Lava Viscosity
Background and Objective:
This lab activity allows you to explore the effect of silica content on the viscosity of lava. Silica is one of the most abundant (there is a lot of it) minerals found in the Earth’s crust. On Earth it is found in the form of the mineral quartz (SiO2) and is the major component of most sand. The silica content of magma ranges from about 50% to 70 %. The physical property of viscosity describes how easy it is for a liquid to flow. Liquids with low viscosity flow easily and liquids with high viscosity flow with difficulty.
Materials:
· Ramp, Masking Tape, Block, ruler
· Three lava samples in containers: A, B and C
· Silica sand, paper towel, stopwatch, plastic
Procedure:
1. Put on Safety Goggles
2. Observe the three lava samples A (no silica), B (low silica), and C (high silica)
3. ALREADY COMPLETED FOR YOU: Make a ramp by balancing a cookie sheet on the edge of the wooden block. Use your masking tape to create three starting lines at the 25-centimeter mark (the bottom of the masking tape should be 25 centimeters from the end of the ramp). Record this distance on the "Rate of Flow Results" (Table 1).
4. Predict how the silica content of each liquid will affect the speed with which the liquid flows down the ramp. Which liquid will have the fastest speed down the ramp? Which will have the slowest? Record your predictions on your "Data Sheet" handout.
5. Pour one plastic teaspoonful of one of the liquids just before the top of the masking tape and start timing as soon as the liquid passes the bottom of the tape and touches the ramp surface. Stop the timer when the liquid reaches the bottom of the masking tape 25 cm mark. Record the time (s) in the data table. Clean the ramp and repeat the test two more times, using a new line each time. Average your results.
6. Calculate the flow rate by dividing the distance of the ramp (25 cm) by the average time it took the liquid to cover that distance. Record the flow rate or speed in your data table.
7. Repeat steps 7 and 8 for the other two liquids.
8. Display your average flow rate results for the three liquids in an appropriate graph. Do not forget a title and axis labels and units where appropriate. Refer to your graphing rubric in your binder.
Name ______Date ______Period______
Silica and Viscosity Data Sheet
I. Prediction:
Given that sand is made almost entirely of silica (quartz grains), predict which liquids (A, B or C) will flow most quickly? Which will flow the slowest and which in between?
Explain your reasoning:
II. Data:
A. Table 1
Silica Content Vs Rate of Flow (cm/s)Silica Content / Distance / Time to Flow 25 cm (s)
Trial1 Trial 2 Trial 3 / Average Time (s) / Flow rate (cm/s) = d/t
A (no silica) / 25 cm
B (low) / 25 cm
C (high) / 25 cm
Table 1
Use this space to show your math calculations :
B. Graph A: Using a piece of graph paper and the graphing rubric in your binder to create an appropriate graph comparing the average flow rates of the “lava samples.”
III. Analysis and Conclusions
1. By adding sand to each liquid, the silica content was increased. Use the data to explain how the silica content of each liquid affected the time it took to flow down the board.
2. Use data and background knowledge to answer: Which sample had the highest viscosity? Which had the lowest viscosity? Which was in between? Explain why.
3. Discuss two ways this model is like real magma.
4. Discuss two ways this model is unlike real magma.
5. Look at the graphs on page 207 of your textbook. Which beaker (A, B, or C) contained liquid most like Basalt-forming magma? Which beaker contained liquid most like Rhyolitic-forming magma? Explain why.
Time (s) for Bubbles to reach the surface of each liquid:
Liquid A ______
Liquid B ______
Liquid C ______
6. THINK: What process were you modeling when you blew into the samples?
7. Use the data to explain which sample gas escaped quickly from and which gas escaped more slowly.