Unit 2 - Post-Assessment

The density of aluminum is 2.7 g/mL. A student takes a 0.45 cm3 cube of aluminum and collects data from 3 balances. Which balance is precise, but not accurate? (DOK 2)

• Balance A

• Balance B

• Balance C

• Balance D

A student is trying to identify an unknown substance by finding its density. He finds the mass of a weighting boat to be 2.69 g and the mass of the unknown pieces, including the weighing boat, to be 18.01 g. To find the volume he measured out 25.7 mL of water in a graduated cylinder and then added the pieces to find a new measurement of 32.3 mL. What is the identity of the substance? (DOK 1)

• Halite

• Quartz

• Fluorite

• Gypsum

What is the density of 2.0 g of a substance that has a volume of 5.0 mL? (DOK 1)

• 0.40 g/mL

• 10.0 g/mL

• 2.5 g/mL

• 7.0 g/mL

In lab students were asked to make a statement as to whether adding mentos to coke was a chemical or physical change. Which gives the best compelling evidence to classify this reaction as a chemical or physical change? (DOK 3)

• Physical, nothing new is produced, the gas or carbon dioxide is merely separating from the solution when mentos and coke combine

• Chemical, when a gas is given off a chemical change is always produced

• Chemical, matter is clearly lost in the reaction of coke and mentos as evident in the geyser of foam coming off of the reaction. A new product is produced

• Physical, matter is not lost in the reaction of coke and mentos

In a fume hood, students took a 50.0 mL beaker of nitric acid and dropped a penny into the beaker. The students observed the following: a strong metallic smell, violent bubbling and a brownish/green gas given off. The students also observed that the penny became shiny and then completely disappeared. Which of the following is the best indicator that a chemical reaction has occurred between these two reactants? (DOK 2)

• The penny becomes shiny when it comes in contact with nitric acid

• A brownish/green gas is given off

• The nitric acid bubbling/boiling

• The volume of the solution increased after the addition of the penny

A student in chemistry classes mixes two clear solutions together. Which of the following is the best indicator that a chemical reaction has occurred? (DOK 1)

• The solutions are soluble when mixed together

• Yellow precipitate is formed when mixed together

• Volume of the solution increases

• Two beakers were mixed together

Burning wood is an example of which kind of change? (DOK 1)

• Physical

• Nuclear

• Chemical

• All of these

A cup of gold colored metal beads was measured to have a mass 425.0 grams. By water displacement, the volume of the beads was calculated to be 48.00 cm³. Given the following densities, identify the metal and choose the answer that is the most accurate. (DOK 2)

• The metal is gold but the answer is not accurate

• The density of the metal is 19.30 g/cm³ but the answer choices are in milliliters therefore none of the answers are correct

• The density of the metal is 8.85 g/cm3 which means the metal is copper. The answer is accurate because it is very close to the accepted value. The units 1 mL of water = 1 cm³ of water

• The density of the metal 8.85 g/cm3 which means the metal is copper. The answer is not accurate because the density for copper is listed as 8.86 g/mL which is not accurate and the unit is incorrect mL do not = cm³

When given 5 g of a mysterious white powder to identify, two students discuss how to plan an experiment to determine the identity of the unknown powder. They know it is one of six possible substances. Which of the following is a logical first step in an experiment that could be used to determine the identity of the mystery powder? (DOK 1)

• Pick one physical property and test it on the mysterious powder first before doing anymore planning

• Determine physical and chemical tests for the six known substances and then compare the mystery powder’s properties to these

• Use the 5 g of white powder to determine if it is flammable or not before doing anymore planning

• Give each team member 2.5 g of the mystery powder and let them determine what tests to run once they get into the lab

A student in a chemistry class mixes together two chemicals and observes bubbling and the beaker getting warmer. Which of the following would NOT provide the student with evidence that a chemical reaction has occurred? (DOK 1)

• Bubbling represents a gas being produced

• A clear solution being formed

• A new substance is being formed

• Heat indicates that an energy change is occurring