You have a powder that dissolves in water to form a strong acid. You dissolve 2g of the powder in 100ml of water, and measure the pH to be 4. You would like to form 100ml of a solution with pH 5. How many grams of the powder do you dissolve in 100ml of water?

The mass of the powder to dissolve in 100ml of water to form a solution with pH 5 is 0.2 g

Explanation:

pH = -Log [H⁺]

when the pH of the solution = 4,

the concentration is calculated as follows

10⁻⁴ = [H⁺] = 1 X 10⁻⁴ M/L

when the pH of the solution = 5,

10⁻⁵ = [H⁺] = 1 X 10⁻⁵ M/L

Also concentration, = number of moles/liters of solution

number of moles = Reacting mass (Rm)/Molar mass

Concentration is directly proportional to reacting mass

Thus, C₁/Rm₁ = C₂/Rm₂

Rm₂ = (C₂Rm₁)/C₁

Rm₂ = (1 X 10⁻⁵ * 2g)/(1 X 10⁻⁴)

Rm₂ = 0.2 g

Therefore, the mass of the powder to dissolve in 100ml of water to form a solution with pH 5 is 0.2 g

in the given question, the partial pressure is calculated by using the ideal gas equation, that is, pv = nrt

here, p is pressure, v is volume = 25 l, n is number of moles = 0.0104 moles, r is gas constant = -0.0821 l.atm / mol.k

t is temperature = 273 k

p = nrt / v

p = (0.0104 mol × 0.0821 l.atm / mol.k × 273 k) / 25 l

= 0.0093 atm