IAPS End of Unit B Review

Ms. Langsdale masses a sample of playdough on a balance. She successfully creates it into the shape of a sphere, a cube, and a flat circle massing the playdough after each creation. Which playdough creation will have the greatest mass?

• sphere

• cube

• Flat circle

• The mass will be the same for all

Answer explanation

The Law of Conservation of mass applies to all changes, chemical and physical. The mass of the playdough that came out of the container is the same no matter what shape it gets made into.

In the chemical reaction below, how many different elements are used on the product side the equation?

 $6CO_2\ +\ 6H_2O\ \rightarrow\ C_6H_{12}O_6+\ 6O_2$  

• 1 element

• 2 elements

• 3 elements

• 4 elements

Answer explanation

The products side of the equation is the side the arrow points toward. In this equation, the products side shows  $C_6H_{12}O_6\ +\ 6O_2$  which has Carbon, Hydrogen, and Oxygen for a total of 3 different elements.

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In the chemical reaction below, what is the total number of atoms on the product side the equation?

 $6CO_2\ +\ 6H_2O\ \rightarrow\ C_6H_{12}O_6+\ 6O_2$  

• 7 atoms

• 24 atoms

• 36 atoms

• 42 atoms

Answer explanation

The products side of the equation is the side the arrow points toward. In this equation, the products side shows  $C_6H_{12}O_6\ +\ 6O_2$ . The molecule of  $C_6H_{12}O_6$  has 6 Carbon atoms, 12 Hydrogen atoms, and 6 Oxygen atoms; each of the 6 molecules of  $O_2$  has 2 oxygen atoms combined which makes for a total of 6x2=12 oxygen atoms from those molecules. In total on the product side, you have 6 + 12 + 6 + 12 = 36 atoms.

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Copper is a reddish-brown metal that is an excellent conductor. Copper tarnishes and becomes black when exposed to air and light. The density of copper is 8.96 g/cm³ . The melting point is 1,085^oC and the boiling point is 2562^oC. Check all of the physical properties of copper.

• tarnishing

• melting point

• boiling point

• density

Answer explanation

The color change when copper tarnishes proves that tarnishing is a chemical change. Melting and boiling changes in the state of matter and do not involve a chemical change in the substance. Density is also a physical property that does not involve a change in the substance.

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A chemical reaction occurs in a closed system. What conclusion can you make about the mass of the substances involved before and after the reaction?

• The mass will not change

• The mass will go down because some gas will escape

• The mass will go up because some gas will escape

• The mass will go up because new substances will be made

Answer explanation

Since the reaction takes place in a closed system, by the law of conservation of mass the mass will be the same before and after the reaction.

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Check all statements below that describe chemical reactions.

• Solid Zinc is dropped into hydrochloric acid and a gas is produced

• Liquid sodium hydroxide and liquid copper chloride are mixed together and a solid forms at the bottom of the container

• A sample of solid elemental sodium is dropped into water and an explosion occurs

• A puddle evaporates on a hot Florida day

Answer explanation

Evaporation is a change in state of matter which is a physical change. All other answer options describe chemical changes.

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Sam wants to test the effect that different concentrations of acid will have on the dissolution of a particular kind of candy. As she sets up and completes her experiment, which of the following experimental designs would be most likely to help her answer her question?

• Allow several pieces of candy to soak in different amounts of acid of a single concentration and then measure the amount of dissolution on each.

• Prepare solutions of different acid concentrations, measure 50 milliliters of each into different beakers, and place the same number and type of candy into each of the beakers.

• After allowing a piece of candy to be exposed to one acid concentration, place it in different acid concentrations, and then measure the surface area that is dissolved.

• Prepare solutions of different acid concentrations, measure 50 milliliters of each into different beakers, and place different types and amounts of candies into the beakers.

Answer explanation

This experiment aims to measure the effect of different acid concentrations. In order to make sure the only thing affecting the results is the acid concentration, the concentration should be the only thing that changes between trials (independent variable). Sam is trying to figure out if these different concentrations will affect how much a piece of candy dissolves, so this is the things that needs measured (dependent variable). The amount of acid, the amount of candy, and the type of candy are all things that should be kept the same in each trial (constant variables)

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Barry is convinced that he discovered a new element after only one experiment, but he is frustrated that the Science Journal would not publish his work. What advice could you provide Barry to get his work published in the future?

• Conduct multiple trials to verify his findings (repetition)

• Add more data tables and graphs to his report

• Scrap the whole idea and start over

• Send an email to a well respected scientist asking if they will publish the findings under their name

Answer explanation

In science, in order for new findings to be considered by the scientific community, repeated trials need to be conducted to verify the accuracy of the findings.

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Lucas used a computer simulation to build different types of molecules. He used a computer simulation because real molecules are too small to see and the simulation is a simple representation for a complex concept. The computer simulation was used as

• scientific models

• experimentation

• claim, evidence, and reasoning statements

• Manipulatives to help develop motor skills

Answer explanation

Scientists use models to represent things that are too big or too small to be seen.

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How do science and society interact? Check all that apply.

• Science and society do not interact.

• Society can drive scientific research by providing support and funding opportunities for projects that are considered important by decision makers.

• Science can affect society by providing new technologies and advancements to meet the needs of society.

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