National 5 Unit 2 - Nature's Chemistry

Front

What is produced when hydrocarbons burn in a plentiful supply of oxygen?

Back

carbon dioxide and water

Answer explanation

When hydrocarbons burn in a plentiful supply of oxygen, they undergo complete combustion, producing carbon dioxide and water as the main products. Thus, the correct answer is carbon dioxide and water.

Front

Homologous series

Back

A group of hydrocarbons with the same general formula and similar chemical properties

Answer explanation

A homologous series consists of hydrocarbons that share the same general formula (e.g., CnH2n+2 for alkanes) and exhibit similar chemical properties due to their structural similarities, making the correct choice the one that specifies this.

Front

What is the correct general formula for the alkanes? Options: CnH2n+2, CnH2n, CnH2n-2, CnHn

Back

CnH2n+2

Answer explanation

The correct general formula for alkanes is CnH2n+2, where 'n' is the number of carbon atoms. This formula accounts for the maximum number of hydrogen atoms that can bond with carbon in a saturated hydrocarbon.

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Hydrocarbon

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Compounds containing carbon and hydrogen only.

Answer explanation

The term hydrocarbon refers specifically to compounds that contain only carbon and hydrogen. Therefore, the correct answer is 'Compounds containing carbon and hydrogen only,' as it excludes any other elements.

Front

What is the correct general formula for the alkenes? Options: CnH2n+2, CnH2n, CnH2n-2, CnHn

Back

CnH2n

Answer explanation

The general formula for alkenes is CnH2n, where 'n' is the number of carbon atoms. This formula reflects the presence of a double bond, which reduces the number of hydrogen atoms compared to alkanes (CnH2n+2).

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isomer

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Compounds which have the same chemical formula but a different structural formula

Answer explanation

Isomers are compounds that share the same chemical formula but differ in their structural arrangement. This distinction is crucial, as it leads to different chemical properties, making the correct choice 'Compounds which have the same chemical formula but a different structural formula'.

Front

How many carbon atoms are there in a molecule of butane?

Back

4

Answer explanation

Butane is an alkane with the chemical formula C4H10, indicating it contains 4 carbon atoms. Therefore, the correct answer is 4.

Front

How many hydrogen atoms are there in a molecule of pentane?

Back

12

Answer explanation

Pentane (C5H12) has 5 carbon atoms and follows the formula CnH(2n+2). For n=5, H=2(5)+2=12. Thus, a molecule of pentane contains 12 hydrogen atoms.

Front

What is the correct general formula for the cycloalkanes? Options: CnH2n+2, CnH2n, CnH2n-2, CnHn

Back

CnH2n

Answer explanation

Cycloalkanes are hydrocarbons with carbon atoms arranged in a ring. Their general formula is CnH2n, where n is the number of carbon atoms. This formula accounts for the two hydrogen atoms less than in alkanes due to ring formation.

Front

What type of reaction do alkenes undergo when they react with bromine water?

Back

Addition

Answer explanation

Alkenes undergo an addition reaction with bromine water, where bromine adds across the double bond, resulting in a dibrominated alkane. This process is a hallmark of halogenation, but specifically, it is classified as an addition reaction.