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Unit 6 8th Grade Science Midterm Study Guide
Terms in this set (96)
What is matter?
Matter is anything that has mass and takes up space (has volume).
What can you think of that is not made of matter?
Light, sound waves, and energy are not made of matter because they do not take up space and do not have volume.
What is the definition of mass?
Mass is the measure of the amount of matter in an object.
How is mass measured?
Mass is measured with a balance.
What is the definition of weight?
Weight is a measure of the gravitational force exerted on an object. Its value can change with the location of the object in the universe.
What is the difference between mass and weight?
Mass is the quantity of matter in an object, while weight is a measure of the force of gravity on an object.
Is an object's mass the same on the moon as it is on Earth, since the moon's gravity is less?
The mass of an object doesn't change, even if it is in free fall in space. Its weight is different, though. Weight is the measure of the pull of gravity on an object. The moon, because it has less gravity than Earth, pulls less on objects, so it weighs less.
How do you find the volume of a rectangular solid?
You find the volume of a rectangular solid by multiplying the object's length, width, and height.
Could you measure the volume of a very large solid, such as an airplane, using the same method as you would with a rock?
Yes and no. The principle of water displacement is the same no matter what the size of the object is, so you could use it to find the volume of an airplane. But you probably couldn't do it because you won't be able to find a container large enough to hold the water and the airplane!
What is density?
Density is the ratio of an object's mass to its volume. Mathematically, Density = Mass x Volume.
How would you find the mass of an object from its density and volume?
Multiply the object's density and volume to find its mass.
Is the density of an object dependent on its shape?
No, the shape of an object does not change its density (unless the object is hollowed out or changes the object's volume).
What is the definition of a chemical property?
A chemical property describes a substance's ability to undergo a chemical change.
What are some examples of chemical properties?
Some chemical properties are flammability and reactivity to acids.
What is the definition of a physical property?
A physical property is a characteristic of a substance that does not involve a chemical change, such as density, color, or hardness.
What some examples of physical properties?
Physical properties would include a substance's mass, if it was malleable or brittle, if it was a conductor or insulator, change in state, and density.
What is a main difference between a physical and a chemical property?
In determining a chemical property you attempt to change the material's identity. However, with a physical property, you make observations and measurements on the substance without making changes to it.
Is conductivity a physical or chemical property of matter?
Conductivity is a physical property.
Do properties like density, boiling, or melting point depend on the amount of the material?
No, these properties are independent of the amount of the substance.
What properties of matter are particularly useful in determining the identity of a substance?
Characteristic properties such as boiling point, melting point, density, and flammability are useful in determining a substance's identity. (The amount of a substance does not affect its characteristic properties. So a gold ring and a bar of gold would have the same density, conductivity, and boiling point.)
Why might you not want to investigate the chemical properties of a substance in order to determine its identity?
A chemical property describes a substance's ability to form new substances. By identifying a particular chemical change the original substance may change to a new substance.
Is malleability a characteristic property?
Malleability is not a characteristic property because many substances are malleable.
How does a physical change differ from a chemical change?
In a physical change, no new substances are formed.
How could you determine if a change is a physical change or a chemical change?
Check to see if the properties of substances after the change are the same or different from the properties of the substances before the change. If the chemical properties are the same, then the change was a physical change. If the properties are different, then the change was chemical change.
Can you name some examples of physical changes?
Some examples of physical changes to matter are freezing water, popping a toy balloon, and reheating cooked food.
What are some other examples of chemical changes that you encounter in your everyday life?
Some common chemical changes include respiration, bleaching clothes, cooking eggs, mixing baking soda and vinegar, and lighting matches for candles.
How do you know that a change of matter is happening when fireworks go off?
You can see flashes of light. You can hear a loud explosion. Sometimes you can smell smoke. The lit fireworks look very different from before they were lit. These observations show that a change has happened.
The light produced by a candle is a sign of a chemical change. What physical changes can be seen when a candle burns?
The wax of the candle that does not burn gets soft and melts. This is a physical change.
To get a light stick to work, you have to bend the light stick to break a glass vial inside the stick. Is the breaking of the vial a chemical change or a physical change? Explain your answer.
Breaking the vial is a physical change, because, even though it is broken, all the pieces of the vial are still glass. However, the two chemicals mixing to create light (exothermic reaction) is a chemical change.The production of light in a light stick is a sign that a chemical change is happening.
Why would a light stick glow brighter when placed in hot water in comparison to the light stick in cold water?
The light stick in hot water would be brighter than the light stick in the cold water because heat speeds up chemical changes. The molecules move faster as temperature increases and thus increases the amount of collisions between molecules. This makes the formation of a new substance occur earlier than it would in cooler water.
How could you check that mass is conserved in a chemical change in which a gas is produced?
Conduct the reaction inside a closed container that will collect the gas. Find the mass of the entire container before and after the chemical change.
How could you prevent a car from having the chemical change of rust?
Rust is formed from iron interacting with air. Painting the metal would keep the metal from having contact with air, and so it wouldn't rust.
What physical changes are involved in the process of baking bread? What are the signs of a chemical change? Which of those signs could explain what happened to the missing mass?
Physical changes include some of the ingredients, such as salt, are dissolved in water; the oven and oven trays become hot. Signs of a chemical change are production of a gas or a solid, production of light, thermal energy, or sound, and a change in color or odor. The production of a gas would explain what happened to the missing mass.
Do you think that the particles in all of these objects move?
Yes, it's just that the particles in a solid are restricted to vibrations, where the particles in a liquid or gas can move more freely.
Do the particles in the cup of coffee move faster or slower as it cools?
As the coffee cools down, the particles slow down as well. When you boil coffee, the particles of water in the coffee begin to move so quickly that they become a gas: water vapor.
What is a gas?
A gas is a state of matter where the particles move quickly and the matter has no definite shape or volume.
What shape does a liquid have?
A liquid has the shape of its container, like the coffee inside a coffee cup.
How are gas particles arranged?
The particles are far apart with little contact between one another.
How are solid particles arranged?
The particles are close together and do not move very much, but how they arrange themselves depends on the substance. The particles in crystals, for example, are arranged in geometrical patterns that give it a specific shape and quality.
In which state of matter do particles have the most energy?
Because the particles move quickly in a gas, this is the state of matter with the most energy.
How do you think the arrangement of particles in a solid is related to the amount of energy they have?
In a solid the particles are organized in a fixed structure because they do not have enough energy to break free of the attractive forces that hold them together.
How do the arrangement and energy of particles in water vapor differ from the arrangement and energy of particles that form ice?
Water vapor particles have more energy than particles in ice. Water vapor particles can move freely and spread out, while water particles in ice can only vibrate in fixed positions.
What is needed to add to ice in order for it to change state into water?
To change ice into water energy must be added. The sun, or warmer air, may provide that energy.
When ice is heated in a laboratory experiment, what happens to its temperature as the ice melts?
The temperature of the ice remains at 0°C until all of it is melted.
How can you make water freeze at a lower temperature than 0°C, or achieve a temperature higher than 100°C?
You can add a substance, such as antifreeze, to water to change its freezing temperature. Water under pressure can rise to temperatures higher than 100°C while remaining in a liquid state.
In which state of matter do particles slide past each other?
Particles slide past one another in a liquid.
What would be some of the properties of oxygen, which is normally a gas, if it were turned into a liquid?
Oxygen changes state to a liquid at −183 °C. It can make objects that it touches brittle, and they may also burn very rapidly.
How does a liquid become a gas?
A liquid becomes a gas when its particles gain enough energy to move freely and spread out into the air.
How are solids different from both liquids and gases?
Solids have both a definite shape and definite volume. Unlike solids, liquids have no definite shape. Gases have neither a definite shape nor a definite volume. Particles in a solid move much more slowly than particles in a liquid or gas, because they have less energy.
Is distilled water a mixture or a pure substance?
Distilled water does not have salts or silt in it. It is a compound made from atoms of the elements oxygen and hydrogen. A compound is a pure substance.
Is rainwater a pure substance or a mixture?
Water vapor that rises to form clouds is a pure substance. But raindrops form around tiny particles of dust; when they are large enough they begin to fall. So rain is actually a mixture, not a pure substance.
Do two compounds form a mixture or a pure substance when you put them together mechanically, such as by stirring?
Two compounds combine together mechanically to form a mixture.
How could you separate a mixture of sand and water?
You could wait until the sand settles to the bottom of the container and then drain off the water. Or you could use a filter and pour the mixture through it. If you wanted to drink the water, you should probably do both.
What are some examples of chemical changes?
Some examples of chemical change include burning wood, rusting iron, and dissolving metal by using a strong acid.
What do you call separating water into its component elements, hydrogen and oxygen, and how is it done?
Electrolysis is the process of separating water into hydrogen and oxygen. It is done by passing an electric current through the water.
What are some examples of homogeneous mixtures?
Homogeneous mixtures look the same throughout. Some examples are iced tea, soda without bubbles, salt water, coffee, and vinegar.
What are some examples of heterogeneous mixtures?
In a heterogeneous mixture you can see the component parts, or they settle out after a short time. Some examples are salad dressing, vegetable soup, and pizza.
Are colloids homogeneous or heterogeneous?
Colloids are heterogeneous because they are not uniform throughout.
What are some examples of colloids that include a gas and a liquid?
Fog and mist are colloids composed of water vapor and air. Aerosols, such as hairspray and deodorant, are composed of chemicals and a gas propellant.
What is a pure substance?
A pure substance is an element or compound that cannot be separated by physical changes.
Why aren't powdered mix drinks or saltwater pure substances?
Powdered mix drinks and saltwater are mixtures. They are not made of a single element or compound.
How is a colloid different than a suspension?
While colloids and suspensions are both heterogeneous mixtures, colloids are different than suspensions because their particles will not settle out.
What are some examples of colloids that include a gas and a solid?
Smoke, smog, and air pollution are composed of small particles suspended in the air.
What are some methods for physically separating a mixture?
A mixture can be separated by straining, filtering, magnetizing, and settling.
What is the definition of compound?
A compound is a substance made up of atoms or ions of two or more different elements joined by chemical bonds.
Why is hydrogen a pure substance?
Hydrogen is a pure substance because it is an element.
Why is salt a pure substance?
Salt is a pure substance because it is a chemical compound and its elements can only be separated by chemical means.
How does today's atomic model differ from earlier models?
Today's atomic model includes electrons, protons, and neutrons, which hadn't all been identified in the earliest models. Also, Niels Bohr's model, while largely correct, showed electrons in circular orbits around the nucleus. Our current model shows that electrons are likely to be found in electron clouds outside the nucleus.
Why should we study Niels Bohr's model of the atom that has been shown by today's scientists to be inaccurate?
It is possible that today's accepted model of the atom will, in the future, be shown to be inaccurate, as well. But when discussing something as complex as the atom, it is helpful to use a simpler model in order to understand the basics.
What subatomic particle in an atom has a negative charge?
An electron is a negatively charged subatomic particle found in atoms.
Oxygen has eight neutrons and eight protons in its nucleus. What is its atomic number?
Oxygen's atomic number is 8. We determine an atom's atom number from its number of protons.
What is the difference between atomic number and mass number?
Atomic number is the same as the number of protons while mass number is the number of protons plus neutrons.
Which part of an atom is mostly empty space?
Electron clouds are made up of mostly empty space.
Which subatomic particles in an atom have opposite charges?
An electron has a negative charge and a proton has a positive charge.
Which subatomic particle in an atom has no charge?
A neutron has no charge.
What does the electron cloud in an atomic model represent?
The electron cloud is meant to represent the most likely places within the atom that the electrons are going to be found.
How did Niels Bohr picture the location of the electrons in his model?
Niels Bohr's model showed the electrons circling the nucleus in orbits, like planets around a star.
What would be the atomic number of an atom with 11 protons and 12 neutrons?
An atom that has 11 protons and 12 neutrons would have an atomic number of 11. The atomic number is be the same as the number of protons.
What would be the mass number of an atom with 11 protons and 12 neutrons?
An atom that has 11 protons and 12 neutrons would have a mass number of 23. The mass number comes from adding the protons and neutrons together.
What are the three subatomic particles that we've talked about in this lesson that make up an atom?
An atom is made up of protons, neutrons, and electrons.
Which particles determine the atomic number of an atom? Which particles determines the atom's mass number?
An atom's atomic number is the number of protons in the atom. An atom's mass number is the number of protons plus the number of neutrons in the atom. The number of neutrons in an atom can vary, so atoms of the same element can have different mass numbers. These different versions of an atom are called isotopes.
What are the names of some elements you can think of?
You may have come up with hydrogen, oxygen, carbon, nitrogen, gold, silver, sodium, and boron.
What do you call a substance that is composed of two or more elements, like water or table salt?
A substance composed of two or more elements is a compound. A compound can only be separated by chemical means.
How is a group different from a period?
All of the elements in a group have similar chemical properties, but the elements in a period have properties that vary, often in a predictable way.
What is the difference between an element's atomic number and its atomic mass number?
An atom's atomic number is the number of protons in the atom. An atom's atomic mass number is the number of protons plus the number of neutrons in the atom. The number of neutrons in an atom can vary, so atoms of the same element can have different mass numbers. These different versions of an atom are called isotopes.
How are elements grouped in the periodic table?
Elements are organized by common properties.
Why would it be a good thing to know how the elements are organized?
The periodic table allows us to get an idea of an element's chemical and physical properties based upon where it is found on the periodic table.
How are the properties of metals different from the properties of nonmetals?
Metals are shiny, can conduct electricity, and can be bent easily. Nonmetals are not shiny, are often brittle, and they do not conduct electricity well.
How would you be able to produce a quantity of a group of one element if it is so reactive that it is rarely found free in nature?
Because a reactive element so readily combines with another element, to produce a pure quantity of it would require separating it from a more stable compound that includes it, using some chemical means.
Why is the chemical symbol for silver Ag, lead Pb, and copper Cu?
Many of the elements are given chemical symbols based on their Latin name. Latin was the language used by educated people when many of these elements were first identified. Ag comes from the Latin word "argentum," which means silver. The Latin word for lead is "plumbum." And Cu for copper comes from "cyprium," Latin for Cyprus.
When scientists discover, or synthesize, a new element, how do they decide what to call it?
Usually a new element is named to honor a scientist who made significant discoveries. For example, Lawrencium, Lr, was named for Ernest O. Lawrence, inventor of the cyclotron. Nobelium, No, was named for Alfred Nobel, discoverer of dynamite and founder of the Nobel Prize.
Is calcium (Ca) a metal, metalloid, or nonmetal?
Calcium is a metal.
What is a metalloid?
A metalloid is an element that has properties of both metals and nonmetals. They are also called semiconductors and are very useful in electronics.
Is copper (Cu) a poor conductor or a strong conductor of electricity?
Copper is a metal. It is a strong conductor of electricity.
Can you name two elements that are in the same group?
Sodium and potassium are in the same group, Group 1. Chlorine and bromine are in Group 17. Xenon and neon are in Group 18.
What is the number that is found above the chemical symbol on a periodic table?
The number above the chemical symbol is the atomic number. It is the number of protons in the atoms of that element. It distinguishes the element from all others. Notice how there are no two atomic numbers that are the same.
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