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Methanoic acid, $HCO_2H$, was formerly known as formic acid because it is present in the sting of ants and the Latin name for ant is formica. It was first isolated in 1671 by John Ray who collected a large number of dead ants and extracted the acid from them by distillation.
In this question, you should give all numerical answers to \textbf{two} significant figures.
At room temperature, pure methanoic acid is a liquid which is completely soluble in water.
When we are stung by a 'typical' ant a solution of methanoic acid, $A$, is injected into our skin.
Solution $A$ contains 50% by volume of pure methanoic acid.
A 'typical' ant contains $7.5 \times 10^{-6}$ dm$^3$ of solution A.
(a) (i) Calculate the volume, in cm$^3$, of solution $A$ in one ant.
volume = ..................... cm$^3$
(ii) Use your answer to (i) to calculate the volume, in cm$^3$, of pure methanoic acid in one ant.
volume = ..................... cm$^3$
(iii) Use your answer to (ii) to calculate how many ants would have to be distilled to produce 1 dm$^3$ of pure methanoic acid.
number = ...................................
When we are stung by an ant, the amount of solution $A$ injected is 80% of the total amount of solution $A$ present in one ant.
The density of pure methanoic acid is 1.2 g cm$^{-3}$.
(b) (i) Calculate the volume, in cm$^3$, of pure methanoic acid injected in one ant sting.
volume = ..................... cm$^3$
(ii) Use your answer to (i) to calculate the mass of methanoic acid present in one ant sting.
mass = ..................... g [3]
Bees also sting us by using methanoic acid. One simple treatment for ant or bee stings is to use sodium hydrogencarbonate, $NaHCO_3$.
(c) (i) Construct a balanced equation for the reaction between methanoic acid and sodium hydrogencarbonate.
........................................................................................................
(ii) In a typical bee sting, the mass of methanoic acid injected is $5.4 \times 10^{-3}$ g. Calculate the mass of $NaHCO_3$ needed to neutralise one bee sting.
mass = .............................. g [3]
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The kinetic theory of gases is used to explain the large scale (macroscopic) properties of gases by considering how individual molecules behave.
(a) State two basic assumptions of the kinetic theory as applied to an ideal gas.
(b) State two conditions under which the behaviour of a real gas approaches that of an ideal gas.
(c) Place the following gases in decreasing order of ideal behaviour.
ammonia, neon, nitrogen
Explain your answer.
(d) By using the kinetic-molecular model, explain why a liquid eventually becomes a gas as the temperature is increased
(e) Ethane, $\text{CH}_3\text{CH}_3$ , and fluoromethane, $\text{CH}_3\text{F}$ are \textit{iso}-electronic, that is they have the same total number of electrons in their molecules. Calculate the total number of electrons in one molecule of $\text{CH}_3\text{F}$.
(f) The boiling points of these two compounds are given below.
Suggest explanations for the following.
(i) the close similarity of the boiling points of the two compounds
(ii) the slightly higher boiling point of $\text{CH}_3\text{F}$
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Elements in the same period of the Periodic Table show trends in physical and chemical properties. The grids on this page and on the opposite page refer to the elements of the third period, Na to Cl.
On each of these grids, draw a clear sketch to show the variation of the stated property. Below each grid, briefly explain the variation you have described in your sketch.
For each explanation you should refer to the important factors that cause the differences in the property you are describing.
(a)
Explanation $\text{................}$
$\text{................}$
$\text{................}$
$\text{................}$ [3]
(b)
Explanation $\text{................}$
$\text{................}$
$\text{................}$
$\text{................}$ [4]
(c)
Explanation $\text{................}$
$\text{................}$
$\text{................}$
$\text{................}$ [4]
(d) The melting points of some of the oxides of the elements sodium to sulfur are given in the table below.
[Table_1]
(i) What type of bond is broken when each of the following compounds is melted?
$\text{Na}_{2}\text{O} \text{................}$
$\text{SiO}_{2} \text{................}$
$\text{P}_{4}\text{O}_{6} \text{................}$
(ii) Identify one of these six oxides that has no reaction at all with water.
$\text{................}$ [4]
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The compound trans-4-hydroxy-2-nonenal (HNE) is thought to lead to infections of the lung when cigarettes are smoked.
[Image_1: Chemical structure]
(a) What is the empirical formula of trans-4-hydroxy-2-nonenal?
........................................
[1]
(b) (i) HNE contains an alkene group. Name as fully as you can two other functional groups which are present in the HNE molecule.
........................................................
........................................................
(ii) How would you confirm the presence of the alkene group in HNE? State the reagent used and the observation you would make.
reagent ...............................................
observation ...........................................................................................................
[5]
HNE is a reactive compound.
(c) Give the structural formulae of all of the carbon-containing compounds formed in each case when HNE is reacted separately with the following reagents.
(i) hot concentrated manganate(VII) ions in acid solution
(ii) hot phosphorus trichloride, $PCl_3$
(iii) sodium tetrahydroborate(III), $NaBH_4$
[4]
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Fermentation of sugars by bacteria or moulds produces many different organic compounds.
One compound present in fermented molasses is 2-ethyl-3-methylbutanoic acid which gives a distinctive aroma to rum.
$$(CH_3)_2CHCH(C_2H_5)CO_2H$$
2-ethyl-3-methylbutanoic acid
(a) (i) What is the molecular formula of 2-ethyl-3-methylbutanoic acid?
(ii) How many chiral carbon atoms are present in a molecule of 2-ethyl-3-methylbutanoic acid? If none write 'none'.
[2]
A sample of 2-ethyl-3-methylbutanoic acid may be prepared in a school or college laboratory by the oxidation of 2-ethyl-3-methylbutan-1-ol, $(CH_3)_2CHCH(C_2H_5)CH_2OH$.
(b) (i) State the reagent(s) that would be used for this oxidation. Describe what colour change would be seen.
This reaction is carried out by heating the reacting chemicals together.
(ii) What could be the main organic impurity present in the sample of the acid? Explain your answer.
(iii) State whether a distillation apparatus or a reflux apparatus should be used. Explain your answer.
[6]
(c) A structural isomer of 2-ethyl-3-methylbutan-1-ol is 2-ethyl-3-methylbutan-2-ol, $(CH_3)_2CHC(OH)(C_2H_5)CH_3$.
What colour change would be seen if this were heated with the reagents you have given in (b)(i)? Explain your answer as clearly as you can.
[3]
An isomer of 2-ethyl-3-methylbutanoic acid which is an ethyl ester is a very strong smelling compound which is found in some wines.
(d) This ethyl ester contains a branched hydrocarbon chain and is chiral. Draw the displayed formula of this ethyl ester. Identify the chiral carbon atom with an asterisk (*).
[3]
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