A scientist mixes 0.02 g of a strong base in 83 ml of water and obtains a ph of 12. He then realizes that he forgot to label the container and forgot what base he added. What is the most likely the identity of this base?

Lithium Hydroxide (LiOH) is the most likely identity of the base added to the solution.

Given:

  • Mass of base = 0.02 g
  • Volume of water = 83 mL
  • pH of solution = 12

To determine the identity of the base, we first calculate the concentration of hydroxide ions (OH⁻) in the solution. This can be done using the pH value, as pH is a measure of the concentration of hydrogen ions (H⁺) in a solution.

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Given that the pH is 12, we know that the concentration of hydroxide ions can be found using the equation:

pH = 14 - pOH

pOH = 14 - pH

pOH = 14 - 12 = 2

Now, we know that:

pOH = -log[OH⁻]

So, we can rearrange this equation to solve for [OH⁻]:

[OH⁻] = 10^(-pOH)

[OH⁻] = 10^(-2) ≈ 0.01 M

This tells us that the concentration of hydroxide ions in the solution is approximately 0.01 moles per liter (M).

Now, let's calculate the moles of the base added to the solution:

Given:

  • Mass of base = 0.02 g
  • Molar mass of LiOH = 23.95 g/mol (Li) + 16.00 g/mol (O) + 1.01 g/mol (H) = 40.96 g/mol

Moles of LiOH = Mass / Molar mass = 0.02 g / 40.96 g/mol ≈ 0.00049 moles

Now, let's calculate the volume of the solution in liters:

Volume of solution = 83 mL × (1 L / 1000 mL) = 0.083 L

Now, we can calculate the concentration of LiOH in the solution:

Concentration of LiOH = Moles of LiOH / Volume of solution ≈ 0.00049 moles / 0.083 L ≈ 0.0059 M

Given that lithium hydroxide (LiOH) is a strong base and fully dissociates in water, its concentration should match the concentration of hydroxide ions in the solution. The calculated concentration of LiOH (0.0059 M) is approximately consistent with the concentration of hydroxide ions (0.01 M) in the solution.

Therefore, lithium hydroxide (LiOH) is the most likely identity of the base added to the solution.

Acid-Base Chemistry

Acid-base chemistry is a branch of chemistry that deals with the study of acids, bases, and the reactions between them. Here are some fundamental concepts:

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  1. Acids: Acids are substances that donate protons (H⁺ ions) in aqueous solution. They are characterized by their sour taste, ability to turn blue litmus paper red, and ability to react with bases to form salts and water. Examples include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and acetic acid (CH₃COOH).

  2. Bases: Bases are substances that accept protons or donate hydroxide ions (OH⁻) in aqueous solution. They are characterized by their bitter taste, slippery feel, and ability to turn red litmus paper blue. Examples include sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia (NH₃).

  3. pH: pH is a measure of the acidity or basicity of a solution. It is defined as the negative logarithm of the concentration of hydrogen ions ([H⁺]) in a solution. pH values range from 0 to 14, with values below 7 indicating acidity, values above 7 indicating basicity, and a pH of 7 being neutral.

  4. pH Scale: The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. A change of one pH unit represents a tenfold change in the concentration of hydrogen ions. For example, a solution with a pH of 3 is ten times more acidic than a solution with a pH of 4.

  5. Neutralization Reactions: Neutralization is the chemical reaction between an acid and a base to produce a salt and water. The general form of a neutralization reaction is: Acid + Base → Salt + Water

  6. Strong Acids and Bases: Strong acids and bases completely dissociate in water, yielding a large number of ions. Examples of strong acids include hydrochloric acid (HCl) and sulfuric acid (H₂SO₄). Examples of strong bases include sodium hydroxide (NaOH) and potassium hydroxide (KOH).

  7. Weak Acids and Bases: Weak acids and bases only partially dissociate in water, resulting in an equilibrium between the undissociated molecules and their ions. Examples of weak acids include acetic acid (CH₃COOH) and carbonic acid (H₂CO₃). Examples of weak bases include ammonia (NH₃) and organic amines.

  8. Buffer Solutions: Buffer solutions are solutions that resist changes in pH when small amounts of acid or base are added to them. They typically contain a weak acid and its conjugate base or a weak base and its conjugate acid.

Understanding these concepts is crucial for various applications in chemistry, biochemistry, and everyday life.