Topic 2 - Acids bases and salts

Acids

release H+ ions

Base

Absorb H+ ions

Alkali

A soluble base

Common Acids

Sulfuric acid, acetic acid or ethanoic acid, citric acid

Sulfuric Acid

H2SO4 (Strong Acid)

Ethanoic acid

CH3COOH (weak acid)

citric acid

C6H8O7 (weak acid)

pH indicator

litmus

Nuetral colour

Green

nuetral number

7

Acid colour

red

Acid number

0-6

Alkali colour

blue

alkali number

8 -14

Nuetralization

When an acid and alkali to make a neutral substance/ salt

Nuetralization: hydrogen and hydroxide ions

Makes water

H+(aq) + OH-(aq) ---> H2O(l)

Acid with metal

acid + metal --> salt + hydrogen gas

Acid with base

Metal oxide + acid --> salt + water

Acid with alkali

Matal hydroxide + acid --> salt + water

Acid with metal carbonate

acid + metal carbonate → salt + water + carbon dioxide

Crystallization method

1. Add excess base to make sure all acid has reacted

2. Filter out excess base

3. Water evaporates and leaves crystals behind

Large crystals

Water evaporated slowly by a widow over a few days

Small crystals

Heat until 1/3 of solution remains then leave rest to cool naturally

Titration

process in which a solution of known concentration is used to determine the concentration of another solution

Titration method

1-Use the pipette to add 25 cm3 of alkali to a conical flask and add a few drops of indicator.

2- Fill the burette with acid and note the starting volume. Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.

3- Stop adding the acid when the end-point is reached (the appropriate colour change in the indicator happens). Note the final volume reading.

4-Repeat steps 1 to 3 until you get consistent readings.

Titre

Difference between first and final reading

Adding acid to alkali (graph)

Downward graph

Addiding alkali to acid graph

Upward graph

Consentration

Number of moles per dm³

Titration Calculations

1. Convert all volumes to dm³ (÷1000)

2. Calculate number of moles of the substance and consentration are known (numberof moles = concentration × volume)

3. Calculate unknown concentration (concentration = number of moles ÷ volume)

Strong acids ionise in water

completely

Weak acids ionise in water

Not completely

precipitates

What is the charge of an atom with more electrons than protons?

Negative charge

What is the charge of an atom with more protons than electrons?

Positive charge

What is the electronic configuration equation for energy transitions?

ΔE = E2 - E1 = hν = hc/λ

What techniques are based on electron transitions?

Absorption and Emission spectroscopy (AAS + GFAAS), ICP AES, XRF

What is the significance of the octet rule in chemical bonding?

Atoms achieve stability by having eight electrons in their outer shell.

What type of bonding involves the transfer of electrons?

Ionic bonding

What type of bonding involves the sharing of electrons?

Covalent bonding

What is a single covalent bond represented by?

A single line indicating two electrons are shared.

What is the valency of zinc (Zn)?

+2 (can give up 2 electrons)

What is the valency of chlorine (Cl)?

-1 (can acquire an electron)

What is a Lewis structure?

A representation of molecules showing valence electrons as dots.

What is a pi bond?

A bond formed by the overlap of p orbitals, perpendicular to sigma bonds.

What is a sigma bond?

A single covalent bond formed by the direct overlap of atomic orbitals.

How do atoms achieve an octet?

By transferring or sharing electrons.

What is the result of ionic bonding?

Formation of ions held together by electrostatic forces.

What do Lewis symbols represent?

Valence electrons in the outer shell of an atom.

What is the role of molecular orbitals in spectroscopy?

Illustrate electron distribution in molecules.

What is the combining behavior of elements called?

Valency

What is the formula for sodium chloride?

NaCl (formed from Na+ and Cl- ions)

What does a higher intensity of color in a sigma bond indicate?

Greater probability of bonding electrons being localized between nuclei.

What is the significance of valence electrons?

They are involved in the formation of chemical bonds.

What is the difference between equal and unequal sharing of electrons in covalent bonds?

Equal sharing results in nonpolar covalent bonds; unequal sharing leads to polar covalent bonds.

What are the types of covalent bonds?

Single, double, and triple covalent bonds.

Which bond type has the longest bond length?

Single covalent bonds.

Which bond type has the shortest bond length?

Triple covalent bonds.

What is the bond strength order from weakest to strongest?

Single < Double < Triple.

What is an isolated double bond?

A double bond separated by more than one single bond.

What is a conjugated double bond?

A structure where single and double bonds alternate, allowing delocalized electrons.

What characterizes a cumulated double bond?

Two bonds on one carbon atom.

Define a cyclic compound.

A compound where at least some atoms are connected to form a ring.

What are aromatic compounds?

Hydrocarbons containing benzene or related ring structures.

What is a heterocyclic compound?

A ring structure containing at least one carbon atom and one other element (e.g., N, O, S).

What is UV-Vis absorption spectroscopy?

A technique where UV and visible light are absorbed by electrons in molecules, dependent on molecular structure.

What type of electrons are generally involved in UV-Vis absorption?

π-electrons within π-bonds.

How does the number of conjugated double bonds affect absorption wavelength?

Molecules with more conjugated double bonds absorb at longer wavelengths (lower energy).

What is the Beer-Lambert Law?

A relationship that relates the amount of light absorbed to the concentration and thickness of the sample.

What is the formula for absorbance (A) in the Beer-Lambert Law?

A = -log10(T), where T is transmittance.

What does the extinction coefficient (ε) measure?

How strongly a substance absorbs light at a particular wavelength.

What is the typical range of a UV-Vis spectrophotometer?

Approximately 200 - 800 nm.

What is the visible light range in terms of wavelength?

380 - 700 nm.

What is the significance of molecular orbitals in spectroscopy?

They illustrate electron distribution in molecules, allowing for more transitions than in atoms.

What is the relationship between light intensity (Io) and sample presence (It)?

Io is the intensity without the sample, and It is the intensity with the sample.

What happens to the energy of absorbed light as the wavelength increases?

The energy decreases as wavelength increases.

What is the formula for calculating transmittance (T)?

T = (It / Io) * 100.

What is the impact of delocalization on the color of a compound?

Increased delocalization can shift absorption into the visible spectrum, making the compound colored.

What is an example of a colored compound due to delocalization?

Beta-carotene, which is present in carrots.