Magnesium can interfere with the measurement of the calcium concentration in water samples using colorimetric tests. Write a balanced chemical equation for the reaction of dissolved magnesium chloride with sodium hydroxide to form magnesium hydroxide as a precipitate and sodium chloride. (Reactants -> Products)

Explanation:

Hello.

In this case, since aqueous magnesium chloride reacts with aqueous sodium hydroxide, a precipitate product, magnesium hydroxide is formed as well as aqueous sodium chloride as shown below:

However, since there are two chlorine atoms at the reactants we need a 2 before NaCl on the products in order to balance it. Moreover, there one OH at the  reactants and two OH at the products, that is why we also add a 2 before NaCl as shown below:

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i'm pretty sure its b i might be wrong though!