A substance undergoes a change. Which of the following indicates that the change was a chemical change?

Combustion analysis of a 13.42-g sample of the unknown organic compound (which contains only carbon, hydrogen, and oxygen) produ

kirza4 [7]

Answer: The molecular formula for the given organic compound is $C_{18}H_{20}O_2$

Explanation:

The chemical equation for the combustion of hydrocarbon having carbon, hydrogen and oxygen follows:

$C_xH_yO_z+O_2\rightarrow CO_2+H_2O$

where, 'x', 'y' and 'z' are the subscripts of Carbon, hydrogen and oxygen respectively.

We are given:

Mass of $CO_2=39.61g$

Mass of $H_2O=9.01g$

We know that:

Molar mass of carbon dioxide = 44 g/mol

Molar mass of water = 18 g/mol

For calculating the mass of carbon:

In 44 g of carbon dioxide, 12 g of carbon is contained.

So, in 39.61 g of carbon dioxide, $\frac{12}{44}\times 39.61=10.80g$ of carbon will be contained.

For calculating the mass of hydrogen:

In 18 g of water, 2 g of hydrogen is contained.

So, in 9.01 g of water, $\frac{2}{18}\times 9.01=1.00g$ of hydrogen will be contained.

Mass of oxygen in the compound = (13.42) - (10.80 + 1.00) = 1.62 g

To formulate the empirical formula, we need to follow some steps:

Step 1: Converting the given masses into moles.

Moles of Carbon = $\frac{\text{Given mass of Carbon}}{\text{Molar mass of Carbon}}=\frac{10.80g}{12g/mole}=0.9moles$

Moles of Hydrogen = $\frac{\text{Given mass of Hydrogen}}{\text{Molar mass of Hydrogen}}=\frac{1g}{1g/mole}=1moles$

Moles of Oxygen = $\frac{\text{Given mass of oxygen}}{\text{Molar mass of oxygen}}=\frac{1.62g}{16g/mole}=0.10moles$

Step 2: Calculating the mole ratio of the given elements.

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 0.10 moles.

For Carbon = $\frac{0.9}{0.10}=9$

For Hydrogen = $\frac{1}{0.10}=10$

For Oxygen = $\frac{0.10}{0.10}=1$

Step 3: Taking the mole ratio as their subscripts.

The ratio of C : H : O = 9 : 10 : 1

Hence, the empirical formula for the given compound is $C_9H_{10}O$

For determining the molecular formula, we need to determine the valency which is multiplied by each element to get the molecular formula.

The equation used to calculate the valency is :

$n=\frac{\text{Molecular mass}}{\text{Empirical mass}}$

We are given:

Mass of molecular formula = 268.34 g/mol

Mass of empirical formula = 134 g/mol

Putting values in above equation, we get:

$n=\frac{268.34g/mol}{134g/mol}=2$

Multiplying this valency by the subscript of every element of empirical formula, we get:

$C_{(9\times 2)}H_{(10\times 2)}O_{(1\times 2)}=C_{18}H_{20}O_2$

Thus, the molecular formula for the given organic compound is $C_{18}H_{20}O_2$ .

3 0

3 years ago

What is the Gibbs energy, LaTeX: \Delta GΔ G, when the very first crystal of potassium nitrate forms in solution while cooling,

VARVARA [1.3K]

Answer:

74.344 kJ.

Explanation:

Below is an attachment containing the solution.

3 0

4 years ago

What is the pH of a solution with a 3.8 × 10−4 M hydronium ion concentration?

mamaluj [8]

Answer:

3.4

Explanation:

The pH scale is used to express the acidity or basicity of a solution.

If the pH < 7, the solution is acid.

If the pH = 7, the solution is neutral.

If the pH > 7, the solution is basic.

Given the hydronium ion concentration [H₃O⁺] = 3.8 × 10⁻⁴ M, we can calculate the pH using the following expression.

pH = -log [H₃O⁺]

pH = -log 3.8 × 10⁻⁴

pH = 3.4

This solution is acid.

8 0

3 years ago

Calculate the volume of 150kg of chlorine gas at room temperature and pressure. The volume of one mole of gas at room temperatur

Tom [10]

Answer:

thats now easyyy....................❤.you have to be genuine

Explanation:

gghggg

plssss

6 0

3 years ago

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Compared to most substances, water is unusual because it ____ when it goes from the liquid to solid state.

yuradex [85]

Answer:

expands

Explanation:

Most substances become increasingly compressed when frozen solid, but water is a famous exception.

6 0

3 years ago

Read 2 more answers