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A student notices that a plant near a window grows taller than a plant kept in a dark closet. The student wants to test whether light affects plant growth. What variable should the student deliberately change?
Amount of light
A graduated cylinder contains liquid between the 36 mL and 37 mL markings. What should a student do to obtain the most accurate volume measurement?
Read the bottom of the meniscus at eye level
A student repeatedly measures a sample and gets nearly identical values. What characteristic does this demonstrate?
Precision
A substance has a definite composition and cannot be separated into simpler substances by physical methods. What type of matter could it be?
An element or compound
Which subatomic particle determines the identity of an element?
Proton
A scientist predicts that increasing the concentration of fertilizer will increase plant growth. After collecting data, the scientist compares the results with the prediction. What part of the scientific process is the scientist performing?
Analyzing/interpreting results
A sample has a mass of 72 g and occupies 9 cm³. What is its density?
8 g/cm³
A thermometer reads 99.9°C when the accepted temperature is 100.0°C. Is this measurement accurate?
Yes, because it is very close to the accepted value.
A mixture contains visible pieces of different materials that can be physically distinguished. Is it homogeneous or heterogeneous?
Heterogeneous
An atom has 8 protons and 10 neutrons. What is its mass number?
18
A scientist tests two brands of fertilizer. Both groups of plants receive the same amount of water, soil, and sunlight. Why is keeping these factors the same important?
They are controlled variables, allowing the scientist to determine whether the fertilizer caused the difference.
An object has a density of 4 g/mL and a volume of 12 mL. What is its mass?
48 g
How many significant figures are in 0.006070?
4
A student bends a piece of copper wire into a new shape. Has the identity of the copper changed? Explain.
No. This is a physical change because the substance remains copper.
An atom has 11 protons and 10 electrons. Is it neutral, positive, or negative? What is its charge?
Positive; 1+
A student's experiment produces results that do not support the hypothesis. What should the student do?
Analyze the data, communicate the results, and revise or develop a new hypothesis if appropriate.
Two blocks are made from the same substance. Block A has twice the mass of Block B. What can you conclude about their densities?
They have the same density because density is independent of the amount of substance.
A student records a measurement as 12.0 g. Why is the zero significant?
A zero at the end of a number to the right of a decimal is significant.
A substance reacts with oxygen and produces a new substance with different properties. Is this a physical or chemical change? Explain.
Chemical change because a new substance has formed.
An element has two naturally occurring isotopes. What must be the same in both isotopes, and what must be different?
They must have the same number of protons but different numbers of neutrons.
Two scientists perform the same experiment independently. Both obtain similar results. Why does this make the evidence stronger?
The results are reproducible, meaning another scientist can obtain similar results using the same procedure.
A metal has a mass of 54.0 g and a density of 6.0 g/mL. A student claims that its volume must be 324 mL. Is the student correct? Calculate the correct volume.
No. Volume = mass ÷ density = 54.0 ÷ 6.0 = 9.0 mL
Student A obtains measurements of 8.1, 8.1, and 8.2. Student B obtains 6.2, 7.9, and 9.1. Which student demonstrates greater precision, and why?
Student A because the measurements are much closer together.
A student mixes two clear solutions. The mixture suddenly becomes cloudy because a solid forms. What evidence suggests that a chemical change occurred?
The formation of a precipitate indicates that a new substance formed.
Element X has 7 valence electrons and element Y has 1 valence electron. Predict what is most likely to happen when they interact. Explain whether the resulting bond is likely ionic or covalent.
Element Y is likely to lose one electron and element X is likely to gain one electron, forming an ionic bond. This allows both atoms to achieve a more stable outer electron arrangement.