Question

CaCO3(s) + H3PO4 (aq) -> Ca3(PO4)2(aq) + H20(l) + CO2(g) how many grams of phosphoric acid react with excess calcium carbonate to produce 3.74g ca3(po4)2

Answer 1

After you have balanced the reaction, convert the mass given to moles.
To interconvert between mass and moles, use the relationship:

\(n=\dfrac{m}{M}\)

where, M=molar mass, m=mass, and n= moles.

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Next, use the stoichiometric coefficients to find moles of reagent needed.
Set up a ratio using the species of interest, like so:

e.g. for a general reaction:

\(\color{red}{a}A + \color{blue}{b}B\) \(\rightleftharpoons\) \( \color{green}{c}C\)

where upper case are the species (A,B,C), and lower case (a,b,c) are the coefficients ,

\(\dfrac{n_A}{\color{red}{a}}=\dfrac{n_B}{\color{blue}{b}}=\dfrac{n_C}{\color{green}{c}}\)

From here you can isolate what you need.
For example: if you have 2 moles of B, how many moles of C can you produce?

solve algebraically: \(\dfrac{2}{\color{blue}{b}}=\dfrac{n_C}{\color{green}{c}}\rightarrow n_C=\dfrac{2*\color{green}{c}}{\color{blue}{b}}\)
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