Question 1
What does a lower pH tell you about hydrogen-ion concentration?
Need a hint for Question 1?
Separate the amount per volume from the fraction dissociated.
Check Question 1
The hydrogen-ion concentration is greater.
STUDENT SPACE · TOPIC 1
Acids, alkalis and strength
Use indicators and distinguish acid strength from concentration.
The essentials
- Aqueous acids contain H⁺ ions; aqueous alkalis contain OH⁻ ions.
- Litmus, thymolphthalein and methyl orange distinguish acidic and alkaline solutions.
- At room temperature, pH below 7 is acidic; pH 7 is neutral; pH above 7 is alkaline.
Key vocabulary
| English | Chinese |
|---|---|
| acid | 酸 |
| alkali | 可溶性碱 |
| dissociation | 解离 |
| concentration | 浓度 |
Quick practice
Try each question before opening its hint or answer. Use paper for calculations and diagrams.
Question 2
State thymolphthalein colours in an acid and in an alkali.
Need a hint for Question 2?
Recall the two thymolphthalein indicator colours.
Check Question 2
Colourless in acid; blue in alkali.
Question 3
A student calls a dilute HCl solution a weak acid. Explain the mistake.
Need a hint for Question 3?
Distinguish concentration from extent of ionisation.
Check Question 3
Dilute means a low amount per volume. HCl remains a strong acid because it dissociates completely.
Use Lesson 1 in your worksheet for written practice. Your teacher will discuss those answers in class.