Why can 2-amino acids act as both acids and bases in solution?

They contain both a carboxylic acid group (which can donate a proton) and an amine group (which can accept a proton).

What is a zwitterion?

A molecule with both a positive and a negative charge on different atoms, such as an amino acid with a protonated amine group (-NH₃⁺) and a deprotonated carboxylic acid group (-COO⁻).

Why do aqueous solutions of most 2-amino acids rotate the plane of plane-polarised light?

Because they contain a chiral carbon atom (the alpha carbon with four different groups attached).

Edexcel A-Level Chemistry 9CH0

Atomic Structure and the Periodic Table

Topic overview Protons, neutrons, electrons and isotopes Relative atomic mass and the mass spectrum Ionisation energy and the evidence for sub-shells Orbitals and electron configuration Periodicity across a period and down a group

Bonding and Structure

Topic overview Ionic bonding Covalent bonding, dative bonding and the shapes of molecules Electronegativity, polarity and intermolecular forces Structure and properties

Redox I

Topic overview Oxidation numbers Oxidation, reduction, disproportionation and half-equations

Inorganic Chemistry and the Periodic Table

Topic overview Flame tests and how they work Thermal decomposition of nitrates and carbonates Carrying out flame tests and testing the gases Group 2 elements and their compounds Trends in Group 7 and predicting fluorine and astatine Halogen displacement reactions Disproportionation and the reactions of chlorine Halides with concentrated sulfuric acid, and the hydrogen halides Testing for halide ions with silver nitrate Testing for carbonate and hydrogencarbonate ions Testing for sulfate and ammonium ions

Formulae, Equations and Amounts of Substance

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Organic Chemistry I

Topic overview Formulae, homologous series and functional groups IUPAC nomenclature Types of organic reaction and structural isomerism Stereoisomerism and E/Z nomenclature Practical techniques in organic chemistry Alkanes, crude oil and combustion pollutants Radical substitution Alkenes, the double bond and hydrogenation Electrophilic addition, Markovnikov's rule and the test for an alkene Addition polymers and waste polymers Nucleophilic substitution of halogenoalkanes Rates of hydrolysis and the SN1 and SN2 mechanisms Classifying and oxidising alcohols Alcohols: practical techniques and the core practicals

Modern Analytical Techniques I

Topic overview Mass spectrometry Infrared spectroscopy and the characteristic absorptions Deducing functional groups from an infrared spectrum

Energetics I

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Kinetics I

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Equilibrium I

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Acid-Base Equilibria

Topic overview Bronsted-Lowry acids and bases, and the pH scale Strong and weak acids, Ka and Kw Calculating pH, and titration curves Buffer solutions and the Henderson-Hasselbalch equation Buffers in blood, and the core practical

Energetics II

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Redox II

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Transition Metals

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Kinetics II

Topic overview Rate equations, orders and the rate constant Determining orders from experiments Rate-determining step and mechanisms Arrhenius equation and activation energy

Organic Chemistry II

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Organic Chemistry III

Topic overview The structure of benzene and the evidence for it Electrophilic substitution of benzene Nitration, halogenation, Friedel-Crafts and phenol Amines: structure and basicity Reactions of amines and preparing them Amides and condensation polymers Amino acids, zwitterions and proteins Empirical and molecular formulae from analytical data Grignard reagents and multi-step synthesis Purification techniques and the aspirin preparation

Modern Analytical Techniques II

Topic overview Carbon-13 and proton NMR Splitting, integration and the reference standard Chromatography High-resolution mass spectrometry

Organic Chemistry III

Amino acids, zwitterions and proteins

3 things to know
Papers 2 and 3

Overview

Peptide bonds and condensation to polypeptides, 2-amino acids acting as acids and bases, zwitterions, why most amino acids are optically active but glycine is not, and hydrolysing a protein and separating its amino acids by chromatography.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

How does an amino acid behave in acid and in alkali?

Key term

What type of bond links amino acid residues together in a polypeptide?

Key term

Which amino acid does not rotate plane-polarised light, and why?

Questions from this subtopic

Each one with the model answer underneath.

1
What type of bond links amino acid residues together in a polypeptide?
Model answer
Peptide bonds (-CONH-).
2
What type of polymerisation do amino acids undergo to form polypeptides?
Model answer
Condensation polymerisation.
3
Why can 2-amino acids act as both acids and bases in solution?
Model answer
They contain both a carboxylic acid group (which can donate a proton) and an amine group (which can accept a proton).
4
What is a zwitterion?
Model answer
A molecule with both a positive and a negative charge on different atoms, such as an amino acid with a protonated amine group (-NH₃⁺) and a deprotonated carboxylic acid group (-COO⁻).
5
In what form do 2-amino acids predominantly exist in aqueous solution?
Model answer
As zwitterions.
6
Why do aqueous solutions of most 2-amino acids rotate the plane of plane-polarised light?
Model answer
Because they contain a chiral carbon atom (the alpha carbon with four different groups attached).

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Atomic Structure and the Periodic Table

Bonding and Structure

Redox I

Inorganic Chemistry and the Periodic Table

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AAtomisation turns each element into gaseous atoms.

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Amino acids, zwitterions and proteins

Overview

What you need to know

How does an amino acid behave in acid and in alkali?

What type of bond links amino acid residues together in a polypeptide?

Which amino acid does not rotate plane-polarised light, and why?

Questions from this subtopic

What type of bond links amino acid residues together in a polypeptide?

What type of polymerisation do amino acids undergo to form polypeptides?

Why can 2-amino acids act as both acids and bases in solution?

What is a zwitterion?

In what form do 2-amino acids predominantly exist in aqueous solution?

Why do aqueous solutions of most 2-amino acids rotate the plane of plane-polarised light?

Other ways to work this

What is inside Levo

The 3-step method, run for you

Cram a whole paper in one sitting

Blank Blitz makes facts automatic

Build It gets the exam shape right

Test It catches misconceptions

Brain Breaks between sessions

Every question in Organic Chemistry III, on a schedule.