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3 years ago

How many molecules are equal to 10.35 g of pyridine?

Chemistry

1 answer:

Lera25 [3.4K]3 years ago

7 0

Answer:

0.78× 10 ²³ molecules

Explanation:

Given data:

Mass of pyridine = 10.35 g

Number of molecules = ?

Solution:

Number of moles of pyridine:

Number of moles = mass/molar mass

Number of moles = 10.35 g/ 79.1 g/mol

Number of moles = 0.13 mol

Number of molecules;

1 mole contain 6.022× 10 ²³ molecules

0.13 mol × 6.022× 10 ²³ molecules / 1mol

0.78× 10 ²³ molecules

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Alex777 [14]

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3 sig. fig. as in the mass of formic acid.

<h3>Explanation</h3>

How many moles of formic acid?

Relative atomic mass from a modern periodic table:

H- 1.008,
C- 12.011, and
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Molar mass of formic acid $\text{HCOOH}$ :

$1.008 + 12.011 + 2\times 15.999 + 1.008 = 46.025\;\text{g}\cdot \text{mol}^{-1}$ .

Number of moles of formic acid molecules in the 0.0634 gram sample:

$\displaystyle n = \frac{m}{M} = \frac{0.0634}{46.025} = 1.37751\times 10^{-3}\;\text{mol}$ .

Keep at least one extra sig. fig. to avoid rounding errors.

How many moles of NaOH?

It takes one $\text{OH}^{-}$ ion to neutralize each carbonyl group $-\text{COOH}$ .

There's one carbonyl group in each formic acid $\text{H-}\text{COOH}$ molecule. Each formula unit of NaOH supplies one $\text{OH}^{-}$ ion. As a result, it takes one mole formula units of NaOH to neutralize one mole formic acid molecules.

There are $1.37751\times 10^{-3}\;\text{mol}$ of formic acid in the volumetric flask. It will take the same number of NaOH formula units to reach the equivalence point.

How many liters of NaOH?

$\displaystyle V = \frac{n}{c} = \frac{1.37751\times 10^{-3}\;\text{mol}}{0.1800\;\text{M}}= \frac{1.37751\times 10^{-3}\;\text{mol}}{0.1800\;\text{mol}\cdot\text{L}^{-1}} = 7.65\times 10^{-3}\;\text{L}$ .

How many significant figures?

Number of sig. fig. in data involved in the calculation:

3 in the mass of the formic acid,
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Take the least number of sig. fig. as the number of sig. fig. in the answer. As a result, the volume of NaOH should be rounded to three sig. fig.

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