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Chemistry: Environmental Systems - Miller-Urey Experiment and the Origins of Life

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Miller-Urey experiment (1952) was designed to test the Oparin-Haldane hypothesis, which suggested that life on Earth began in a 'primordial soup' of organic molecules.

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The experiment simulated the conditions of Earth's early atmosphere, which was a reducing atmosphere containing gases like methane (CH4CH_4), ammonia (NH3NH_3), hydrogen (H2H_2), and water vapor (H2OH_2O).

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A crucial aspect of the experiment was the absence of free oxygen (O2O_2), as oxygen is highly reactive and would have prevented the formation of complex organic molecules through oxidation.

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Energy was provided to the system in the form of electrical sparks, which simulated lightning strikes common in the early atmosphere.

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The apparatus included a boiling flask to produce water vapor, an electrode chamber for the spark, and a condenser to cool the gases back into liquid form (simulating rain).

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After one week, the experiment produced several organic compounds, including amino acids like glycine and alanine, which are the building blocks of proteins.

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This demonstrated that the synthesis of organic 'pre-life' molecules from inorganic precursors is possible under specific environmental conditions.

📐Formulae

CH4+NH3+H2+H2O→Electrical DischargeAmino AcidsCH_4 + NH_3 + H_2 + H_2O \xrightarrow{\text{Electrical Discharge}} \text{Amino Acids}

NH2−CH(R)−COOH (General structure of an amino acid)NH_2-CH(R)-COOH \text{ (General structure of an amino acid)}

2H2+O2→2H2O (Formation of water vapor used in the cycle)2H_2 + O_2 \rightarrow 2H_2O \text{ (Formation of water vapor used in the cycle)}

💡Examples

Problem 1:

Identify the four primary gases used in the Miller-Urey experiment to simulate the early atmosphere and explain why O2O_2 was omitted.

Solution:

The four gases used were methane (CH4CH_4), ammonia (NH3NH_3), hydrogen (H2H_2), and water vapor (H2OH_2O). Free oxygen (O2O_2) was omitted because the early Earth had a reducing atmosphere; the presence of O2O_2 would have caused oxidation, breaking down the organic molecules as soon as they formed.

Explanation:

The experiment aimed to recreate the conditions before photosynthesis evolved, where the lack of O2O_2 allowed for the accumulation of complex carbon-based molecules.

Problem 2:

In the context of the Miller-Urey apparatus, what was the purpose of the condenser and which natural process did it represent?

Solution:

The condenser cooled the heated gas mixture, turning the water vapor back into liquid water. This represented the natural process of condensation and precipitation (rain).

Explanation:

This step was necessary to collect the newly formed organic molecules in the 'ocean' (the trap at the bottom of the apparatus) so they could be analyzed.

Problem 3:

Calculate the molar mass of the simplest amino acid produced, Glycine (C2H5NO2C_2H_5NO_2), given the following atomic masses: C=12C = 12, H=1H = 1, N=14N = 14, O=16O = 16.

Solution:

(2×12)+(5×1)+(1×14)+(2×16)24+5+14+3275 g/mol\begin{array}{r} (2 \times 12) + (5 \times 1) + (1 \times 14) + (2 \times 16) \\ 24 + 5 + 14 + 32 \\ \hline 75 \text{ g/mol} \end{array}

Explanation:

To find the molar mass, we sum the products of the number of atoms of each element and their respective atomic masses.