11.7. Carboxylic acids
A subsection of Chemistry, 0620, through 11. Organic chemistry
Listing 10 of 101 questions
This question is about carboxylic acids and alkanes. Table 8.1 shows the names, formulae and boiling points of some carboxylic acids. Table 8.1 name formula boiling point / °C methanoic acid HCOOH ethanoic acid CH3COOH propanoic acid C2H5COOH butanoic acid C3H7COOH Use the information in Table 8.1 to answer these questions. State the trend in the boiling points of the carboxylic acids. Deduce the general formula for carboxylic acids. Complete the word equation for the reaction of ethanoic acid with sodium carbonate. ethanoic acid + sodium carbonate → sodium ethanoate + + Choose the correct formula of sodium ethanoate from the list. Draw a circle around your chosen answer. CH3CH2ONa CH3CH2COONa CH3COONa (CH3COO)2Na Methane, ethane and propane belong to the alkane homologous series. Define the term homologous series. State the type of bonding in a methane molecule. State two types of reaction of the alkanes. , ,
0620_s24_qp_32
THEORY
2024
Paper 3, Variant 2
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A carboxylic acid reacts with an alcohol to produce an ester and water. Under certain conditions, this reaction can be reversed so an ester reacts with water to produce a carboxylic acid X and an alcohol Y. The reaction reaches an equilibrium. CH3CH2COOCH3 + H2O X + Y The forward reaction is endothermic. Deduce the empirical formula of the ester. Name the ester. Name carboxylic acid X and draw its displayed formula. name displayed formula Name alcohol Y and give its structural formula. name structural formula Complete Table 4.1 to show the effect, if any, for each change of condition. Table 4.1 change of condition effect on the concentration of carboxylic acid X at equilibrium temperature is decreased concentration of CH3CH2COOCH3 is decreased more alcohol Y is added a catalyst is added At the beginning of the reaction between the ester and water, no carboxylic acid is present in the reaction mixture. Suggest how the pH of the reaction mixture changes from the start of the reaction until equilibrium is reached. Assume alcohols and esters are neutral. pH at start of reaction pH at equilibrium Identify the ion that causes the change in pH. Name an indicator which can be used to follow the change in pH. ,   ,
0620_s24_qp_42
THEORY
2024
Paper 4, Variant 2
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For Examiner's Use Ethanoic acid is a colourless liquid at room temperature. It has the typical acid properties and forms compounds called ethanoates. A pure sample of ethanoic acid is slowly heated from 0oC to 150oC and its temperature is measured every minute. The results are represented on the graph below. temperature time A B C D E F Name the change that occurs in the region D to E. What would be the difference in the region B to C if an impure sample had been used? Sketch on the graph how the line would continue if the acid was heated to a higher temperature. For Examiner's Use Complete the following table that compares the separation and movement of the molecules in regions C to D with those in E to F. C to D E to F separation (distance between particles) movement of particles random and slow Can particles move apart to fill any volume? Complete the word equations for the reactions of ethanoic acid. calcium + ethanoic acid + + ethanoic acid zinc ethanoate + water Write the symbol equation for the reaction between ethanoic acid and sodium hydroxide.
0620_w05_qp_3
THEORY
2005
Paper 3, Variant 0
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Use The diagram shows the changes in pH in a student’s mouth after she has eaten a sweet. time / minutes pH Describe how the acidity in the student’s mouth changes after she has eaten the sweet. Chewing a sweet stimulates the formation of saliva. Saliva is slightly alkaline. Use this information to explain the shape of the graph. State the name of the type of reaction which occurs when an acid reacts with an alkali. Many sweets contain citric acid. The formula of citric acid is shown below. HO C CH2 CH2 CO2H CO2H CO2H Put a ring around the alcohol functional group on the above formula. State the name of the – CO2H functional group in citric acid. Ethanoic acid also has a – CO2H functional group. Write down the formula for ethanoic acid. Examiner's Use Citric acid can be extracted from lemon juice as follows: stage 1: add calcium carbonate to hot lemon juice stage 2: filter off the precipitate which is formed (calcium citrate) stage 3: wash the calcium citrate precipitate with water stage 4: add sulphuric acid to the calcium citrate to make a solution of citric acid stage 5: crystallise the citric acid When calcium carbonate is added to lemon juice a fizzing is observed. Explain why there is a fizzing. Draw a diagram to show step 2. Label your diagram. Suggest why the calcium citrate precipitate is washed with water. Describe how you would carry out step 5. Nowadays, citric acid is usually made by the fermentation of sugars. Which one of the following is required for fermentation? Put a ring around the correct answer. acid high temperature light microorganisms nitrogen
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THEORY
2007
Paper 2, Variant 0
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Carboxylic acids contain the group O O H C or COOH. Ethanoic acid is a typical carboxylic acid. It forms ethanoates. Complete the following equations. Mg + CH3COOH → + ethanoic acid sodium hydroxide + → + Ethanoic acid reacts with ethanol to form an ester. Give the name of the ester and draw its structural formula. Show all of the bonds. name structural formula Maleic acid is an unsaturated acid. 5.8 g of this acid contained 2.4 g of carbon, 0.2 g of hydrogen and 3.2 g of oxygen. How do you know that the acid contained only carbon, hydrogen and oxygen? Calculate the empirical formula of maleic acid. Number of moles of carbon atoms = Number of moles of hydrogen atoms = Number of moles of oxygen atoms = The empirical formula is The mass of one mole of maleic acid is 116 g. What is its molecular formula? Maleic acid is dibasic. One mole of acid produces two moles of H+. Deduce its structural formula.
0620_w10_qp_33
THEORY
2010
Paper 3, Variant 3
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Vinegar contains ethanoic acid. The formula of ethanoic acid is shown below. C H H H C O O H On the formula above, put a ring around the carboxylic acid functional group. Write the simplest formula for a molecule of ethanoic acid. Ethanoic acid reacts with sodium hydroxide to form the salt sodium ethanoate. ethanoic acid + sodium hydroxide → sodium ethanoate + water What type of chemical reaction is this? Sodium ethanoate is soluble in water. What do you understand by the term soluble ? Which one of the following is the most likely pH value of ethanoic acid? Put a ring around the correct answer. pH 3 pH 7 pH 9 pH 13 All acids react with carbonates. Complete the general equation for this reaction. acid + carbonate → salt + + The structure of sodium carbonate is shown below. CO3 2– Na+ Na+ CO3 2– Na+ Na+ CO3 2– Na+ Na+ CO3 2– Na+ Na+ Write the simplest formula for sodium carbonate.
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THEORY
2012
Paper 2, Variant 3
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Questions Discovered
101