### Brain Teasers

# Knotty Notation

A single drop of water contains 1.70 quintillion molecules. In the chemistry lab, I'm following a procedure that calls for me to add 30 drops of water to a solution. I must report how many hydrogen atoms I have added to the solution. I must write the answer in scientific notation.

What should I report?

What should I report?

### Hint

Consult a dictionary or a chemistry text.### Answer

I should report that I have added 1.02*10^20 hydrogen atoms to the solution.I have added 30 drops of water. Each drop of water contains 1.7 quintillion molecules. So, I have added 51 quintillion molecules (1.7*30=51). Since each molecule of water has 2 hydrogen atoms, you can determine that I have added 102 quintillion hydrogen atoms to the solution (2*51 = 102).

Also, 1 quintillion is equal to 1 followed by 18 zeros. In scientific notation, it's written as 1*10^18. In scientific notation, a number is expressed as a decimal number between 1 and 10 multiplied by a power of 10. So, in scientific notation, 102 quintillion = 1.02*10^20.

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## Comments

WOOHOO! First comment!

I got it pretty easily, but I almost forgot about the amount of Hydrogen in water molecules. Good Teaser!!

I got it pretty easily, but I almost forgot about the amount of Hydrogen in water molecules. Good Teaser!!

cool cool

I liked it. My only disagreement would be the number of significant figures. I'm a chemistry major. The answer I have was 1.0*10^20. Only one decimal place. I thought that was the trick. Cool, though.

I've always been taught to use two digits after the decimal when using scientific notation.

Too easy, usually figures are taken to 3 significant figures when you have to round.

Number of significant figures in result are dependent on input. When multiplying or dividing numbers, find the number with the fewest significant figures, then round the result to that many significant figures.

There as only two significant figures. Also, the size of the drop can vary, so presumably the number of molecules per drop given is based on the size drop produced by the pipet used to add the drops. If 1.02 x 10^20 was the desired answer then the number of molecules per drop should have been given as 1.70 quintillion.

I see the teaser was corrected already.

Fun and simple. I like it!

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