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Showing 7 questions in Chemistry for Class 10. Tap a card to reveal the answer.
ChemistryChemical Reactions and EquationseasyWhen an iron nail is dipped in copper sulphate solution, the blue colour fades. Write the reaction and name its type.
Reveal answer ↓
What it is
A more reactive metal displaces a less reactive one from its salt solution.
Answer
Iron is more reactive than copper, so it displaces copper from copper sulphate: Fe + CuSO4 -> FeSO4 + Cu. The blue colour of CuSO4 fades as it is replaced by the pale green FeSO4, and a brown copper coating forms on the nail. This is a displacement reaction.
Fe + CuSO4 -> FeSO4 + Cu
- •Fe + CuSO4 -> FeSO4 + Cu
- •More reactive metal displaces less reactive one
- •Blue fades, brown Cu deposits
- •Type: displacement (also redox)
Why learn this
It explains rust protection, how metals are extracted and why copper salt is not stored in iron pots.
💡 Memory trick
Higher in the reactivity series pushes the lower one OUT (displacement).
ChemistryAcids, Bases and SaltseasyWhat is the pH scale, and how does pH change as a solution becomes more acidic?
Reveal answer ↓
What it is
pH measures how acidic or basic a solution is, from 0 (acid) to 14 (base), with 7 neutral.
Answer
The pH scale runs from 0 to 14 and measures the concentration of hydrogen ions (H+) in a solution. A pH of 7 is neutral, below 7 is acidic and above 7 is basic. As a solution becomes more acidic, the H+ concentration increases and the pH value decreases.
pH measures H+ concentration (lower pH = more acidic)
- •Scale 0 to 14
- •pH 7 neutral, <7 acidic, >7 basic
- •More acidic -> more H+ -> lower pH
Why learn this
It rules our blood, soil, shampoos, digestion and even why tooth decay happens.
💡 Memory trick
pH goes DOWN as acidity goes UP (more H+ = lower pH). pH = 'power of Hydrogen'.
ChemistryMetals and Non-metalsmediumZinc can displace copper from copper sulphate, but copper cannot displace zinc from zinc sulphate. Explain.
Reveal answer ↓
What it is
Metals higher in the reactivity series displace those lower down, never the reverse.
Answer
In the reactivity series zinc lies above copper, so zinc is more reactive and loses electrons more readily. Therefore zinc displaces the less reactive copper: Zn + CuSO4 -> ZnSO4 + Cu. Copper, being less reactive than zinc, cannot displace zinc, so Cu + ZnSO4 does not react.
Zn + CuSO4 -> ZnSO4 + Cu
- •Reactivity: Zn above Cu
- •More reactive metal displaces less reactive
- •Zn + CuSO4 -> ZnSO4 + Cu
- •Cu + ZnSO4 -> no reaction
Why learn this
It decides how metals are extracted, stored and used to prevent corrosion.
💡 Memory trick
Zinc is above copper, so Zn wins; copper can't push zinc back.
ChemistryCarbon and its CompoundsmediumWhy does carbon form a very large number of compounds?
Reveal answer ↓
What it is
Carbon forms millions of compounds because it makes four strong covalent bonds and chains (catenation).
Answer
Carbon has four valence electrons, so it shares electrons to form four strong covalent bonds rather than gaining or losing electrons. Two special properties help: catenation (carbon atoms link with other carbon atoms to form long chains, branches and rings) and tetravalency (it can bond with four other atoms such as hydrogen, oxygen, nitrogen). Together these give a huge number of stable compounds.
Carbon valency = 4 (forms 4 covalent bonds)
- •4 valence electrons -> 4 covalent bonds
- •Catenation: C-C chains, branches, rings
- •Tetravalency allows bonding with many elements
- •Small size -> strong stable bonds
Why learn this
It's why all life, fuels, plastics and medicines are carbon-based - the reason 'organic' chemistry exists.
💡 Memory trick
Carbon's superpowers: Tetravalency (4 bonds) + Catenation (C-C chains).
ChemistryChemical Reactions and EquationsmediumIn the reaction CuO + H2 -> Cu + H2O, identify the substance oxidised and the substance reduced.
Reveal answer ↓
What it is
In a redox reaction one substance gains oxygen (oxidised) while another loses it (reduced), together.
Answer
Hydrogen gains oxygen to form water, so H2 is oxidised. Copper oxide loses oxygen to form copper, so CuO is reduced. Since oxidation and reduction happen together, this is a redox reaction; here H2 acts as the reducing agent and CuO as the oxidising agent.
CuO + H2 -> Cu + H2O
- •H2 gains oxygen -> oxidised (reducing agent)
- •CuO loses oxygen -> reduced (oxidising agent)
- •Oxidation and reduction occur together = redox
Why learn this
Redox runs respiration, rusting, batteries and photosynthesis - energy in and out of everything.
💡 Memory trick
OIL RIG: Oxidation Is Loss, Reduction Is Gain (of oxygen or electrons).
ChemistryAcids, Bases and SaltseasyWhat is a neutralisation reaction? Give the general equation and one everyday use.
Reveal answer ↓
What it is
A neutralisation reaction is an acid reacting with a base to give a salt and water.
Answer
A neutralisation reaction is the reaction between an acid and a base to form a salt and water. The general equation is: Acid + Base -> Salt + Water (for example, HCl + NaOH -> NaCl + H2O). An everyday use is taking an antacid (a mild base) to neutralise excess acid in the stomach and relieve acidity.
Acid + Base -> Salt + Water
- •Acid + Base -> Salt + Water
- •HCl + NaOH -> NaCl + H2O
- •Use: antacids relieve stomach acidity
Why learn this
It's used in antacids for acidity, in treating soil pH and in soothing insect stings.
💡 Memory trick
Acid + Base -> Salt + Water. The acid and base cancel (neutralise) each other.
ChemistryCarbon and its CompoundsmediumWhat is a homologous series? State two of its characteristics.
Reveal answer ↓
What it is
A homologous series is a family of carbon compounds with the same general formula, differing by CH2.
Answer
A homologous series is a group of organic compounds having the same general formula and the same functional group, in which each successive member differs from the previous one by a -CH2- unit. Two characteristics are: (1) all members have similar chemical properties because of the same functional group, and (2) their physical properties such as boiling point change gradually as the molecule gets bigger. The alkanes (CH4, C2H6, C3H8, ...) are an example.
Successive members differ by CH2
- •Same general formula and functional group
- •Successive members differ by -CH2-
- •Similar chemical properties; gradual change in physical properties
- •Example: alkanes
Why learn this
It lets chemists predict the properties of thousands of organic compounds from one pattern.
💡 Memory trick
Each member differs by CH2; same functional group, gradually changing physical properties.