ALCOHOLS [dchemlc]

what is the functional group of alcohols?

• 
• 
• 
• 

Answer explanation

What we commonly refer to as 'alcohol' is just one member of a large family (homologous series) of similar compounds. Alcohols all contain the functional group

- OH covalently bonded to a carbon chain.

name the given alcohol.

Ethanol is a biofuel. What will be produced when ethanol is burnt in air?

• carbon dioxide

• water

• oxygen

• carbon monoxide

• hydrogen

Answer explanation

All alcohols burn to form carbon dioxide and water. With ethanol:

C₂H₅OH_(I) + 3O_2(g) ------>

2CO_2(g) + 3H₂O_(l)

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

which of the following microorganisms will help oxidize ethanol into ethanoic acid?

• yeast

• penicillin

• ameoba

• paramecium

Answer explanation

The ethanol in the wine is oxidised by air with the help of microorganisms such as bacteria or yeast to form ethanoic acid, CH₃COOH.

Tags

NGSS.HS-LS2-3

Yeast is added to a sugar (or starch) solution and left in the warm (about 30 °C} for several days in the absence of air (anaerobic conditions). Enzymes (biological catalysts) in the yeast convert the sugar into ethanol and carbon dioxide. What is the name of this process?

Tags

NGSS.HS-LS2-3

what will be produced by the enzymes in the yeast when glucose is subjected to aerobic fermentation?

• ethanol

• water

• carbon dioxide

• carbon monoxide

• butanol

Answer explanation

In the presence of air (aerobic conditions), enzymes in the yeast produce carbon dioxide and water instead of ethanol.

Tags

NGSS.HS-LS1-7

NGSS.HS-LS2-3

what is the optimum temperature needed for the anaerobic fermentation of glucose to ethanol?

• 30⁰C

• 40⁰C

• 20⁰C

• 10⁰C

Answer explanation

The enzymes are protein catalysts and if the temperature is increased much above 40°C they lose their structure and don't work any longer. The proteins are said to be denatured. At a lower temperature, the reaction is too slow. Somewhere between 30 and 40°C is the optimum temperature for the reaction.

Tags

NGSS.HS-LS2-3

NGSS.HS-PS1-5

what is the method used to purify ethanol?

• fractional distillation

• steam distillation

• simple distillation

• vaccum distillation

Answer explanation

The alcohol is purified by fractional distillation. This takes advantage of the difference in boiling point between ethanol and water. Water boils at 100°C whereas ethanol boils at 78°C.

Ethanol can be made by reacting ethene with steam, a process known as hydration . What is the catalyst used in this process?

• phosphoric acid

• hydrochloric acid

• sulphuric acid

• nitric acid

Answer explanation

Starting materials: ethene and steam

Temperature: 300°C

Pressure: 60-70 atmospheres

Catalyst: phosphoric acid (H₃PO₄)

Tags

NGSS.HS-PS1-6

ethanol can be oxidized by heating with potassium dichromate (VI) in dilute sulphuric acid. What is the colour change observed in this reaction?

• orange to green

• green to orange

• purple to colourless

• purple to green

Answer explanation

A few drops of ethanol are added to a solution containing the orange mixture of potassium dichromate(VI) and dilute sulfuric acid in a test-tube. The tube is heated in a hot water bath.

The solution turns green indicating the presence of Cr³⁺ ions, which are formed when the potassium dichromate(VI) is reduced.

Tags

NGSS.HS-PS1-2