Calculate the concentration in Molarity (M) when 10.0g ✓ Solved

Week 3 Exercise 2: Acids and Bases Calculations Complete the following calculations. Show your work to obtain ALL of the points.

1) Calculate the concentration in Molarity (M) when 10.0g of sodium hydroxide (NaOH) are dissolved in 250.0mL of DI water.

a. What is the pH of the solution?

2) What is the pH and pOH of a 0.955M solution of nitric acid, HNO3(aq)?

3) The human blood maintains a pH of 7.40. What is the hydronium ion [H3O+] and hydroxide [OH-] concentrations of human blood?

4) How many grams of potassium hydroxide (KOH) are needed to neutralize 50.0 mL of 1.33M hydrochloric acid (HCl(aq))?

Paper For Above Instructions

Understanding how to calculate concentrations, pH, and the quantities required for neutralization reactions is fundamental in acid-base chemistry. Below are detailed calculations for each of the questions presented.

1. Molarity of Sodium Hydroxide Solution

First, we calculate the molarity (M) of the sodium hydroxide (NaOH) solution when 10.0g is dissolved in 250.0mL of water.

The formula for molarity is:

M = moles of solute / liters of solution

To find the number of moles of NaOH, we use the formula:

moles = mass (g) / molar mass (g/mol)

The molar mass of NaOH is approximately 40.00 g/mol. Therefore:

moles of NaOH = 10.0 g / 40.00 g/mol = 0.250 moles

Next, we convert the volume from mL to L:

250.0 mL = 0.250 L

Now, we can calculate the molarity:

M = 0.250 moles / 0.250 L = 1.00 M

To find the pH of the solution, we consider that NaOH is a strong base and fully dissociates in solution:

NaOH → Na+ + OH-

Thus, the concentration of hydroxide ions [OH-] is equal to the molarity of NaOH, which is 1.00 M. The pOH can be calculated as:

pOH = -log[OH-] = -log(1.00) = 0

Using the relationship between pH and pOH:

pH + pOH = 14

So:

pH = 14 - pOH = 14 - 0 = 14

2. pH and pOH of Nitric Acid (HNO3)

Next, we need to calculate the pH and pOH of a 0.955 M solution of nitric acid (HNO3). Since HNO3 is a strong acid, it also fully dissociates in solution:

HNO3 → H+ + NO3-

Therefore, the concentration of hydrogen ions [H+] is 0.955 M.

Now we calculate the pH:

pH = -log[H+] = -log(0.955) ≈ 0.018

Next, we find the pOH:

pOH = 14 - pH = 14 - 0.018 = 13.982

3. Hydronium and Hydroxide Concentrations in Human Blood

The typical pH level of human blood is 7.40. To find the concentrations of [H+] and [OH-], we can use:

[H+] = 10-pH = 10-7.40 ≈ 3.98 × 10-8 M

To find [OH-], we use the relationship:

pOH = 14 - pH = 14 - 7.40 = 6.60

Thus:

[OH-] = 10-pOH = 10-6.60 ≈ 2.51 × 10-7 M

4. Grams of Potassium Hydroxide Needed for Neutralization

For the fourth calculation, we need to neutralize 50.0 mL of 1.33 M hydrochloric acid (HCl). The reaction is:

HCl + KOH → KCl + H2O

This indicates a 1:1 molar ratio between HCl and KOH. First, calculate the moles of HCl:

moles of HCl = concentration × volume = 1.33 M × 0.050 L = 0.0665 moles

Since the ratio is 1:1, we also need 0.0665 moles of KOH. The molar mass of KOH is approximately 56.11 g/mol.

Now, convert moles of KOH to grams:

mass = moles × molar mass

mass of KOH = 0.0665 moles × 56.11 g/mol ≈ 3.73 g

Summary of Results

  • 1. Molarity of NaOH: 1.00 M, pH: 14

  • 2. pH of 0.955 M HNO3: 0.018, pOH: 13.982

  • 3. [H+] in blood: 3.98 × 10-8 M, [OH-]: 2.51 × 10-7 M

  • 4. Grams of KOH needed: 3.73 g

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