General Chemistry

Lecture-2-

College of Pharmacy

Dr. Kosar Hikmat Hama Aziz

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2019-2020

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Some common terms in Analytical Chemistry

Analysis: A process that provides chemical or physical

information about the constituents in the sample or the

sample itself.

In an analysis we determine the identity, concentration, or

properties of an analyte.

Analyte: The component of interest in the sample is called

the analyte. Or A substance to be measured in a given

sample.

Matrix: All other constituents in a sample except for the

analytes. (Everything else in the sample).

Preconcentration: The process of increasing an analyte’s

concentration before its analysis.

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Selectivity: the selectivity of a method is a measure of how

capable it is of measuring the analyte alone in the presence

of other compounds contained in the sample.

Selectivity is a measure of a method’s freedom from

interferences

The most selective analytical methods involve a chromatographic separation.

Interferences: Other compounds in the sample matrix that

interfere with the measurement of the analyte.

blank solution contains the solvent and all of the reagents

used in an analysis (except analyte). A true analytical blank

should reflect all the operations to which the analyte in a

real sample is subjected.

Blank Solution is usually used to calibrate instruments such as

a colorimeter

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Sensitivity: This term can be defined as the ability of a

reagent or a technique to differentiate between two close

concentrations.

Or we can define it as the ability of a reagent or a

technique to detect a concentration as small as possible.

Limit of Detection (LOD): is the smallest amount (the lowest

concentration) of an analyte which can be detected by a

particular method.

LOD does not necessarily mean concentration can be

measured and quantified.

Limit of Quantification (LOQ): is the smallest amount

(lowest concentration) of analyte in a sample which can be

determined quantitatively, with a given accuracy and

precision.

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1. Understanding the Problem (Defining the Problem)

2. Design or Select an Analytical Procedure

3. Sampling and Sample Storage

4. Sample Preparation - Conversion into a Measurable Form

for Analysis

5. Chemical Analysis and Data Analysis (Statistical Analysis)

6. Report

7. Interpretation and Documentation

General Steps in a Chemical Analysis

drug analysis is a technical analysis of a biological sample

such as urine, hair, blood, breath air and sweat to determine

the presence or absence of specified parent drugs or their

metabolites. Or is the analysis of drug in pharmaceutical

formulations.

The Preparation of Aqueous Solutions

o To prepare a solution that contains a specified concentration of a

substance, it is necessary to dissolve the desired number of moles

of solute in enough solvent to give the desired final volume of

solution.

o Preparing a solution of known concentration is perhaps the most

common activity in any analytical laboratory.

o Bulb pipette, Burrette and volumetric flasks are used for

measuring volume when a solution’s concentration must be exact.

o Graduated cylinders, beakers, and reagent bottles suffice when

concentrations need only be approximate.

A stock solution is a concentrated solution that will be diluted to

some lower concentration for actual use. Stock solutions are used

to save preparation time, conserve materials, reduce storage

space, and improve the accuracy with which working lower

concentration solutions are prepared.

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A stock solution is prepared by weighting out an appropriate

mass of a pure solid or by measuring out an appropriate volume

of a pure liquid and diluting to a known volume.

To prepare a solution with a desired molarity (Solid materials)

you would weigh out an appropriate mass of the reagent,

dissolve it in a portion of solvent, and bring to the desired

volume.

To prepare a solution where the solute’s concentration is given

as a volume percent (Liquid sample), you would measure out

an appropriate volume of solute and add sufficient solvent to

obtain the desired total volume.

Preparing Stock solutions

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Relationship of units

A. Molarity & Normality

N = nM

B. Molarity & %

𝑀 =% × 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 × 10

𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡

C. Molarity & ppm

𝑝𝑝𝑚 =𝑀 × 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 × 1000

𝑑𝑒𝑛𝑠𝑖𝑡𝑦

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• Example: A laboratory procedure calls for 250 mL of an approximately

0.10 M solution of NH3. Describe how you would prepare this solution

using a stock solution of concentrated NH3 (14.8 M).

• SOLUTION

• No. of mmol before dilution = No. of mmol after dilution

• 14.8 mmol/mL X Vo = 0.10 mmol/mL X 250 mL

• Vo = 1.69 mL.

• Measure 1.7 mL of concentrated NH3 using a graduated cylinder,

transfer it into a beaker, and add sufficient water to bring the total

solution volume to 250 mL.

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Example: Describe how you would prepare the following three solutions:

1. A 500 mL of 0.20 M NaCl ? Na = 23, Cl = 35.5 2. A 250 mL of 1M HCl from the following information: w/w% = 37, Sp.Gr = 1.18, Cl = 35.5, H = 1 3. 2 L of 40 ppm sodium chloride?

Example: If a tablet containing 100 mg of caffeine

(C8H10N4O2) is dissolved in water to give 300 mL of solution,

what is the molar concentration of caffeine in the solution?

d = 1.023 g/mL

C = 12, H = 1, N = 14 and O = 16

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Example: An experiment required 200 mL of a 0.33 M solution of

Na2CrO4. A stock solution of Na2CrO4 containing 20% solute by

mass with a density of 1.19 g/cm3 was used to prepare this

solution. Describe how to prepare 200.0 mL of a 0.330 M solution

of Na2CrO4 using the stock solution. Cr = 52, Na = 23, O =16

Example: What is the molar concentration of each solution?

a) 12.8 g of sodium hydrogen sulfate in 400 mL of solution

b) 7.5 g of potassium hydrogen phosphate in 250 mL of solution

c) 11.4 g of barium chloride in 350 mL of solution

d) 4.3 g of tartaric acid (C4H6O6) in 250 mL of solution

Na = 23, K = 39, S = 32, P = 31, O = 16, C = 12, Ba = 137 , Cl = 35.5