Experiment 1

Experiment 1: Density of Liquids - Measurement and Error in Chemical Analysis

Experimental Objectives:

• Determine the density of 6 solutions 5 known and 1 unknown using two different pieces of lab equipment

  • Find the density of of DI water and see which method yield the best result by comparing the densities of DI water at their temperature

Learning Objectives: 

• Know the concepts of random error, systematic error, precision and accuracy and understand how they are applied in results and measurements

• Know that experimental results must be repeatable

• Properly measure/dispense liquids using graduated pipets and burets, know how to use analytical/top-loading balances

• Know how salt concentration affects solution density

Background/Theory

• Materials 

  • DI water

  • 2, 4, 6, 8 % of NaCl (table salt can be throw in the drain)

• Error of Graduated Pipet, Buret, and Balances

  • ALWAYS read a buret to the nearest 0.02 mL

  • Read and record graduated pipet to the nearest ½ of the smallest graduation

  • Most of the graduated pipets in our lab are TD “To-Deliver”

  •  Balances have an error of 1 in the last displayed decimal place

• Comparison of Accuracy/Precision of Instruments:

  • Scientists used different types of methods to see which method yielded the best result, cost, efficiency and practicality. 

  • In the lab, for density and liquid ( measurement and errors in chemical analysis ) we find the mass % concentration of an unknown solution by finding the density and comparing it to the density of the known solutions mass % concentration.

  • We do that by finding the mass and volume through different types of measurement.

    • Mass: analytical balance- precise (error- 0.0001), while top loading balance (carry more weights, massive and larger sample- 0.001g.)

    • Volume- graduated pipet and buret. 

      • Graduated cylinder measure imprecise volume measurement

      • Graduated pipet and buret - measurement the volume of liquid being transferred more accurate and precise

• Uncertainty and Types of Error

  • Last digit of the number is uncertain 

  • Instrument have different degree of uncertainty 

    • Last dig fluctuates 

    • Random error: equal and arbitrary chance that the last digit is too high and too low

    • Systematic error: error skewed in direction that are attributed by experimental design, user error, or poor calibrated instrument 

    • Random error is alway there, systematic error can eliminated

• Precision vs Accuracy Definition

  • Accuracy: how close your value is to the true value, can be quality by percent accuracy 

  • Precision: two method in regard to the data

    • Number of sig figs that a instrument can measure (top loading - 0.01, analytical balance - 0.001 - more precise)

    • Repeatability of the results , quantity through standard deviation error or percent error 

  • Quantitative results have to be reported with error

Procedure

Notes:

• Use SAME balance for each mass measurement

  • Why: calibration differ between balances therefore use the same balance 

• We are using “weigh by difference”: Final measure (Solution and beaker) SUBTRACTED by initial measure (empty beaker)

Part 1 Graduated Pipet Trail - For all Solutions

1. Wash pipet 2 times in 1-2 ml of each solution

   1. Why?: There are residual droplets from previous solution remaining in the pipet after draining

2. Measure/record mass of beaker

3. Measure ~5 mL of solution using graduated pipet, record with precision

   1. Check if pipet is TD or TC

4. Pour solution into beaker, allowing the pipet to drain for 5-10 seconds

5. Record combined mass of beaker and solution, then temperature of solution

6. Repeat for all the different NaCl concentrations and DI water

Note on Data collection: 

• For DI-Water Trial: Collect 4 sets of data with other students with the same temperature as yours

Safety Tips:

• Do not waste or pour excess sample depending on the nature of the solution, dispose to the appropriate disposal, give to students, do not put it back in the solute bottle to avoid contamination.

Part 2: Buret Trial - For all Solutions

1. Weigh the mass of the beaker

2. Record the initial volume in the buret

3. Then dispense 5 ml of solution to the beaker

4. Recond the final volume, the combined beaker and solution, and the solution temperature

Note on Data collection: 

• For DI-Water Trial: Collect 4 sets of data with other students with the same temperature as yours

Safety Tips:

• Record the beaker under eye level of the instrument; do not fill the buret form top, lower to a safe height; add more solution using funnel then remove then connect buret to a buret clamp.

Analyzing data/observations:

• Calculate density of solutions each trials

• Standard deviation and average of densities in DI waters from DI pool measurement

• Using %error to compare standard deviations  

  • Why? Which trial yield the best result 

  • Why is density too high or too low play a role on the result

• Graph density vs % concentration 

• Use the LINEST graph and densities of the unknown for each trail to find mass % concentration

• Use error propagation because it is one trial 

Experimental Results:

• Density average and standard deviation for each trial including measurement and temperature (need to be in g/ml)

• % error for average density and the known density of water at that temperature 

• Record the graph

• Record unknown solution

Here are the flashcards in question-and-answer format:

1. Q: What is Density? A: Mass per unit volume of a substance, commonly expressed in g/mL.

2. Q: What is Systematic Error? A: Error that is skewed in one direction, often due to experimental design, user error, or poorly calibrated instruments.

3. Q: What is Random Error? A: Error that has an equal chance of being too high or too low, inherent in all measurements.

4. Q: What is Precision? A: The degree to which repeated measurements under unchanged conditions show the same results.

5. Q: What is Accuracy? A: The closeness of a measured value to a standard or known true value.

6. Q: What is a Graduated Pipet? A: A laboratory instrument used to measure and dispense precise volumes of liquid.

7. Q: What is a Buret? A: A long, graduated glass tube with a tap at one end, used to dispense precise amounts of liquid.

8. Q: What is a TD Pipet? A: A pipet designed to deliver a specific volume of liquid, where the remaining liquid in the pipet is not counted.

9. Q: What is a TC Pipet? A: A pipet designed to contain a specific volume of liquid, where the entire contents must be delivered to ensure accurate measurement.

10. Q: What is Repeatability? A: The ability to obtain consistent results when repeating an experiment.

11. Q: What is Percent Error? A: A measure of how inaccurate a measurement is, expressed as a percentage of the true value.

12. Q: What is an Analytical Balance? A: A high-precision balance that measures mass to a very fine degree, typically 0.0001 g.

13. Q: What is a Top-Loading Balance? A: A balance that is less precise than an analytical balance but can measure larger sample weights, usually accurate to 0.001 g.

14. Q: What is Standard Deviation? A: A measure of the amount of variation or dispersion in a set of values.

15. Q: What is Mass Percent Concentration? A: The mass of solute divided by the total mass of the solution, multiplied by 100.

16. Q: What is DI Water? A: Deionized water, free of ions and impurities, often used in experiments.

17. Q: What is NaCl? A: Sodium chloride, commonly known as table salt, used in solutions to affect density.

18. Q: What is Error Propagation? A: The process of determining the uncertainty of a calculated value based on the uncertainties of the measurements used to calculate it.

19. Q: How does temperature affect density? A: Density can change with temperature; it's crucial to measure density at consistent temperatures.

20. Q: What is the linearity of Density vs Concentration? A: The relationship between density and concentration can often be represented with a linear graph.

21. Q: What is a Laboratory Safety Tip? A: Always dispose of chemicals according to proper disposal protocols to avoid contamination.

22. Q: What does Weigh by Difference mean? A: A technique where the mass of an object is determined by subtracting the mass of the empty container from the mass of the container with the substance.

23. Q: What is Error in Measurement? A: The deviation of a measured value from the true value, which can arise from various sources.

24. Q: What is Readability of Measuring Instruments? A: The least count or smallest division one can accurately read on a measuring instrument.

25. Q: What is Calibration? A: The process of adjusting the accuracy of a measurement instrument.

26. Q: What is Trial Replication? A: Conducting multiple trials to verify the reliability of results.

27. Q: What is Data Collection? A: The process of gathering and measuring information on targeted variables.

28. Q: What is Concentration? A: The abundance of a constituent divided by the total volume of a mixture.

29. Q: What does Discard Technique mean? A: Proper disposal methods for lab samples to maintain safety and cleanliness.

30. Q: What are Residual Droplets? A: Small amounts of liquid that may remain in a pipet or container after transfer.

31. Q: What is Mass Measurement Accuracy? A: Using the same balance for mass measurements to reduce discrepancies.

32. Q: What is Chemical Analysis? A: The process of determining the chemical composition or structure of a substance.

33. Q: What are Research Protocols? A: Standard procedures followed to ensure consistency and accuracy in experimental and data collection.

34. Q: What is Graphing Results? A: Plotting data points on a graph to visualize relationships and trends.

35. Q: What does Cross-Experiment Comparison mean? A: Comparing results from different experiments to evaluate consistency and reliability.

36. Q: What is Solution Density? A: Density of a solution, which can be affected by the solute concentration.

37. Q: What are Volume Measurement Techniques? A: Methods used to accurately measure liquids, such as graduated pipets and burets.

38. Q: What are Data Analysis Techniques? A: Methods applied to interpret and evaluate collected experimental data.

39. Q: What is the Temperature Impact on Solutions? A: How variations in temperature can affect the density and behavior of liquid solutions.

40. Q: What is Volume Dispensation? A: The act of delivering a specific volume of liquid from a measuring instrument.