[isaiahtx]

Hi! This is my first post to the Chemical Forums. I am currently a student taking AP Chemistry in high school and I absolutely love it. Last week we had a lab in class where we reacted Hydrochloric Acid (HCl) & Magnesium (Mg) to make Magnesium Chloride (MgCl₂)

We found the initial mass of the Magnesium and we had an excess amount of Hydrochloric Acid. We then heated the product in a evaporating dish over a hot plate 10 minutes at a time, each time weighing until the liquid HCl/water was all evaporated (hope this makes sense). We did this three times, each with a steady decrease of about "x" grams each time we heated. We had to leave for lunch and me and my lab partner were not able to finish drying the product fully, so we set the dish in the fume hood and went to our next class. An hour later we came back during lunch and weighed the mass again (without heating it again) and found that to our dismay it had increased by "2x" grams. we just used our second-to-last mass to find the empirical formula (the goal of the lab). Our teacher told us to look up the reason why this might have happened, but I am not able to find an explanation. Obviously MgCl₂ would not oxidize, so I see no other reason why it might obtain mass.

I hope this makes sense and thank you so much!

-isaiahtx

[Borek]

Have you read the wikipedia article on magnesium chloride? Section on general properties contains several important hints that should put you on the right track.

What is composition of the air (what gases are present)?

[isaiahtx]

Have you read the wikipedia article on magnesium chloride? Section on general properties contains several important hints that should put you on the right track.

What is composition of the air (what gases are present)?

thanks for the response, but I don’t really see what I the article could help me, as to be honest, it’s over my head in a multitude of ways.

[Borek]

Have you read the very first phrase:

Magnesium chloride is the name for the chemical compound with the formula MgCl₂ and its various hydrates MgCl₂·H₂O_x.

Check what hydrates are.

And I will repeat my question: what gases are present in the air?