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Unknown Liquids
Administration Procedures
Grades 5-8 Performance Task
Contributed by: New York State Alternative Assessment in Science Project (NYSED)
1996 Administration


Students study two bottles containing unknown liquids and descriptions of the bottles. Based on this information, they then design and conduct an experiment to determine which bottle has the liquid of greater density.

The task assesses students' abilities to design and conduct an experiment, make simple observations, apply their observations to test an unknown, and make generalized inferences from their observations.

This task is designed to take students approximately 10-15 minutes to complete.

Overall Task Content Area:

Physical Science

Specific Knowledge Areas:

Properties of solutions

Performance Expectations:

  • conducting investigations
  • using equipment
  • gathering, organizing, and representing data
  • formulating conclusions from investigational data

National Science Education Standards:

8 B PS 1: Properties and changes of properties in matter: Grades 5-8
1.1 A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.

8 A SI 1: Abilities necessary to do scientific inquiry: Grades 5-8
1.2 Design and conduct a scientific investigation. Students should develop general abilities, such as systemic observation, making accurate measurements, and identifying and controlling variables. They should also develop the ability to clarify their ideas that are influencing and guiding the inquiry, and to understand how those ideas compare with current scientific knowledge. Students can learn to formulate questions, design investigations, execute investigations, interpret data, use evidence to generate explanations, propose alternative explanations, and critique explanations and procedures.

1.4 Develop descriptions, explanations, predictions, and models using evidence. Students should base their explanation on what they observed, and as they develop cognitive skills, they should be able to differentiate explanation from description--providing causes for effects and establishing relationships based on evidence and logical argument. This standard requires a subject matter knowledge base so the students can effectively conduct investigations, because developing explanations establishes connections between the content of science and the contexts within which students develop new knowledge.

(Use the "hot" link on the PALS home page to check the full text of related National Science Education Standards, if desired.)

National Council of Teachers of Mathematics:

PS2: Solve problems that arise in mathematics and in other contexts:
Grades 6-8

General Instructions to the Teacher:

This task is designed to take students approximately 10-15 minutes to complete.

Students will be working individually for the experiment/activity part of this exercise.

The materials should be set out at each lab station, if possible. A central supply area, if needed, should be easily accessible. All supplies should be clearly labeled.

Materials for "Unknown Liquids":

In preparation for the activity the teacher needs:
  • Yellow and blue food coloring
  • Water
  • Rubbing alcohol
  • Salt
  • Sealant--hot glue or paraffin

Students will need:

  • 2 screw top bottles (28 ml) with solutions X and Z
  • Triple beam or double pan balance
  • Eye goggles
  • calculator

Advance Preparation:

  • The yellow solution (Z) is a saturated salt solution with yellow food coloring. Start with one liter (1000 ml) of warm water. Add as much salt that will dissolve with constant stirring. Let cool. Filter out any undissolved salt. Add a few drops of yellow food coloring.
  • The blue solution (X) is isopropyl rubbing alcohol and blue food coloring.
  • Bottle- screw cap vials- flit glass, 28 ml.
  • Seal the caps on the bottles with glue or liquid paraffin to avoid evaporation and facilitate reuse.
  • Determine the mass of the bottles before student use.
  • Pretest the mass difference between X and Z to determine if adequate for proper grading.


  • Students should wear safety goggles.
  • Students should be instructed not to open the vials.
  • Caution with breakage of glass bottles.
  • Check MSDS (Materials Safety Data Sheet) for further laboratory precautions.
  • Proper laboratory safety procedures required.
  • Be careful.
  • Teachers and students should always exercise appropriate safety precautions and utilize appropriate laboratory safety procedures and equipment when working on science performance tasks.


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