SC23 Flashcards
SC23a
1) State the name and formula of the alcohol in alcoholic drinks.
2) Describe how alcoholic drinks are made from carbohydrates.
3) State the word equation for the formation of ethanol from carbohydrates.
1) Ethanol is the alcohol present in alcoholic drinks. It’s formula is C2H5OH.
2) The ethanol in alcoholic drinks is made from sugars (sugars belong to the carbohydrate group). Plant material containing sugars are mixed with warm water and yeast. Enzymes in the yeast turn the sugars into ethanol and carbon dioxide in a process called fermentation.
3) Glucose —> ethanol + carbon dioxide
SC23a
1) Write balanced equations for the formation of ethanol from carbohydrates.
2) Explain how fractional distillation can be used to produce more concentrated alcohol solutions.
1) C6H12O6 —> 2C2H5OH + 2CO2
2) This is done using fractional distillation. The mixture is heated to 78 ºC which is the boiling point of ethanol but below that of water (100 ºC). The ethanol evaporates and its vapours pass through a condenser, where they cool and condense, forming liquid ethanol. Placing a fractionating column between the flask and the condenser instead of using simple distillation allows the apparatus to create a more concentrated solution of ethanol.
SC23b
1) State the names, formulae and structures of the first four members of the alcohol homologous series.
2) State the functional group present in all alcohols.
3) Describe 3 chemical reactions of alcohols.
1) The chemical formula for the alcohols: CnH2n+1OH
Methnol: CH3OH
Ethanol: C2H5OH
Propanol: C3H7OH
Butanol: C4H9OH
2) The functional group is OH.
3) All alcohols have similar chemical properties. They all:
- They produce carbon dioxide and water during complete combustion
- They can be oxidised to form carboxylic acids
- They react with reactive metals to form hydrogen gas as one of the products
SC23b
1) Explain why alcohols have similar chemical properties.
2) Use the chemical properties of the first four alcohols to predict the properties of other alcohols.
1) The atom or group of atoms in a molecule that is responsible for its main chemical reactions is called a functional group. Alcohols have similar properties because they all contain one -OH functional group.
2) The other alcohols will have similar properties to the first 4 alcohols, as they all have the same functional group. Therefore, other alcohols:
- They produce carbon dioxide and water during complete combustion
- They can be oxidised to form carboxylic acids
- They react with reactive metals to form hydrogen gas as one of the products
SC23c
1) State the names, formulae and structures of the first four members of the carboxylic acid series.
2) Recall the functional group present in all carboxylic acids.
3) How can carboxylic acids be formed?
1) The functional formula is CnH2n+1COOH. (n = 1 starts at ethanoic acid.)
Methanoic acid: HCOOH
Ethanoic acid: CH3COOH
Propanoic acid: C2H5COOH
Butanoic acid: C3H7COOH
2) The functional group is COOH.
3) Carboxylic acids can be formed by the oxidation of alcohols.
SC23c
1) Describe some chemical properties of carboxylic acids.
2) Explain why carboxylic acids take part in similar chemical reactions.
3) Use the properties of the first four carboxylic acids to predict the properties of other carboxylic acids.
1) The carboxylic acids have similar chemical properties. They all:
- Form solutions with a pH less than 7 (if soluble)
- React with metals to form a salt and hydrogen
- React with bases to form a salt and water
- React with carbonates to form a salt, water and carbon dioxide
2) The atom or group of atoms in a molecule that is responsible for its main chemical reactions is called a functional group. Carboxylic acids have similar properties because they all contain one -COOH functional group.
3) The other carboxylic acids will have similar properties to the first 4 carboxylic acids, as they all have the same functional group. Therefore, other carboxylic acids:
- Form solutions with a pH less than 7 (if soluble)
- React with metals to form a salt and hydrogen
- React with bases to form a salt and water
- React with carbonates to form a salt, water and carbon dioxide
SC23b - Core Practical
1) What is the aim of the combustion of alcohols core practical?
2) What is the method for the combustion of alcohols core practical?
1) Investigate the temperature rise produced in a known mass of water by the combustion of alcohols ethanol, propanol, butanol and pentanol.
2) Method
Wear eye protection. Do not refill the alcohol burner if there are any naked flames nearby.
A. Measure the mass of an alcohol burner and cap. Record the mass and the name of the alcohol.
B. Place the alcohol burner in the centre of a heat-resistant mat.
C. Use a measuring cylinder to add 100 cm3 of cold water to a conical flask. D Measure and record the initial temperature of the water and clamp the flask above the alcohol burner.
E. Light the wick of the burner and allow the water to heat up by about 40°C.
F. Replace the cap on the burner and measure and record the final temperature of the water.
G. Measure the mass of the alcohol burner and cap again and record the mass.
H. Calculate the mass of the alcohol burned to produce a 1 °C rise in temperature.
I. Repeat steps A to H using fresh, cold water and a different alcohol.
SC23b - Core Practical
1) What are the independent and dependent variables for the combustion of alcohols core practical?
2) What are the safety hazards for this core practical?
1) The independent variable is the type of alcohol. The dependent variable is the temperature rise.
2) Wear eye protection, do not pour alcohols near naked flames, and take care not to spill the contents of the burners.
SC23b - Core Practical
State 4 possible sources of error in the investigation (combustion of alcohols core practical), as well as the main source of error from this experiment
Four possible sources of error are: measuring volume of water; measuring mass of burner (before and/or after experiment); measuring temperature; loss of heat/energy to surroundings.
However, the main source of error is heat loss to the surroundings.
SC23b - Core Practical
1) Explain why fresh water has to be used when repeating the experiment (combustion of alcohols core practical)
2) Explain the purpose of the draught screen/insulation
1) Water from the previous experiment will be warm at the start when repeating the experiment with other alcohols; this may affect the final temperature rise.
2) The draught screen is to prevent heat loss; so the energy released goes into heating up the water.
