test for negative ions

Question 1

What happens to the carbon dioxide in limewater?

Answer 1

It reacts with calcium hydroxide to form a white precipitate of calcium carbonate, which turns the limewater cloudy

Question 2

How can an unknown compound be tested to see if it has a halide (chloride, bromide or iodide) in it?

Answer 2

First dilute nitric acid is added, and then silver nitrate is added too. If a precipitate forms, there are halide ions present

Question 3

Why is the nitric acid added before the silver nitrate solution?

Answer 3

It dissolves the compound and removes any carbonate ions, which would interfere with the test by forming a precipitate with the silver ions

Question 4

In a test for halides, what colour is the precipitate formed for chloride (Cl-) ions?

Answer 4

White

Question 5

In a test for halides, what colour is the precipitate formed for bromide (Br-) ions?

Answer 5

Cream

Question 6

In a test for halides, what colour is the precipitate formed for iodide (I-) ions?

Answer 6

Pale yellow

Question 7

What is the general ionic equation with the test for a carbonate?

Answer 7

2H^+(aq) + CO3^2-(s) —> CO2(g) + H2O(l)

Question 8

What is the general ionic equation with the test for a halide?

Answer 8

Ag^+(aq) + X^-(aq) —> AgX(s)

Question 9

How is it possible to test a unknown substance for a carbonate?

Answer 9

If dilute hydrochloric acidic is added to a carbonate, it fizzes and produces carbon dioxide gas

Question 10

What substances are formed when a negative ion reacts with dilute hydrochloric acid in a test for carbonates?

Answer 10

A metal chloride, water and carbon dioxide

Question 11

What substances are formed when a negative ion reacts with silver nitrate solution in a test for halides?

Answer 11

A metal nitrate and a silver halide

Question 12

What substances are formed when a negative ion reacts with barium chloride solution in a test for sulfates?

Answer 12

A metal chloride and barium sulfate

Question 13

How can a compound be tested for containing sulfate ions?

Answer 13

By adding dilute hydrochloric acid, followed by barium chloride solution

Question 14

Why is dilute hydrochloric acid added before the barium sulfate solution?

Answer 14

To remove the carbonate ions that would form a precipitate with the barium ions

Question 15

What forms when sulfate ions are present?

Answer 15

A white precipitate

Question 16

What is the white precipitate formed in the test for sulfate ions when they are present?

Answer 16

Barium sulfate (BaSO4), which is an insoluble salt

Question 17

What is the general ionic equation with the test for a sulfate?

Answer 17

Ba^2+(aq) + SO4^2-(aq) —> BaSO4(s)