Chapter 1, Problem 1.3E

On October 21, 1982, the Bureau of the Mint changed the composition of pennies (see Exercise 120). Instead of an alloy of 95% Cu and 5% Zn by mass, a core of 99.2% Zn and 0.8% Cu with a thin shell of copper was adopted. The overall composition of the new penny was 97.6% Zn and 2.4% Cu by mass. Does this account for the difference in mass among die pennies in Exercise 120? Assume the volume of the individual metals that make up each penny can be added together to give the overall volume of the penny, and assume each penny is the same size. (Density of Cu = 8.96 g/cm3; density of Zn = 7.14 g/cm3).

Some ice cubes are homogeneous and some are heterogeneous. Into which group do ice cubes from your home refrigerator fall? If homogeneous ice cubes are floating on water in a glass, are the contents of the glass homogeneous or heterogeneous? Justify both answers.

You receive a mixture of table salt and sand and have to separate the mixture into pure substances. Explain how you would carry out this task. Is your method based on physical or chemical properties? Explain.

1f a piece of hard, white blackboard chalk is heated strongly in a flame, the mass of the piece of chalk will decrease, and eventually the chalk will crumble into a white dust. Does this change suggest that the chalk is composed of an element or a compound?

Which of the following represent physical properties or changes, and which represent chemical properties or changes? You curl your hair with a curling iron. You curl your hair by getting a “permanent wave” at the hair salon. Ice on your sidewalk melts when you put salt on it. A glass of water evaporates overnight when it is left on the bedside table. Your steak chars if the skillet is too hot. Alcohol feels cool when it is spilled on the skin. Alcohol ignites when a flame is brought near it. Baking powder causes biscuits to rise.

Which of the following figures represents (a) a pure element,(b) a mixture of two elements, (c) a pure compound, (d) amixture of an element and a compound? (More than onepicture might fit each description.)

Sodium and potassium are both shiny metals in pure form, but corrode rapidly in the presence of oxygen and humidity to form compounds.  Does this fact describe a physical or chemical property of these two metals?

The molecular liquid chloroform (CHCl3) has a density of 1.48 g/mL, while the molecular liquid bromoform (CHBr3) has a density of 2.89 g/mL.(a) When 44.0 mL of CHCl3 and 39.2 mL of CHBr3 are mixed, a clear liquid solution forms. Is this a chemical or a physical change?

A homogeneous mixture of two or more substances is called ________   a. a mess. b. a solution. c. an electrolyte. d. a solvent. e. a compound.