The molecule shown here is leucine, one of the amino acids that are the building blocks of proteins. The color key for the atoms is carbon (black), hydrogen (light gray), oxygen (red), and nitrogen (blue).

a. How many different elements are in a molecule of leucine?

b. How many carbon atoms are in a molecule of leucine?

c. Which element has the largest number of atoms in a leucine molecule?

d. What is the total number of atoms in a molecule of leucine?

Which of the following figures represents (a) a pure element, (More than one picture might fit each description.)

Which of the following figures represents (b) a mixture of two elements, (More than one picture might fit each description.)

Which of the following figures represents (c) a pure compound, (More than one picture might fit each description.)

Which of the following figures represents (d) a mixture of an element and a compound? (More than one picture might fit each description.)

Musical instruments like trumpets and trombones are made from an alloy called brass. Brass is composed of copper and zinc atoms and appears homogeneous under an optical microscope. The approximate composition of most brass objects is a 2:1 ratio of copper to zinc atoms, but the exact ratio varies somewhat from one piece of brass to another. (a) Would you classify brass as an element, a compound, a homogeneous mixture, or a heterogeneous mixture?

Which of the following is the best description for the formation of frost on windows in the winter:

i. a solid is turning into a gas,

ii. a liquid is turning into a solid,

iii. a gas is turning into a liquid,

iv. a gas is turning into a solid, or

v. a solid is turning into a liquid?

Consider the two spheres shown here, one made of silver and the other of aluminum. (a) What is the mass of each sphere in kg?

Consider the two spheres shown here, one made of silver and the other of aluminum. (a) What is the mass of each sphere in kg?

Consider the two spheres shown here, one made of silver and the other of aluminum. (d) If you release the spheres simultaneously, they will have the same velocity when they hit the ground. Will they have the same kinetic energy? If not, which sphere will have more kinetic energy?

Is the separation method used in brewing a cup of coffee best described as distillation, filtration, or chromatography?

(a) Three spheres of equal size are composed of aluminum (density = 2.70 g/cm³), silver (density = 10.49 g/cm³), and nickel (density = 8.90 g/cm³). List the spheres from lightest to heaviest.

(b) Three cubes of equal mass are composed of gold (density = 19.32 g/cm³), platinum (density = 21.45 g/cm³), and lead (density = 11.35 g/cm³). List the cubes from smallest to largest.

The three targets from a rifle range shown below were produced by: (A) the instructor firing a newly acquired target rifle; (B) the instructor firing his personal target rifle; and (C) a student who has fired his target rifle only a few times. (b) For the A and C results in the future to look like those in B, what needs to happen?

(a) What is the length of the pencil in the following figure if the ruler reads in centimeters? How many significant figures are there in this measurement?

(b) An automobile speedometer with circular scales reading both miles per hour and kilometers per hour is shown. What speed is indicated, in both units? How many significant figures are in the measurements?

(a) How many significant figures should be reported for the volume of the metal bar shown here?

Consider the jar of jelly beans in the photo. To get an estimate of the number of beans in the jar you weigh six beans and obtain masses of 3.15, 3.12, 2.98, 3.14, 3.02, and 3.09 g. Then you weigh the jar with all the beans in it, and obtain a mass of 2082 g. The empty jar has a mass of 653 g. Based on these data, estimate the number of beans in the jar. Justify the number of significant figures you use in your estimate.

Which of the following statements about atoms and molecules is false?

a. Atoms and molecules are forms of matter.

b. A molecule contains two or more atoms.

c. The atoms of two different elements can be the same.

d. Atoms and molecules have mass and occupy space.

e. A molecule can contain atoms from a single element.

The molecular model of a molecule has four black spheres, ten light gray spheres, and one red sphere. Which of the following statements is or are true?

i. There are 15 atoms in the molecule.

ii. The black spheres are atoms of the same element.

iii. There are atoms of three different elements in the molecule.

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: c. magnesium

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: d. crushed ice.

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: a. gasoline vapor,

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: (b) sugar crystals

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: (c) a hardboiled egg

Classify each of the following as a pure substance or a mixture. If a mixture, indicate whether it is homogeneous or heterogeneous: (d) sawdust.

Give the chemical symbol or name for the following elements, as appropriate: c. potassium

Give the chemical symbol or name for each of the following elements, as appropriate: a. carbon

You are hiking in the mountains and find a shiny gold nugget. It might be the element gold, or it might be “fool’s gold,” which is a nickname for iron pyrite, FeS₂. Which of the following physical properties do you think would help determine if the shiny nugget is really gold—appearance, melting point, density, or physical state?

In the process of attempting to characterize a substance, a chemist makes the following observations: The substance is a silvery white, lustrous metal. It melts at 649 °C and boils at 1105 °C. Its density at 20 °C is 1.738 g/cm³. The substance burns in air, producing an intense white light. It reacts with chlorine to give a brittle white solid. The substance can be pounded into thin sheets or drawn into wires. It is a good conductor of electricity. Which of these characteristics are physical properties, and which are chemical properties?