Question #4e6bd

2 Answers
Nov 20, 2017

Answer:

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#

Nov 22, 2017

Answer:

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#)