Analytical chemistry - open

What is accuracy?

Accuracy is how close a measured value is to the true or accepted value.

Define Gravimetric analysis?

quantitative analytical method in which the amount of an analyte is determined by measuring the mass of a pure compound formed from it (usually a precipitate)

Which substance called redox indicators?

substances that change color when they are oxidized or reduced (when their oxidation state changes).

What is absorbance? write its formula?

measure of how much light is absorbed by a solution.

Formula:

A = log₁₀(I₀ / I)

Where:

I₀ = intensity of incident light

I = intensity of transmitted light

What is elution?

process of removing adsorbed substance from a stationary phase by passing a solvent through it, usually in chromatography.

What is molecular ion?

A molecular ion is a molecule that has lost or gained an electron without breaking, shown as M⁺

Which factors important for choosing methods?

1. Accuracy and precision

2. Sensitivity

3. Selectivity

4. Speed

5. Cost

6. Safety

7. Availability of equipment

What is systematic error?

error that consistently occurs in same direction, causing measurements to be too high/ too low compared to true value.

It is reproducible and can often corrected.

Write formula Gibs free energy?

Delta G = Delta H - T Delta S

Where:

Delta G = change in Gibbs free energy

Delta H = change in enthalpy

T = absolute temperature (in Kelvin)

Delta S = change in entropy

Write acid base theories?

1. Arrhenius Theory

Acid: produces H⁺ (protons) in water

Base: produces OH⁻ in water

2. Brønsted-Lowry Theory

Acid: proton donor

Base: proton acceptor

3. Lewis Theory

Acid: electron pair acceptor

Base: electron pair donor

Define conjugate base?

is what remains of an acid after it donates a proton (H⁺)

What is gravimetric factors? How we calculate it?

number used in gravimetric analysis to relate the mass of a precipitate to the mass of the analyte.

GF = molar mass analyte / molar mass precipitate

steps:

1. Write chemical formula of precipitate.

2. Identify analyte in precipitate.

3. Find molar masses of analyte and precipitate.

4. Divide molar mass of analyte by of precipitate.

Write solubility constant for precipitate Ag2CrO4?

AgCrO(s) -> 2Ag(aq) + CrO(aq)

So solubility : Ksp= (Ag)2(CrO)

Define redox reaction?

chemical reaction in which oxidation and reduction occur simultaneously.

• Oxidation: loss of electrons

• Reduction: gain of electrons

Write types of electrodes?

1. Metallic Electrodes - made of metal in contact with ion solution

2. Non-Metallic Electrodes - made of non-metals

3. Reference Electrodes - have stable and known potential

4. Indicator Electrodes - respond to concentration of specific ion in solution

What is color?

perception of light different wavelengths by human eye.

• depends on wavelengths of visible light that reflected, transmitted, or emitted by object

What is the eluent?

mobile phase in chromatography—the solvent that flows through stationary phase and carries analytes with it.

What is use of chromatography?

to separate, identify, sometimes quantify the components of mixture.

What is nitrogen rule?

organic compound with odd number of nitrogen atoms has odd molecular mass, while one with zero or even number of nitrogen atoms has even molecular mass.

What is oxidizing agent ? Reducing agent?

Oxidizing agent: substance that accepts electrons and causes oxidation of another substance; it reduced itself.

Reducing agent: substance that donates electrons and causes reduction of another substance; it oxidized itself.

Define analytical chemistry?

branch of chemistry concerned with separating, identifying, and determining amount of chemical components in sample.

What is chromatography?

technique used to separate components of mixture based on their different distribution between stationary phase and mobile phase.

What is transmittance? Write formula?

the fraction of incident light that passes through a sample.

Formula: T = i/i0

where I = transmitted light intensity, I_0 = incident light intensity.

What is formula for PH and PoH?

pH= -log[H+]

pOH= -log [OH-]

What is PH?

measure of the acidity or alkalinity of a solution, defined as the negative logarithm of hydrogen ion concentration

pH= -log[H+]

What is a label? Which information?

Label: information attached to a product or container that identifies it and gives essential details.

includes:

• Name of the substance

• Strength or concentration

• Dosage form

• Manufacturer's name

• Batch/lot number

• Expiry date

• Storage conditions

• Directions or warnings

How to prepare solution?

1. Calculate and weigh the solute.

2. Dissolve in part of the solvent.

3. Transfer to a flask and add solvent to final volume.

4. Mix well and label.

Which methods you know of analysis?

• Gravimetric

• Volumetric (titrimetric)

• Spectroscopic

• Chromatography

• Electrochemical

• Thermal

Types of titration?

1. Acid-base titration

2. Redox titration

3. Complexometric titration

4. Precipitation titration

Concentration? Units?

amount of solute in a given amount of solution or solvent.

Units:

•Molarity (M): moles/L solution

•Molality (m): moles/kg solvent

•Normality (N): equivalents/L solution

•Percent (%)

• (ppm) = mg solute / L solution

•(ppb) = µg solute / L solution

•Mole fraction (χ) = moles solute / total moles

Formula percentage concentration?

W/V = mass solute (g) / volume solution (mL) x 100

Indicators?

substances that change color to show the end point of a reaction, usually in titrations.

Define strong/weak acids?

Strong acid: completely ionizes in water, releasing all its H⁺ ions

Weak acid: partially ionizes in water, releasing only some of its H⁺ ions

Strong electrolytes and weak electrolytes?

• Strong electrolytes: completely dissociate into ions in solution → conduct electricity well

• Weak electrolytes: partially dissociate into ions → conduct electricity poorly

How make calibration? Which glass volumetric?

Making calibration solution :

1. Weigh the solute accurately.

2. Dissolve in small amount solvent.

3. Transfer to volumetric flask of known volume.

4. Add solvent up to mark on the flask.

5. Mix thoroughly.

6. Label with concentration, date, and substance name.

Glassware used:

• Volumetric flask

• Pipette

• Burette

What is Henderson-Hasselbalch equation?

pH = pKa + log [A-]/[HA]

Formula of : molarity , molality , weight percent, mass percent, ppm, ppb?

Molarity: moles solute/liters solution

Molality: moles solute/ kg solvent

Weight percent : mass solute/ mass solution x 100

Ppm : mass solute/ volume solution

Ppb : mass solute/ volume solution