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3 years ago

5

What are periods on the periodic table? How many are there?

1 answer:

Brums [2.3K]3 years ago

8 0

A period is a horizontal row of the periodic table. There are seven periods in the periodic table, with each one beginning at the far left. A new period begins when a new principal energy level begins filling with electrons. Period 1 has only two elements (hydrogen and helium), while periods 2 and 3 have 8 elements.

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Which law represents a balanced chemical equation?

Montano1993 [528]

Answer:

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3 years ago

The pH of a 0.78M solution of 4-pyridinecarboxylic acid HC6H4NO2is measured to be 2.53.Calculate the acid dissociation constant

nika2105 [10]

Answer : The value of acid dissociation constant is, $1.1\times 10^{-5}$

Solution : Given,

Concentration pyridinecarboxylic acid = 0.78 M

pH = 2.53

First we have to calculate the hydrogen ion concentration.

$pH=-\log [H^+]$

$2.53=-\log [H^+]$

$[H^+]=2.95\times 106{-3}M$

Now we have to calculate the acid dissociation constant.

The equilibrium reaction for dissociation of (weak acid) is,

$HC_6H_4NO_2\rightleftharpoons C_6H_4NO_2^-+H^+$

initially conc. 0.78 0 0

At eqm. (0.78-x) x x

The expression of acid dissociation constant for acid is:

$k_a=\frac{[C_6H_4NO_2^-][H^+]}{[C_6H_4NO_2]}$

As, $[H^+]=[C_6H_4NO_2^-]=x$

So, $x=2.95\times 106{-3}M$

Now put all the given values in this formula ,we get:

$k_a=\frac{(x)\times (x)}{(0.78-x)}$

$k_a=\frac{(2.95\times 106{-3})\times (2.95\times 106{-3})}{(0.78-2.95\times 106{-3})}$

$K_a=1.1\times 10^{-5}$

Therefore, the value of acid dissociation constant is, $1.1\times 10^{-5}$

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