Final answer:
To find the Henry's law constant for helium, divide the solubility of helium (7.0 × 10⁻⁵ M) by the partial pressure (0.20 atm).
Step-by-step explanation:
The question asks us to determine the Henry's law constant (K) for helium (He) in water given the solubility of He at a certain temperature and pressure. According to Henry's law, the solubility of a gas in a liquid at a particular temperature is proportional to the partial pressure of that gas above the liquid. The proportionality constant is the Henry's law constant. Thus, the law can be represented as S = kP, where S is the solubility, k is Henry's law constant, and P is the partial pressure.
To find the Henry's law constant for He, we use the given values: the solubility (S) is 7.0 × 10⁻⁵ M and the partial pressure (P) is 0.20 atm. By rearranging the equation to k = S/P, and substituting the given values, we find that k = (7.0 × 10⁻⁵ M) / (0.20 atm), which gives us the Henry's law constant for helium in water at 25 °C.