12. Experimental techniques and chemical analysis
A section of Chemistry, 0620
Listing 10 of 677 questions
This question is about nitrogen and compounds of nitrogen. Nitrogen is a non-metal. Nitrogen is a poor electrical conductor. Describe two other physical properties which are typical of non-metals.  Oxides of nitrogen are air pollutants which contribute to acid rain. State one source of oxides of nitrogen in the air. State one other adverse effect of oxides of nitrogen. Ammonia is a simple molecule with covalent bonds. Describe a covalent bond. Complete Fig.8.1 to show the dot-and-cross diagram for a molecule of ammonia. Show outer shell electrons only. N H H H  Aqueous ammonia is alkaline. Choose from the list, the pH value that is alkaline. Draw a circle around your chosen answer. pH 1 pH 5 pH 7 pH 10 Aqueous ammonia releases ammonia gas. Ammonia gas turns damp red litmus paper blue. A long glass tube is set up as shown in Fig.8.2. long glass tube cotton wool soaked in aqueous ammonia damp red litmus paper At first, the litmus paper does not turn blue. After a short time, the litmus paper turns blue. Explain these results in terms of the kinetic particle theory. 
0620_s23_qp_31
THEORY
2023
Paper 3, Variant 1
View
Blood plasma is the liquid part of blood. Table 2.1 shows the mass, in mg, of some ions present in 100 cm3 of blood plasma. Table 2.1 name of ion formula of ion mass of ion in 100 cm3 of blood plasma / mg calcium Ca2+ 10.0 chloride Cl – 365.6 hydrogencarbonate HCO3 – 164.7 hydrogen phosphate HPO4 2– 9.6 magnesium Mg2+ 3.6 potassium K+ 19.5 sodium Na+ 326.6 SO4 2– 4.8 Answer these questions using information from Table 2.1. Name the positive ion in Table 2.1 that is present in the lowest concentration in blood plasma. Name the ion in Table 2.1 that contains an element in Group V of the Periodic Table. Name the compound containing Na+ ions and SO4 2– ions. Describe a test for chloride ions. test observations Choose from the list the salt that is insoluble in water. Tick (✓) one box. calcium sulfate magnesium chloride potassium sulfate sodium chloride Table 2.2 shows some properties of the Group I metals. Table 2.2 metal density in g / cm3 observations on reaction with water lithium 0.53 bubbles form very slowly and no flame sodium 0.97 potassium 0.86 bubbles form very rapidly and flame rubidium explodes Use the information in Table 2.2 to: ● suggest why it is difficult to predict the density of rubidium ● describe the observations when sodium reacts with water. State how the melting point of the Group I elements changes down the Group. Sodium oxide, Na2O, can be made by heating sodium in a limited supply of oxygen. Complete the symbol equation for this reaction. Na + O2 → Na2O , ,
0620_s24_qp_32
THEORY
2024
Paper 3, Variant 2
View
A student set up an experiment to demonstrate rusting as shown below. He made observations at the start of the experiment, after 2 weeks and after 4 weeks. measuring cylinder air water 10 cm3 8 cm3 iron wool 8 cm3 start after 2 weeks after 4 weeks What conditions are needed for the iron wool to rust? Two weeks after the start of the experiment, the volume of air in the measuring cylinder had decreased. After a further two weeks there was no change in the volume of air. Explain the results of this experiment. What change would you observe in the iron wool as it rusted? appearance at start appearance after 2 weeks Rust contains iron(ions. Describe a test for iron(ions. test result Clean iron reacts with dilute hydrochloric acid. Fe + 2HCl → FeCl 2 + H2 Write a word equation for this reaction.
0620_w11_qp_21
THEORY
2011
Paper 2, Variant 1
View
Until recently, arsenic poisoning, either deliberate or accidental, has been a frequent cause of death. The symptoms of arsenic poisoning are identical with those of a common illness, cholera. A reliable test was needed to prove the presence of arsenic in a body. In 1840, Marsh devised a reliable test for arsenic. hydrochloric acid H2 and arsine burning pieces of zinc and arsenic compound black stain shows presence of arsenic cold surface Hydrogen is formed in this reaction. Any arsenic compound reacts with this hydrogen to form arsine which is arsenic hydride, AsH3. The mixture of hydrogen and arsine is burnt at the jet and arsenic forms as a black stain on the glass. Write an equation for the reaction which forms hydrogen. Draw a diagram which shows the arrangement of the outer electrons in one molecule of the covalent compound arsine. The electron distribution of arsenic is 2 + 8 + 18 + 5. Use x to represent an electron from an arsenic atom. Use o to represent an electron from a hydrogen atom. Another hydride of arsenic has the composition below. arsenic 97.4 % hydrogen 2.6 % Calculate the empirical formula of this hydride from the above data. Show your working. The mass of one mole of this hydride is 154 g. What is its molecular formula? Deduce the structural formula of this hydride. Hair is a natural protein. Hair absorbs arsenic from the body. Analysis of the hair provides a measurement of a person’s exposure to arsenic. To release the absorbed arsenic for analysis, the protein has to be hydrolysed. What is the name of the linkage in proteins? Name a reagent which can be used to hydrolyse proteins. What type of compound is formed by the hydrolysis of proteins? In the 19th Century, a bright green pigment, copper(arsenate(was used to kill rats and insects. In damp conditions, micro-organisms can act on this compound to produce the very poisonous gas, arsine. Suggest a reason why it is necessary to include the oxidation states in the name of the compound. The formula for the arsenate(ion is AsO4 3–. Complete the ionic equation for the formation of copper(arsenate(. Cu2+ + AsO4 3– →
0620_w12_qp_33
THEORY
2012
Paper 3, Variant 3
View
Choose from the list of compounds below to answer the following questions. ammonia ammonium chloride calcium carbonate calcium oxide copper(sulfate ethane iron(chloride methane water Each compound can be used once, more than once or not at all. Which compound: is an alkaline gas, is a gas contributing to climate change, is a salt containing only non-metals, turns blue cobalt chloride paper pink, reacts with an acid to release carbon dioxide, gives a light blue precipitate when aqueous sodium hydroxide is added to a solution of its aqueous ions? What is the meaning of the term compound ? Complete the following symbol equation for the complete combustion of methane in oxygen. CH4 + O2 → + 2H2O
0620_w13_qp_22
THEORY
2013
Paper 2, Variant 2
View
The structures of six substances are shown below. Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag Ag A Fe Fe Fe Fe Fe Fe Ni Ni Ni Fe Fe Fe Xe Xe Xe Xe Xe B Na+ I– Na+ I– Na+ I– Na+ I– Na+ I– Na+ I– C D E F N O O N O O N O O F F F F F F F F Answer the following questions about these substances. Each substance may be used once, more than once or not at all. Which substance, A, B, C, D, E or F, is a simple molecular compound, is an alloy, is a compound, whose aqueous solution gives a yellow precipitate on addition of aqueous silver nitrate, is an atmospheric pollutant arising from reactions taking place in car engines, is a diatomic molecule, conducts electricity when molten but not when solid? Substance A is an element. What is meant by the term element ? Substance D oxidises water to oxygen. Complete the symbol equation for this reaction. 2F2 + 2H2O → HF +
0620_w15_qp_22
THEORY
2015
Paper 2, Variant 2
View
Questions Discovered
677