Quantitative Measurement
Background:
The study of chemistry involves not only observing changes in matter, but also measuring these changes. In fact, most chemical principles cannot be fully understood without obtaining and analyzing some quantitative data. The techniques of data collection, data analysis, and measurement are important parts of chemistry.
Careful attention should be given to the degree of uncertainty in your measurements. Record only those digits, which are significant, and use only those digits in your calculations.
The accuracy of your methods can be reported with your results in terms of percent error. The percent error in calculations and measurements is a comparison of the difference between experimental results and theoretical values, expressed as a percentage. Percentage error can be determined as follows.
% error = |experimental value – theoretical value / theoretical value X 100
A useful way of comparing the chemistry of two substances is to compare their densities. By carefully measuring the mass and volume of two substances, their densities can be calculated as follows.
density =mass / volume
In conducting this experiment, you will make several mass and volume measurements and use these measurements to determine the density of water, some other known liquids, and some known solids. You will then determine the uncertainty of your results by calculating percent error.
Pre-Lab: Density of Water
Clean and thoroughly dry a 50 ml graduated cylinder.
Place the graduated cylinder on the electronic balance and tare the device.
Add 45.00-48.00g of distilled water to the cylinder.
Record the exact mass of the water in data table.
Record the volume of water in the graduated cylinder in the data table.
Calculate the density of water with the proper significant digits.
Calculate the percent error using the theoretical value from reference manual.
Make your hypothesis about the other substances to be tested.
Purposes:
After experimentally determining the density of water, how will the densities of glycerin, mineral oil, brass, aluminum, copper, stainless steel, lead, and iron compare to that of water?
Hypothesis:
Procedure and Materials:
Manipulated variable:
Responding variable:
Controlled variables:
Experimental control:
Detailed Methods:
Safety goggles must be worn for this experiment.
Tip: Measure all liquids from the bottom of the meniscus to the highest level
of precision.
Density of a Solid
Density of Liquids
Possible materials: Goggles, 2 graduated cylinders (10ml and 50ml), electronic balance, 100 ml beaker
Drawing of lab set up...
Results:
Pre-lab data table (should be in background):
Substance | Mass (g) | Volume (ml) | Density (g/ml) | Theoretical Value (g/ml) | % Error |
Water |
Data table:
Substance | Mass (g) | Volume (ml) | Density (g/ml) |
Average Density |
Theoretical Value (g/ml) | % Error | ||||||
Brass |
Alloy |
X |
||||||||||
Aluminum |
||||||||||||
Copper |
||||||||||||
Stainless Steel |
Alloy |
X |
||||||||||
Lead |
||||||||||||
Iron |
||||||||||||
Glycerin |
||||||||||||
Mineral Oil |
Analysis:
What calculations did you make, how, why?
Make a graph for the data with the manipulated variable on the x axis and the responding variable on the y axis.
Conclusion:
Write a relationship statement including data from your table. Did you
support your hypothesis? How do you know?
How accurate were your measurements? How do you know?
What were some possible sources of error? How did they affect your results? What
could you done to improve your validity?
Real World Application:
Describe briefly a general method that could be used to determine the density
of a solid or a liquid in the real world.
Will these methods work for all liquids and solids? Why not?
What is another possible method for these solids? Explain another real world
application for the concepts from this lab.
Recommendations:
What new question could you investigate that would help you understand
density more?
Briefly explain the methods you would use to test this question