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NPCIL Trainee Organic Chemistry — practice questions

Explore 13 free Organic Chemistry questions in NPCIL Trainee Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Organic Chemistry questions and exercises with answers

Showing questions 1–13 of 13.

Organic compounds that contain only the elements carbon and hydrogen are called:Read the answer and worked solution →In alkanes, each carbon atom is best described as:Read the answer and worked solution →What is the general molecular formula for a noncyclic (straight or branched-chain) alkane containing n carbon atoms?Read the answer and worked solution →The largest database of organic compounds lists roughly how many known substances?Read the answer and worked solution →In 2-butene, the isomer with both methyl groups on the same side of the C=C double bond is called the:Read the answer and worked solution →The C-Cl portion of a chloroethane molecule is an example of a:Read the answer and worked solution →Ethers contain the functional group -O- and have which general formula?Read the answer and worked solution →Diethyl ether, the most widely used compound of its class, was first put to what use in 1846?Read the answer and worked solution →Dimethyl ketone, CH3COCH3, is the simplest ketone and is better known by what common name?Read the answer and worked solution →Formic acid, the simplest carboxylic acid, takes its name from the Latin word "formicus," which means:Read the answer and worked solution →Acetic acid, CH3CO2H, constitutes approximately what percentage of ordinary vinegar?Read the answer and worked solution →Amines are organic molecules defined by the presence of which type of bond?Read the answer and worked solution →The ester ethyl acetate (CH3CO2CH2CH3) forms when acetic acid reacts with which alcohol?Read the answer and worked solution →

Worked practice questions

Organic compounds that contain only the elements carbon and hydrogen are called:

  1. hydrocarbons
  2. alcohols
  3. esters
  4. amines
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Correct answer: A. hydrocarbons

1. The stem describes molecules built from exactly two elements: carbon and hydrogen. 2. The text states directly: "The simplest organic compounds contain only the elements carbon and hydrogen, and are called hydrocarbons." 3. Alcohols, esters, and amines all additionally contain oxygen or nitrogen atoms, so they do not fit this two-element description. 4. So compounds made only of carbon and hydrogen are called hydrocarbons. _Source: OpenStax Chemistry Ch 20 "Organic Chemistry", p.1098 §20.1 Hydrocarbons_

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In alkanes, each carbon atom is best described as:

  1. sp hybridized, bonded to two atoms
  2. sp3 hybridized, bonded to four other atoms
  3. sp2 hybridized, bonded to three atoms
  4. sp3d hybridized, bonded to five atoms
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Correct answer: B. sp3 hybridized, bonded to four other atoms

1. Alkanes are saturated hydrocarbons, meaning every carbon-carbon bond is a single bond. 2. The text states: "Each of the carbon atoms in an alkane has sp3 hybrid orbitals and is bonded to four other atoms, each of which is either carbon or hydrogen." 3. This sp3 geometry is what gives alkane chains their characteristic zigzag shape, with bond angles near 109.5°. 4. So alkane carbons are sp3 hybridized and four-bonded, not sp/sp2 hybridized with fewer bonds, or sp3d hybridized with an extra bond. _Source: OpenStax Chemistry Ch 20 "Organic Chemistry", p.1098 §20.1 Hydrocarbons_

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What is the general molecular formula for a noncyclic (straight or branched-chain) alkane containing n carbon atoms?

  1. CnH2n
  2. CnH2n-2
  3. CnH2n+2
  4. CnHn
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Correct answer: C. CnH2n+2

1. Every carbon in an alkane is fully saturated with single bonds, maximizing the number of attached hydrogens. 2. The text states: "noncyclic alkanes all have a formula of CnH2n+2." 3. The other formulas correspond to more unsaturated hydrocarbon families (alkenes and alkynes), not fully saturated alkanes. 4. So the general formula for a noncyclic alkane is CnH2n+2. _Source: OpenStax Chemistry Ch 20 "Organic Chemistry", p.1102 §20.1 Hydrocarbons_

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