Meniscus

Malay: Meniskus · Chinese: 弯月面

The meniscus is the curved upper surface a liquid forms inside a narrow tube such as a burette, a pipette or a measuring cylinder. For water and most aqueous solutions the surface curves downward in the middle, making a small dip. The rule you must know for the SPM Chemistry papers (4541) is simple: read the volume from the bottom of the meniscus, with your eye level with that point. Following this rule consistently is what makes a volume reading correct and repeatable.

For example, when you read 25.00 cm³ from a burette, your line of sight should be horizontal and aimed at the lowest point of the curved surface, not at the liquid where it climbs the glass at the sides. Placing a white card with a dark strip behind the tube makes the bottom of the meniscus stand out and easier to read to the nearest graduation. A few coloured liquids, such as concentrated potassium manganate(VII), are so dark that the bottom cannot be seen, and for those the top of the meniscus is read instead, but for the water-based solutions you meet most often, the bottom is the rule.

The confusion to avoid is failing to read the meniscus at eye level, which leads directly to parallax error, a reading that is too high or too low because the eye was above or below the surface. A second slip is reading from the top of the curve instead of the bottom; always use the bottom for these common solutions. These small errors add up quickly in a titration.

Within the apparatus section, the meniscus links every accurate volume measurement, pipette, burette and measuring cylinder, to the skill of reading a scale correctly. Our teachers check your eye position so your readings are free of parallax error.