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Answer:
a solution color becoming less intense due to dilution- is not an evidence of a chemical reaction
bubbles (gas formation) - evidence of a chemical reaction
explosion or fire - evidence of a chemical reaction
changes in color- evidence of a chemical reaction
precipitation- evidence of a chemical reaction
changes in temperature - evidence of a chemical reaction
a solid liquifying - is not an evidence of a chemical reaction
solution colors mixing - is not an evidence of a chemical reaction
Explanation:
A chemical change is not easily reversible and yields new substances. It is often accompanied by a loss or gain of heat.
In the answer section, i have shown some evidences that lead us to conclude that a chemical reaction has taken place. The occurrence of a chemical change often goes with the formation of new substances as earlier stated and any of these signs may accompany the process.
For instance, when a metal is dropped in dilute acid solution, bubble of hydrogen gas indicates that a chemical reaction has taken place.
Answer:
6.6 x 10⁻⁵ mol/L
Explanation:
First, we have to convert the moles from μmol to mol:
moles of solute= 33.0 μmol x (1 x 10⁶ mol)/1 μmol = 3.3 x 10⁻⁵ mol
Then, we convert the volume from mL to L:
volume = 500.0 mL x 1 L/1000 mL = 0.5 L
Finally, we calculate the concentration of the solution in mol/L by dividing the moles into the volume in liters, as follows:
mol/L = moles of solute/volume = 3.3 x 10⁻⁵ mol/(0.5 L) = 6.6 x 10⁻⁵ mol/L
An element is a pure substance made up of only one kind of atom. An element is composed of atoms in which it is composed of neutrons and protons. The nucleus is surrounded by electrons. The answer to this problem is A. element