2017 Grade 8 PRACTICE Final 1

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2017 Grade 8 PRACTICE Final

Part 1 Structural Design—Bridges (3Q)

Figure 1. Cardboard / Figure 2. Brooklyn Bridge

1practice. We have used corrugated cardboard as a building material (Figure 1). Identify the false statement and correct it.

  1. Cardboard folds flat for shipping without losing its strength.
  2. Cardboard is recyclable and biodegradable.
  3. Cardboard is equally strong in both directions (length and width). NOT
  4. Cardboard is easy to cut with a simple tool like a knife.

2practice. We studied the making of the Brooklyn Bridge, which has a suspension design (Figure 2). Its chief engineer, Washington Roebling, decided to use cables made of steel instead of iron or rope. This decision was based primarily on considerations of

  1. Cost
  2. Functionality
  3. Aesthetics
  4. Availability

3practice. This structural shape is LEAST able to handle forces of tension and compression.

  1. Arch
  2. Triangle
  3. Rectangle

Part 2 Chemistry—Matter properties, types, and changes (10 Q)

4practice. By definition, “matter” has to have two properties. Circle which of the following items is matter, and explain why in terms of the two properties.

feartimesoilheat

Soil is matter because it has both mass and volume.

5practice. I have found a compound “A” that is like compound “B” for in terms of conductivity, malleability, and density. Material A is different from B in terms of boiling point. Could these two materials have the same chemical formula? Explain your thinking.

These two materials cannot be the same. Boiling point is a characteristic property. For the two materials to be the same, they have to have the same boiling point.
Figure 3. Nail or shell

6practice. We have studied density, which can be calculated by the formula d = m/v, where d = density, m = mass, and v = volume.

  1. Name a unit that can be used to label mass. GRAM
  2. Name a tool that can be used to measure the mass of a solid material with a irregular shape, like a nail or shell (Figure 3), and describe how it works.

A triple beam balance can be used to measure mass. The mass to be measured sits on a pan that counterbalances known masses on each of three beams.

7practice. An object will float in water if its density is less than the density of water. Use the information provided here to calculate the density of water and of object D. Show your answers in Table 1. Reminder: Density = mass/volume

  1. Does object D float or sink in water?
  2. Show your work to the hundredths place.
  3. Label your density results.

Table 1.
Material / Mass / Volume / density / Does D float or sink in water?
Water / 250 grams / 250 mL / 1gm/mL
Object D / 35 grams / 40 mL / .88 gm/mL / D floats in water

8-9practice. Identify each of the following changes as physical or chemical. Offer one reason for each of your answers.

Change / Physical or chemical change—with one reason
  1. Water freezes.
/ This is a physical change because it can be reversed. Phase changes are physical.
  1. Sugar burns down into a lump of black carbon.
/ This is a chemical change because a new substance is formed with different properties, and it cannot be reversed.
  1. A green banana turns yellow, and then spotted and soft over time.
/ This is a chemical change, indicated by a change in color.
  1. A cookie crumbles.
/ This is a physical change because no new substance is formed, only the shape is changed.

10practice. What is the difference between a mixture and a compound? Identify the false statement, and make it true.

  1. A mixture combines substances physically, not chemically.
  2. A mixture is always unevenly blended (think chocolate chip cookie). SOMETIMES
  3. The materials in a mixture retain their identities.

11practice. What is the difference between a compound and an element? Identify the false statement, and make it true.

  1. A compound is composed of all the same kind of atom. NOT
  2. The properties of a compound are different from the properties of the individual substances in it.
  3. A compound contains two or more different elements.

12practice. There are three types of mixtures—colloids, suspensions, and solutions. Which of these settles into layers because of particle size and density?

Suspensions settle into layers because of particle size and density.

13practice. For our lab on mixtures, you had to separate salt, sand, and iron filings. Why did you separate out the iron filings BEFORE adding water to separate the salt from the sand?

  1. There was no special order. We could have added water anytime.
  2. We wanted to avoid a chemical reaction between the iron and water.
  3. It was easiest to separate out the most dense material first (iron).

Part 3. Chemistry-- The Periodic Table of Elements (8 Q)

Figure 4. The Periodic Table of Elements

14practice. Name and number each type of atom in the following molecules. Use your periodic table to help with abbreviations. An example follows.

Example
water
H2O / 2 atoms hydrogen (H)
1 atom oxygen (O)
a.sodium bicarbonate NaHCO3 / 1 atom sodium (Na)
1 atom hydrogen (H)
1 atom carbon (C)
3 atoms oxygen (O)
b.barium hydroxide
Ba(OH)2 / 1 atom barium (Ba)
2 atoms oxygen (O)
2 atoms hydrogen (H)
c.potassium sulfite
K2SO3 / 2 atoms potassium (K)
1 atom sulfur (S)
3 atoms oxygen (O)

15practice.An element can be identified when you know its period and family/group number or name. Complete the table below. There is an example to help you.

Period / Family/group / Element
Example
3 / 6 / Sulfur
2 / 7A / Fluorine
3 / 5A / Phosphorus
5 / 4A / Tin

16practice.An element can be identified by its atomic number. What is the atomic number?

  1. The atomic number is the mass of the element.
  2. The atomic number is the number of protons in the nucleus.
  3. The atomic number is the number of protons and neutrons in the nucleus.

17practice. What ELEMENT do you get when…

a.You add a proton to gold? / mercury
b.You add a neutron to radium? / radium (a heavier isotope)
c.You add an electron to oxygen? / Oxygen (an anion)

18practice.We used the story of a cookie to illustrate different ways in which elements react to each other. Elements with low numbers of valence electrons tend to give them up in chemical reactions. Where are these “giver” elements found on the Periodic Table? (hint: remember what group/family means).

Elements that give up electrons are located to the left on the table.

19practiceWe used the story of a cookie to illustrate different ways in which elements react to each other. Elements with a middle number of valence electrons tend to share them in chemical reactions to achieve a stable outer shell of 8 electrons. Where are these “sharing” elements found in the Periodic Table? (hint: Remember what group/family means).

Elements that share electrons are located in the middle of the table.

20practice.Radioactive elements are unstable, and will release particles and energy until they achieve a more stable form.Elements that have a high or low ratio of neutrons to protons tend to be radioactive. One radioactive isotope of plutonium, for example,has a mass of 226amu. What is its ratio of neutrons to protons? Show your work.

Plutonium is element 94.
The neutral atom of plutonium has 94 neutrons and 94 protons (mass 188amu).
To make a total mass of 239amu, there must be 145 neutrons in this isotope
(145 + 94 = 239).
The ratio of neutrons to protons, therefore, is 145/94 = 1.54.

21test. Use your Periodic Table to determine two ways in which the elements carbon and nitrogen are the same, and two ways in which they are different.

Same-- Both elements are nonmetals, and both have two energy orbitals for electrons.
Different-- Carbon has a lower atomic number and mass than nitrogen, and fewer valence electrons.

Part 4. Hydraulic Machines (2 Q)

Figure 5. A hydraulic “claw” model / Figure 6. A real hydraulic “claw” at work

22practice. Hydraulic machines make work easier for us in different ways. Describe how a full size hydraulic claw (Figure 6) makes work easier in terms of distance or direction.

A claw extends your reach in every direction. You can be in a comfortable spot while the claw works elsewhere.

23practice. Safety is important when using tools that could be dangerous. Choose from among the tools we used-- awl, hot glue gun, or wire cutter. Name two precautions we can use to be safe when using this tool.

Carry pointed tools facing downward.
Pass a tool to another person by placing it on a table, handle toward the other person.
Unplug the hot glue gun when not in use.
Cut away from yourself.
Keep blades in a closed position when not in use.
Do not touch directly any hot or sharp surface.

Part 5. Scientific Process and Engineering Design (7 Q)

24-27practice. Jon and Kayla complete a density lab in science class in which they cause a raw egg to float, sink, or stay suspended in water by changing the density of the water with salt. They wonder if the egg would act differently if it were cooked instead of raw. They decide to test it out. They take a raw egg, a soft-boiled egg, and a hard-boiled egg, and compare how well these eggs float in waters of different densities.

24practice. What would be a suitable hypothesis for this experiment?

The eggs will act the same, whether raw or cooked.

25practice. What would be the independent variable for this experiment?

The type of egg—raw, soft-boiled, or hard-boiled

26practice. What would be the dependent variable for this experiment?

The level at which each egg floats in each type of water.

27practice. What would be two effective controls to use to make sure the experiment is fair?

Use eggs the same size.
Use test water with the same amount of salt for each egg.

28-30practice. This year we built hydraulic machines using different materials (cardboard, wood, wire, string). In school we use many different types of devices to do tasks that help us, like dispensers (cups, tape, snacks, water) and organizers (binders, clips, folders). Set up a design challenge for a dispenser or organizer that would be suitable for middle school students.

28practice.What could be a suitable engineering goal?

29practice. What could be several (3-4) criteria by which the design could be judged?

30practice. What might be constraints (3-4) that would limit or restrict the design?