实验技术

Density is calculated by dividing an object's mass by its volume. This measurement indicates how compact a substance or object is. When a dense object is placed in a liquid with lower density, it sinks; when less dense, it floats. When densities match, the object suspends in the liquid.

A volumetric flask provides more precise volume measurements because it has a narrow neck with a single fill mark, reducing reading error. The graduated cylinder has multiple lines spaced 0.2 mL apart, allowing readings only to the hundredths place. Volumetric flasks are designed specifically for accurate volume measurement in laboratory work.

Percent error measures the accuracy of experimental measurements by comparing them to a theoretical value. It is calculated by subtracting the theoretical value from the experimental value, dividing by the theoretical value, and multiplying by 100. In this experiment, the volumetric flask measurement serves as the theoretical value to evaluate other measurement methods.

An egg's density is determined by creating a salt solution with matching density, causing the egg to suspend. The egg's mass is measured directly on a balance. Its volume is calculated using water displacement—measuring the beaker's initial liquid level, adding the egg, and subtracting to find displacement volume. Density equals mass divided by volume.

Always view graduated cylinder measurements at eye level and read from the bottom of the meniscus, the curved liquid surface. Place a blank sheet of paper behind the cylinder for clarity. The lines are 0.2 mL apart, allowing readings to the hundredths place. Proper technique minimizes parallax error and ensures accurate volume measurement.

Salt solution has higher density than pure water because dissolved salt increases the solution's mass without significantly increasing its volume. Pure water has a density of 1 g/mL, so 20 mL weighs 20 g. When salt is added, the same 20 mL volume weighs more, resulting in a higher density value.

Error in egg density calculations arises primarily from volume measurement readings. Inaccuracies occur when using beaker markings compared to volumetric glassware, parallax errors in reading meniscus levels, and uncertainty in measuring water displacement height and beaker diameter. These combined measurement errors create disparity between calculated egg density and salt solution density.