https://steemitimages.com/DQmU8XmEVP9ixsABLQ3e3zduXvRZjiERuMGG4wGFdcjKJRm/Chemistry_quiz.jpg

As weekend is about to start very soon, you may feel freed from the burden of your daily job and full of energy. This might be the right moment to try to solve my little chemistry quiz below and at the same time having the opportunity to win up to 6 steem. :-)

Rules - what are the requirements to win the prize?

You have to upvote this article with at least 20 % of your voting power (no 1 % votes please :).
Winner is the person who is the first one to post the correct solution (correct number and correct unit). The prize for the correct answer are 5 steem. I will send it to the winner immediately after I received the rewards for this article.
If the winner had also resteemed my article, he will receive one additional steem (altogether (5 + 1) steem = 6 steem).
If nobody finds the solution until Wednesday, April 12th, 2017 at 10 pm (German time!) the prize (5 steem) will be added to the next competition.

Calcium crystals:

https://cdn.steemitimages.com/DQmcaedy3RzsvVeAkE2nqnDP6u9mVxfXVHuATDNeCfuAyX7/Calcium.jpeg

Von Alexander C. Wimmer, CC BY-SA 3.0 at, https://commons.wikimedia.org/w/index.php?curid=17611906

Challenge to solve:

Assumed you have a certain number of calcium atoms ₂₀Ca, where the sum of the electrical charges of the Ca-nuclei is Q = 3.8589 ∙ 10⁶ C.

One single ₂₀Ca atom has a mass of 40 u (please use this rounded number for your calculations).

1 g = 6.022 ∙ 10²³ u.

The elementary charge of one proton is e = 1.602 ∙ 10^-19 C.

Question: what is the overall mass (the sum of the masses) of all ₂₀Ca atoms in g?
m(overall-₂₀Ca) = ?

Remark: this is the first time I offer a challenge. I tried to make both the rules and the question clear enough. However I really appreciate your feedback in case something is not clear or any necessary information about the rules is missing. I also would like to hear your opinion about the question which I asked you to solve: Do you like these kind of quizzes? Was it too difficult or too easy? Should I offer another competition in future? Thanks in advance for sharing your view! :)