Think Like a Scientist
A student records, “The liquid is blue.” Is this a qualitative or quantitative observation?
What is a qualitative observation?
Qualitative observations describe qualities, such as color, smell, or texture. Quantitative observations include numbers or measurements, such as “The liquid has a volume of 50 mL.”
Matter is anything that has these two characteristics.
What are mass and volume?
Matter has mass and takes up space. The amount of space it occupies is its volume. Air is matter even though we usually cannot see it.
Name the changes from solid to liquid and from liquid to solid.
What are melting and freezing?
Melting occurs when a solid absorbs energy and becomes a liquid. Freezing occurs when a liquid releases energy and becomes a solid. These changes do not create a new substance.
Is an object’s color a physical property or a chemical property?
What is a physical property?
You can observe color without changing the object into a new substance. Other physical properties include mass, volume, density, and state of matter.
Name the three main subatomic particles.
What are protons, neutrons, and electrons?
Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. Protons and neutrons are in the nucleus. Electrons occupy the surrounding electron cloud.
A student sees water on the floor and says, “Someone probably spilled their drink.” Is the statement an observation or an inference?
What is an inference?
Seeing water on the floor is an observation. Saying someone spilled a drink is an inference because it is a possible explanation. The student did not directly observe how the water got there.
Name the state of matter described by each statement:
What are solid, liquid, and gas?
A solid keeps its shape and volume. A liquid flows and changes shape while keeping its volume. A gas spreads out to occupy the available space in its container.
Name the changes from liquid to gas and from gas to liquid.
What are vaporization and condensation?
Vaporization includes evaporation and boiling. Condensation happens when a gas becomes a liquid, such as water vapor forming droplets on a cold surface.
Which is a chemical property?
A. Color
B. Volume
C. Flammability
D. Shape
What is C, flammability?
Flammability describes whether a substance can burn. Burning involves a chemical reaction that produces new substances. Color, volume, and shape can be observed without causing that reaction.
This number tells how many protons an atom has and identifies its element.
What is atomic number?
Every element has a unique number of protons. For example, every carbon atom has 6 protons. Changing the proton count changes the element.
A student tests how water temperature affects the time sugar takes to dissolve. Identify the independent and dependent variables.
What are water temperature as the independent variable and dissolving time as the dependent variable?
The independent variable is purposely changed. The dependent variable is measured to see how it responds. Here, the student changes the temperature and measures how long dissolving takes.
Do particles in a solid stop moving? Explain how they move.
What is no—they vibrate in place?
Solid particles stay in relatively fixed positions but still move back and forth. Liquid particles can slide past one another, while gas particles move freely through the available space.
Dry ice changes directly from solid to gas. Water vapor can change directly into frost. Name both changes.
What are sublimation and deposition?
Sublimation is solid directly to gas and requires energy to be absorbed. Deposition is gas directly to solid and releases energy. Both skip the liquid state.
Classify each as a physical or chemical change:
What are physical, chemical, and physical changes, in that order?
Cutting changes the paper’s size and shape. Melting changes water’s state. Burning produces new substances, including gases and ash. The key question is whether a new substance forms.
A neutral atom has 8 protons and 9 neutrons. How many electrons does it have, and what is its mass number?
What are 8 electrons and a mass number of 17?
A neutral atom has equal numbers of protons and electrons. Mass number equals protons plus neutrons, so 8 + 9 = 17. Electrons are not included in mass number.
A student tests whether fertilizer affects plant growth. Name two things that should stay the same between the groups.
What are the amount of water and the amount of sunlight?
These are constants, or controlled variables. Keeping them the same helps the student determine whether fertilizer caused a difference in growth. Also accept plant type, soil type, pot size, or growing time.
What generally happens to particle speed when a substance’s temperature increases?
What is the particles move faster?
Temperature measures the particles’ average kinetic energy. Kinetic energy is energy of motion. A higher temperature means greater average kinetic energy, so particles generally move faster.
A small cup and a large pot contain water at the same temperature. Which has more total thermal energy, and why?
What is the large pot, because it contains more water particles?
The same temperature means the particles have the same average kinetic energy. However, the pot contains more particles, giving it more total thermal energy. Thermal energy depends on the substance, its amount, and its temperature.
An object has a mass of 60 g and a volume of 20 cm³. Calculate its density.
What is 3 g/cm³?
Density equals mass divided by volume. Divide 60 by 20 to get 3 g/cm³. This means each cubic centimeter of the material has a mass of 3 grams.
What are the names for horizontal rows and vertical columns on the periodic table?
What are periods for horizontal rows and groups for vertical columns?
Periods run across the table, and groups run down it. Elements in the same group often have similar chemical properties. The table has 7 periods and 18 groups.
The accepted mass of an object is 50 g. A student measures it three times and gets 42 g, 42 g, and 42 g. Are these measurements accurate, precise, or both?
What is precise but not accurate?
The measurements are precise because they agree with each other. They are not accurate because they differ from the accepted mass. Precision means measurements are close together; accuracy means they are close to the correct value.
Match each description to the correct term: plasma, Bose–Einstein condensate, or absolute zero.
What are plasma, Bose–Einstein condensate, and absolute zero, in that order?
Plasma contains charged particles, including ions and free electrons. A Bose–Einstein condensate forms when certain particles are cooled to extremely low temperatures and behave collectively. Absolute zero is 0 kelvin, where a system reaches its minimum possible thermal energy.
On a heating graph, the line becomes flat while pure ice melts. What does the flat section mean?
A. The temperature stays constant while the substance changes state.
B. The substance stops absorbing energy.
What is A?
The ice continues absorbing energy, but its temperature stays constant during melting at constant pressure. The energy helps particles overcome the attractions holding them in the solid arrangement. Once melting finishes, continued heating raises the liquid’s temperature.
Ice and liquid water are made of the same substance. Why does ice float in liquid water?
A. Freezing makes the water molecules disappear.
B. Ice has a more open particle arrangement, making it less dense than liquid water.
What is B?
When water freezes, its molecules form an arrangement with more space between them. The same mass occupies more volume, lowering its density. Ice floats because it is less dense than liquid water.
Why is the modern periodic table arranged by atomic number instead of strictly by atomic mass?
A. Atomic number identifies the element by its proton count, while atomic mass does not always increase in that order.
B. Atomic number measures the size of an atom.
Atomic number gives a consistent order based on proton count. Atomic mass is an average based on the masses and relative amounts of an element’s naturally occurring isotopes. Isotopes have the same proton count but different neutron counts, so atomic mass does not always increase from one element to the next.