Purpose: The purpose of this lab is to determine how the change in the density of three group 4 elements (Si, Sn, Pb) be used to predict the density of one other Group 4 element (Ge)?

Hypothesis: If the densities of three group 4 elements are determined experimentally, then the density of the unknown group 4 element can be predicted because density shows a periodic trend within a group or family.

Variables

Independent Variable:  The period (row)

Dependent Variable:  Density

Control Variable:  The accepted densities of the group 4 elements

Materials:

Safety:

Procedure: In this experiment the mass and volume of the elements in group 4 were measured and the density was calculated.  The technique involved using water displacement to determine the volume of the metal samples.  The results were displayed graphically and the density of the unknown group 4 element was predicted.

Pre-lab Assignment: Answer the following questions in complete sentences, using the data from the lab to support your answers.

1.  One of the elements Mendeleev predicted was eka-aluminum, corresponding to a gap in the fourth row or period of the Group 3A elements, between aluminum and indium.  A graph of density vs. period number is shown below.  Use the graph above to answer the following questions. 

1. Is this trend consistent with what Mendeleev expected? Explain your answer.

Yes, this trend is consistent with what Mendeleeve expected because he predicted that the density of elements within a group would increase from top to bottom.

2. Use your graph to predict the density of eka-aluminum. 

 density = 2.94*4-6.45 =5.31 g/ml

3. What known element in the modern Periodic Table corresponds to eka-aluminum?  Explain 

The known element in the periodic table which corresponds to eka-aluminum is Gallium because…

4. Look up the density of the modern element in a reference source and record its actual value. 

The actual value for the density is 5.94 g/ml

5. Use the equation for percent error to calculate the percent error between the predicted and actual values for the density of eka-aluminum. 

% = [(5.31 - 5.94) / 5.94 ] x 100 = 10.6 %

6. How do the actual and predicted density values compare? Use your percent error to support your answer.  

The actual and predicted values are in good comparison to each other because the percent error was 10.6% which is a small amount of error.

7. Discuss the accuracy of these results?

The results can be considered to be very accurate because the error was well within our range of limits of 20% or less.  Since 10.6% is less than 20%, we can accept these results as being accurate.