Introduction
 
Matters and Properties of Matters
 
Atomic Structure with Examples
 
Periodic Table
 
The Mole Concept with Examples
 
Gases with Examples
 
Chemical Reactions with Examples
 
Nuclear Chemistry (Radioactivity)
 
Solutions
 
--Solubility and Factors Affecting Solubility
 
--Concentration with Examples
 
--Dilution and Density of Solutions
 
--Concentration of Ions with Examples
 
--Properties of Solutions and Solution Calculations
 
--Solutionns Cheat Sheet
 
Acids and Bases
 
Thermochemistry
 
Rates of Reactions (Chemical Kinetics)
 
Chemical Equilibrium
 
Chemical Bonds
 
Exams and Problem Solutions
 
Old Version
 


Menu

Concentration of Ions with Examples


Concentration of Ions with Examples

We examine concentration of ions with examples.

Example: 500 mL solution includes 0,2 mole Ca(NO3)2. Find concentration of ions in this solution.

When Ca(NO3)2 dissolves in water;

Ca(NO3)2(aq) → Ca+2(aq) + 2NO3-(aq)

1 mole Ca(NO3)2 gives 1 mole Ca+2 and 2 moles NO3- ions to solution.

1 mole Ca(NO3)2 gives 1 mole Ca+2 ion

0,2 mole Ca(NO3)2 gives ? mole Ca+2 ion

───────────────────────────

?=0,2 mole Ca+2 ion

1 mole Ca(NO3)2 gives 2 mole NO3- ion

0,2 mole Ca(NO3)2 gives ? mole NO3- ion

───────────────────────────

?=0,4 mole NO3- ion

Since volume of solution is 500 mL=0,5 L, molar concentration of solution becomes;

M=nsolution/V

M=0,2/0,5=0,4 mol/L

Molar concentrations of ions ;

[Ca+2]=nCa+2/V=0,2/0,5=0,4 mol/L

[NO3-]=nNO3-/V=0,4/0,5=0,8 mol/L

Example: 2,68 g Na2SO4.xH2O solute dissolves in water and 100 mL solution is prepared. If the concentration of Na+ ion in this solution is 0,2 molar, find x in the formula of compound. (Na2SO4=142 and H2O=18)

Solution:

We first find moles of Na+ ion using following concentration formula;

[Na+]=nNa+/V

V=100mL=0,1L and [Na+]=0,2 molar

nNa+=[Na+].V=(0,1).(0,2)=0,02 mole

We find mole of solution including 0,02 mole Na+;

1 mole Na2SO4.xH2O includes  2 mole Na+ ion

? mole Na2SO4.xH2O includes  0,02 mole Na+ ion

───────────────────────────

?=0,01 mole Na2SO4.xH2O

Molar mass of compound;

0,01 mole Na2SO4.xH2O is    2,68 g

1 mole  Na2SO4.xH2O is      ? g

─────────────────────

?=268 g

Na2SO4.xH2O=268 g

142 + x(18)=268

x=7

Example: We mix two solutions having 4 liters 0,2 molar K2(SO4) and 1 liter Al2(SO4)3. If molar concentration of SO4-2 ion is 0,4 molar, find molar concentration of Al2(SO4)3.

Solution:

Moles of K2(SO4)

nK2(SO4)=V.M=4.0,2=0,8 mole

Since 1 mole K2(SO4) gives 1 mole SO4-2, 0,8 mole K2(SO4) gives 0,8 mole SO4-2.

Moles of Al2(SO4)3,

nAl2(SO4)3=V.M=1.X=x moles (x is molarity of Al2(SO4)3

Since 1 mole Al2(SO4)3 gives 3 moles SO4-2, x mole Al2(SO4)3 gives 3x mole SO4-2

Total number of moles of SO4-2 in solution is;

nSO4-2=0,8 + 3x

Volume of solution is;

Vsolution=4 + 1=5 L

Molar concentration of SO4-2;

[SO4-2]=nSO4-2/Vsol

0,4=(0,8+3x)/5

x=0,4 molar.

Example: During dissolution of Al(NO3)3 and Ca(NO3)2 in water, graph given below shows change in the number of moles of Al+3 and NO3- ions. If final ion concentration of Ca+2 is 0,05 molar, find volume of solution.

Solution:

We see that final moles of NO3- is 0,16 and Al+3 is 0,04.

1 mole Al(NO3)3 gives 1 mole Al+3 and 3 mole  NO3-

If 1 mole Al(NO3)3 gives  3 mole  NO3-

0,04 mole Al(NO3)3 gives     ? mole NO3-

───────────────────────────

?=0,12 mole NO3-

Since there are 0,16 mole NO3-in solution, 0,16-0,12=0,04 mole NO3- comes from Ca(NO3)2.

mole Ca(NO3)2 gives 1 mole Ca+2 and 2 mole  NO3-

If 1 mole Ca+2 reacts with  2 mole  NO3-

? mole Ca+2 reacts with  0,04 mole NO3-

───────────────────────────

?=0,02 mole Ca+2

Molar concentration of Ca+2;

[Ca+2]=nCa+2/V

0,05=0,02/V

V=0,4 L=400 mL.

Solutions Exams and  Problem Solutions


Author:




Tags:


© Copyright www.ChemistryTutorials.org, Reproduction in electronic and written form is expressly forbidden without written permission of www.ChemistryTutorials.org. Privacy Policy