AAMC Question Bank C/P #79

[MC789]

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can someone please explain how you know to write the following equation Ca + 2H20 --> Ca2+ + 20H- + H2 , given info that Ca reacted with water? How do you know its 2H20 that reacted with Ca instead of just one? and how can you predict the products? I took gen chem 5 years ago and tried looking up lessons to refresh my memory but according to the foil method, isn't Ca+2h2o supposed to give CaOH + h+?

 

[aldol16]

1) You don't need to know the reaction to answer the question but 2) remember the charge on Ca. What's its charge? And therefore, how many OH are required to balance that charge in an ionic compound, which must be electrically neutral?

 

[MC789]

1) You don't need to know the reaction to answer the question but 2) remember the charge on Ca. What's its charge? And therefore, how many OH are required to balance that charge in an ionic compound, which must be electrically neutral?

Ca has 2+ charges and so 2 OH- ions are required to balance that charge. That makes sense, thanks so much!!