The Density of 3 Liquids

Work individually. Groups of two or more are not permitted.

The Report

One report per person. Use standard headings for lab reports. Include your data, the calculations, and one graph with three lines on it, as well as the answers to the questions.

The Problem

Using the techniques from this lab you will be able to make measurements of mass and volume and analyze the data by means of graphs.

Reagents and Equipment

3 burets each filled with a different liquid: methanol, water, and saline

small Erlenmeyer flask

balance

graph paper

Data

Name of liquid assigned by teacher: ______

Volume of liquid assigned by teacher: _____ mL

mass of flask before adding liquid: ______g

burette reading before adding liquid: ______mL

burette reading after adding liquid: ______mL

mass of flask after adding liquid: ______g

Procedure

  1. You will be assigned a liquid and an approximate volume of the liquid to use. Record the name and volume.
  1. Find and record the mass of an Erlenmeyer flask. It is essential that the flask is dry on the outside, though it may be wet on the inside.
  1. Go to a burette that contains the liquid you are using. Ensure the burette has enough liquid in it. If not, then fill the burette first.
  1. Read the level on the burette and record the value to TWO decimal places. You may feel like you are guessing a bit on the second decimal place, but that is OK. If the level appears to be exactly on a whole number, then record the value with two zeros after the decimal. For example, record 7.00 mL, not 7 mL.
  2. Open the valve and add approximately the volume that you were assigned. It is not important that you add exactly the assigned amount, but it is critical that you read the levels on the burette as accurately as possible.
  1. Read and record the level of the burette after adding the liquid.
  1. Take the Erlenmeyer back to the scales. Record the mass of the Erlenmeyer flask and liquid.
  1. Clean up by pouring the liquid down the sink.

Calculations and Analysis of Data

  1. Calculate the mass and volume of the liquid added by subtracting the initial mass and volume from the final mass and volume. Show the calculation including the values used as well as the units. (Each number that is written down will have a unit after it.)
  1. There will be a class record of all the mass and volume measurements for each liquid. Record your mass and volume on the class record.
  1. Use the class data to plot a fully labeled graph of Mass versus Volume with all three liquids shown on the same graph paper (volume is on the x-axis). Mark data points with squares, circles and triangles to differentiate between liquids. Title the graph “The Density of Three Liquids”.
  1. Draw in a “best fit” line for each. This is to be a straight line that runs through zero, and which has an equal number of data points on either side of it. Note that there is no requirement that the data point furthest from the origin be on the line. In fact, if the points are somewhat scattered, there may be no data points touching the line. This is OK. The line represents the best average.
  1. Determine the slope of each best fit line by dividing the rise by the run. Record this relationship on the graph beside each line.

Questions(Responses written in the form of sentence fragments will not be marked.)

  1. What physical property does the slope of the graph represent?
  1. Use the slope of your graph to calculate the mass of 6.5 mL of saline.
  1. The accepted value for the density of methanol is 0.78 g/mL. Calculate
    the relative error of your results as follows:

(accepted value – your experimental value)

% error = ------x 100%

accepted value

4. a) What is the density of molasses if 58.31 g of it has a volume of 49.26 mL?

b) Does molasses float or sink in water? Explain.