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Assam ASSEB HSLC General Science study materials
Assam ASSEB HSLC General Science study resources

Assam ASSEB HSLC General Science practice questions

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Question 1Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which of the following is a physical change?

  1. Rusting of iron
  2. Burning of magnesium ribbon
  3. Curdling of milk
  4. Melting of wax Correct answer.

Explanation

A physical change alters only the state or appearance of a substance without forming a new substance. Melting wax changes solid wax to liquid wax, which can be solidified again, so its chemical identity is unchanged. Burning, rusting and curdling all produce new substances with different properties.

Question 2Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which statement correctly describes a compound?

  1. Its components can be separated by filtration
  2. It always contains only one kind of atom
  3. Its components retain their individual properties
  4. It contains two or more elements combined in a fixed ratio by mass Correct answer.

Explanation

A compound is formed when two or more elements combine chemically in a definite proportion by mass. The constituent elements lose their individual properties and can be separated only by chemical means, not by physical methods such as filtration.

Question 3Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which of the following mixtures is a homogeneous mixture?

  1. Chalk powder in water
  2. Salt dissolved in water Correct answer.
  3. Sand and iron filings
  4. Oil and water

Explanation

A homogeneous mixture has a uniform composition throughout, with no visible boundaries between components. Salt dissolves completely in water to give a single transparent phase. The other mixtures show separate phases or settle out.

Question 4Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

The process of changing a liquid into vapour at a temperature below its boiling point is called

  1. Sublimation
  2. Filtration
  3. Evaporation Correct answer.
  4. Condensation

Explanation

Evaporation is the slow change of a liquid into vapour from its surface at any temperature below the boiling point. Condensation is the reverse process, sublimation is solid-to-vapour change, and filtration separates insoluble solids from liquids.

Question 5Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which property of particles best explains why gases can be compressed easily but solids cannot?

  1. Gas particles move more slowly than solid particles
  2. Large empty spaces exist between gas particles Correct answer.
  3. Gas particles attract each other more strongly
  4. Gas particles are lighter than solid particles

Explanation

In a gas the particles are far apart with large intermolecular spaces, so applied pressure can push them closer together. In a solid the particles are closely packed with little free space, so compression is negligible. Particle mass and speed do not determine compressibility.

Question 6Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

A student adds common salt to water and stirs until no more salt dissolves. The resulting solution is said to be

  1. Colloidal
  2. Saturated Correct answer.
  3. Unsaturated
  4. Dilute

Explanation

A saturated solution is one in which no more solute can be dissolved at that temperature. Once excess salt remains undissolved despite stirring, the solvent has reached its limit at that temperature.

Question 7Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which method is most suitable for separating a mixture of ammonium chloride and common salt?

  1. Filtration
  2. Magnetic separation
  3. Sublimation Correct answer.
  4. Decantation

Explanation

Ammonium chloride sublimes on heating, changing directly into vapour, while common salt does not. The vapour can be cooled and collected as a solid, leaving the salt behind. Filtration, magnetism and decantation cannot distinguish these two soluble solids.

Question 8Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which of the following is an element?

  1. Water
  2. Graphite Correct answer.
  3. Brass
  4. Air

Explanation

An element consists of only one kind of atom. Graphite is made entirely of carbon atoms. Water, brass and air are a compound, an alloy and a mixture respectively.

Question 9Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

When a solid is heated, its particles gain energy. Which change in particle behaviour correctly explains melting?

  1. Particles break into atoms of a new element
  2. Particles lose kinetic energy and settle at the bottom
  3. Particles become fixed more rigidly in position
  4. Particles overcome the forces holding them in fixed positions and begin to slide past one another Correct answer.

Explanation

On heating, particles vibrate more strongly until they overcome the attractive forces fixing them in the solid lattice. They then move past one another, giving the liquid state. The substance keeps its chemical identity, so no new element is formed.

Question 10Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which mixture can be separated by using a separating funnel?

  1. A mixture of sand and water
  2. A mixture of two immiscible liquids such as oil and water Correct answer.
  3. A mixture of two miscible liquids such as alcohol and water
  4. A solution of sugar in water

Explanation

A separating funnel works when two liquids form separate layers because they are immiscible and differ in density. The lower layer is run off first, then the upper layer. Miscible liquids form one phase and cannot be separated this way.

Question 11Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which statement about a solution is correct?

  1. The solute is the component present in smaller amount and is dissolved in the solvent Correct answer.
  2. The solute settles at the bottom on standing
  3. The solute is always a solid and the solvent always a liquid
  4. The solute and solvent can be separated by filtration

Explanation

In a solution the solute is the component that dissolves and is present in smaller quantity, while the solvent is the medium that dissolves it. Solutions are homogeneous, so the solute does not settle and cannot be removed by filtration.

Question 12Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which of the following changes is a chemical change?

  1. Souring of milk Correct answer.
  2. Melting of ice
  3. Breaking of glass
  4. Dissolving sugar in water

Explanation

A chemical change produces new substances with different properties and is usually irreversible. Souring of milk forms lactic acid, a new substance. The other options only change state or size and can be reversed.

Question 13Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

A mixture of iron filings and sulphur powder is heated strongly. The product formed is

  1. An element formed by the combination
  2. A mixture that can still be separated by a magnet
  3. A solution of iron in sulphur
  4. A compound, iron sulphide, that cannot be separated by a magnet Correct answer.

Explanation

Heating iron and sulphur causes a chemical reaction that forms iron sulphide, a compound. In the compound the iron is chemically bonded to sulphur, so it is no longer attracted by a magnet and cannot be separated physically.

Question 14Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which sequence correctly describes the steps used to obtain pure crystals of copper sulphate from an impure sample dissolved in water?

  1. Dissolve, filter, concentrate by heating, cool to crystallise Correct answer.
  2. Sedimentation, magnetic separation, condensation
  3. Decantation, distillation, sublimation
  4. Filtration, evaporation to dryness, sublimation

Explanation

The impure solid is dissolved, insoluble impurities are removed by filtration, and the filtrate is heated to concentrate it. On cooling, pure copper sulphate crystallises out while soluble impurities stay in the mother liquor.

Question 15Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Two liquids A and B have boiling points of 78 °C and 110 °C. Which method will best separate them?

  1. Sublimation
  2. Fractional distillation Correct answer.
  3. Filtration
  4. Centrifugation

Explanation

Miscible liquids with sufficiently different boiling points are separated by fractional distillation. The liquid with the lower boiling point, A, vaporises first and is condensed separately, then B is collected. Filtration and centrifugation separate solids, and sublimation applies to solids.

Question 16Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which observation indicates that a chemical reaction has taken place when dilute hydrochloric acid is added to zinc granules?

  1. The zinc granules become smaller only
  2. The acid changes colour from colourless to colourless
  3. Bubbles of gas are produced and the mixture warms up Correct answer.
  4. The zinc settles at the bottom

Explanation

Zinc reacts with dilute hydrochloric acid to release hydrogen gas and produce zinc chloride, and the reaction is exothermic. Evolution of gas and a temperature change are evidence of a chemical reaction.

Question 17Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which statement about the effect of temperature on the solubility of a gas in water is correct?

  1. Solubility of a gas increases only when pressure is lowered
  2. Solubility of a gas generally decreases with rise in temperature Correct answer.
  3. Solubility of a gas always increases with rise in temperature
  4. Solubility of a gas is independent of temperature

Explanation

Dissolution of a gas in water is generally exothermic, so raising the temperature shifts the equilibrium towards the gas phase. As a result, gases become less soluble in warm water, which is why warm water holds less dissolved oxygen.

Question 18Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which of the following is a characteristic property of a suspension?

  1. Its particles are smaller than atoms
  2. It is always transparent
  3. Its particles settle on standing and can be filtered out Correct answer.
  4. It cannot be separated by any physical method

Explanation

In a suspension the solid particles are large enough to settle under gravity and to be trapped by filter paper. The mixture is heterogeneous and often appears cloudy. Solutions, by contrast, are transparent and do not settle.

Question 19Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

A beaker containing a liquid is cooled and its particles lose kinetic energy until they vibrate about fixed positions. Which change of state has occurred?

  1. Freezing Correct answer.
  2. Sublimation
  3. Evaporation
  4. Melting

Explanation

Freezing is the change from liquid to solid, in which particles lose kinetic energy and become locked into fixed positions in a lattice. Melting and evaporation involve the opposite energy flow, and sublimation is solid-to-vapour change.

Question 20Matter and Its Nature: states of matter, physical and chemical changes, elements, compounds and mixtures, solutions, separation techniques

Which pair correctly matches a separation method with the property it relies on?

  1. Sublimation - difference in densities of liquids
  2. Distillation - difference in boiling points Correct answer.
  3. Winnowing - difference in solubility in water
  4. Filtration - difference in magnetic properties

Explanation

Distillation separates components by their different boiling points, since the more volatile component vaporises first. Each separation technique depends on a specific difference in physical properties, so the other pairings are mismatched.

Question 21Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

An atom of an element has atomic number 13 and mass number 27. How many neutrons are present in its nucleus?

  1. 14 Correct answer.
  2. 27
  3. 40
  4. 13

Explanation

The number of neutrons equals the mass number minus the atomic number, so 27 minus 13 gives 14 neutrons. The atomic number 13 counts protons only, and the mass number 27 is the total of protons and neutrons.

Question 22Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Which subatomic particle carries a negative charge and occupies the space around the nucleus?

  1. Neutron
  2. Proton
  3. Electron Correct answer.
  4. Nucleon

Explanation

Electrons are negatively charged particles that revolve in shells around the nucleus. Protons are positive and neutrons are neutral, and both reside inside the nucleus.

Question 23Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

The electronic configuration of a chlorine atom (atomic number 17) is written as 2, 8, 7. What does the outermost shell value indicate about chlorine?

  1. It has seven valence electrons and needs one more to complete an octet Correct answer.
  2. It has seven shells in total around the nucleus
  3. It has seven protons in its outermost shell
  4. It has seven neutrons in its nucleus

Explanation

The last number in the configuration gives the electrons in the valence shell, here seven. Chlorine therefore gains one electron to reach the stable eight-electron arrangement.

Question 24Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

What is the valency of magnesium in magnesium chloride, formed when magnesium loses two electrons?

  1. 1
  2. 0
  3. 2 Correct answer.
  4. 3

Explanation

Valency is the combining capacity of an element, equal to the number of electrons lost, gained or shared. Magnesium loses two electrons to form Mg2+, so its valency is two.

Question 25Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Which of the following is the correct chemical formula of aluminium oxide?

  1. Al3O2
  2. Al2O3 Correct answer.
  3. AlO
  4. Al2O

Explanation

Aluminium has valency 3 and oxygen has valency 2, so the ions combine as Al2O3 to balance charges. Cross-multiplying the valencies gives two aluminium ions for every three oxide ions.

Question 26Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

In the reaction Zn + CuSO4 -> ZnSO4 + Cu, which substance is oxidised?

  1. Zinc Correct answer.
  2. Copper sulphate
  3. Copper
  4. Sulphate ion

Explanation

Zinc loses electrons and its oxidation state rises from 0 to +2, so it is oxidised. Copper ions gain those electrons and are reduced to copper metal.

Question 27Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

An ionic bond is formed between two atoms when one atom transfers electrons to another. Which pair of elements most readily forms an ionic bond?

  1. Oxygen and nitrogen
  2. Sodium and chlorine Correct answer.
  3. Carbon and hydrogen
  4. Chlorine and chlorine

Explanation

Ionic bonding needs a metal that loses electrons easily and a non-metal that gains them. Sodium, a group 1 metal, transfers its single valence electron to chlorine, a group 17 non-metal.

Question 28Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Which statement correctly describes a covalent bond in a molecule of methane, CH4?

  1. Hydrogen transfers its electron completely to carbon
  2. Carbon donates both electrons of each bond to hydrogen
  3. Each hydrogen shares one electron pair with carbon Correct answer.
  4. The atoms are held by electrostatic attraction between ions

Explanation

In a covalent bond the bonding atoms share electron pairs. In methane, carbon shares one pair with each of four hydrogen atoms to complete its octet.

Question 29Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

A sodium ion is written as Na+. What does the plus sign indicate?

  1. The ion has lost one proton
  2. The ion has one more proton than electrons Correct answer.
  3. The ion has one extra neutron
  4. The ion has one extra electron

Explanation

A sodium atom loses one electron to form Na+, so protons outnumber electrons by one, giving a single positive charge. The nucleus and its proton count remain unchanged.

Question 30Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

What is the valency of the sulphate radical, SO4, when it combines with a metal to form a salt?

  1. 4
  2. 2 Correct answer.
  3. 3
  4. 1

Explanation

The sulphate radical carries a charge of 2- and therefore has a combining capacity of two. This is why sodium sulphate is written Na2SO4, with two sodium ions for one sulphate ion.

Question 31Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Which of the following equations is correctly balanced?

  1. H2 + O2 -> 2H2O
  2. 2H2 + 2O2 -> 2H2O
  3. 2H2 + O2 -> 2H2O Correct answer.
  4. H2 + O2 -> H2O

Explanation

A balanced equation has equal numbers of each kind of atom on both sides. Here four hydrogen atoms and two oxygen atoms appear on each side.

Question 32Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Two atoms of oxygen combine to form an oxygen molecule, O2. What type of bond joins them?

  1. A triple covalent bond
  2. A single ionic bond
  3. A double covalent bond Correct answer.
  4. A single covalent bond

Explanation

Each oxygen atom needs two electrons to complete its octet, so the two atoms share two pairs. Sharing two electron pairs constitutes a double covalent bond.

Question 33Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Which property is characteristic of compounds held together by ionic bonds?

  1. They conduct electricity when molten Correct answer.
  2. They do not dissolve in water
  3. They are always gases at room temperature
  4. They exist as discrete molecules with low melting points

Explanation

Molten ionic compounds contain free-moving ions that carry current, so they conduct electricity. In the solid state the ions are fixed in a lattice and cannot move.

Question 34Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

An element X has electronic configuration 2, 8, 1 and another element Y has configuration 2, 6. What is the most likely formula of the compound formed between X and Y?

  1. XY
  2. XY2
  3. X2Y3
  4. X2Y Correct answer.

Explanation

X loses one electron to become X+ and Y gains two electrons to become Y2-. Two X+ ions are needed for each Y2- ion, giving the formula X2Y.

Question 35Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

In the reaction 2Mg + O2 -> 2MgO, what is the oxidation state of magnesium in magnesium oxide?

  1. -2
  2. 0
  3. +1
  4. +2 Correct answer.

Explanation

Magnesium in MgO has lost two electrons to oxygen, so its oxidation state is +2. Oxygen takes the -2 state, keeping the compound electrically neutral.

Question 36Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

An atom has mass number 39 and 20 neutrons. What is its electronic configuration?

  1. 2, 8, 8, 1 Correct answer.
  2. 2, 8, 18, 1
  3. 2, 8, 9
  4. 2, 8, 8

Explanation

The atomic number is 39 minus 20, giving 19 protons and therefore 19 electrons. Filling the shells in order gives 2, 8, 8, 1, the configuration of potassium.

Question 37Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Sodium chloride is written as NaCl while calcium chloride is written as CaCl2. Which statement best explains this difference?

  1. Calcium has valency 2 while sodium has valency 1, so two chloride ions are needed Correct answer.
  2. Calcium chloride contains twice as many atoms of chlorine by mass
  3. Sodium chloride is covalent and calcium chloride is ionic
  4. Chlorine shows a valency of 2 with calcium and valency of 1 with sodium

Explanation

The formula balances the total positive and negative charges. Calcium forms Ca2+ and needs two Cl- ions, whereas sodium forms Na+ and needs only one.

Question 38Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Which pair of atoms would be expected to form a covalent compound rather than an ionic one?

  1. Potassium and fluorine
  2. Magnesium and chlorine
  3. Sodium and oxygen
  4. Carbon and oxygen Correct answer.

Explanation

Covalent bonding occurs between non-metals that share electrons. Carbon and oxygen are both non-metals, so they combine by electron sharing, as in carbon dioxide.

Question 39Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

A compound contains an element whose atom loses three electrons to form a stable ion. What is the valency of that element and the formula of its oxide?

  1. Valency 1, formula X2O
  2. Valency 3, formula XO3
  3. Valency 3, formula X2O3 Correct answer.
  4. Valency 2, formula XO

Explanation

Loss of three electrons gives a valency of three, and oxygen has a valency of two. Cross-multiplying the valencies gives X2O3, balancing six units of charge on each side.

Question 40Atomic Structure and Chemical Bonding: atoms, molecules, ions, valency, formulae, simple bonding and chemical equations

Which statement about the structure of an atom is correct?

  1. The nucleus contains protons and electrons in equal numbers
  2. Electrons carry most of the mass of the atom
  3. Almost all the mass is concentrated in the nucleus, while most of the volume is empty space occupied by electrons Correct answer.
  4. Protons and electrons are packed together in the nucleus

Explanation

Protons and neutrons, which carry nearly all the atomic mass, are packed into the tiny nucleus. Electrons occupy the much larger region outside it, so most of the atom is empty space.

Question 41Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

A solution turns blue litmus paper red. Which type of substance is present in the solution?

  1. A neutral salt
  2. An acid Correct answer.
  3. A metallic oxide that dissolves to give hydroxide ions
  4. A base

Explanation

Litmus is a natural indicator that turns red in acidic solution and blue in basic solution. Since the paper changed from blue to red, the solution must contain an acid, which releases hydrogen ions in water.

Question 42Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

Which ion is responsible for the acidic behaviour of a solution of hydrochloric acid in water?

  1. Hydroxide ion
  2. Oxide ion
  3. Hydrogen ion Correct answer.
  4. Chloride ion

Explanation

Acids ionise in water to give hydrogen ions, and it is these hydrogen ions that produce the sour taste and the turning of blue litmus red. The chloride ion is the negative part of the acid and does not cause acidity.

Question 43Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

Which of the following is a strong base that is completely ionised in dilute aqueous solution?

  1. Carbonic acid
  2. Acetic acid
  3. Ammonium hydroxide
  4. Sodium hydroxide Correct answer.

Explanation

Sodium hydroxide is an alkali metal hydroxide and dissociates completely in water, so it is a strong base. Ammonium hydroxide is only weakly ionised, and the two acids listed are not bases at all.

Question 44Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

A solution has a pH of 3. What does this tell us about the solution?

  1. It is acidic and contains more hydrogen ions than hydroxide ions. Correct answer.
  2. It is neutral because the pH is close to the middle of the scale.
  3. It is weakly basic and contains more hydroxide ions than hydrogen ions.
  4. It is strongly basic and will turn red litmus blue.

Explanation

On the pH scale, values below 7 indicate acidity, and lower values mean a higher concentration of hydrogen ions. A pH of 3 is therefore acidic, with hydrogen ions outnumbering hydroxide ions in the solution.

Question 45Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

What is the product formed when an acid reacts with a base in a neutralisation reaction, apart from water?

  1. A salt Correct answer.
  2. An indicator
  3. An oxide
  4. A metal

Explanation

Neutralisation is the reaction between an acid and a base to give a salt and water. The hydrogen ions of the acid and the hydroxide ions of the base combine to form water, while the remaining ions form the salt.

Question 46Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

A farmer finds that his soil is too acidic for a crop. Which substance is most suitable for spreading on the soil to reduce its acidity?

  1. Vinegar
  2. Quicklime Correct answer.
  3. Lemon juice
  4. Common salt

Explanation

Quicklime is calcium oxide, a basic substance that neutralises excess acid in the soil and raises its pH. Acidic materials such as vinegar or lemon juice would make the soil more acidic rather than less.

Question 47Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

Baking soda is used in cooking and also as an antacid. What is its chemical name and formula?

  1. Sodium carbonate, Na2CO3
  2. Calcium carbonate, CaCO3
  3. Sodium chloride, NaCl
  4. Sodium hydrogen carbonate, NaHCO3 Correct answer.

Explanation

Baking soda is sodium hydrogen carbonate, NaHCO3, a mildly basic salt that releases carbon dioxide when heated or treated with acid. It is this mild basicity that allows it to neutralise excess stomach acid.

Question 48Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

A student adds a few drops of phenolphthalein to a dilute sodium hydroxide solution. What colour is observed?

  1. Yellow
  2. Colourless
  3. Pink Correct answer.
  4. Blue

Explanation

Phenolphthalein is colourless in acidic and neutral solutions but turns pink in basic solutions. Sodium hydroxide is a strong base, so the indicator shows its characteristic pink colour.

Question 49Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

Which of the following salts is used in the manufacture of bleaching powder?

  1. Copper sulphate
  2. Potassium nitrate
  3. Calcium hydroxide Correct answer.
  4. Sodium bicarbonate

Explanation

Bleaching powder is made by passing chlorine over dry slaked lime, which is calcium hydroxide. The product contains calcium, chlorine and oxygen and releases chlorine when treated with acid.

Question 50Acids, Bases and Salts: properties, indicators, neutralisation, pH, common salts and their uses

When dilute sulphuric acid is added to zinc granules, a gas is evolved. What is the gas, and how would you confirm it?

  1. Carbon dioxide, confirmed because it turns limewater milky
  2. Chlorine, confirmed because it bleaches litmus paper
  3. Oxygen, confirmed because it relights a glowing splint
  4. Hydrogen, confirmed because it burns with a pop sound Correct answer.

Explanation

A dilute acid reacts with an active metal such as zinc to release hydrogen gas, while the metal dissolves to form a salt. Hydrogen is identified by bringing a burning splint near the gas, which gives a characteristic pop.