume

The equation states that the product of the initial concentration and volume equals the product of the final concentration and volume. This relationship holds true because the number of moles of solute remains constant during dilution or concentration changes.

To use this equation effectively, follow these steps:

  1. Identify the known variables and the unknown variable you need to solve for.
  2. Plug the known values into the equation.
  3. Rearrange the equation to isolate the unknown variable.
  4. Solve for the unknown variable.

The equation can be rearranged to solve for any of the four variables:

  • M1 = (M2 * V2) / V1
  • V1 = (M2 * V2) / M1
  • M2 = (M1 * V1) / V2
  • V2 = (M1 * V1) / M2

Let's explore some practical examples to illustrate the application of this equation:

Example 1: Dilution

Suppose you have 100 mL of a 0.5 M NaCl solution and want to dilute it to 0.2 M. To find the final volume, use the equation:

(0.5 M)(100 mL) = (0.2 M)(V2)

Solving for V2: V2 = (0.5 M * 100 mL) / 0.2 M = 250 mL

This means you need to add water to the original solution until the total volume reaches 250 mL to achieve the desired concentration.

Example 2: Evaporation

If you heat a 500 mL solution of 0.3 M glucose until 100 mL of water evaporates, the new concentration can be calculated:

(0.3 M)(500 mL) = (M2)(400 mL)

Solving for M2: M2 = (0.3 M * 500 mL) / 400 mL = 0.375 M

The concentration increases as water evaporates, concentrating the solute.

Example 3: Combining Solutions

When mixing 200 mL of 0.4 M HCl with 300 mL of 0.6 M HCl, use the equation to find the final concentration:

(0.4 M * 200 mL) + (0.6 M * 300 mL) = M2 * 500 mL

Solving for M2: M2 = (80 mmol + 180 mmol) / 500 mL = 0.52 M

This equation is invaluable for calculating molarity in various scenarios, from preparing laboratory solutions to understanding environmental changes in concentration. It's widely used in analytical chemistry, pharmaceutical formulations, and industrial processes where precise control of concentration is crucial.

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Practical Applications of Molarity

Molarity, a fundamental concept in chemistry, plays a crucial role in numerous real-world applications across various scientific fields. Understanding and applying molarity is essential for accurate solution preparation, standardization of reagents, and ensuring precise concentrations in laboratory settings and industries. This knowledge is particularly valuable in fields such as pharmaceuticals, environmental science, and food science.

In laboratory settings, molarity is extensively used for preparing solutions and standardizing reagents. Chemists routinely prepare solutions of specific concentrations for experiments, analyses, and calibrations. For instance, when conducting titrations, a common analytical technique, scientists must prepare solutions of known molarity to determine the concentration of unknown samples accurately. Similarly, in spectrophotometry, standard solutions of precise molarity are crucial for creating calibration curves and quantifying analytes in unknown samples.

The pharmaceutical industry heavily relies on molarity calculations to ensure the accurate and safe formulation of medications. Drug manufacturers must precisely control the concentration of active ingredients in their products to guarantee efficacy and safety. For example, when preparing intravenous solutions or liquid medications, pharmacists use molarity calculations to ensure the correct dosage is administered to patients. This precision is critical in preventing potentially life-threatening errors in medication administration.

Environmental scientists frequently employ molarity in their work, particularly when analyzing water quality and pollution levels. For instance, when measuring the concentration of pollutants in water samples, scientists often use molarity to express the results. This allows for standardized reporting and comparison of data across different studies and locations. Additionally, molarity calculations are essential in preparing standard solutions for calibrating instruments used in environmental monitoring, such as pH meters and conductivity probes.

In the food science industry, molarity plays a vital role in quality control and product development. Food scientists use molarity calculations to determine the concentration of additives, preservatives, and nutrients in food products. For example, when formulating beverages, the molarity of acids and sweeteners must be carefully controlled to achieve the desired taste and shelf life. Similarly, in the production of canned foods, the molarity of preservatives is crucial for ensuring food safety and extending product longevity.

Molarity is also indispensable in the field of agriculture, particularly in the preparation of fertilizers and pesticides. Agronomists and farmers use molarity calculations to determine the appropriate concentration of nutrients in fertilizer solutions, ensuring optimal plant growth without risking over-fertilization. Similarly, when preparing pesticide solutions, precise molarity calculations are necessary to achieve effective pest control while minimizing environmental impact and crop damage.

In the realm of materials science and engineering, molarity is essential for processes such as electroplating and etching. Engineers use molarity calculations to prepare solutions with specific concentrations of metal ions for electroplating applications, ensuring uniform and high-quality coatings. In semiconductor manufacturing, precise control of etchant concentrations through molarity calculations is crucial for achieving the desired etching rates and patterns on silicon wafers.

Understanding and applying molarity is also vital in the field of forensic science. Forensic analysts use molarity calculations when preparing reagents for various tests, such as blood alcohol analysis or drug detection. The accuracy of these tests, which can have significant legal implications, depends on the precise preparation of solutions with known molarities.

In conclusion, molarity is a fundamental concept with wide-ranging applications across numerous scientific fields. From laboratory techniques and pharmaceutical formulations to environmental monitoring and food science, the ability to accurately calculate and apply molarity is essential for ensuring precision, safety, and reliability in scientific and industrial processes. As science and technology continue to advance, the importance of understanding and utilizing molarity in real-world applications will only grow, underscoring its significance in modern scientific practice.

Common Mistakes and Tips for Calculating Molarity

Calculating molarity is a fundamental skill in chemistry, but it's one that many students struggle with. Understanding common errors and learning effective problem-solving strategies can significantly improve your accuracy in molarity calculations. Let's explore some frequent mistakes and provide tips to avoid them.

Common Errors in Molarity Calculations

  1. Unit Conversion Errors: One of the most common mistakes is failing to convert units properly. For example, students might forget to convert grams to moles or milliliters to liters.
  2. Ignoring Ionic Compounds: When dealing with ionic compounds, students often forget to consider the number of ions produced when the compound dissociates in solution.
  3. Misinterpreting Problem Statements: Failing to carefully read and understand the given information can lead to using incorrect values or solving for the wrong variable.
  4. Calculation Mistakes: Simple arithmetic errors can lead to incorrect final answers, even if the conceptual understanding is correct.

Tips to Avoid Common Mistakes

  • Always write down the given information and clearly identify the unknown variable.
  • Use dimensional analysis to ensure proper unit conversions.
  • For ionic compounds, determine the number of moles of ions produced per mole of compound.
  • Double-check your calculations and use estimation to verify if your answer makes sense.

Step-by-Step Approach to Solving Molarity Problems

  1. Read the problem carefully and identify the given information and the unknown variable.
  2. Convert all units to moles, liters, and moles/liter as needed.
  3. Write out the molarity formula: M = moles of solute / liters of solution.
  4. Plug in the known values and solve for the unknown.
  5. Check your answer for reasonableness and proper units.

Practice Problems

Problem 1: Calculate the molarity of a solution prepared by dissolving 5.85 g of NaCl in enough water to make 500.0 mL of solution.

Solution:

  1. Convert 5.85 g NaCl to moles: 5.85 g ÷ 58.44 g/mol = 0.1001 mol NaCl
  2. Convert 500.0 mL to L: 500.0 mL × (1 L / 1000 mL) = 0.5000 L
  3. Apply the molarity formula: M = 0.1001 mol / 0.5000 L = 0.2002 M

Problem 2: How many grams of Ca(NO) are needed to prepare 250 mL of a 0.15 M solution?

Solution:

  1. Calculate moles of Ca(NO) needed: 0.15 M × 0.250 L = 0.0375 mol
  2. Convert moles to grams: 0.0375 mol × 164.09 g/mol = 6.15 g Ca(NO)

By understanding these common errors and following a systematic approach, you can improve your accuracy in molarity calculations. Remember to practice molarity problems regularly and always double-check your work. With time and experience, these calculations will become second nature, allowing you to tackle more complex chemistry problems with confidence.

Conclusion

In this article, we've explored the crucial concept of molarity in chemistry. We've covered its definition, calculation methods, and practical applications in laboratory settings. The introductory video provided a visual representation of molarity, helping to solidify your understanding. Remember, molarity is essential for preparing solutions and conducting accurate experiments. To further enhance your grasp of this topic, consider practicing with additional problems or exploring online resources. Apply this knowledge in your chemistry studies and lab work to improve your precision and efficiency. Whether you're a student or a professional, mastering molarity will significantly benefit your chemistry endeavors. Don't hesitate to revisit the concepts and examples provided here as you continue your journey in chemistry. By consistently applying and expanding your understanding of molarity, you'll be well-equipped to tackle more complex chemical calculations and experiments in the future.

Molarity and Concentration

Definition of Molarity

Step 1: Introduction to Molarity

Molarity is a fundamental concept in chemistry, particularly when dealing with solutions. It is a measure of the concentration of a solute in a solution. Understanding molarity is crucial for various chemical calculations and experiments. In this guide, we will explore the definition of molarity, how it is calculated, and its significance in chemical terms.

Step 2: Definition of Molarity

Molarity, often denoted by the symbol M, is defined as the number of moles of a substance (solute) per unit volume of solution. In simpler terms, it tells us how much of a substance is present in a given amount of space. The formula for molarity is:

Molarity (M) = Moles of Solute / Volume of Solution in Litres

This definition can be broken down into two main components:

  • Moles of Solute: This refers to the amount of the substance being dissolved in the solution. Moles are a standard unit in chemistry that represent a specific number of atoms, molecules, or ions.
  • Volume of Solution: This is the total space in which the solute is dissolved, measured in litres. It represents the capacity of the solution to hold the solute.

Step 3: Conceptual Understanding of Molarity

To better understand molarity, consider the following analogy: Imagine you have a box (representing the unit volume) and you place one atom inside it. The concentration, or molarity, would be one atom per box. If you add another atom to the same box, the concentration doubles to two atoms per box. This illustrates how molarity measures the amount of substance in a given space.

In chemical terms, molarity is used to describe the concentration of molecules, ions, or particles in a solution. It helps chemists understand how much of a substance is present in a specific volume, which is essential for reactions and experiments.

Step 4: Calculating Molarity

To calculate molarity, you need to know two things: the number of moles of the solute and the volume of the solution in litres. The formula is straightforward:

M = n / V

Where:

  • M is the molarity in moles per litre (mol/L).
  • n is the number of moles of the solute.
  • V is the volume of the solution in litres.

For example, if you have 2 moles of a solute dissolved in 1 litre of solution, the molarity would be:

M = 2 moles / 1 litre = 2 M

Step 5: Importance of Molarity in Chemistry

Molarity is a crucial concept in chemistry because it allows chemists to:

  • Standardize Solutions: Molarity provides a way to prepare solutions with precise concentrations, which is essential for reproducible experiments and reactions.
  • Predict Reaction Outcomes: Knowing the molarity of reactants helps in predicting the amount of products formed in a chemical reaction.
  • Control Reaction Rates: The concentration of reactants can influence the rate of a reaction. Higher molarity often leads to faster reactions.
  • Calculate Dilutions: Molarity is used to determine how to dilute concentrated solutions to achieve desired concentrations.

Step 6: Practical Applications of Molarity

Molarity is widely used in various fields of chemistry, including:

  • Analytical Chemistry: Molarity is used to prepare standard solutions for titrations and other quantitative analyses.
  • Biochemistry: Molarity helps in preparing buffer solutions and understanding enzyme kinetics.
  • Pharmaceuticals: Accurate molarity calculations are essential for drug formulation and quality control.
  • Environmental Science: Molarity is used to measure pollutant concentrations in water and soil samples.

Step 7: Conclusion

In summary, molarity is a key concept in chemistry that defines the concentration of a solute in a solution. It is measured in moles per litre and is essential for various chemical calculations and experiments. By understanding molarity, chemists can accurately prepare solutions, predict reaction outcomes, and control reaction rates. Whether in the laboratory or in industrial applications, molarity plays a vital role in the field of chemistry.

FAQs

  1. How is molarity calculated?

    Molarity (M) is calculated using the formula: M = moles of solute / liters of solution. To find moles of solute, divide the mass of the solute by its molar mass. Ensure the volume is in liters. For example, if you have 5.85g of NaCl in 500mL of solution: First, convert 5.85g to moles (5.85g ÷ 58.44g/mol = 0.1001 mol), then divide by the volume in liters (0.5L): 0.1001 mol / 0.5L = 0.2002 M.

  2. How to calculate molarity from pH?

    To calculate molarity from pH for a strong acid or base, use the formula: M = 10^(-pH) for acids or M = 10^(-pOH) for bases, where pOH = 14 - pH. For example, if a strong acid solution has a pH of 2, its molarity would be 10^(-2) = 0.01 M. Remember, this method only applies to strong acids and bases that fully dissociate in solution.

  3. What is the formula for calculating molality from molarity?

    The formula to convert molarity (M) to molality (m) is: m = M / (ρ - M * MW/1000), where ρ is the density of the solution in g/mL, M is molarity, and MW is the molecular weight of the solute in g/mol. This conversion requires knowing the density of the solution and the molecular weight of the solute.

  4. How do you find the molarity of a given solution?

    To find the molarity of a given solution, you need to know the amount of solute (in moles) and the volume of the solution (in liters). Follow these steps: 1) Calculate the moles of solute by dividing its mass by its molar mass. 2) Ensure the solution volume is in liters. 3) Divide the moles of solute by the volume in liters. The result is the molarity of the solution.

  5. How to Calculate Molarity for a Solution?

    To calculate molarity for a solution: 1) Determine the moles of solute (divide mass by molar mass if given in grams). 2) Convert the solution volume to liters. 3) Use the formula M = moles of solute / liters of solution. For example, to find the molarity of 20g of NaOH in 500mL of solution: First, calculate moles of NaOH (20g ÷ 40g/mol = 0.5 mol), then divide by volume in liters (0.5L): 0.5 mol / 0.5L = 1 M NaOH.

Prerequisite Topics

Understanding the foundation of chemistry is crucial for mastering more complex concepts like molarity. One of the most essential prerequisite topics for molarity is unit conversions in chemistry. This fundamental skill is vital because molarity calculations often require converting between different units of measurement.

Molarity, a key concept in chemistry, represents the concentration of a solute in a solution. It is defined as the number of moles of solute per liter of solution. To effectively work with molarity, students must be proficient in unit conversion in chemistry. This skill allows them to navigate between various units of mass, volume, and moles seamlessly.

When dealing with molarity problems, you'll frequently encounter scenarios where you need to convert grams to moles, milliliters to liters, or even switch between different concentration units. Without a solid grasp of unit conversions in chemistry, these calculations can become overwhelming and error-prone.

For instance, imagine you're given the mass of a solute in grams and the volume of a solution in milliliters. To calculate molarity, you'll need to convert grams to moles and milliliters to liters. This is where your knowledge of unit conversions in chemistry becomes invaluable. It allows you to manipulate the given information into the required units for molarity calculations.

Moreover, understanding unit conversions in chemistry helps you interpret and communicate scientific data more effectively. In laboratory settings, you may need to prepare solutions of specific molarities or dilute existing solutions. These tasks require a solid foundation in unit conversions to ensure accuracy and precision in your work.

As you progress in your chemistry studies, you'll find that molarity is just one of many concepts that rely heavily on unit conversion skills. From stoichiometry to equilibrium constants, the ability to convert between units remains a constant requirement. By mastering unit conversions in chemistry, you're not only preparing yourself for molarity calculations but also building a strong foundation for your entire chemistry journey.

In conclusion, the importance of understanding unit conversions in chemistry as a prerequisite to molarity cannot be overstated. It's a fundamental skill that empowers you to tackle complex molarity problems with confidence and accuracy. By investing time in mastering this prerequisite topic, you're setting yourself up for success in molarity and numerous other areas of chemistry.

In this lesson, we will learn:
  • The definition of molarity and how to describe it.
  • An equation to calculate the concentration of ions in solution.
  • An equation to find the change in concentration of a substance in solution.

Notes:
  • We now have an understanding of what a solution is and what a solution does to chemical properties when substances are dissolved. These depend on the molarity of substances in solution.

  • Molarity measures the number of moles of a substance per unit volume. It is how concentration is measured for chemical substances in solution – it asks "how much stuff in how much space?" for a chemical substance.

  • The units of molarity are moles per liter (written mol/L or mol L-1), or mol per cubic decimeter (mol/dm3 or mol/dm3). Both of these are equivalent and are often just given the symbol M.
    • Calculating molarity is done by dividing the number of moles by the volume in liters according to the equation:

      • MolarityMolarity (molL−1)= (mol L^{-1}) = molvolume(L){mol}\over{volume (L)}

    • When answering problems related to molarity, volume is often given in mL in chemical reactions – you'll need to convert from mL to L if you are finding concentration of a solution! This is done by dividing by 1000 (or use the unit conversion method; 1 L = 1000 mL).
    • In some problems you may be told the mass of the substance used (mass measured in grams). In this case you need to convert from mass to moles by finding molar mass of the substance. You can then use the unit conversion method to get the number of moles of the substance.
    • Remember, concentration is always measured with respect to 1 L of substance, so M can always be written as mol over liters, for example:

      • 0.6M=0.60.6 M = 0.6 molL−1= mol L^{-1} = 0.6mol1L{0.6 mol} \over {1L}

  • The molarity equation lets chemists compare the concentration of two different solutions which may have different quantities – solutions with high molarity are called concentrated solutions, while low molarity solutions are called dilute solutions.
    • Dilution is when more solvent is added to a solution. This has the effect of increasing the volume of the solution, therefore decreasing molarity (see the molarity equation!). This would be like adding water to a juice drink; the same number of 'juice particles' are spread amongst more water than before so the drink is less concentrated.
    • Similarly, removing some solvent, by evaporating it for example, will decrease the volume of your solution and lead to a higher molarity. This would be concentrating your solution; the same amount of 'juice particles' in less water.

  • Calculating concentration is also very important for many chemical reactions. Knowing the concentration of solutions, for example acids and alkali, enables chemists to use appropriate amounts of the reactants in experiments. When writing concentration of chemical substances, square brackets [ ] are used.
    • For example [HCl] = 0.2 M tells chemists that a solution of hydrochloric acid has a concentration of 0.2 mol per liter.

  • Molarity concentrations will often be used to find concentration of ions in solution that react in rather than the formal chemical compounds. This is for two reasons:
    1. It is the ions that actually cause the chemical properties and processes in solution to happen.
    2. Many ionic compounds dissociate into more than just two oppositely charged ions! For example every molecule of phosphoric acid H3PO4 dissociates in solution into three H+ ions, the particle which actually take part in acid-base reactions. You need to multiply the concentration of the compound by the number of specific ions the compound produces to take this into account.
    • For example: A solution of 0.4 M phosphoric acid, H3PO4, is made. As the formula shows, three H atoms are present in each molecule. Therefore in solution each single molecule will dissociate to form three H+ ions, so to find H+ concentration as multiply the concentration by three to find 0.4 * 3 = 1.2 M [H+].

  • There is an equation that relates the volume and concentration before and after a dilution has taken place. This equation allows you to measure change in concentration of a solution, whether solvent or another solution is added or removed:
    • MiViM_iV_i = = MfVf M_fV_f
    Where:
    Mi = initial molarity or concentration
    Mf = final molarity or concentration
    Vi = initial volume or concentration
    Vf = final volume or concentration