New chat PYQ Library Doubts Rank report

Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →

Some Basic Concepts of Chemistry question

2023 · 31 Jan · Shift 2 · Q1

Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.

PYQ Library
JEE Main
Chemistry
Some Basic Concepts of Chemistry
2023 · 31 Jan · Shift 2 · Q1

Some Basic Concepts of Chemistry question

2023 · 31 Jan · Shift 2 · Q1

JEE MainChemistrySome Basic Concepts of ChemistryMCQ+4 / −1

When a hydrocarbon A undergoes complete combustion it requires 11 equivalents of oxygen and produces 4 equivalents of water. What is the molecular formula of

A

?

A
$\mathrm{C}_{9} \mathrm{H}_{8}$
B
$\mathrm{C}_{5} \mathrm{H}_{8}$
C
$\mathrm{C}_{11} \mathrm{H}_{4}$
D
$\mathrm{C}_{11} \mathrm{H}_{8}$

View written solutionFree

Correct answer: A

Let the hydrocarbon be $\mathrm{C}_x\mathrm{H}_y$ .
For complete combustion:

\mathrm{C}_x\mathrm{H}_y + \left(x + \frac{y}{4}\right)\mathrm{O}_2 \rightarrow x\mathrm{CO}_2 + \frac{y}{2}\mathrm{H}_2\mathrm{O}

Given:

Oxygen required $= 11$ equivalents
Water produced $= 4$ equivalents

For combustion of a hydrocarbon, the number of moles of water formed is:

\frac{y}{2} = 4

So,

y = 8

Oxygen required is:

x + \frac{y}{4} = 11

Substitute $y=8$ :

x + \frac{8}{4} = 11

x + 2 = 11

x = 9

Therefore, the molecular formula is:

\mathrm{C}_9\mathrm{H}_8

Checking options:

A: $\mathrm{C}_9\mathrm{H}_8$ ✅
B: $\mathrm{C}_5\mathrm{H}_8$ gives oxygen needed $= 5+2=7$ ❌
C: $\mathrm{C}_{11}\mathrm{H}_4$ gives water $=2$ ❌
D: $\mathrm{C}_{11}\mathrm{H}_8$ gives oxygen needed $=11+2=13$ ❌

Hence, the correct answer is Option A.

More from Some Basic Concepts of Chemistry

Assume carbon burns according to the following equation : $2 C_{(s)} + O_{2 (g)} \to 2 CO (g)$ when $48 g$ carbon is burnt in $48 g$ of oxygen, the volume of…2023 · Numerical
A sample of a metal oxide has formula $M_{0.83} O_{1.00}$ . The metal $M$ can exist in two oxidation states $+ 2$ and $+ 3$ . In the sample of $M_{0.83} O_{1.00}$ , the percentage of metal ions…2023 · Numerical
If a rocket runs on a fuel ( $C_{15} H_{30}$ ) and liquid oxygen, the weight of oxygen required and $C O_{2}$ released for every litre of fuel respectively are : (Given : density of the fuel is 0.756 g/mL)2022 · MCQ
A 0.166 g sample of an organic compound was digested with conc. $H_{2} S O_{4}$ and then distilled with $N a O H$ . The ammonia gas evolved was passed through 50.0 mL of 0.5 N $H_{2} S O_{4}$ . The used acid required 30.0 mL of 0.25 N $N a O H$ for complete…2022 · Numerical
120 g of an organic compound that contains only carbon and hydrogen gives 330 g of $C O_{2}$ and 270 g of water on complete combustion. The percentage of carbon and hydrogen, respectively are2022 · MCQ
$SO_{2} Cl_{2}$ on reaction with excess of water results into acidic mixture $SO_{2} Cl_{2} + 2 H_{2} O \to H_{2} SO_{4} + 2 HCl$ 16 moles of $NaOH$ …2022 · MCQ
56.0 L of nitrogen gas is mixed with excess hydrogen gas and it is found that 20 L of ammonia gas is produced. The volume of unused nitrogen gas is found to be L.2022 · Numerical
A sample of 4.5 mg of an unknown monohydric alcohol, $R - O H$ was added to methylmagnesium iodide. A gas is evolved and is collected and its volume measured to be 3.1 mL. The molecular weight of the unknown alcohol is …2022 · Numerical