Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeSO4 solution and silver metal
(d) AgNO3 solution and copper metal.
(d) AgNO3 solution and copper metal
Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) All of the above.
(c) Applying a coating of zinc
(We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and paint would get destroyed.)
An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
(a) The element is likely to be calcium.
Food cans are coated with tin and not with zinc because (a) zinc is costlier than tin.
(b) zinc has a higher melting point than tin.
(c) zinc is more reactive than tin.
(d) zinc is less reactive than tin.
(c) Food cans are coated with tin and not with zinc because zinc is more reactive than tin.
You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non – metals.
(a) With the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non-metal. Similarly, we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.
(b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved in these tests.
What are amphoteric oxides? Give two examples of amphoteric oxides.
Those oxides that behave as both acidic and basic oxides are called amphoteric oxides.
Examples: aluminium oxide (Al2O3)
Al2O3 + 6HCl → 2AlCl3 + 3H2O [ Basic ]
Al2O3 + 2NaOH → 2NaAlO2 + H2O [ Acidic ]
Zinc oxide (ZnO) is also an amphoteric oxide.
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Metals that are more reactive than hydrogen displace it from dilute acids.
For example: sodium and potassium.
Metals that are less reactive than hydrogen do not displace it.
For example: copper and silver.
In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
In the electrolytic refining of a metal M:
Anode → Impure metal M
Cathode → Thin strip of pure metal M
Electrolyte → Solution of salt of the metal M
Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.
(a) What will be the action of gas on (i) dry litmus paper?
(ii) moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
(a) (i) There will be no action on dry litmus paper.
(ii) Since the gas is sulphur dioxide (SO2), it turns moist blue litmus paper to red because sulphur dioxide reacts with moisture to form sulphurous acid.
(b) 𝑆(𝑠)+𝑂2 (𝑔) → 𝑆𝑂2 (𝑔)
𝑆𝑂2 (𝑔)+𝐻2𝑂 (𝑙) → 𝐻2𝑆𝑂3 (𝑎𝑞)
State two ways to prevent the rusting of iron.
Two ways to prevent the rusting of iron are:
Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
Galvanisation: An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.