Basic Chemistry and Laboratory Calculations.

Basic Chemistry and Laboratory Calculations

Basic Chemistry and Laboratory Calculations

• DEFINITIONS
• Atom, Molecule, Molecular weight ,Valence , Equivalent weight , Electrolyte,Oxidation ,Reduction, Radicles ,Acid , Base, 
• Neutralisation reaction 
• HYDROGEN ION CONCENTRATION AND pH, Measurement of pH
• pH meter
• SOLUTIONS
• CHEMICAL ANALYSES
• STANDARD SOLUTIONS
• INDICATORS
• SI UNITS
• STATISTICS IN CLINICAL LABORATORY

Basic Chemistry and Laboratory Calculations

A  Knowledge of terms used in basic chemistry A is essential for full understanding of chemical reactions in Clinical Chemistry.

DEFINITIONS

Atom 

Atoms are the smallest particles of which any substance is made of that take part in a chemical reaction. An atom is composed of central compact nucleus. This nucleus contains two types of particles, protons and neutrons.

• The protons are positively charged while neutrons have no electrical charge. The whole nucleus is surrounded by negatively charged particles called electrons. 

• An atom is said to be electrically neutral because the number of protons is equal to the that of electrons. Atomic number of an element is equal to the number of protons. 

• Atomic weight of an element is the sum of the number of protons and neutrons. Isotopes are the atoms of the same element which have the same number of protons, but a different number of neutrons. 

Molecule 

 It is the smallest particle of an element or compound that can exist independantly. For example, one atom of sodium (Na) and one atom of chloride (CI) combine to form one molecule of sodium chloride (NaCl).

Molecular weight 

Molecular weight (or relative molecular mass) is the sum of all atomic weights of which the molecule is composed. For example, molecular weight of NaCl is 58.5 where atomic weight of Na is 23 and that of Cl is 35.5. 

Valence 

The valence of a substance is the number of hydrogen atoms which will combine with, liberate or replace one atom of the substance. For example, the valence of oxygen in water (HO) is 2. 

Equivalent weight 

The equivalent weight is the weight that combines with, liberates or replaces one atom of hydrogen. This is equal to molecular weight divided by the valence.

Ie.Molecular Weight/Valence

Electrolyte 

An electrolyte is a compound which when dissolved in water will conduct electric current. The passage of electric current through an electrolyte is called electrolysis which results in the dissociation of molecules into positively charged and negatively charged ions known respectively as cations and anions. 

Oxidation  

This is a reaction in which an atom loses electrons. It is in effect, the addition of oxygen or removal of hydrogen from a substance.

Reduction 

This is a reaction in which oxygen is removed or hydrogen added to the substance; that is, an atom gains electrons.

Radicles   

These are units or groups of atoms which when combined in a compound behave as a single atom. For example, NOZ, SONH, 

Acid It is a substance or compound that gives off hydrogen ion (H*) in solution and can donate a proton.

Base It is a substance or compound which gives off hydroxyl ions (OH) in solution and can accept a proton.

An example of acid-base reaction:

Acid HCI + Base NaOH = Salt NaCl + Water H2O 

Neutralisation reaction 

The reaction between an acid and a base to produce a neutral solution of salt and water is known as neutralisation reaction. A neutral solution contains equal numbers of hydroxyl (OH) and hydrogen (H) ions.

HYDROGEN ION CONCENTRATION AND pH

Sorensen in 1909 divided the units of pH (puissance d'hydrogen) as strength of hydrogen ions, or POH (puissance d'hydroxyl) as strength of hydroxyl ions as a more convenient way to express the hydrogen ion concentrations of solutions. pH is defined as the logarithm to the base 10 of the reciprocal of the hydrogen ion concentration.

• A solution, whether acid or base, always contains H* and OH ions. The predominance of one type of ion over the other determines the degree of acidity or alkalinity. It is usual to refer to this acidity or alkalinity as hydrogen ion concentration. 

• Pure water contains 0.0000001 g or 10-'g of hydrogen ions per litre at 25°C. The concentration of hyrogen ions of water is expressed as H* (Pure water) = 1 x 10 mol/L (The molecular mass of hydrogen is 1). pH is expressed aspH =  pH of pure water = log 10-7^-7=7 (neutral)

• The pH scale is expressed from 0 to 14 units. A neutral solution has a pH of 7.0, an acid has a pH less than 7.0, and an alkali has a pH greater than 7.0.

•  Since strong acids like hydrochloric acid (HCI), sulphuric acid (H SO.) or nitric acid (HNO3), dissociate completely in solution, they have a very low pH.

• Weak acids such as lactic or acetic acid do not completely dissociate even in dilute solutions and so they have a comparatively higher pH. The same is true for strong and weak bases where strong bases have much higher pH than weak bases.

Measurement of pH

pH can be measured using

1. pH papers, which give approximate pH values.

2. A colorimeter,with indicators and series of standards.

3. pH meter, which gives the most accurate value of pH

pH meter

pH meter is a very sensitive instrument used to measure the hydrogen ion concentration (pH) of solutions. Generally, pH meter is used in the preparation and quality control of reagents. The measurement of pH is also referred to as potentiometric analysis.   (continue reading ..)

 

BUFFER SOLUTIONS

A buffer solution is that which tends to resist changes in pH on the addition of small quantities of acid or alkali. Buffer solutions are made up of a weak acid and a salt of a strong base; or a weak base and a salt of a strong acid. Buffers vary in their buffering capacities. Using various proportions of the constituents in a buffer system, solutions of different pH can be prepared           (continue reading ..)

SOLUTIONS

A solution is composed of a solvent which is the liquid, and a substance or the solute which is dissolved or diluted in the solvent. Molecules or ions of the solute are evenly distributed throughout the solvent.   (Continue Reading ..)

DILUTING SOLUTIONS

It is frequently necessary to dilute solutions during various laboratory investigations. To dilute a solution is to reduce its concentration, i.e., make a weaker solution from a stronger one. It is therefore necessary for a laboratory worker to be capable of solving simple dilution problems. The dilutions can be single or in series. (continue reading ..)

1. Single Dilutions

2. Serial Dilutions

CHEMICAL ANALYSES 

A chemical analysis can be performed in three ways:

1. Qualitative

2. Semi quantitative or

3. Quantitative.                   (continue reading ..)

STANDARD SOLUTIONS

There are two types of standard solutions in titrimetric (volumetric) analysis—the primary and the secondary standard solutions.  (continue reading ..)

INDICATORS

Certain substances dissociate in solution to give two or more different coloured forms. These substances are known as indicators. The nature of coloured forms is dependent on the pH of the solution. For example, phenol red changes from yellow at pH 6.8 to a deep red at pH 8.4. Indicators are used to determine the pH of liquids and the end points of acid-base titrations.    (Continue Reading ..)

SI UNITS

The International System of Units (or Systeme Internationale, SI) is now adapted by nearly all the international scientific bodies. The system is ac. claimed as being "logical and coherent". It provides a uniform scientific language for weights and measures.    (Continue Reading ..)

STATISTICS IN CLINICAL LABORATORY

Statistics is the area of mathematics which deals with the collection, analysis, interpretation and presentation of data. The enormous data that is generated in a clinical laboratory can be more useful to the laboratory personnel and clinicians if it is analysed with the help of statistical tests.    (Continue Reading ..) 

Analytical Errors in Clinical Laboratory

An error, in simple terms, is the difference between the result obtained and the result expected (true value). Laboratory errors which occur during analysis can be minimised if attention is paid to proper laboratory procedures and techniques. Such analytical errors are of two types, namely, random error and systematic error.  (Continue Reading ..)