Question

question 1 of 4 points possible: 1.00 not yet answered a 0.784 g sample of magnesium is added to a 250 ml flask and dissolved in 150 ml of water. magnesium hydroxide obtained from the reaction required 215.0 ml of 0.300 m hydrochloric acid to completely react. how many moles of mg were used? select one. a. 0.323 mol b. 0.0645 mol c. 0.0323 mol d. 0.0161 mol

Explanation:

Step1: Write the chemical reaction equation

The reaction between magnesium ($Mg$) and hydrochloric acid ($HCl$) is $Mg + 2HCl=MgCl_{2}+H_{2}\uparrow$.

Step2: Calculate the moles of $HCl$

Use the formula $n = M\times V$, where $M = 0.300\ M$ and $V=215.0\ mL=0.215\ L$. So $n_{HCl}=0.300\ mol/L\times0.215\ L = 0.0645\ mol$.

Step3: Determine the moles of $Mg$ from the mole - ratio

From the balanced chemical equation, the mole - ratio of $Mg$ to $HCl$ is $1:2$. Let the moles of $Mg$ be $n_{Mg}$. Then $n_{Mg}=\frac{n_{HCl}}{2}$. Substituting $n_{HCl}=0.0645\ mol$, we get $n_{Mg}=\frac{0.0645\ mol}{2}=0.03225\ mol\approx0.0323\ mol$.

Answer:

c. 0.0323 mol