Salts and Chemical Tests

Question 1

describe tests for the cations

Answer 1

Li+, Na+, K+, Ca2+ using flame tests Lithium: red Sodium: orange (so strong can mask other colours) Potassium: lilac Calcium: brick red

Question 2

describe how to use sodium hydroxide solution to test for the presence of Cu2+, Fe2+ and Fe3+ ions insolution

Answer 2

* most metal hydroxides are insoluble * add sodium hydroxide to a solution containing the ions *no precipitate but a smell of ammonia shows the presents of ammonia ions- NH4+ * Cu2+ ion- blue * Fe3+ ion- orange-brown *Fe2+ ion- green

Question 3

describe tests for the anions

Answer 3

Cl-, Br- and I-, using dilute nitric acid and silver nitrate solution Chloride ions + nitric acid + silver nitrate > white precipitate (silver chloride) Bromide ions + nitric acid + silver nitrate > cream precipitate (silver bromide) Iodide ions + nitric acid + silver nitrate > yellow precipitate (silver iodide)

Question 4

test for sulfates

Answer 4

• add hydrochloric acid (HCl), followed by barium chloride solution (BaCl₂)
• a white precipitate of barium sulfate means the original compound was a sulfate
• Ba²⁺_(aq) + SO₄^2-_(aq) > BaSO_4(s)

Question 5

test for carbonates

Answer 5

• add dilute hydrochloric acid (HCl) to test sample
• if carbonates (CO₃^2-) are present then carbon dioxide will be released
• CO₃^2-_(s) + 2H⁺_(aq) > CO_2(g) + H₂O_(l)
• you can test for carbon dioxide using limewater

Question 6

describe experiments to prepare soluble salts from acids

Answer 6

• Dilute sulphuric acid is added to an excess of magnesium.
• Mg + H2SO4 > MgSO4 + H2
• The left over magnesium is filtered off and the mixture boiled down slowly to concentrate.
• When it is cooled, crystals will form, these can be blotted dry with a piece of paper.
• This can be done with other metals and acids: Nitric, sulphuric and hydrochloric acids make soluble salts with most metals. ammonium, potassium and sodium make soluble salts with acids

Question 7

describe experiments to prepare insoluble salts using precipitation reactions

Answer 7

Silver nitrate and sodium chloride are added together, the product, silver chloride is made, this salt is insoluable and so will form a white precipitate in the solution. AgNO3 + NaCl > AgCl + NaNO3