Solutions Flashcards
What is a solution?
A mixture of two or more substances - solid-solid, solid-liquid, etc
What is molarity?
Molarity is the number of moles of solute per litre of solution. …
• M = no of moles litre of solution
Unit of molarity
mol/dm^3
Mass concentration
Molarity x Molar mass
Molar concentration
Mass conc / Molar mass
What is molality?
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
Unit of molality
The unit for molality is expressed as ‘m,’ molal, or moles per kilogram.
Formula of molality
Molality, or molal concentration , m, is the number of moles of solute per kilogram of solvent.
The molality of a solution is always greater than the molarity
True
Molality changes with temperature. True or False
False
Which is a more accurate way of measuring solutes in solution in dynamic conditions?
Molality
Uses of molality
- To compare and
determine colligative properties of solutions - Measurement of solute conc in dynamic conditions
What are colligative properties?
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.
Examples of colligative properties
Boiling point
Vapour pressure
Freezing point
Osmotic pressure
Mass of solution
= Solute + Solvent
Normality (N) is dependent on the reaction. True or false?
True
Formula for normality
- Equivalent weight per liter of solution
2. Molarity x Equivalent number
What is the equivalent number?
- no of electrons or protons transferred in reactions
- valence state of an element or compound
- In acids and bases , the no. of hydrogen ions transferred (H+) or hydroxyl (OH) ions
Why is normality so important?
It helps to determine the strength between acids or solvents
What is equivalent weight?
Equivalent weight is the molar mass divided by the no. of equivalent number.
The strength of a solution is described by:
Normality Molarity Molality Equivalent mass Strength of solution Percentage concentration
A normal solution is…
…one containing 1g equivalent of the dissolved solute in 1 litre of its solution
Normality depends on…
Dilution
Temperature
The equivalent weight of a substance is…
…the mass in grams of that substance which combines or reacts with a standard weight of a reference element or compound.
If the equivalent weight of a substance, is the same as the molecular weight of that substance which combines or reacts, then…
…normality = molarity
What is concentration?
It is the amount of solute dissolved in a solvent to make a solution. It can be dilute or concentrated.
Concentration in Physical Units
➢% w/v
➢% w/w
➢% v/v
What is standardization?
Standardization is the process of determining the exact concentration (molarity) of an unknown solution.
Why is it important to standardise solutions?
●Reagents for assay must be of high purity
●Solutions concentration must be known before use
●For accuracy
A standard solution is…
…a solution containing a precisely known concentration of an element or a substance.
Examples of a primary standard
Anhydrous Sodium Carbonate Na2CO3
•Sodium chloride NaCl
•Potassium Dichromate K2Cr2O7
•Potassium Hydrogen phthalate (KHP) KHC8H4O4.
Properties of a primary standard
- 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
A secondary standard is…
…a solution whose unknown accurate concentration has been determined (standardised) while using a primary standard of known concentration and purity.
Examples of secondary standard
- Potassium permanganate, KMnO4
- Sodium hydroxide, NaOH
- HCl
- EDTA - Ethylenediamminetatraacetic acid
Properties of a secondary standard
- 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
Why is KMNO4 unsuitable as a primary standard? But as a secondary standard
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.
What is the factor of a solution?
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
Formula for factor
Actual strength / Nominal strength
Typical situations when you might use normality include
Acid-base chemistry
Redox reactions
Precipitation reactions