Lead is an elementary substance that occurs as a malleable metal with a density of 11.4 g/mL at ambient temperature and pressure. Lead metal can be extracted from a mineral called galena, which contains 86.6%% lead by mass. A particular ore contains 68.5% galena by mass   If the lead can be extracted with 92.5%% efficiency, what mass of ore is required to make a lead sphere with a 7.00 cm radius? Express your answer with the appropriate units.

As part of a science project, you study traffic patterns in your city at an intersection in the middle of downtown. You set up a device that counts the ears passing through this intersection for a 24-hr period during a weekday. The graph of hourly traffic looks like this. a. At what time(s) does the highest number of cars pass through die intersection? b. At what time(s) does the lowest number of cars pass through die intersection? c. Briefly describe the trend in numbers of cars over the course of die day. d. Provide a hypothesis explaining the trend in numbers of cars over the course of the day. e. Provide a possible experiment that could test your hypothesis.

A 15.5 g sample of sodium carbonate is added to a solution of acetic acid weighing 19.7 g. The two substances react, releasing carbon dioxide gas to the atmosphere. After reaction, the contents of the reaction vessel weigh 28.7 g. What is the mass of carbon dioxide given off during the reaction?

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).