8th Grade Science Summer Lab Name: ______
Changing the density of a liquid—Adding salt
Can the density of a liquid be changed?
Procedure
1. Half-fill a tall clear plastic or glass cup with room-temperature water.
2. Place a slice of carrot in the cup.
Does the carrot slice float or sink?
What does this say about the density of the carrot slice compared to the density of water?
______
3. Add 1 teaspoon of salt and stir with a spoon until the salt dissolves.
4. Continue adding salt, 1 teaspoon at a time, measure the height of the carrot in the cup and record in the table below.
* If you do not have a ruler at home, cut out the ruler on the back page.
Table title (descriptive): ______
1 tsp
2 tsp
3 tsp
4 tsp
5 tsp
6 tsp
7 tsp
8 tsp
9 tsp
10 tsp
11 tsp
12 tsp
13 tsp
14 tsp
Does the carrot slice float or sink at this point? ______
What does this say about the density of the fresh water compared to the density of the salt water?
______
Create a scatter plot of these data on the graph below:
Graph Title (descriptive): ______
Amount of salt (tsp)
Observational Study: Very carefully add fresh water to the top of the salt water until the carrot begins to sink.
If the carrot sinks to the bottom, add small amounts of salt and fresh water as needed to cause it to hover (halfway between the top and bottom).
Once your carrot slice is hovering, what do you know about the density of the carrot slice compared to the density of this salt water?
______
______
Let’s say that you tried the same activity with a piece of potato. If potato is more dense than
carrot, would you need to dissolve more or less salt in the water to make the potato float?
______
Explain your answer.
______
What is the independent variable in this experiment (the variable you tested)?
What is the dependent variable in this experiment (the outcome or result of your test)?
What are 2 controls or constants in this experiment?
Answer the density problems below, using these formulas:
Formulas:
Density = volume of a cube = side3
1) Gloria needs to find the density of a cube. Each side of the cube measures 3 cm and the mass of the cube is 12 g. What is the approximate density of the cube? Include units for all three measurements below!!!
Mass = ______
Volume = ______
Density = ______
2) Two mineral samples have the same mass. Which of the following statements is therefore TRUE?
A They are the same size and shape.
B They do not necessarily have the same density.
C They have the same volume.
D They are the same material.
3)
What is the density of the rock sample shown in the illustration? Include units for all three measurements below!!!!
Mass = ______
Volume = ______
Density = ______
4) Mary decided to find the density of her metal house key to try and identify what the key was made from. She found the volume of the key to be 5 ml and the mass to be 39.5 g. Using the chart to the right, what type of material is the key made from?