Unit 8 check
Unit 8 check: Acids and Bases
11 questions from 11 lessons in Unit 8. Answer each one, and if you miss, follow the link back to where it is taught, then try again. Your score counts first tries.
Question 1 · from 8.1 · Calculate
The hydronium ion concentration of a sample of rainwater is 3.2 × 10⁻⁵ M. What is its pH? Give the number of decimal places that two significant figures in the concentration allow.
Question 2 · from 8.2 · Calculate
A student makes a 0.0150 M solution of barium hydroxide, Ba(OH)₂, a strong base, at 25 °C. What is the pH? Give three decimal places.
Question 3 · from 8.3 · Calculate
A 0.100 M solution of a weak acid has a pH of 2.85. What is the percent ionization of the acid? Give two significant figures.
Question 4 · from 8.4 · Multiple choice
Acetic acid, CH₃COOH, a weak acid, is mixed with ammonia, NH₃, a weak base. Which equation represents the reaction?
Setup for question 5
The equivalence point does not sit at pH 7 for every titration. Decide which sample is the weak acid, then rank four titrations by the pH at their equivalence points. These numbers are a teaching example.
Question 5 · from 8.5 · Decide and justify
Two 25.00 mL samples, each 0.1000 M, are titrated with 0.1000 M NaOH. One sample is a strong acid and the other is a weak acid. Acid X has a pH of 7.00 at 25.00 mL of base. Acid Y has a pH of 8.62 at 25.00 mL of base, where its curve is steepest. Which acid is the weak acid?
Which reason supports your decision?
Setup for question 6
Four carboxylic acids are compared at 25 °C. Each Ka is the acid ionization constant of the -COOH group. These numbers are a teaching example, rounded from standard tables.
| Acid | Formula | Ka |
|---|---|---|
| Acetic acid | CH₃COOH | 1.8 × 10⁻⁵ |
| Formic acid | HCOOH | 1.8 × 10⁻⁴ |
| Chloroacetic acid | ClCH₂COOH | 1.4 × 10⁻³ |
| Fluoroacetic acid | FCH₂COOH | 2.6 × 10⁻³ |
Question 6 · from 8.6 · Multiple choice
Using the table: which acid has the weakest conjugate base?
Setup for question 7
A student adds a few drops of four different indicators to four separate samples of one unknown solution and records the colors. The table gives each indicator's pKa and the color of each of its forms. These numbers are a teaching example.
| Indicator | pKa | Acid form, HIn | Base form, In⁻ | Color in the unknown |
|---|---|---|---|---|
| Methyl orange | 3.5 | red | yellow | yellow |
| Methyl red | 5.0 | red | yellow | red |
| Bromothymol blue | 7.1 | yellow | blue | yellow |
| Phenolphthalein | 9.4 | colorless | pink | colorless |
Question 7 · from 8.7 · Multiple choice
Using the table: which statement about the pH of the unknown solution is supported by the colors?
Setup for question 8
A student measures the pH of four 100.0 mL solutions, adds 1.0 mL of 1.0 M HCl to each, and measures the pH again. The HCl adds 0.0010 mol of H₃O⁺ to each solution. These numbers are a teaching example.
| Solution | Contents | pH before | pH after |
|---|---|---|---|
| A | Pure water | 7.00 | 2.00 |
| B | 0.10 M CH₃COOH and 0.10 M CH₃COO⁻ | 4.76 | 4.67 |
| C | 0.10 M NaCl | 7.00 | 2.00 |
| D | 0.10 M CH₃COOH only | 2.88 | 2.00 |
Question 8 · from 8.8 · Multiple choice
Using the table: which reaction mainly accounts for the small change in the pH of solution B when the HCl is added?
Question 9 · from 8.9 · Spot the error
A student finds the pH of a buffer made from 0.10 M HCOOH and 0.30 M HCOO⁻, with a pKa of 3.75. Tap the line with the mistake.
Question 10 · from 8.10 · Spot the error
A student compares 100.0 mL of buffer A, 0.10 M HF and 0.10 M NaF, with 100.0 mL of buffer B, 1.0 M HF and 1.0 M NaF. Tap the line with the mistake.
Question 11 · from 8.11 · Multiple choice
The weak acid HF has a pKa of 3.17. In a solution at pH 2.0, which form of the acid is present in the greater amount?
0 of 11 answered.