# Question #4e6bd

Nov 20, 2017

88.5$g m o {l}^{-} 1$

Likely to be Y atomic mass of 88.9)

Or Sr (atomic mass of 87.62)

#### Explanation:

So you can calculate how many mols of $O {H}^{-}$ ions you have in the solution;

n = $\frac{\text{Molarity*Volume}}{1000}$ = $\frac{\text{0.00656*400}}{1000}$ = 0.0026mols

From the reaction, you can see that you need 2 mols of Hydroxide ions for one metal ion. Therefore, you have half the number of metal ions in the solution that hydroxide ions.

$\frac{\text{0.0026mols}}{2}$ = 0.0013mols of metal ions

We can now calculate the metals molar mass;

relative atomic mass = $\text{mass(g)"/"number of mols}$ = $\text{0.115g"/"0.0013mols}$ = 88.5$g m o l {s}^{-} 1$

Nov 22, 2017

Molar mass = 87.7 g/mol. The element is strontium.

#### Explanation:

The chemical equation for the overall reaction is

${\text{M + 2H"_2"O" → "M"^"2+" +2"OH"^"-" + "H}}_{2}$

Calculate the moles of $\text{OH"^"-}$

$\text{Moles of OH"^"-" = 0.400 color(red)(cancel(color(black)("dm"^3))) × 6.56 × 10^"-3"color(white)(l) "mol"·color(red)(cancel(color(black)("dm"^"-3"))) = 2.624 × 10^"-3"color(white)(l) "mol OH"^"-}$

Calculate the moles of $\text{M}$

$\text{Moles of M" = 2.624 × 10^"-3" color(red)(cancel(color(black)("mol OH"^"-"))) × "1 mol M"/(2 color(red)(cancel(color(black)("mol OH"^"-")))) = 1.312 × 10^"-3"color(white)(l) "mol M}$

Calculate the molar mass of $\text{M}$

$\text{Molar mass of M" = "mass"/"moles" = ("0.115 g")/(1.312 × 10^"-3"color(white)(l) "mol") = "87.7 g/mol}$

Identify $\text{M}$

The Group 2 element with molar mass closest to 87.7 g/mol is
strontium ($\text{Sr} , {M}_{\textrm{r}} = 87.62$)