How Much Propylmagnesium Bromide is Needed for This Grignard Reaction?

[ampersand15]

I'm in organic chemistry 1. We haven't gone over the Grignard reaction in class, but there was a stoichiometry problem assigned about one and I don't know how to get it started.

Homework Statement

The following Grignard reaction is performed.

Calculate how much of a 0.50M solution of propylmagnesium bromide is required to react completely with 25g of the starting material. Assume you need a 15% excess of the Grignard reagent. Then predict the amount of product based upon a 78% yield.

Homework Equations

If I can get past the first step it's just dimensional analysis.

The Attempt at a Solution

I'm having trouble at the first step, balancing the reaction. I end up with 7C, 16H, 2O, 1Mg, 1Br on the reactant side, and 7C, 14H, 2O, 1Mg, and 1Br on the product side. The only thing I can do that balances the equation is to ignore the H3O+. Is this what I'm supposed to do? Not including H3O+ in the calculation leaves me with 7C, 13H, and 1O on both sides. I'm assuming this has something to do with the Grignard reaction that I haven't encountered yet?

Thanks

 

[Borek]

Don't worry too much about exact reaction. First of all, check how the Grignard reagent works. The only information you need to solve is the molar ratio between butenal and propylmagnesium bromide.