Name:______

Period:_____

Law of Conservation of Mass

A scientific law describes a phenomenon in nature. One of the basic laws of science which concerns chemists is the law of conservation of mass. It states that mass is always conserved in reactions and that the total mass can not be increased or decreased (matter can not be created or destroyed)

In this investigation, you will test this law by performing a chemical reaction and carefully measuring the starting materials (reactants) and comparing them to the measurements of the ending materials (products). You will then interpret your results to see if they support the law of conservation.

Purpose: The purpose of this experiment is to become familiar with the chemistry laboratory, determine the mass of compounds, combine compounds, observe the change, and test the law of conservation.

Materials:goggles and apron (safety is important because these chemicals are toxic)

2 beakers

compound X and Y

graduated cylinder

balance

Procedure:

  1. Measure the mass of a clean, dry beaker. Pour about 10 mL of compound X into the beaker and measure the mass of the beaker and compound X. Observe any physical properties.
  1. Repeat step #1 with a different beaker and compound Y.
  1. Pour the contents of one beaker into the other. Swirl the mixture gently and record your observations. Measure the mass of the mixture and the beaker.
  1. Discard the mixture in the waste beaker by the sink. Repeat steps for second trial.
  1. Clean up after yourself and put everything back the way you found it.

Data: (always use units when recording numerical data!!)

Trial 1Trial 2

Mass of the beaker…………………………………………..______

Mass of the beaker and compound X……………………….______

Observations of compound X:

Data (cont.):

Trial 1Trial 2

Mass of the beaker…………………………………………..______

Mass of the beaker and compound Y……………………….______

Observations of compound Y:

Mass of beaker and mixture of compounds…………………______

Observations of mixture:

Analysis:

Total mass of reactants without beaker mass………………______

*Total mass of products without beaker mass……………..______

(experimental value)

*Often you will be asked to calculate your percent error in an experiment which compares your experimental value (what you come up with in lab) to an actual or theoretical value (the known or expected value). Here is the formula in order to calculate percent error:

percent=experimental – actualx100

erroractual

The experimental value in this experiment is the total mass of products without beaker mass. Think about the law of conservation in order to determine the actual value and then calculate the percent for each trial. Round your answer to the nearest tenth of a percent.

Trial 1 - ______%Trial 2 - ______%

Conclusions: (answer in complete sentences where applicable)

  1. What type of change took place when you mixed the compound? What were the 2 indications of this change that you witnessed?
  1. What is one possible source of error in this experiment and exactly how did it affect your results?
  1. If a math student manually adds the following numbers (439 + 294 + 92 + 137) and gets 981, what is this student’s percent error to the nearest tenth of a percent?