Question

Question #4e6bd

Answer 1

88.5`gmol^-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 `OH^-` ions you have in the solution;

n = `"Molarity*Volume"/1000` = `"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.

`"0.0026mols"/2` = 0.0013mols of metal ions

We can now calculate the metals molar mass;

relative atomic mass = `"mass(g)"/"number of mols"` = `"0.115g"/"0.0013mols"` = 88.5`gmols^-1`

Answer 2

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

Explanation:

The chemical equation for the overall reaction is

`"M + 2H"_2"O" → "M"^"2+" +2"OH"^"-" + "H"_2`

Calculate the moles of `"OH"^"-"`

`"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 `"M"`

`"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 `"M"`

`"Molar mass of M" = "mass"/"moles" = ("0.115 g")/(1.312 × 10^"-3"color(white)(l) "mol") = "87.7 g/mol"`

Identify `"M"`

The Group 2 element with molar mass closest to 87.7 g/mol is
strontium (`"Sr", M_text(r) = 87.62`)