3 years ago

How many significant figures in 4300 ?

Chemistry

1 answer:

sammy [17]3 years ago

7 0

Answer:

Four significant figures

Explanation:

The number of significant figures is defined as the number of digits that can be assumed to be correct, starting at the left with the first nonzero digit, and proceeding to the right.

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What is the pH of a 900 mL solution containing 3.40 grams of hydrocyanic acid

Allushta [10]

Answer:

$pH = 5.05$

Explanation:

pH is derived from the concentration of hydronium ions in a solution. Hydrocyanic acid is HCN.

First, we shall figure out the moles of HCN:

$\frac{3.4g}{27.03g/mol} = 0.125786$

If HCN was a strong acid:

HCN has a 1:1 ratio of H+ ions, the moles of H+ is also the same.

To find the molarity, we now divide by Liters. This gets us:

$\frac{0.125786 moles}{0.9L} = 0.139762 M$

Finally, we plug it into the definition of pH:

$pH = -log[H^{+} ]$

$pH = -log(0.139762)$

$pH = 0.855$

However, since HCN is a weak acid, it only partially dissociates. The $K_a$ of HCN is $6.2 * 10^{-10}$ .

$K_a = \frac{[H^+][A^-]}{[HA]}$

We can use an ice table to determine that when x = H+,

$K_a = \frac{x^2}{0.125786-x}$

$[H^+] = 8.83*10^{-6}$

$pH = -log[H^{+} ]$

$pH = -log(8.83 * 10^{-6} )$

$pH = 5.05$

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