Overview
https://www.youtube.com/watch?v=FYBNuoPKf_g
https://www.youtube.com/watch?v=pxz_sf-ErEg
https://www.youtube.com/watch?v=ZeN_jgoWRbo
DENSITY OF SOLIDS AND LIQUIDS
OBJECTIVES
- Make accurate laboratory measurements for mass, length, volume, and temperature
- Determine the density of regular and irregular objects using the formula method and water displacement method
- Use graphical method to determine the density of a liquid
INTRODUCTION
We have all seen that ice and wood float on water while coins and marbles sink. Why do certain substances float while others sink? The answer is density. Objects sink or float depending on their relative densities. When an object is placed in a fluid medium (liquid or gas), it will sink if it has a higher density than the fluid medium (marble in water) and it will float if it has a lower density than the fluid medium (helium balloon in air). At least one substance must be a fluid in order to observe the sink or float property.
So what is density? Density is defined as the ratio of a substance’s mass (m) packed in a given volume (V). The equation for density (d) is given below.
[Image unavailable: Density equation]
In order to determine the density of a substance, both its mass and volume must be measured. Typically, mass is measured in the laboratory in the units of gram (g) using a digital (electronic) balance. Volume is measured in units of cm3 or mL, using a variety of methods in the laboratory.
For liquids, volume is often measured using the graduated cylinder. Liquids such as water form a curved surface, called a meniscus, inside the graduated cylinder. The proper procedure to read the volume is at the bottom of the meniscus at eye level as shown in the figure below.
[Image unavailable: Meniscus]
The volume of a solid object is commonly measured in two ways in the laboratory—the formula method and the water displacement method. In the formula method, various lengths (side, radius, height, etc.) are measured using a ruler and then substituted into the appropriate formula to calculate the volume. The formulas for the volumes for regular objects such as cubes, spheres, and cylinders are given below.
[Image unavailable: equations]
In the water displacement method, a graduated cylinder is filled about half-way with water and the initial volume recorded. Then the object is carefully placed into the cylinder and the new volume is read. The difference between the two readings gives the volume of the object.
[Image unavailable: water displacement]
As stated above, density is a derived (calculated) quantity with units of g/cm3 (solids), g/mL (liquids), and g/L (gases). For pure substances, density at a given temperature and pressure is a fixed quantity and thus it can be used to identify substances.
Although density of a substance varies with temperature (due to contraction or expansion in volume), it does not vary with the size or amount of substance. For instance, 10 mL of water has the same density as 20 mL of water, provided that both are at the same temperature (see table in the Introduction).
One easy way to see the relationship between two variables is by graphical method. Below are some general guidelines for drawing line graphs (also see the sample graph).
General guidelines for drawing line graphs
- Provide a title for the graph. It should clearly show what two variables are being studied.
- The axes should be labeled with the variable and units. The independent variable is typically on the x-axis while the dependent variable is on the y-axis.
- Using the maximum and minimum data points as guidelines, divide the grid lines evenly. Label major grid lines.
- Plot and mark the data points with dots.
- Look at the data points on the graph and draw a “best-fit” line that represents the datapoints. This can be a straight or curved line (never connect the dots to produce jaggedlines) and should contain as many data points as possible. In some cases, the points might be too scattered so they may not fall on a straight or curved line. In this case draw the best line so that the data points are equally divided—same number below and above the line.
- Make the graph as large as possible in the space given. In other words, the best-fit line should fill the entire
given area of the graph paper.
- In some cases, the data points can be extrapolated beyond the region where the data points were obtained. In
that case, a dashed line is used to show the extrapolated parts.
[Image unavailable: Mass vs volume graph]
The slope of the line can be calculated by selecting two points on the line (but is not one of the data points). For this example, the two points selected are (0.00 mL, 0.00 g) and (5.00 mL, 5.00 g). The slope can then calculated as follows:
[Image unavailable: slope equation]
Fill out the pages of your lab manual as if you were in lab. All the data for the lab is given below. Watch the brief introductory videos for additional context of the data. Clicking the links will take you to the full-size pictures, allowing you to record measurements from them.
------------ Part I ------------
In Part I of the experiment, you will determine the density of an unknown cube and based on its density, identify the cube from a list of possibilities below.[Image unavailable: possible unknowns]
Introduction to part I
https://youtu.be/FYBNuoPKf_gLinks to an external site.
Cube #1
- mass: 24.99 g
- length Download length width Download widthheightDownload height
Cube #2
- mass: 8.59 g
- length Download lengthwidth Download widthheightDownload height
Cube #3
- mass: 10.83 g
- length Download lengthwidth Download widthheightDownload height
Cube #4
- mass: 18.42 g
- length Download lengthwidth Download widthheightDownload height
Cube #5
- mass: 8.66 g
- length Download lengthwidth Download widthheightDownload height
Cube #6
- mass: 18.89 g
- length Download lengthwidth Download widthheightDownload height
Cube #7
- mass: 147.41 g
- length Download lengthwidth Download widthheightDownload height
Cube #8
- mass: 137.92 g
- length Download lengthwidth Download widthheightDownload height
Cube #9
- mass: 127.78 g
- length Download lengthwidth Download widthheightDownload height
Cube #10
- 45.48 g
- length Download lengthwidth Download widthheightDownload height
------------ Part II ------------
In Part II of the experiment, you will determine the density of an irregular object using water displacement method.
Introduction to part II
https://youtu.be/pxz_sf-ErEgLinks to an external site.
- Size of rubber stopper: #2
Mass of stopper (g)
- Trial 1: 8.48 g
- Trial 2: 8.48 g
Initial volume of water (mL)
- Trial 1: 60.0 mL Download Trial 1: 60.0 mL
- Trial 2Download Trial 2
Volume of water + stopper (mL)
- Trial 1 Download Trial 1
- Trial 2Download Trial 2
------------ Part III ------------
In Part III of this experiment, you will measure the mass of various volumes of water and graph the data to observe the relationship between mass and volume. The slope of the line (experimental average density) will be computed and its value will be compared with true (literature) value.
Introduction to part III
https://youtu.be/ZeN_jgoWRboLinks to an external site.
Minimize Video
- Temperature of waterDownload Temperature of water
Volume of water (mL), Mass of cylinder + water (g)
- 10.00 mL, 96.47 g
- 20.01 mL, 106.72 g
- 30.00 mL, 116.60 g
- 40.00 mL, 126.61 g
- 49.95 mL, 136.31 g
Complete the pre-lab questions and data analysis part 1, 2, 3 Download pre-lab questions and data analysis part 1, 2, 3 as instructed by your lab instructo