12.5. Identification of ions and gases
A subsection of Chemistry, 0620, through 12. Experimental techniques and chemical analysis
Listing 10 of 359 questions
The bar charts compare the concentrations of the main ions in two samples of seawater, sampleA and sampleB. Na+ Ca2+ K+ Mg2+ SiO3 2– Cl – HCO3 – concentration in mg / dm3 Na+ Ca2+ K+ Mg2+ SiO3 2– Cl – HCO3 – sample B concentration in mg / dm3 sample A Use the information in the bar charts to answer the following questions. Describe two differences in the composition of the seawater in sampleA and sampleB. Which positive ion has the lowest concentration in sample A? Calculate the mass of sodium ions in 200 cm3 of sample B. Show all your working. [1 dm3 = 1000 cm3] mass = mg Describe a test for sodium ions. test result River water contains small particles of clay. When these particles are viewed under a microscope they show a random, jumpy motion even when the water is still. What name is given to this type of movement? Carbon dioxide dissolves in water to form a mixture which contains hydrogencarbonate ions and hydrogen ions. CO2+ H2OHCO3 –+ H+What is the meaning of the symbol ? The solution formed is slightly acidic. Describe how you would use Universal Indicator paper to determine the pH of this solution. Carbon dioxide is a greenhouse gas which causes climate change. Explain how carbon dioxide contributes to climate change. State the name of one other greenhouse gas and give one source of this gas. gas source
0620_w16_qp_31
THEORY
2016
Paper 3, Variant 1
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A porous pot has tiny holes in its walls which allow gases to move in or out of the pot. A teacher filled a porous pot with green chlorine gas. The teacher then placed the pot in a large jar of air. After 10 minutes, a green colour was seen outside the porous pot. chlorine gas air porous pot at the start after 10 minutes Use the kinetic particle model of matter to explain this observation. A porous barrier can be used to separate uranium fluoride molecules containing different isotopes of uranium. State the main use of the radioactive isotope 235U. Give one medical use of radioactive isotopes. The accurate relative atomic mass of uranium is 238.03. Define the term relative atomic mass. Chlorine reacts with potassium bromide to form bromine and potassium chloride. Complete the chemical equation for this reaction. + 2KBr → Br2 + KCl Give one use of chlorine. Chlorine forms an oxide with the formula Cl 2O7. Is this oxide an acidic or a basic oxide? Explain your answer. A teacher heated a test-tube containing anhydrous copper(chloride. A piece of damp litmus paper was placed at the top of the test-tube. heat litmus paper anhydrous copper(chloride The anhydrous copper(chloride decomposed and chlorine was formed. Describe the colour change of the litmus paper.
0620_w16_qp_31
THEORY
2016
Paper 3, Variant 1
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The bar charts compare the concentrations of ions in two samples of water, sampleA and sampleB. Na+ Ca2+ K+ Mg2+ SiO3 2– Cl – HCO3 – sample A concentration in mg / dm3 Na+ Ca2+ K+ Mg2+ SiO3 2– Cl – HCO3 – sample B concentration in mg / dm3 Use the information in the bar charts to answer the following questions. Describe two differences in the composition of sample A and sample B. Which positive ion has the lowest concentration in sample B? Calculate the mass of chloride ions present in 100 cm3 of sample B. Show all your working. [1 dm3 = 1000 cm3] mass = mg Describe a test for chloride ions. test result River water contains small particles of clay. These particles show Brownian motion. Which one of these statements best describes Brownian motion? Tick one box. the diffusion of gases the random movement of particles in a suspension the downward movement of particles in a suspension Silicon in river water comes from silicate rocks. Some of these contain silicon(oxide. Explain why silicon(oxide is an acidic oxide. River water contains dissolved oxygen. The graph shows how the concentration of dissolved oxygen changes with temperature. temperature / °C concentration of dissolved oxygen in mg / dm3 Describe how the concentration of dissolved oxygen changes with temperature. Determine the concentration of oxygen present in the water at 10 °C. Suggest how the rate of corrosion of iron water pipes changes with temperature. Explain your answer. Describe how water is treated to make it suitable to drink. Oxides of nitrogen are common pollutants in the air. State one source of oxides of nitrogen in the air. State one adverse effect of oxides of nitrogen on health.
0620_w16_qp_32
THEORY
2016
Paper 3, Variant 2
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A scientist analysed the substances present in a 1 dm3 sample of river water in an agricultural area. The table shows the mass of each ion dissolved in the 1 dm3 sample. name of ion formula of ion mass / g calcium Ca2+ 1.2 chloride Cl – 0.1 hydrogencarbonate HCO3 – 1.0 magnesium Mg2+ 0.5 nitrate NO3 – 1.0 sodium Na+ SO4 2– 0.5 phosphate PO4 3– 1.2 Total 6.0 Which negative ion has the highest concentration, in g / dm3, in this sample of water? Give the name of the ion with the formula SO4 2–. Calculate the mass of sodium ions in 1 dm3 of this river water. Describe a test for nitrate ions. test result The sample of river water also contains insoluble materials such as clay and the remains of dead animals and plants. What method could be used to separate insoluble materials from river water? Some of the remains of dead animals and plants contain food materials. Which two of the following substances are constituents of food? Tick two boxes. alkane carbohydrate graphite protein Particles of clay suspended in river water show Brownian motion. Describe the movement of these particles. Most of the nitrate ions in river water come from fertilisers. Explain why farmers use fertilisers. Ammonium nitrate is a fertiliser. Ammonium nitrate reacts with calcium hydroxide. ammonium nitrate + calcium hydroxide → calcium nitrate + ammonia + water Explain why adding calcium hydroxide to the soil at the same time as nitrate fertilisers results in loss of nitrogen from the soil.
0620_w16_qp_33
THEORY
2016
Paper 3, Variant 3
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Lime (calcium oxide) is made by heating limestone (calcium carbonate). CaCO3CaO+ CO2Is this reaction exothermic or endothermic? Explain your answer. The reaction is reversible. What information in the equation shows that this reaction is reversible? The diagram shows a furnace for making lime. mixture of limestone and coke On the diagram, write • the letter C to show where the waste gases exit the furnace, • the letter L to show where the lime is removed from the furnace. Suggest a reason for adding coke to the furnace. Explain why farmers use lime to treat acidic soils. Limestone is used to manufacture cement. The limestone is mixed with clay and heated to 1500 °C. It is then mixed with calcium sulfate and crushed. Describe the test for sulfate ions. test result Concrete is a mixture of cement, silicates and water. Part of the structure of a silicate is shown. = silicon atom = oxygen atom key Deduce the formula for this silicate. Concrete contains small amounts of calcium oxide. This can react with rainwater to form calcium hydroxide. Calcium hydroxide is strongly alkaline. What is the most likely pH of a strongly alkaline solution? Draw a ring around the correct answer. pH 2 pH 6 pH 7 pH 12 The calcium hydroxide on the surface of a piece of concrete reacts with carbon dioxide in the air. Complete the chemical equation for this reaction. Ca(OH)2 + CO2 → CaCO3 + Limewater is an aqueous solution of calcium hydroxide. A teacher left an open beaker of limewater in the laboratory. After a week, the solution in the beaker was pH7 and a white precipitate was observed. Use the information in and to help you explain these observations.
0620_w16_qp_33
THEORY
2016
Paper 3, Variant 3
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Questions Discovered
359