Which of the following provide evidence that a chemical reaction has occurred. a

Question

Which of the following provide evidence that a chemical reaction has occurred. a. Temperature change b. precipitate formed c. Gas formed d. All of the above e. only (a) and (c) above If a radioactive isotope (atom) has a half-life of 1-day, how much of an original sample is left at the end of the 3rd day? a. Cannot be determined without know what element (substance) it is b. One-half as much c. One-fourth as much d. One-eighth as much e. the same amount. Radioactive analysis of C-14 in an old ax handle yields that it is one-fourth as radioactive as a cut tree branch. How old is the ax handle? (note the half-life of C-14 is 5, 730 years) a. about 11, 460 years b. about 17, 190 years c. about 22, 920 years d about 1, 432.5 years e. about 5, 730 years

Explanation / Answer

Answers:

5. Option d

All of the above

Explanation: Evidence of chemical reaction might be a color change, a gas given off (it may be smell), an energy (temerature light) change, the formation of precipitate (a new solid formed).

6. Option d

One eigth of as much

Explanation: 1/4th of the initial amount will be left at the end of the second day, 1/8th of the initial amount will be left at the end of the third day, 1/16th of the initial amount will be left as the end of the fourth day.

7. Option c

About 22,920 years

Explanation: If an object has 1/2 of the expected Carbon-14 must be 5,730 years old, if it has 1/4 of the radioactive cut tree branch has 11,460 years old ( 5,730+5,730), 1/8th of the C-14 has 17,190 years old, 1/16th of the C-14 has the 22,920 years old.

Age of the ax handle is 4*5730= 22,920 years

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