MCAT C/P doubt

[MC789]

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I was doing practice problems and came across a question that said elemental Calcium reacted with water and to find g formed of one of the products. I was on the right track in problem solving but got the wrong answer because I wrote out the equation wrong. I thought the products formed were H2 gas (given) and CaO since Ca is +2 and O is -2, which fits perfectly. But actually, the second product formed was Ca(OH)2. Could someone please help me understand how to complete the equations like this? this isn't the first time I got a question like this wrong. 🙁

 

[mk04447]

Don't look at me, but I have some motivational thoughts. Pass that damn test and you can forget that Greek forever.

 

[AdaptPrep]

Hi, MC789--

The easiest thing to remember is that metals from group 1 and group 2 form metal hydroxides when reacting with water.

Also, if you look at a table of Standard Electrode Potentials, you will find: Ca2+(aq) + 2 e- -> Ca(s) and 2H2O(l) + 2e- -> H2(g) + 2OH-(aq). You would reverse the first equation so the two equations add correctly. However, you will not find: H2O (l) + 2e- -> H2 (g) + O2- (aq) on the table.

I hope that helps a little.

 

[MC789]

That helps! thank you!