Solve and Explain (BIOCHEMISTRY) A sample of pure water is heated to a temperatu

Question

Solve and Explain (BIOCHEMISTRY)

A sample of pure water is heated to a temperature of 112 C at a pressure of 20 MPa, where the ionization constant for water is 4.0 times 10-12 What is the OH- concentration in the pure water at these conditions? Show your work. Assume that 100 mM HCl is added to a sample of pure water at the conditions (pressure of 20 MPa and a temperature of 112 C) described in part (a). Which of these choices is closest to the pH of the sample? Circle one best choice. When pure water is heated at atmosphere pressure, its ionization constant (Kw) will: increase decrease stay the same

Explanation / Answer

1. Ionization constant for water is Kw = 4.0 * 10-12

For pure water,the [H+] ions concentration will be same as [OH-] ions concentration

so, it becomes [ H+ ] = [ OH- ]

Since Kw = Product of [H+] and [OH-] ions concentrations it becomes

4.0 * 10-12 = [ H+ ] [ OH- ]

= [ OH - ]2

Thus, [ OH-] = sqrroot ( 4.0 * 10-12 ) = 2.0 * 10-6

2.

When 100mM of HCl sample is added, the pH would depend upon the amount added,

Let us assume 1 ml was added,

then amount of HCl remaining = 1.0 * 10-4 - 2.0 * 10-6

= 9.8 * 10-5

pH = 4.008 ( indicating acidic nature )

So, pH - 4 is best

3. when pure water is heated at atmospheric pressure ( at 100degrees Celsius) then ionization constant will be increased

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