Solutions

Question 1

What is a solution?

Answer 1

A mixture of two or more substances - solid-solid, solid-liquid, etc

Question 2

What is molarity?

Answer 2

Molarity is the number of moles of solute per litre of solution. …
• M = no of moles litre of solution

Question 3

Unit of molarity

Answer 3

mol/dm^3

Question 4

Mass concentration

Answer 4

Molarity x Molar mass

Question 5

Molar concentration

Answer 5

Mass conc / Molar mass

Question 6

What is molality?

Answer 6

Molality, is a measure of the concentration of a solute in a solution in terms of the amount of substance in a specified amount of mass of the solvent.

Conc of solute = Molality
Amount of substance in mass of solvent = Formula

Question 7

Unit of molality

Answer 7

The unit for molality is expressed as ‘m,’ molal, or moles per kilogram.

Question 8

Formula of molality

Answer 8

Molality, or molal concentration , m, is the number of moles of solute per kilogram of solvent.

Question 9

The molality of a solution is always greater than the molarity

Answer 9

True

Question 10

Molality changes with temperature. True or False

Answer 10

False

Question 11

Which is a more accurate way of measuring solutes in solution in dynamic conditions?

Answer 11

Molality

Question 12

Uses of molality

Answer 12

• To compare and
  determine colligative properties of solutions
• Measurement of solute conc in dynamic conditions

Question 13

What are colligative properties?

Answer 13

Colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity or nature of the chemical species or solute.

Question 14

Examples of colligative properties

Answer 14

Boiling point
Vapour pressure
Freezing point
Osmotic pressure

Question 15

Mass of solution

Answer 15

= Solute + Solvent

Question 16

Normality (N) is dependent on the reaction. True or false?

Answer 16

True

Question 17

Formula for normality

Answer 17

1. Equivalent weight per liter of solution

2. Molarity x Equivalent number

Question 18

What is the equivalent number?

Answer 18

1. no of electrons or protons transferred in reactions
2. valence state of an element or compound
3. In acids and bases , the no. of hydrogen ions transferred (H+) or hydroxyl (OH) ions

Question 19

Why is normality so important?

Answer 19

It helps to determine the strength between acids or solvents

Question 20

What is equivalent weight?

Answer 20

Equivalent weight is the molar mass divided by the no. of equivalent number.

Question 21

The strength of a solution is described by:

Answer 21

Normality
Molarity
 Molality
Equivalent mass
Strength of solution
Percentage concentration

Question 22

A normal solution is…

Answer 22

…one containing 1g equivalent of the dissolved solute in 1 litre of its solution

Question 23

Normality depends on…

Answer 23

Dilution

Temperature

Question 24

The equivalent weight of a substance is…

Answer 24

…the mass in grams of that substance which combines or reacts with a standard weight of a reference element or compound.

Question 25

If the equivalent weight of a substance, is the same as the molecular weight of that substance which combines or reacts, then...

Answer 25

...normality = molarity

Question 26

What is concentration?

Answer 26

It is the amount of solute dissolved in a solvent to make a solution. It can be dilute or concentrated.

Question 27

Concentration in Physical Units

Answer 27

➢% w/v ➢% w/w ➢% v/v

Question 28

What is standardization?

Answer 28

Standardization is the process of determining the exact concentration (molarity) of an unknown solution.

Question 29

Why is it important to standardise solutions?

Answer 29

●Reagents for assay must be of high purity ●Solutions concentration must be known before use ●For accuracy

Question 30

A standard solution is...

Answer 30

...a solution containing a precisely known concentration of an element or a substance.

Question 31

Examples of a primary standard

Answer 31

Anhydrous Sodium Carbonate Na2CO3 •Sodium chloride NaCl •Potassium Dichromate K2Cr2O7 •Potassium Hydrogen phthalate (KHP) KHC8H4O4.

Question 32

Properties of a primary standard

Answer 32

- Must be very pure - Should not be affected by exposure to moisture or air (non-hygroscopic) - Should maintain purity during storage - Rxns involving it must be stoichiometric and fast - High molecular and equivalent weight

Question 33

A secondary standard is...

Answer 33

...a solution whose unknown accurate concentration has been determined (standardised) while using a primary standard of known concentration and purity.

Question 34

Examples of secondary standard

Answer 34

* Potassium permanganate, KMnO4 * Sodium hydroxide, NaOH * HCl * EDTA - Ethylenediamminetatraacetic acid

Question 35

Properties of a secondary standard

Answer 35

- Concentration can’t be calculated using regular molarity parameters - Exact conc determined by titration against a primary standard - Not very pure - More reactive - Used specifically for certain analyses

Question 36

Why is KMNO4 unsuitable as a primary standard? But as a secondary standard

Answer 36

It is a good oxidizing agent so it is reactive and less stable. More often, due to its reactivity, its own oxidized product, manganese oxide (MnO2), contaminates the content.

Question 37

What is the factor of a solution?

Answer 37

It is the relation of the exact strength of a solution to its nominal strength and is defined as the number of milliliters of exact (actual) strength which is equivalent to 1 ml of the solution of its nominal strength

Question 38

Formula for factor

Answer 38

Actual strength / Nominal strength

Question 39

Typical situations when you might use normality include

Answer 39

Acid-base chemistry Redox reactions Precipitation reactions