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A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?

Answer: Goldsmith used a solution known as Aqua regia, which is known as royal water in Latin. It's made up of a 3:1 combination of concentrated... View Article

Differentiate between metal and non-metal on the basis of their chemical properties.

Answer: Metals and non-metals are two distinct types of materials that we see every day. Elements can be divided into metals and non-metals and... View Article

You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Answer: Copper reacts with moist carbon dioxide in the air to form copper carbonate, and the shiny brown surface of the copper vessel is covered... View Article

Give reasons: (a) Platinum, gold and silver are used to make jewellery. (b) Sodium, potassium and lithium are stored under oil. (c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. (d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction

Answer: (a) Platinum, gold and silver are used to make jewellery because the metals used in jewellery are always be chosen on the basis of its... View Article

What type of oxides are formed when non-metals combine with oxygen?

Answer: Metals and non-metals are different kinds of materials that exist surrounding us. Elements can be classified into metals and non-metals... View Article

In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Answer: Electrolytic refining is a technique that is used for the extraction and purification of metals that are obtained by refining methods.... View Article

Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Answer: The reactivity series of metals, also known as the activity series, refers to the arrangement of metals in the descending order of their... View Article

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.

Answer: (a) How could you use them to distinguish between samples of metals and non-metals? Metals are malleable and can quickly be beaten into... View Article

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.

Answer: (c) Zinc is more reactive than tin Zinc has a higher reactivity than tin. Tin interacts only with extremely strong acids. Zinc, on the... View Article

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) Calcium (b) Carbon (c) Silicon (d) Iron

Answer: (a) Calcium Calcium reacts with oxygen to give calcium oxide. The chemical formula of calcium oxide is CaO. The molecule is formed by... View Article

Which of the following methods is suitable for preventing an iron frying pan from rusting? (1) Applying grease (2) Applying paint (3) Applying a coating of zinc (4) All of the above

Answer: (3) Applying a coating of zinc The formation of rust, that is a mixture of iron oxides, on the surface of iron objects or structures. The... View Article

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

Answer: (d) AgNO3 solution and copper metal A displacement reaction is the one wherein the atom or a set of atoms is displaced by another atom in... View Article

What chemical process is used for obtaining a metal from its oxide?

Answer: Reduction method is used to obtain metal from its oxide. Metallic oxide is reduced to metal during the extraction of metals. Metallurgy... View Article

Define the following terms. (i) Mineral (ii) Ore (iii) Gangue

Answer: Mineral is a naturally occurring inorganic solid with a definite chemical composition and a crystalline structure. Mineral elements... View Article

(i) Write the electron-dot structures for sodium and oxygen. (ii) Show the formation of Na₂O and MgO by the transfer of electrons. (iii)What are the ions present in these compounds?

Answer: Electron dot structures or Lewis dot formula can be drawn if the molecular formula of the compound is known. It defines the nature of... View Article

What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.

Answer: When zinc is introduced to an iron sulphate solution, the colour of the iron sulphate solution changes. Since zinc is more reactive than... View Article

Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄.

Answer: The reactivity series of metals, also known as the activity series, refers to the arrangement of metals in the descending order of their... View Article

Give an example of a metal which (i) Is a liquid at room temperature? (ii) Can be easily cut with a knife? (iii) Is the best conductor of heat? (iv) Is a poor conductor of heat?

Answer: Metals are minerals or substances that form naturally below the surface of the Earth. Most metals are lustrous or shiny. Metals are... View Article

Plaster of Paris should be stored in a moisture-proof container. Explain why?

Answer: Plaster of Paris is a popular substance that is utilized most commonly for sculpting materials and in gauze bandages. Plaster of Paris... View Article

A milkman adds a very small amount of baking soda to fresh milk.(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?(b) Why does this milk take a long time to set as curd?

Answer: The pH value of milk is 6 since it is acidic in nature. When the milk is converted into curd due to the action of bacteria lactic acid... View Article

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