Reef Chemistry Question of the Day #192 Cycling and Alkalinity

[Randy Holmes-Farley]

Reef Chemistry Question of the Day [HASHTAG]#192[/HASHTAG]

You are cycling a reef tank by adding ammonia (as ammonium hydroxide) and using dead rock. Three times you add exactly 1 mg/L ammonia, and three times it eventually all is converted into nitrate, forming 10.9 mg/L of nitrate, which you accurately detect in the water.

Before any additions, the alkalinity of the water is 9 dKH (3.2 meq/L).

What is the alkalinity after all of the ammonia has been converted into nitrate?

A. 10 dKH (3.6 meq/L)
B. 9.5 dKH (3.4 meq/L)
C. 9 dKH (3.2 meq/L)
D. 8.5 dKH (3.0 meq/L)
E. 8 dKH (2.9 meq/L)

Good luck!


























.

 

[fab]

E. 8 dKH (2.9 dKH)

Shouldn't this be 2.9 meq/L ??

 

[Randy Holmes-Farley]

Shouldn't this be 2.9 meq/L ??

Yes, thanks. I changed it.

 

[andys]

My answer is C. not sure if ammonia has a affect on Alk

 

[brandon429]

I must guess e not googling the conversion specifics. the bac use the alk component for carbon access removing some, this is how I got through algebra, so lets guess it up/. I cant recall if that's called biogenic decalcification or decarbonation?

 

[Sabellafella]

Atleast 8.5

 

[Retro Reefer]

Tried to do the math just got a headache I'm semi guessing E

 

[JimWelsh]

10.9 mg/L of NO3- is about 0.176 millimoles (NO3 is one N = atomic weight 14, plus three O = atomic weight 16, for a total of 62, so 10.9 mg/L divided by 62 = 0.176 millimoles) , so it will reduce alkalinity by 0.176 meq/L. Rounded, the answer is D.

 

[drernesto]

10.9 mg/L of NO3- is about 0.176 millimoles (NO3 is one N = atomic weight 14, plus three O = atomic weight 16, for a total of 62, so 10.9 mg/L divided by 62 = 0.176 millimoles) , so it will reduce alkalinity by 0.176 meq/L. Rounded, the answer is D.

[emoji15] is this alien language or English??

 

[brandon429]

as guessers do, they second guess, id edited my answer to e ha! burn for having doubted. I think I have a real math dislike or phobia.

what causes the consumption was it indeed biotic

 

[JimWelsh]

[emoji15] is this alien language or English??

I will try again, using only words in complete English language sentences.

There are two basic ways that concentrations of substances are usually expressed in chemistry.

One of those ways is in proportion to the total amount of stuff, either as weight or volume, such as milligrams per liter or milligrams per kilogram. This way of expressing concentration is also sometimes referred to "parts per million" (or trillion or thousand, or whatever scale is appropriate).

The other way concentration is generally expressed is in terms of the number of atoms or molecules of something in a given volume, and it is expressed in units known as "moles". The textbook definition of a mole uses a very big number that nobody needs to memorize called "Avogadro's Number". One mole of a substance is the same thing as one Avogadro's Number of molecules of that substance. The "molarity" of a substance in a solution is the number of moles per liter of that substance.

Many calculations in chemistry require conversion from the one form of expression to the other.

Now, each substance is made up of one or more atoms of one or more elements. Each element has its own atomic mass, and the molecular mass of a substance is simply the sum of all the atomic masses of its constituent atoms. The nice thing about moles and Avogadro's Number is that they chose Avogadro's Number so that it just so happens that one mole of a substance has a mass equal to that substance's molecular mass, in grams. This makes it very easy to convert units between the two forms of expression, IF you know the substance's molecular mass. To convert grams per liter to molarity, divide by the molecular mass. To convert molarity to grams per liter, multiply by the molecular mass. It doesn't get much easier than that!

In this case, the substance in question is the nitrate ion. Nitrate has one nitrogen atom, and three oxygen atoms. Nitrogen has an atomic mass of about fourteen. Oxygen has an atomic mass of about sixteen. One times fourteen plus three times sixteen equals sixty-two. So, in this case, ten point nine milligrams per liter divided by sixty-two equals about zero point one seven six millimoles. Since there is only one negative charge on the nitrate ion, then the millimoles is the same thing as the milliequivalents per liter, so when the answer is rounded to just one decimal place, it becomes zero point two milliequivalents per liter.

But, seriously, this stuff isn't really that hard, and if more aquarists understood it better, they would be much more empowered to then understand and also to perform these kinds of calculations for themselves (and not have to come to forums like this to get spoon-fed answers without having actually learned anything to help them in the future).

 

[Randy Holmes-Farley]

[emoji15] is this alien language or English??

Here's my translation for you:

 

[andys]

I will try again, using only words in complete English language sentences.

There are two basic ways that concentrations of substances are usually expressed in chemistry.

One of those ways is in proportion to the total amount of stuff, either as weight or volume, such as milligrams per liter or milligrams per killigram. This way of expressing concentration is also sometimes referred to "parts per million" (or trillion or thousand, or whatever scale is appropriate).

The other way concentration is generally expressed is in terms of the number of atoms or molecules of something in a given volume, and it is expressed in units known as "moles". The textbook definition of a mole uses a very big number that nobody needs to memorize called "Avogadro's Number". One mole of a substance is the same thing as one Avogadro's Number of molecules of that substance. The "molarity" of a substance in a solution is the number of moles per liter of that substance.

Many calculations in chemistry require conversion from the one form of expression to the other.

Now, each substance is made up of one or more atoms of one or more elements. Each element has its own atomic mass, and the molecular mass of a substance is simply the sum of all the atomic masses of its constituent atoms. The nice thing about moles and Avogadro's Number is that they chose Avogadro's Number so that it just so happens that one mole of a substance has a mass equal to that substance's molecular mass, in grams. This makes it very easy to convert units between the two forms of expression, IF you know the substance's molecular mass. To convert grams per liter to molarity, divide by the molecular mass. To convert molarity to grams per liter, multiply by the molecular mass. It doesn't get much easier than that!

In this case, the substance in question is the nitrate ion. Nitrate has one nitrogen atom, and three oxygen atoms. Nitrogen has an atomic mass of about fourteen. Oxygen has an atomic mass of about sixteen. One times fourteen plus three times sixteen equals sixty-two. So, in this case, ten point nine milligrams per liter divided by sixty-two equals about zero point one seven six millimoles. Since there is only one negative charge on the nitrate ion, then the millimoles is the same thing as the milliequivalents per liter, so when the answer is rounded to just one decimal place, it becomes zero point two milliequivalents per liter.

But, seriously, this stuff isn't really that hard, and if more aquarists understood it better, they would be much more empowered to then understand and also to perform these kinds of calculations for themselves (and not have to come to forums like this to get spoon-fed answers without having actually learned anything to help them in the future).

Well i don't learn as well as i used to. but it would be nice to get some sort of understanding

 

[brandon429]

did bacteria cause the alk loss?>

 

[Randy Holmes-Farley]

did bacteria cause the alk loss?>

I'll go over it in the answer, but even a pure chemical reaction without bacteria that converts ammonia into nitrate gives the same answer.

 

[Randy Holmes-Farley]

it would be nice to get some sort of understanding

That's really the purpose of these questions of the day. I usually give the answer after a few days and try to explain everything. Don't feel bad if it is hard to follow so far..

 

[Randy Holmes-Farley]

10.9 mg/L of NO3- is about 0.176 millimoles (NO3 is one N = atomic weight 14, plus three O = atomic weight 16, for a total of 62, so 10.9 mg/L divided by 62 = 0.176 millimoles) , so it will reduce alkalinity by 0.176 meq/L. Rounded, the answer is D.

What I don't see is a balanced chemical reaction that shows alkalinity being produced or consumed, and if so, by how much.

 

[todda5914]

Without giving the volume for the tank, I'll suspiciously assume a trick and guess C.

 

[drernesto]

Here's my translation for you:

Aha thanks Dr. Now I understand what it was about! [emoji6]

 

[Salty1962]

c