Competizione a squadre – Manche 1

An organic compound consisting of carbon, hydrogen, and oxygen has given the following results: C = 63.12%, H = 8.85% and O = 28.03%. Determine which of the following is the minimum formula of the compound.

• C3H5O

• C7HO3

• CHO

• CHO2

Indicate the mass in grams of 12.6 mmol of Ca(OH)2 (MM = 74.093 g/mol) considering the correct number of significant figures:

• 0.934 g

• 0.93357 g

• 933.6 g

• 0.9336 g

The isotopes of neon 20Ne and 22Ne differ by:

• Two neutrons

• One proton and one electron

• One proton and one neutron

• Two protons

Indicate how many atoms are present in a mole of gaseous molecular nitrogen.

• 1.204 × 10^24

• 6.022 × 10^23

• 3.011 × 10^23

• 4.818 × 10^24

The triplicate analysis of a sample of a mineral containing copper provides the following concentration values expressed in % of Cu: 24.87%, 24.93%, 24.69%. What is the absolute error:

• 0.23%

• 0.70%

• 0.15%

• None of the other answers

In column chromatography on alumina, using n-hexane as the eluent, predict the likely order of elution of the following compounds: butanol, isobutyl chloride, n-octane.

• n-Octane, isobutyl chloride, butanol

• Butanol, isobutyl chloride, n-octane

• Isobutyl chloride, n-octane, butanol

• It is not possible to predict the order of elution

State the correct combination of stoichiometric coefficients for the following combustion reaction: C5H12 + O2 → CO2 + H2O

• 1, 8, 5, 6

• 1, 6, 5, 6

• 1, 8, 6, 5

• 1, 5, 6, 5

The infrared (IR) spectrum of 2-propanone is recorded. Indicate at what wave number the C=O stretching band will be positioned:

• 1700 cm-1

• 1200 cm-1

• 3200 cm-1

• 900 cm-1

What is the definition of chromatographic resolution?

• The distance between two resolved peaks in a chromatogram

• The limit of detectability based on the detector used

• The number of theoretical plates

• The operator's injection capacity

Indicate which acid/base pair of H3PO4 is advisable to use if one wants to prepare a buffer solution at pH = 7.4 (pKa1 = 2.1, pKa2 = 7.2, pKa3 = 12.3):

• H2PO4−/HPO42−

• H3PO4/H2PO4−

• HPO42−/PO43−

• H3PO4/HPO42−