Grade 10 chemisty โ Introduction to Salts Quiz
1. What is a salt in chemistry?
A salt is produced when an acid reacts with a base (neutralisation) and the hydrogen ion (H+) from the acid is replaced by a metal or ammonium ion, giving an ionic compound.
2. When hydrochloric acid (HCl) reacts completely with sodium hydroxide (NaOH), which salt is formed?
HCl + NaOH โ NaCl + H2O. The sodium ion from NaOH and the chloride ion from HCl form sodium chloride.
3. What is the correct formula for calcium carbonate (the main component of limestone)?
Calcium has a 2+ charge and the carbonate ion is CO3 2โ, so they combine in a 1:1 ratio to give CaCO3.
4. Which statement best describes electrical conductivity of common ionic salts?
In the solid state ions are fixed in place so salts do not conduct; when molten or in solution ions are free to move and can carry electric current.
5. What is the common name of NaCl used daily in Kenyan households?
Sodium chloride (NaCl) is the common table salt used in food; baking soda is sodium bicarbonate, Epsom salt is magnesium sulfate.
6. When aqueous silver nitrate and aqueous sodium chloride are mixed, what happens?
Ag+ and Clโ form AgCl, which is insoluble in water and appears as a white precipitate: AgNO3 + NaCl โ AgCl(s) + NaNO3.
7. Which salt is produced when potassium hydroxide (KOH) neutralises sulfuric acid (H2SO4)?
H2SO4 provides SO4 2โ and two K+ from KOH are needed to balance the 2โ charge, giving K2SO4.
8. What is the chemical formula of magnesium sulfate, the salt often used in gardening as Epsom salt?
Magnesium has a 2+ charge and sulfate is SO4 2โ, so they combine in a 1:1 ratio to form MgSO4.
9. A salt formed from a strong acid and a strong base will usually produce a solution with what pH?
Salts from strong acid + strong base (e.g., NaCl from HCl + NaOH) do not hydrolyse significantly, so the solution is approximately neutral (pH โ 7).
10. Which of the following solutions is an electrolyte and will conduct electricity when dissolved in water?
Ionic salts like NaCl dissociate into ions in water and conduct electricity; sugar dissolves but does not form ions, so it is a non-electrolyte.
11. How can copper(II) sulfate (CuSO4) be prepared in the school laboratory safely?
A metal oxide reacts with acid to form the corresponding salt and water: CuO + H2SO4 โ CuSO4 + H2O; copper metal does not react with dilute acid easily without special conditions.
12. When ammonia gas reacts with hydrochloric acid gas, which salt is formed?
NH3 (a base) accepts a proton from HCl forming the ammonium ion, NH4+, which pairs with Clโ to make NH4Cl.
13. Which anion almost always forms soluble salts in water?
Nitrate salts are generally soluble for all common cations; carbonate and hydroxide have many insoluble examples and some sulfates (like BaSO4) are insoluble.
14. Which salt is commonly used as a nitrogen fertiliser in agriculture?
Ammonium nitrate supplies nitrogen (NH4+ and NO3โ) which plants use; NaCl and CaCO3 do not provide nitrogen; CuSO4 supplies copper and can be a fungicide.
15. What is the main salt formed in the reaction between hydrochloric acid and sodium hydroxide during a titration in the lab?
HCl + NaOH โ NaCl + H2O; during such acid-base titrations the corresponding salt (here NaCl) is produced.
16. If zinc metal is placed in a solution of copper(II) sulfate, which salt will be formed after the reaction?
Zinc is more reactive than copper and displaces copper from CuSO4: Zn + CuSO4 โ ZnSO4 + Cu. The salt formed is ZnSO4.
17. Which of these salts is largely insoluble in water and appears as a white solid when formed?
AgCl is insoluble and precipitates as a white solid; NaCl, KNO3 and NH4NO3 are soluble in water.
18. What type of bonding holds the ions together in typical salts like NaCl?
Ionic bonding is the strong electrostatic force between oppositely charged ions in a salt lattice, e.g., Na+ and Clโ in NaCl.
19. What happens to the boiling point of water when a salt is dissolved in it?
Dissolving a salt increases the boiling point of water slightly because dissolved particles change colligative properties (boiling-point elevation).
20. What is the correct name for Na2CO3, a salt sometimes used in laundry detergents?
Na2CO3 is sodium carbonate; sodium bicarbonate is NaHCO3 and has a different composition.
21. Which salt gives a characteristic blue colour in aqueous solution, often used in school tests for copper ions?
Cu2+ ions in copper(II) sulfate solutions give a blue colour; Fe2+ typically gives greenish solutions and Na salts are colourless.
22. Why is an aqueous solution of sodium acetate (CH3COONa) slightly basic?
Acetate (CH3COOโ) accepts H+ from water (hydrolysis), producing OHโ and making the solution slightly basic.
23. When aqueous barium chloride (BaCl2) is mixed with aqueous sodium sulfate (Na2SO4), which solid precipitate forms?
Ba2+ and SO4 2โ form BaSO4, which is insoluble and precipitates: BaCl2 + Na2SO4 โ BaSO4(s) + 2 NaCl.
24. Which safety practice should students follow when preparing salts in the school laboratory?
Protective equipment and careful handling prevent chemical splashes and burns; smelling or tasting chemicals is unsafe and working unsupervised is not allowed.
25. Which physical property is typical of ionic solids (salts) such as sodium chloride?
Ionic lattices are rigid and can shatter (brittle) when layers are forced past each other; they are not malleable like metals.
26. What is a salt in chemistry?
A salt is formed by neutralisation between an acid and a base, producing an ionic compound composed of cations and anions.
27. How is sodium chloride normally formed in a neutralisation reaction?
Neutralisation of HCl with NaOH produces NaCl and H2O: HCl + NaOH โ NaCl + H2O, a common school method to make sodium chloride.
28. Why do aqueous solutions of salts conduct electricity?
Dissolved salts dissociate into positive and negative ions which are free to move and transport electric charge through the solution.
29. A salt made from a strong acid and a strong base typically gives a solution with what pH?
Salts from strong acid + strong base (for example NaCl from HCl + NaOH) give solutions that are approximately neutral (pH โ 7).
30. What is the typical pH of a salt solution formed from a weak acid and a strong base?
Salts from a weak acid and strong base (e.g., sodium acetate from acetic acid + NaOH) produce basic solutions due to hydrolysis of the conjugate base.
31. What type of solution is formed by a salt from a strong acid and a weak base?
Salts from strong acid + weak base (e.g., NH4Cl from HCl + NH3) produce acidic solutions because the conjugate acid (NH4+) releases H+ by hydrolysis.
32. Which salt is produced when ammonia reacts with hydrochloric acid?
NH3 + HCl โ NH4Cl. Ammonia, a weak base, reacts with HCl to form the salt ammonium chloride (NH4Cl).
33. Which property is typical of ionic salts?
Ionic salts have strong attractions between oppositely charged ions in a lattice, resulting in high melting and boiling points.
34. Which test is commonly used in school to identify chloride ions in solution?
Clโ reacts with Ag+ to form insoluble AgCl, a white precipitate, which is the standard test for chloride ions.
35. Which of these salts is the common table salt used in Kenya for cooking and preserving food?
Sodium chloride (NaCl) is common table salt used in cooking and preserving food in Kenya and worldwide.
36. What happens when aqueous solutions of silver nitrate and sodium chloride are mixed?
AgNO3 + NaCl โ AgCl(s) + NaNO3. AgCl is insoluble and appears as a white precipitate.
37. Which statement about nitrate salts is correct?
Nitrate ions (NO3โ) form salts that are generally soluble with all common cations, a simple solubility rule taught in school.
38. Which salt is produced when sulphuric acid reacts with sodium hydroxide?
H2SO4 + 2NaOH โ Na2SO4 + 2H2O. The correct product is sodium sulphate (Na2SO4).
39. What is efflorescence in salts?
Efflorescence occurs when hydrated salts lose their water of crystallisation to the air and become powdery.
40. Which of the following is a hydrated salt commonly used in school experiments and appears blue?
Copper(II) sulphate pentahydrate (CuSO4ยท5H2O) forms bright blue crystals and is a typical example of a hydrated salt.
41. Why are ionic salts generally brittle?
Applying force shifts ionic layers so like charges align and repel, causing the brittle fracture typical of ionic crystals.
42. What salt is formed when magnesium oxide reacts with hydrochloric acid?
MgO + 2HCl โ MgCl2 + H2O. The reaction of a metal oxide with an acid produces the corresponding salt, magnesium chloride.
43. What is a basic salt?
Basic salts (e.g., sodium carbonate) contain anions that hydrolyse in water to produce OHโ, making the solution alkaline.
44. Which salt would give a solution with pH above 7 when dissolved in water?
Sodium carbonate (a salt of a strong base and weak acid) hydrolyses to give OHโ and produces an alkaline solution.
45. Which method is commonly used in school to prepare a pure crystalline salt after neutralisation?
In the lab students neutralise by titration to get the right proportions, then evaporate the solvent to crystallise and collect pure salt.
46. Which of the following is an example of a double displacement reaction that forms a salt as a precipitate?
BaCl2 + Na2SO4 โ BaSO4(s) + 2NaCl. This is a double displacement reaction producing insoluble BaSO4 as a precipitate.
47. Which salt is commonly used as a nitrogen fertiliser in agriculture in Kenya?
Ammonium nitrate supplies nitrogen essential for crops and is a widely used fertiliser in many farming systems.
48. In a solution of sodium ethanoate (sodium acetate), which ion hydrolyses to produce OHโ?
CH3COOโ (conjugate base of a weak acid) reacts with water to produce OHโ, making the solution basic; Na+ is a spectator.
49. What salt is formed when nitric acid reacts with potassium hydroxide?
HNO3 + KOH โ KNO3 + H2O. The neutralisation of nitric acid with KOH forms potassium nitrate.
50. Which factors tend to increase the lattice energy of an ionic salt, giving it higher melting point?
Lattice energy increases when ions are smaller and have greater charges, because electrostatic attraction between ions is stronger.