CHEM1112 Lecture Notes - Lecture 9: Bromothymol Blue, Methyl Orange, Semimetal

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17 May 2018
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Titrations
Equivalence point: Number of moles of added base= original number of moles of acid
SA+SB= 7
WA+SB>7
SA+SB<7
End point: when colour change observed, indicator chosen that changes color close to equivalence
point. Methyl orange: 3.2-4.4, methyl purple 4.8-5.6, bromothymol blue 6-7.6, phenolphthalein
8.2-10
Recognise trends in the periodic table and the correlation between the trends in atomic radii,
ionization energies and electronegativity
Atomic radii: inc. from top> bottom of group, dec. from left> right (e/e repulsion). Electron
movement, inc effective nuclear charge= size radii decrease, across period. Increase down group=
inc. principal quantum number, n. increase shell size. Electrons in inner shells shield nuclear
charge. Core charge= number protons- number core elctrons eg: effectiveZ(Li)= 3-2=1
Ionisation energy: inc. left>right, dec. up > down.
Electronegativity: tendency of atom to attract electrons towards itself, dec. with atomic size.
Pure elements: metallic bonding> covalent > semimetals
Predict reactivity based on trends, particularly how the acid, base or amphoteric character of an
element's oxide and hydroxide are related to its position in the periodic table
Oxides and hydroxides: non metal oxides= acidic, covalent bonds to oxygen due to low
electronegativity difference. Dissolve in basic solutions to form salt + H2O . Semimetal oxides-
amphoteric, electronegativity between metal and non-metal.
List the types of intermolecular forces and their relative strengths
More polarised H-X = stonger acid. Inc. electronegativity& acidity & inc bond length= inc acidity.
Identify the intermolecular forces and their relative forces
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Document Summary

Titrations, equivalence point: number of moles of added base= original number of moles of acid. Sa+sb<7: end point: when colour change observed, indicator chosen that changes color close to equivalence point. Methyl orange: 3. 2-4. 4, methyl purple 4. 8-5. 6, bromothymol blue 6-7. 6, phenolphthalein. 8. 2-10: recognise trends in the periodic table and the correlation between the trends in atomic radii, ionization energies and electronegativity, atomic radii: inc. from top> bottom of group, dec. from left> right (e/e repulsion). Electron movement, inc effective nuclear charge= size radii decrease, across period. Increase down group= inc. principal quantum number, n. increase shell size. Core charge= number protons- number core elctrons eg: effectivez(li)= 3-2=1. Dissolve in basic solutions to form salt + h2o . Semimetal oxides- amphoteric, electronegativity between metal and non-metal. List the types of intermolecular forces and their relative strengths: more polarised h-x = stonger acid. Inc. electronegativity& acidity & inc bond length= inc acidity. Identify the intermolecular forces and their relative forces.

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