M+ is an unknown metal cation with a +1 charge. A student dissolves the chloride of the unknown metal, MCl, in enough water to make 100.0 mL of solution. The student then mixes the solution with excess AgNO3 solution, causing AgCl to precipitate.
The student collects the precipitate by filtration, dries it, and records the data shown below. (The molar mass of AgCl is 143 g/mol.)
mass of unknown chloride, MCl 0.74 g mass of filter paper 0.80 g
mass of filter paper plus AgCl precipitate 2.23 g

What is the identity of the metal chloride?
A: NaCl
B: KCl
C: CuCl
D: LiCl

Quote from: Ansam on September 19, 2022, 07:25:04 PM
What is the identity of the metal chloride?
A: NaCl
B: KCl
C: CuCl
D: LiCl

Elements and compounds can be identified from their atomic masses or molar masses.
In the given question, during the experiment following reaction took place.
MCl (aq) + AgNO₃ (aq)----> AgCl (s) + MNO₃ (aq)
After precipitation and filtration of AgCl we can calculate the mass of AgCl formed by subtracting mass of only filter paper from  (AgCl+ filter paper ) .
Now convert mass of AgCl to moles of AgCl to moles of MCl. Using the mass of MCl and moles of MCl calculated, get the molar mass of MCl.From this molar mass subtract atomic mass of MCl to get the atomic mass of M .Now identify M from the periodic table from its atomic mass.

Here is the calculations in dimensional format

(2.23-0.80) g AgCl x  (1mol AgCl)/(143 g) X (1mol MCl)/(1mol AgCl )  =Calculate moles of MCl
Molar mass = mass of MCl /moles of MCl
Atomic mass of metal = molar mass of MCl ? atomic mass of Cl (35.45g/mol)
                                             = 38.55 g/mol (closer to 39 g/mol value)
Experimental value is slightly different from accurate value because of unavoidable experimental errors.
It means metal is potassium and salt is KCl