A farmer uses a soil-testing map before choosing fertiliser. Fig. 1 shows two soil samples placed on a white tile with universal indicator. Sample M becomes...
Question 1 Report
A farmer uses a soil-testing map before choosing fertiliser. Fig. 1 shows two soil samples placed on a white tile with universal indicator. Sample M becomes orange and sample N becomes blue-green. The farmer plans to grow beans in field M. Beans grow poorly if the soil is strongly acidic because some mineral ions are then less available to the roots.
(a) Give the colour that indicates an acidic solution in this test. [1]
(b) Use the results to describe which sample has the lower pH. [1]
(c) Give a suitable substance the farmer could add to field M and describe its effect. [2]
A community laboratory receives an unknown liquid after a spill near a metal store. Fig. 1 shows separate tests on small samples. In test A, universal indicator becomes red. In test B, copper turnings are added and no visible change occurs. In test C, sodium carbonate powder is added and rapid bubbling is seen. The laboratory must identify the liquid before deciding how to clean the area.
(a) Use tests A and C to give the type of unknown liquid. [1]
(b) Describe why copper gives no visible reaction in test B, even though the liquid is acidic. [1]
(c) Give two observations that distinguish an acid from water using the tests shown. [2]
Answer Details
Soil samples
(a) An acidic solution can give universal indicator colours orange, red, or yellow. [1]
(b) Sample M has the lower pH because orange indicates an acidic solution, whereas blue-green is nearer neutral or alkaline. [1]
(c) Add limestone, calcium carbonate, or lime to field M. It neutralises the acid and raises the pH, making the soil less acidic. [2]
Unknown liquid
(a) The unknown liquid is an acid. Universal indicator turning red and bubbling with sodium carbonate are both acid reactions. [1]
(b) Copper gives no visible reaction because it is less reactive than hydrogen and does not react with dilute acid to displace hydrogen gas. [1]
(c) An acid turns universal indicator red, whereas water gives green universal indicator. Also, an acid fizzes with sodium carbonate, whereas water does not. Any two contrasting observations gain credit. [2]
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