Asample of hydrogen (h2) gas is collected over water at 35oc and 725 mm. the volume of the gas collected is 72.0 ml. how many moles of h2 gas has been collected? how many grams of h2 gas has been collected?

2.56 × 10⁻³ mol

5.17 × 10⁻³ g

Explanation:

Given data

Temperature = 35°C + 273 = 308 K

Pressure = 725 mmHg

Volume = 72.0 mL = 0.0720 L

The vapor pressure of water at 35°C is 42.20 mmHg. The total pressure is equal to the sum of the partial pressures.

P = pH₂ + pH₂O

pH₂ = P - pH₂O = 725 mmHg - 42.20 mmHg = 683 mmHg

pH₂ = 683 mmHg × (1 atm / 760 mmHg) = 0.899 atm

We can find the moles of H₂ using the ideal gas equation.

P × V = n × R × T

0.899 atm × 0.0720 L = n × (0.08206 atm.L/mol.K) × 308 K

n = 2.56 × 10⁻³ mol

The molar mass of H₂ is 2.02 g/mol. The mass of H₂ is:

2.56 × 10⁻³ mol × 2.02 g/mol = 5.17 × 10⁻³ g

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answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.