12. Nitrogen and sulfur
A section of Chemistry, 9701
Listing 10 of 350 questions
Hydrogen fluoride, HF, behaves as a weak acid in water, with Ka = 5.6 × 10–4 mol dm–3. Calculate the pH of a 0.050 mol dm–3 solution of HF. pH = Gaseous ammonia and hydrogen fluoride react together to give solid ionic ammonium fluoride. NH3+ HFNH4FΔH = –147 kJ mol–1 What type of reaction is this? Draw dot-and-cross diagrams (outer shells only) describing the bonding in the three compounds involved in this reaction. NH3 HF NH4F There are three types of bonding in NH4F. Give the names of each of the three types, and state where in the compound each type occurs. The reaction between NH3 and HF is reversible. What conditions of temperature and pressure would favour the reverse reaction, i.e. the dissociation of NH4F? Explain your answer. Many commercial copper and brass polishes contain ammonia. The tarnish that forms on the surface of copper is often copper sulfide, CuS. In the presence of O2 from the air, NH3 can combine with this copper sulfide to produce the soluble cuprammonium sulfate, [Cu(NH3)4]SO4. Construct an equation for this reaction. State the colour of cuprammonium sulfate solution. Describe what you would see if a solution of cuprammonium sulfate was diluted with water. Explain your answer. When sulfuric acid is added to Cu2+, no colour change occurs, but when concentrated hydrochloric acid is added to Cu2+, the solution turns yellow-green. The solution reverts to its original colour when it is diluted with water. Suggest the type of reaction occurring with HCl, suggest what is formed during the reaction, and write an equation for the change.
9701_s11_qp_42
THEORY
2011
Paper 4, Variant 2
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Hydrogen fluoride, HF, behaves as a weak acid in water, with Ka = 5.6 × 10–4 mol dm–3. Calculate the pH of a 0.050 mol dm–3 solution of HF. pH = Gaseous ammonia and hydrogen fluoride react together to give solid ionic ammonium fluoride. NH3+ HFNH4FΔH = –147 kJ mol–1 What type of reaction is this? Draw dot-and-cross diagrams (outer shells only) describing the bonding in the three compounds involved in this reaction. NH3 HF NH4F There are three types of bonding in NH4F. Give the names of each of the three types, and state where in the compound each type occurs. The reaction between NH3 and HF is reversible. What conditions of temperature and pressure would favour the reverse reaction, i.e. the dissociation of NH4F? Explain your answer. Many commercial copper and brass polishes contain ammonia. The tarnish that forms on the surface of copper is often copper sulfide, CuS. In the presence of O2 from the air, NH3 can combine with this copper sulfide to produce the soluble cuprammonium sulfate, [Cu(NH3)4]SO4. Construct an equation for this reaction. State the colour of cuprammonium sulfate solution. Describe what you would see if a solution of cuprammonium sulfate was diluted with water. Explain your answer. When sulfuric acid is added to Cu2+, no colour change occurs, but when concentrated hydrochloric acid is added to Cu2+, the solution turns yellow-green. The solution reverts to its original colour when it is diluted with water. Suggest the type of reaction occurring with HCl, suggest what is formed during the reaction, and write an equation for the change.
9701_s11_qp_43
THEORY
2011
Paper 4, Variant 3
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Ammonium sulfate, (NH4)2SO4, is widely used as a fertiliser. In order to determine its percentage purity, a sample of ammonium sulfate fertiliser was analysed by reacting a known amount with an excess of NaOHand then titrating the unreacted NaOH with dilute HCl. Ammonium sulfate reacts with NaOH in a 1 : 2 ratio. Complete and balance the equation for this reaction. (NH4)2SO4 + 2NaOH → NH3 + + A 5.00 g sample of a fertiliser containing (NH4)2SO4 was warmed with 50.0 cm3 (an excess) of 2.00 mol dm–3 NaOH. When all of the ammonia had been driven off, the solution was cooled. The remaining NaOH was then titrated with 1.00 mol dm–3 HCl and 31.2 cm3 were required for neutralisation. Write a balanced equation for the reaction between NaOH and HCl. Calculate the amount, in moles, of HCl in 31.2 cm3 of 1.00 mol dm–3 HCl. Calculate the amount, in moles, of NaOH in 50.0 cm3 of 2.00 mol dm–3 NaOH. Use your answers to , and to calculate the amount, in moles, of NaOH used up in the reaction with (NH4)2SO4. Use your answer to and the equation in to calculate the amount, in moles, of (NH4)2SO4 that reacted with NaOH. Use your answer to to calculate the mass of (NH4)2SO4 that reacted with NaOH. Hence, calculate the percentage purity of the ammonium sulfate fertiliser.
9701_s12_qp_21
THEORY
2012
Paper 2, Variant 1
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The table shows the structures of four amino acids found in proteins in the human body. Complete the table by indicating the type of tertiary interaction each side-chain is most likely to have when its amino acid is present in a protein chain. amino acid structure type of interaction alanine H2NCH(CH3)CO2H cysteine H2NCH(CH2SH)CO2H lysine H2NCH((CH2)4NH2)CO2H serine H2NCH(CH2OH)CO2H Metal ions play an important role in the biochemistry of the human body. For each of the following metal ions, outline one of the places in the body it can be found and its main role there. iron potassium zinc Many chemical reactions at a cellular level require energy in order to take place. This energy is largely provided by the breakdown of one particular compound. Write an equation showing the breakdown of this compound. What type of chemical reaction is this? Cystic fi brosis is a genetic disease caused by a mutation in the DNA sequence resulting in the production of a faulty version of an important protein which acts as an ion pump in the cell membrane. This pump controls the fl ow of ions into and out of cells. People with the faulty protein show two major symptoms. ● water is retained in cells in the lungs resulting in the formation of a thick, sticky mucous outside the cells; ● their sweat is very salty. Based on the information given for people with cystic fi brosis, suggest which ions are involved in the ion fl ow, suggest and explain what type of bonding might result in thick or sticky mucous.
9701_s12_qp_42
THEORY
2012
Paper 4, Variant 2
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Questions Discovered
350