1 Define a Compound 7.2 Calculate the percentage of chromium in K2Cr2O7. 7.3 An inorganic substance was…

Question

1 Define a Compound 7.2 Calculate the percentage of chromium in K2Cr2O7. 7.3 An inorganic substance was analysed and found to be containing 65,31% of oxygen, 32,65% of Sulphur and 2,04% of hydrogen. 7.3.1 Define an empirical formula. 7.3.2 Determine the empirical formula for the compound.

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7.1. A compound is a substance formed when two or more different chemical elements are chemically bonded together in a fixed ratio.

7.2. To calculate the percentage of chromium in K₂Cr₂O₇:

Determine the molar mass of K₂Cr₂O₇.
The atomic masses are approximately: K = $39.10 \text{ g/mol}$ , Cr = $52.00 \text{ g/mol}$ , O = $16.00 \text{ g/mol}$ .
$\text{Molar mass of K}_2\text{Cr}_2\text{O}_7 = (2 \times 39.10) + (2 \times 52.00) + (7 \times 16.00)$ $= 78.20 + 104.00 + 112.00$ $= 294.20 \text{ g/mol}$
Calculate the total mass of chromium in one mole of K₂Cr₂O₇.
$\text{Mass of Cr} = 2 \times 52.00 \text{ g/mol} = 104.00 \text{ g/mol}$
Calculate the percentage of chromium.
$\text{Percentage of Cr} = \frac{\text{Mass of Cr}}{\text{Molar mass of K}_2\text{Cr}_2\text{O}_7} \times 100\%$ $= \frac{104.00 \text{ g/mol}}{294.20 \text{ g/mol}} \times 100\%$ $= 35.35\%$
The percentage of chromium in K₂Cr₂O₇ is \boxed{\text{35.35%}}.

7.3.1. An empirical formula shows the simplest whole-number ratio of atoms of each element in a compound.

7.3.2. To determine the empirical formula for the compound:
Assume a $100 \text{ g}$ sample and convert percentages to masses.
- Mass of Oxygen (O) = $65.31 \text{ g}$
- Mass of Sulphur (S) = $32.65 \text{ g}$
- Mass of Hydrogen (H) = $2.04 \text{ g}$
Convert the mass of each element to moles using their atomic masses (O = $16.00 \text{ g/mol}$ , S = $32.07 \text{ g/mol}$ , H = $1.01 \text{ g/mol}$ ).
$\text{Moles of O} = \frac{65.31 \text{ g}}{16.00 \text{ g/mol}} = 4.08 \text{ mol}$ $\text{Moles of S} = \frac{32.65 \text{ g}}{32.07 \text{ g/mol}} = 1.02 \text{ mol}$ $\text{Moles of H} = \frac{2.04 \text{ g}}{1.01 \text{ g/mol}} = 2.02 \text{ mol}$
Divide each mole value by the smallest number of moles to find the simplest ratio.
The smallest number of moles is $1.02 \text{ mol}$ (for Sulphur).
$\text{Ratio for O} = \frac{4.08}{1.02} \approx 4$ $\text{Ratio for S} = \frac{1.02}{1.02} = 1$ $\text{Ratio for H} = \frac{2.02}{1.02} \approx 2$
Write the empirical formula using these whole-number ratios.
The empirical formula is $\boxed{\text{H}_2\text{SO}_4}$ .

1 Define a Compound 7.2 Calculate the percentage of chromium in K2Cr2O7. 7.3 An inorganic substance was analysed and found to be containing 65,31% of oxygen, 32,65% of Sulphur and 2,04% of hydrogen. 7.3.1 Define an empirical formula. 7.3.2 Determine the empirical formula for the compound.

Answer

Step-by-step solution

Determine the molar mass of K₂Cr₂O₇.

Calculate the total mass of chromium in one mole of K₂Cr₂O₇.

Calculate the percentage of chromium.

Assume a $100 \text{ g}$ sample and convert percentages to masses.

Convert the mass of each element to moles using their atomic masses (O = $16.00 \text{ g/mol}$ , S = $32.07 \text{ g/mol}$ , H = $1.01 \text{ g/mol}$ ).

Divide each mole value by the smallest number of moles to find the simplest ratio.

Write the empirical formula using these whole-number ratios.

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More Chemistry Questions

1 Define a Compound 7.2 Calculate the percentage of chromium in K2Cr2O7. 7.3 An inorganic substance was analysed and found to be containing 65,31% of oxygen, 32,65% of Sulphur and 2,04% of hydrogen. 7.3.1 Define an empirical formula. 7.3.2 Determine the empirical formula for the compound.

Answer

Step-by-step solution

Determine the molar mass of K₂Cr₂O₇.

Calculate the total mass of chromium in one mole of K₂Cr₂O₇.

Calculate the percentage of chromium.

Assume a 100 g100 \text{ g}100 g sample and convert percentages to masses.

Convert the mass of each element to moles using their atomic masses (O = 16.00 g/mol16.00 \text{ g/mol}16.00 g/mol, S = 32.07 g/mol32.07 \text{ g/mol}32.07 g/mol, H = 1.01 g/mol1.01 \text{ g/mol}1.01 g/mol).

Divide each mole value by the smallest number of moles to find the simplest ratio.

Write the empirical formula using these whole-number ratios.

Try one yourself

Still stuck on this one?

More Chemistry Questions

Assume a $100 \text{ g}$ sample and convert percentages to masses.

Convert the mass of each element to moles using their atomic masses (O = $16.00 \text{ g/mol}$ , S = $32.07 \text{ g/mol}$ , H = $1.01 \text{ g/mol}$ ).