Chemists use the mole as the unit for the amount of substance. One mole is equal to 6.02 x 10^23 (just like one dozen is equal to 12). A 40.1 g sample of calcium contains approximately 1 mole of calcium atoms. How many calcium atoms are in a 4 kg sample of calcium?

How has the scientific community addressed the safety of chemicals? a. chemicals are repeatedly tested, even those that have existed for a long time. b. existing chemicals are tested if they have never been tested before. c. chemicals are tested if they are suspected to have caused a problem. d. only new chemicals are tested.

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Which statement describes how phase changes can be diagrammed as a substance is heated? the phase is on the y-axis and the temperature is on the x-axis. the temperature is on the y-axis and the phase is on the x-axis. the time is on the y-axis and the temperature is on the x-axis. the temperature is on the y-axis and the time is on the x-axis.