For which of the following activities might you want to hire a chemist?
Answer: D. testing a rock sample for gold content
Which of the following procedures involves a physical change in one of the substances?
Answer: C. separating a salt solution by evaporating the water
The answer is C since both charge and mass have to be balanced on both sides of the equation.
The following does NOT indicate that a chemical change
may have taken place is fracture formation. A chemical change happens when the
substance changes its physical state and composition resulting from a chemical
reaction. This chemical reaction may either give off or absorb energy. A change
in color is a chemical change. For example, litmus paper turns to red when
placed in an acid solution. Production of gas is a chemical change. For
example, adding hydrochloric acid to the tiles of the bathroom gives a hissing
sound with gases given off. Formation of a precipitate is also a chemical
change. Change in shape is not a chemical change.
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Answer:
111.15 g are required to prepare 500 ml of a 3 M solution
Explanation:
In a 3 M solution of Ca(OH)₂ there are 3 moles of Ca(OH)₂ per liter solution. In 500 ml of this solution, there will be (3 mol/2) 1.5 mol Ca(OH)₂.
Since 1 mol of Ca(OH)₂ has a mass of 74.1 g, 1.5 mol will have a mass of
(1.5 mol Ca(OH)₂ *(74.1 g / 1 mol)) 111.15 g. This mass of Ca(OH)₂ is required to prepare the 500 ml 3 M solution.
