5.4 Salts From Metals

Question 1

When do reactions between metals and acids occur?

Answer 1

When the metal is more reactive than the hydrogen in the acid

Question 2

Salt def

Answer 2

A compound formed when the hydrogen in an acid is wholly, or partially, replaced by metal (or ammonium) ions

Question 3

Complete the equation: metal + acid —>

Answer 3

metal + acid —> salt + hydrogen

Question 4

Why are alkali metals never added to acid?

Answer 4

The reaction will be too violent

Question 5

How can pure dry crystals be obtained from a solution?

Answer 5

• some water is evaporated from the solution by heating it until the point of crystallisation
• at this point, the solution is saturated and crystals will appear at the edge of the salt solution being heated in an evaporating dish

Question 6

How do you prepare the best sample of salt crystals?

Answer 6

salt solution should be left at room temperature for the remaining water to evaporate slowly

Question 7

Salts formed when you react metals with HCl (hydrochloric acid)

Answer 7

Chlorides (containing Cl- ions)

Question 8

Salts formed when you react metals with H2SO4 (sulphuric acid)

Answer 8

Sulphates (Containing SO42- ions)

Question 9

Salts formed when you react a metals with nitric acid (HNO3)

Answer 9

Nitrates (containing NO3- ions)

Question 10

What happens when you react magnesium with dilute sulphuric acid

Answer 10

• hydrogen ions will be displaced from solution by magnesium (magnesium is more reactive than hydrogen)
• magnesium has a stronger tendency to form positive ions than hydrogen has
• MgSo4 (magnesium sulphate) + H2 is formed

Question 11

Is magnesium oxidised or reduced in a reaction with sulphuric acid

Answer 11

• magnesium atoms have lost electrons, so oxidised
• Half-equation: Mg(s) —> Mg2+(aq) + 2e-

Question 12

When magnesium loses electrons in a reaction with sulphuric acid, where do they go?

Answer 12

• magnesium loses two electrons from its outer shell
• it gives these electrons to two hydrogen ions in the solution (2H+), forming two hydrogen atoms
• these bond to each other (sharing a pair of electrons in a covalent bond) to make a molecule of hydrogen gas (H2)

Question 13

Is the reaction between a metal and an acid a redox reaction?

Answer 13

• yes
• metal atoms always give electrons to the hydrogen ions, displacing hydrogen as a gas and leaving metal ions in the solution