12.5. Identification of ions and gases
A subsection of Chemistry, 0620, through 12. Experimental techniques and chemical analysis
Listing 10 of 359 questions
For Examiner's Use Caesium is a metal in Group I of the Periodic Table. State two physical properties of caesium. State the number of electrons in the outer shell of a caesium atom. An isotope of caesium has a mass number of 133. What do you understand by the term isotope? Calculate the number of neutrons in this isotope of caesium. Complete the following table to estimate the boiling point of caesium and predict the reactivity of caesium with water. Group I metal density / g / cm3 boiling point / °C reactivity with water sodium 0.97 fizzes quickly, disappears gradually and does not burst into flame potassium 0.86 fizzes very quickly, disappears quickly and bursts into flame with a little spitting rubidium 1.53 fizzes extremely quickly, bursts into flame then spits violently and may explode caesium 1.88 For Examiner's Use The diagram shows the structure of caesium chloride. Cs+ Cl – Cs+ Cl – Cs+ Cl – Cs+ Cl – Cs+ Cl – Cs+ Cl – Cs+ Cl – Cs+ Cl – Cs+ Cl – Use this diagram to work out the simplest formula for caesium chloride. Caesium chloride dissolves in water to form a neutral solution. State the pH of a neutral solution. Describe a test for chloride ions. test result
0620_w09_qp_2
THEORY
2009
Paper 2, Variant 0
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Both strontium and sulfur have chlorides of the type XCl 2. The table below compares some of their properties. strontium chloride sulfur chloride appearance white crystals red liquid formula SrCl 2 SCl 2 melting point / °C –120 boiling point / °C conductivity of liquid good poor solubility in water dissolves to form a neutral solution reacts to form a solution of pH 1 Use the data in the table to explain why sulfur chloride is a liquid at room temperature, 25 °C. Strontium is a metal and sulfur is a non-metal. Explain why both have chlorides of the type XCl 2. The electron distribution of a strontium atom is 2 + 8 + 18 + 8 + 2. Deduce the name of the acidic compound formed when sulfur chloride reacts with water. Explain the difference in the electrical conductivity of liquid strontium chloride and liquid sulfur chloride. Strontium chloride-6-water can be made from the insoluble compound, strontium carbonate, by the following reactions. SrCO3+ 2HCl → SrCl 2+ CO2+ H2OSrCl 2 + 6H2O→ SrCl 2.6H2OThe following method was used to prepare the crystals. Add excess strontium carbonate to hot hydrochloric acid. Filter the resulting mixture. Partially evaporate the filtrate and allow to cool. Filter off the crystals of SrCl 2.6H2O. Dry the crystals between filter papers. How would you know when excess strontium carbonate had been added in step 1? Why is it necessary to fi lter the mixture in step 2? In step 3, why partially evaporate the fi ltrate rather than evaporate to dryness? In the above experiment, 50.0 cm3 of hydrochloric acid of concentration 2.0 mol / dm3 was used. 6.4 g of SrCl 2.6H2O was made. Calculate the percentage yield. number of moles of HCl used = number of moles of SrCl 2.6H2O which could be formed = mass of one mole of SrCl 2.6H2O is 267 g theoretical yield of SrCl 2.6H2O = g percentage yield = %
0620_w12_qp_31
THEORY
2012
Paper 3, Variant 1
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For each of the following, name an element which matches the description. It is used as a fuel in nuclear reactors. It is the only non-metal which is a good conductor of electricity. Inert electrodes are made from this metal. This gaseous element is used to fi ll balloons in preference to hydrogen. An element which can form an ion of the type X3–. It has the same electron distribution as the calcium ion, Ca2+. The element is in Period 5 and Group VI.
0620_w13_qp_31
THEORY
2013
Paper 3, Variant 1
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The diagram shows a bottle of mineral water. The concentration of the ions present in the water is shown on the label. The pH of the water is also shown. polybottle ions present pH = 6.6 chloride, Cl – X, F– magnesium, Mg2+ manganese, Mn2+ Y, NO3 – potassium, K+ sodium, Na+ concentration in mg / 1000 cm3 0.71 0.31 0.02 0.01 0.70 0.44 1.22 Which positively charged ion is present in the highest concentration? State the name of: ion X ion Y Calculate the mass, in mg, of sodium ions in 200 cm3 of mineral water. mg Which one of the following phrases best describes the pH of this mineral water? Tick one box. neutral strongly acidic strongly alkaline weakly acidic weakly alkaline Describe a test for chloride ions. test result The mineral water bottle is made of poly. Complete the following sentence about polyusing words from the list below. atom ionic monomer polymer reactant saturated Polyis a made by the addition of units.
0620_w14_qp_21
THEORY
2014
Paper 2, Variant 1
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The table shows some properties of the Group I elements. element melting point / °C density in g / cm3 observations during reaction with water lithium slow bubbling no flame sodium rapid bubbling no flame potassium 0.86 rapid bubbling lilac flame rubidium 1.53 caesium 1.88 explodes Complete the table by predicting: ● the melting point of rubidium ● the density of lithium. Predict the observations when rubidium reacts with water. Deduce the electronic structure of potassium. Use the Periodic Table to help you. Lithium reacts with water to produce aqueous lithiumhydroxide and a gas which ‘pops’ with a lighted splint. Name the gas which ‘pops’ with a lighted splint. Choose one pH value from the list that best describes the pH of aqueous lithiumhydroxide. Draw a circle around the correct answer. pH 2 pH 5 pH 7 pH 13 Lithium reacts with nitrogen. Complete the chemical equation for this reaction. Li + N2 → Li3N 
0620_w21_qp_31
THEORY
2021
Paper 3, Variant 1
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The table shows some properties of the GroupI elements. element melting point / °C density in g / cm3 observations during reaction with water lithium 0.53 sodium rapid bubbling no flame potassium 0.86 rapid bubbling lilac flame rubidium 1.53 very rapid bubbling red flame caesium 1.88 explodes francium Complete the table by predicting: ● the melting point of potassium ● the density of francium. Describe the observations when lithium reacts with water. Deduce the electronic structure of sodium. Use the Periodic Table to help you. Explain why a potassium ion has a single positive charge. Sodium reacts with water to produce aqueous sodiumhydroxide and a gas which ‘pops’ with a lighted splint. Complete the chemical equation for this reaction. 2Na + 2H2O → NaOH +  Choose one value from the list that best describes the pH of aqueous sodiumhydroxide. Draw a circle around the correct answer. pH 1 pH 4 pH 7 pH 14 
0620_w21_qp_32
THEORY
2021
Paper 3, Variant 2
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Questions Discovered
359